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Vitamin C for Sports & Fitness

Why Use

Vitamin C

Why Do Athletes Use It?*

Some athletes say that vitamin C helps keep the immune system functioning optimally and decreases recovery time between workouts.

What Do the Advocates Say?*

Vitamin C is important for connective tissue repair. Although beneficial to athletes participating in a variety of sports, vitamin C is especially important to body builders whose training causes the most connective tissue damage.

Vitamin C is also important to athletes because, as an antioxidant, it may help to reverse some of the oxidative damage that may occur from exercise. This oxidative damage, caused by free radicals, may interfere with the cells’ ability to function normally and is believed to play a role in many different health conditions, including the aging process, cancer, and heart disease.

Vitamin C promotes a healthy immune system and may help to prevent the dip in immune function that may occur right after exercise.

*Athletes and fitness advocates may claim benefits for this supplement based on their personal or professional experience. These are individual opinions and testimonials that may or may not be supported by controlled clinical studies or published scientific articles.

Dosage & Side Effects

Vitamin C

How Much Is Usually Taken by Athletes?

Placebo-controlled research, some of it double-blind, has shown that taking 400 to 3,000 mg of vitamin C per day for several days before and after intense exercise may reduce pain and speed up muscle strength recovery.1 , 2 , 3 However, taking vitamin C only after such exercise was not effective in another double-blind study.4

In most well-controlled studies, exercise performance has not been shown to improve following supplementation with vitamin C, unless a deficiency exists, as might occur in athletes with unhealthy or irrational eating patterns.5 , 6 Similarly, vitamin E has not benefited exercise performance, 7 , 8 except possibly at high altitudes.9 , 10

Side Effects

Caution: People with the following conditions should consult their doctor before supplementing with vitamin C: glucose-6-phosphate dehydrogenase deficiency, iron overload (hemosiderosis or hemochromatosis), history of kidney stones, or kidney failure.

Some people develop diarrhea after as little as a few grams of vitamin C per day, while others are not bothered by ten times this amount. Strong scientific evidence to define and defend an upper tolerable limit for vitamin C is not available. A review of the available research concluded that high intakes (2–4 grams per day) are well-tolerated by healthy people.11

It is widely (and mistakenly) believed that mothers who consume large amounts of vitamin C during pregnancy are at risk of giving birth to an infant with a higher-than-normal requirement for the vitamin. The concern is that the infant could suffer “rebound scurvy,” a vitamin C deficiency caused by not having this increased need met. Even some medical textbooks have subscribed to this theory.12 In fact, however, the concept of “rebound scurvy” in infants is supported by extremely weak evidence.13 Since the publication in 1965 of the report upon which this mistaken notion is based, millions of women have consumed high amounts of vitamin C during pregnancy and not a single new case of rebound scurvy has been reported.14

A preliminary study found that people who took 500 mg per day of vitamin C supplements for one year had a greater increase in wall thickness of the carotid arteries (vessels in the neck that supply blood to the brain) than those who did not take vitamin C.15 Thickness of carotid artery walls is an indicator of progression of atherosclerosis. Currently, no evidence supports a cause-and-effect relationship for the outcome reported in this study. The vast preponderance of research suggests either a protective or therapeutic effect of vitamin C for heart disease, or no effect at all.

It has been suggested that people who form calcium oxalate kidney stones should avoid vitamin C supplements, because vitamin C can be converted into oxalate and increase urinary oxalate.16 , 17 Initially, these concerns were questioned because of potential errors in the laboratory measurement of oxalate.18 , 19 However, using newer methodology that rules out this problem, recent evidence shows that as little as 1 gram of vitamin C per day can increase the urinary oxalate levels in some people, even those without a history of kidney stones.20 , 21 In one case, 8 grams per day of vitamin C led to dramatic increases in urinary oxalate excretion and kidney stone crystal formation causing bloody urine.22 People with a history of kidney stones should consult a doctor before taking large amounts (1 gram or more per day) of supplemental vitamin C.

Despite possible therapeutic effects of vitamin C in people with diabetes at lower intakes, one case of increased blood sugar levels was reported after taking 4.5 grams per day.23

Interactions with Supplements, Foods, & Other Compounds

Intake of large amounts of vitamin C can deplete the body of copper24 , 25—an essential nutrient. People should be sure to maintain adequate copper intake at higher intakes of vitamin C. Copper is found in many multivitamin-mineral supplements. Vitamin C increases the absorption of iron and should be avoided by people with iron overload diseases (e.g., hemochromatosis, hemosiderosis). Vitamin C helps recycle the antioxidant, vitamin E.

Interactions with Medicines

Certain medicines interact with this supplement.

Types of interactions: Beneficial Adverse Check

Replenish Depleted Nutrients

  • Ampicillin

    Test tube studies show that ampicillin significantly reduces the amount of vitamin C in the blood.26 Controlled research is needed to determine whether individuals might benefit from supplementing vitamin C while taking ampicillin.

    The interaction is supported by preliminary, weak, fragmentary, and/or contradictory scientific evidence.
  • Aspirin

    Taking aspirin has been associated with increased loss of vitamin C in urine and has been linked to depletion of vitamin C.27 People who take aspirin regularly should consider supplementing at least a few hundred milligrams of vitamin C per day. Such an amount is often found in a multivitamin.

  • Desogestrel-Ethinyl Estradiol

    A review of literature suggests that women who use oral contraceptives may experience decreased vitamin B1, B2, B3, B12, C, and zinc levels.62 , 63 , 64 Oral contraceptive use has been associated with increased absorption of calcium and copper and with increased blood levels of copper and vitamin A.65 , 66 Oral contraceptives may interfere with manganese absorption.67 The clinical importance of these actions remains unclear.

    The interaction is supported by preliminary, weak, fragmentary, and/or contradictory scientific evidence.
  • Dexamethasone

    Oral corticosteroids have been found to increase urinary loss of vitamin K, vitamin C, selenium, and zinc.68 The importance of these losses is unknown.

    The interaction is supported by preliminary, weak, fragmentary, and/or contradictory scientific evidence.
  • Ethinyl Estradiol and Levonorgestrel

    A review of literature suggests that women who use oral contraceptives may experience decreased vitamin B1, B2, B3, B12, C, and zinc levels.83 , 84 , 85 Oral contraceptive use has been associated with increased absorption of calcium and copper and with increased blood levels of copper and vitamin A.86 , 87 Oral contraceptives may interfere with manganese absorption.88 The clinical importance of these actions remains unclear.

    The interaction is supported by preliminary, weak, fragmentary, and/or contradictory scientific evidence.
  • Ethinyl Estradiol and Norethindrone

    A review of literature suggests that women who use OCs may experience decreased vitamin B1, B2, B3, B12, C, and zinc levels.89 , 90 , 91 OC use has been associated with increased absorption of calcium and copper and with increased blood levels of copper and vitamin A.92 , 93 OCs may interfere with manganese absorption.94 The clinical importance of these actions remains unclear.

    The interaction is supported by preliminary, weak, fragmentary, and/or contradictory scientific evidence.
  • Ethinyl Estradiol and Norgestimate

    A review of literature suggests that women who use OCs may experience decreased vitamin B1, B2, B3, B12, C, and zinc levels.95 , 96 , 97 OC use has been associated with increased absorption of calcium and copper and with increased blood levels of copper and vitamin A.98 , 99 OCs may interfere with manganese absorption.100 The clinical importance of these actions remains unclear.

    The interaction is supported by preliminary, weak, fragmentary, and/or contradictory scientific evidence.
  • Ethinyl Estradiol and Norgestrel

    A review of literature suggests that women who use oral contraceptives may experience decreased vitamin B1, B2, B3, B12, C, and zinc levels.101 , 102 , 103 Oral contraceptive use has been associated with increased absorption of calcium and copper and with increased blood levels of copper and vitamin A.104 , 105 , 106 Oral contraceptives may interfere with manganese absorption.107 The clinical importance of these actions remains unclear.

    The interaction is supported by preliminary, weak, fragmentary, and/or contradictory scientific evidence.
  • Indomethacin

    Indomethacin has been reported to decrease absorption of folic acid and vitamin C.128 Under certain circumstances, indomethacin may interfere with the actions of vitamin C.129 Calcium and phosphate levels may also be reduced with indomethacin therapy.130 It remains unclear whether people taking this drug need to supplement any of these nutrients.

  • Levonorgestrel

    A review of literature suggests that women who use oral contraceptives may experience decreased vitamin B1, B2, B3, B12, C, and zinc levels.139 , 140 , 141 Oral contraceptive use has been associated with increased absorption of calcium and copper and with increased blood levels of copper and vitamin A.142 , 143 , 144 Oral contraceptives may interfere with manganese absorption.145 The clinical importance of these actions remains unclear.

    The interaction is supported by preliminary, weak, fragmentary, and/or contradictory scientific evidence.
  • Levonorgestrel-Ethinyl Estrad

    A review of literature suggests that women who use oral contraceptives may experience decreased vitamin B1, B2, B3, B12, C, and zinc levels.146 , 147 , 148 Oral contraceptive use has been associated with increased absorption of calcium and copper and with increased blood levels of copper and vitamin A.149 , 150 , 151 Oral contraceptives may interfere with manganese absorption.152 The clinical importance of these actions remains unclear.

    The interaction is supported by preliminary, weak, fragmentary, and/or contradictory scientific evidence.
  • Mestranol and Norethindrone

    A review of literature suggests that women who use oral contraceptives may experience decreased vitamin B1, B2, B3, B12, C, and zinc levels.177 , 178 , 179 Oral contraceptive use has been associated with increased absorption of calcium and copper and with increased blood levels of copper and vitamin A.180 , 181 , 182 Oral contraceptives may interfere with manganese absorption.183 The clinical importance of these actions remains unclear.

    The interaction is supported by preliminary, weak, fragmentary, and/or contradictory scientific evidence.
  • Norgestimate-Ethinyl Estradiol

    A review of literature suggests that women who use oral contraceptives may experience decreased vitamin B1, B2, B3, B12, C, and zinc levels.187 , 188 , 189 Oral contraceptive use has been associated with increased absorption of calcium and copper and with increased blood levels of copper and vitamin A.190 , 191 , 192 Oral contraceptives may interfere with manganese absorption.193 The clinical importance of these actions remains unclear.

    The interaction is supported by preliminary, weak, fragmentary, and/or contradictory scientific evidence.
  • Omeprazole

    Treatment of healthy volunteers with omeprazole for four weeks resulted in a 12.3% decrease in blood levels of vitamin C.194

  • Salsalate

    Salsalate and aspirin are rapidly converted in the body to salicylic acid. Controlled studies show that taking aspirin increases the elimination of vitamin C from the body and lowers blood levels.201 Further controlled research is needed to determine whether salsalate specifically reduces vitamin C levels and whether people taking the drug are at risk for vitamin C deficiency.

    The interaction is supported by preliminary, weak, fragmentary, and/or contradictory scientific evidence.

Reduce Side Effects

  • Busulfan

    Chemotherapy can injure cancer cells by creating oxidative damage. As a result, some oncologists recommend that patients avoid supplementing antioxidants if they are undergoing chemotherapy. Limited test tube research occasionally does support the idea that an antioxidant can interfere with oxidative damage to cancer cells.28 However, most scientific research does not support this supposition.

    A modified form of vitamin A has been reported to work synergistically with chemotherapy in test tube research.29 Vitamin C appears to increase the effectiveness of chemotherapy in animals30 and with human breast cancer cells in test tube research.31 In a double-blind study, Japanese researchers found that the combination of vitamin E, vitamin C, and N-acetyl cysteine (NAC)—all antioxidants—protected against chemotherapy-induced heart damage without interfering with the action of the chemotherapy.32

    A comprehensive review of antioxidants and chemotherapy leaves open the question of whether supplemental antioxidants definitely help people with chemotherapy side effects, but neither does it show that antioxidants should be avoided for fear that the actions of chemotherapy are interfered with.33 Although research remains incomplete, the idea that people taking chemotherapy should avoid antioxidants is not supported by scientific research.

    The interaction is supported by preliminary, weak, fragmentary, and/or contradictory scientific evidence.
  • Carboplatin

    Chemotherapy can injure cancer cells by creating oxidative damage. As a result, some oncologists recommend that patients avoid supplementing antioxidants if they are undergoing chemotherapy. Limited test tube research occasionally does support the idea that an antioxidant can interfere with oxidative damage to cancer cells.36 However, most scientific research does not support this supposition.

    A modified form of vitamin A has been reported to work synergistically with chemotherapy in test tube research.37 Vitamin C appears to increase the effectiveness of chemotherapy in animals38 and with human breast cancer cells in test tube research.39 In a double-blind study, Japanese researchers found that the combination of vitamin E, vitamin C, and N-acetyl cysteine (NAC)—all antioxidants—protected against chemotherapy-induced heart damage without interfering with the action of the chemotherapy.40

    A comprehensive review of antioxidants and chemotherapy leaves open the question of whether supplemental antioxidants definitely help people with chemotherapy side effects, but neither does it show that antioxidants should be avoided for fear that the actions of chemotherapy are interfered with.41 Although research remains incomplete, the idea that people taking chemotherapy should avoid antioxidants is not supported by scientific research.

  • Carmustine

    Chemotherapy can injure cancer cells by creating oxidative damage. As a result, some oncologists recommend that patients avoid supplementing antioxidants if they are undergoing chemotherapy. Limited test tube research occasionally does support the idea that an antioxidant can interfere with oxidative damage to cancer cells.42 However, most scientific research does not support this supposition.

    A modified form of vitamin A has been reported to work synergistically with chemotherapy in test tube research.43 Vitamin C appears to increase the effectiveness of chemotherapy in animals44 and with human breast cancer cells in test tube research.45 In a double-blind study, Japanese researchers found that the combination of vitamin E, vitamin C, and N-acetyl cysteine (NAC)—all antioxidants—protected against chemotherapy-induced heart damage without interfering with the action of the chemotherapy.46

    A comprehensive review of antioxidants and chemotherapy leaves open the question of whether supplemental antioxidants definitely help people with chemotherapy side effects, but neither does it show that antioxidants should be avoided for fear that the actions of chemotherapy are interfered with.47 Although research remains incomplete, the idea that people taking chemotherapy should avoid antioxidants is not supported by scientific research.

    The interaction is supported by preliminary, weak, fragmentary, and/or contradictory scientific evidence.
  • Chlorambucil

    Chemotherapy can injure cancer cells by creating oxidative damage. As a result, some oncologists recommend that patients avoid supplementing antioxidants if they are undergoing chemotherapy. Limited test tube research occasionally does support the idea that an antioxidant can interfere with oxidative damage to cancer cells.48 However, most scientific research does not support this supposition.

    A modified form of vitamin A has been reported to work synergistically with chemotherapy in test tube research.49 Vitamin C appears to increase the effectiveness of chemotherapy in animals50 and with human breast cancer cells in test tube research.51 In a double-blind study, Japanese researchers found that the combination of vitamin E, vitamin C, and N-acetyl cysteine (NAC)—all antioxidants—protected against chemotherapy-induced heart damage without interfering with the action of the chemotherapy.52

    A comprehensive review of antioxidants and chemotherapy leaves open the question of whether supplemental antioxidants definitely help people with chemotherapy side effects, but neither does it show that antioxidants should be avoided for fear that the actions of chemotherapy are interfered with.53 Although research remains incomplete, the idea that people taking chemotherapy should avoid antioxidants is not supported by scientific research.

    The interaction is supported by preliminary, weak, fragmentary, and/or contradictory scientific evidence.
  • Cladribine

    Chemotherapy can injure cancer cells by creating oxidative damage. As a result, some oncologists recommend that patients avoid supplementing antioxidants if they are undergoing chemotherapy. Limited test tube research occasionally does support the idea that an antioxidant can interfere with oxidative damage to cancer cells.54 However, most scientific research does not support this supposition.

    A modified form of vitamin A has been reported to work synergistically with chemotherapy in test tube research.55 Vitamin C appears to increase the effectiveness of chemotherapy in animals56 and with human breast cancer cells in test tube research.57 In a double-blind study, Japanese researchers found that the combination of vitamin E, vitamin C, and N-acetyl cysteine (NAC)—all antioxidants—protected against chemotherapy-induced heart damage without interfering with the action of the chemotherapy.58

    A comprehensive review of antioxidants and chemotherapy leaves open the question of whether supplemental antioxidants definitely help people with chemotherapy side effects, but neither does it show that antioxidants should be avoided for fear that the actions of chemotherapy are interfered with.59 Although research remains incomplete, the idea that people taking chemotherapy should avoid antioxidants is not supported by scientific research.

    The interaction is supported by preliminary, weak, fragmentary, and/or contradictory scientific evidence.
  • Clozapine

    Clozapine can inhibit the formation of immune cells that protect the body from invading organisms. Test tube studies show that N-acetyl-cysteine and vitamin C block the formation of immune cell–damaging compounds produced when clozapine is broken down.60 Controlled studies are necessary to determine whether supplementing N-acetyl-cysteine and vitamin C might prevent harmful side effects in people taking clozapine.

  • Dapsone

    In large amounts, dapsone causes oxidative damage to red blood cells. This damage may be reduced by using lower amounts of dapsone. Fifteen people who took dapsone for dermatitis herpetiformis were given 800 IU of vitamin E per day for four weeks, followed by four weeks with 1,000 mg of vitamin C per day, followed by four weeks of vitamin E and vitamin C together.61 The authors reported only vitamin E therapy offered some protection against dapsone-induced hemolysis.

    The interaction is supported by preliminary, weak, fragmentary, and/or contradictory scientific evidence.
  • Doxorubicin

    The antioxidant vitamin C has protected against cardiotoxicity (damage to the heart) of doxorubicin in an animal study.76 In this trial, vitamin C significantly increased the life expectancy of mice and guinea pigs without interfering with anticancer action of the drug. Despite the lack of human data, some doctors recommend that patients taking doxorubicin supplement at least 1 gram of vitamin C per day.

    The interaction is supported by preliminary, weak, fragmentary, and/or contradictory scientific evidence.
  • Erlotinib

    Chemotherapy can injure cancer cells by creating oxidative damage. As a result, some oncologists recommend that patients avoid supplementing antioxidants if they are undergoing chemotherapy. Limited test tube research occasionally does support the idea that an antioxidant can interfere with oxidative damage to cancer cells.77 However, most scientific research does not support this supposition.

    A modified form of vitamin A has been reported to work synergistically with chemotherapy in test tube research.78 Vitamin C appears to increase the effectiveness of chemotherapy in animals79 and with human breast cancer cells in test tube research.80 In a double-blind study, Japanese researchers found that the combination of vitamin E, vitamin C, and N-acetyl cysteine (NAC)—all antioxidants—protected against chemotherapy-induced heart damage without interfering with the action of the chemotherapy.81

    A comprehensive review of antioxidants and chemotherapy leaves open the question of whether supplemental antioxidants definitely help people with chemotherapy side effects, but neither does it show that antioxidants should be avoided for fear that the actions of chemotherapy are interfered with.82 Although research remains incomplete, the idea that people taking chemotherapy should avoid antioxidants is not supported by scientific research.

    The interaction is supported by preliminary, weak, fragmentary, and/or contradictory scientific evidence.
  • Fenofibrate

    Several studies have shown that fenofibrate enhances the toxic effect of ultraviolet (UV) radiation from the sun, which might result in side effects such as skin rashes. One controlled study showed that taking 2 grams of vitamin C and 1,000 IU of vitamin E prior to ultraviolet exposure dramatically blocked UV-fenofibrate damage to red blood cells.108 though further controlled studies are needed, people taking fenofibrate should probably supplement with vitamins C and E until more information is available.

  • Floxuridine

    Chemotherapy can injure cancer cells by creating oxidative damage. As a result, some oncologists recommend that patients avoid supplementing antioxidants if they are undergoing chemotherapy. Limited test tube research occasionally does support the idea that an antioxidant can interfere with oxidative damage to cancer cells.109 However, most scientific research does not support this supposition.

    A modified form of vitamin A has been reported to work synergistically with chemotherapy in test tube research.110 Vitamin C appears to increase the effectiveness of chemotherapy in animals111 and with human breast cancer cells in test tube research.112 In a double-blind study, Japanese researchers found that the combination of vitamin E, vitamin C, and N-acetyl cysteine (NAC)—all antioxidants—protected against chemotherapy-induced heart damage without interfering with the action of the chemotherapy.113

    A comprehensive review of antioxidants and chemotherapy leaves open the question of whether supplemental antioxidants definitely help people with chemotherapy side effects, but neither does it show that antioxidants should be avoided for fear that the actions of chemotherapy are interfered with.114 Although research remains incomplete, the idea that people taking chemotherapy should avoid antioxidants is not supported by scientific research.

    The interaction is supported by preliminary, weak, fragmentary, and/or contradictory scientific evidence.
  • Fludarabine

    Chemotherapy can injure cancer cells by creating oxidative damage. As a result, some oncologists recommend that patients avoid supplementing antioxidants if they are undergoing chemotherapy. Limited test tube research occasionally does support the idea that an antioxidant can interfere with oxidative damage to cancer cells.115 However, most scientific research does not support this supposition.

    A modified form of vitamin A has been reported to work synergistically with chemotherapy in test tube research.116 Vitamin C appears to increase the effectiveness of chemotherapy in animals117 and with human breast cancer cells in test tube research.118 In a double-blind study, Japanese researchers found that the combination of vitamin E, vitamin C, and N-acetyl cysteine (NAC)—all antioxidants—protected against chemotherapy-induced heart damage without interfering with the action of the chemotherapy.119

    A comprehensive review of antioxidants and chemotherapy leaves open the question of whether supplemental antioxidants definitely help people with chemotherapy side effects, but neither does it show that antioxidants should be avoided for fear that the actions of chemotherapy are interfered with.120 Although research remains incomplete, the idea that people taking chemotherapy should avoid antioxidants is not supported by scientific research.

    The interaction is supported by preliminary, weak, fragmentary, and/or contradictory scientific evidence.
  • Haloperidol

    In a preliminary trial, daily supplementation with omega-3 fatty acids (360 mg of eicosapentaenoic acid plus 240 mg of docosahexaenoic acid), 800 IU of vitamin E, and 1,000 mg of vitamin C for four months decreased the severity of abnormal movements (akathisia) caused by haloperidol.121

  • Ifosfamide

    Chemotherapy can injure cancer cells by creating oxidative damage. As a result, some oncologists recommend that patients avoid supplementing antioxidants if they are undergoing chemotherapy. Limited test tube research occasionally does support the idea that an antioxidant can interfere with oxidative damage to cancer cells.122 However, most scientific research does not support this supposition.

    A modified form of vitamin A has been reported to work synergistically with chemotherapy in test tube research.123 Vitamin C appears to increase the effectiveness of chemotherapy in animals124 and with human breast cancer cells in test tube research.125 In a double-blind study, Japanese researchers found that the combination of vitamin E, vitamin C, and N-acetyl cysteine (NAC)—all antioxidants—protected against chemotherapy-induced heart damage without interfering with the action of the chemotherapy.126

    A comprehensive review of antioxidants and chemotherapy leaves open the question of whether supplemental antioxidants definitely help people with chemotherapy side effects, but neither does it show that antioxidants should be avoided for fear that the actions of chemotherapy are interfered with.127 Although research remains incomplete, the idea that people taking chemotherapy should avoid antioxidants is not supported by scientific research.

    The interaction is supported by preliminary, weak, fragmentary, and/or contradictory scientific evidence.
  • Irinotecan

    Chemotherapy can injure cancer cells by creating oxidative damage. As a result, some oncologists recommend that patients avoid supplementing antioxidants if they are undergoing chemotherapy. Limited test tube research occasionally does support the idea that an antioxidant can interfere with oxidative damage to cancer cells.131 However, most scientific research does not support this supposition.

    A modified form of vitamin A has been reported to work synergistically with chemotherapy in test tube research.132 Vitamin C appears to increase the effectiveness of chemotherapy in animals133 and with human breast cancer cells in test tube research.134 In a double-blind study, Japanese researchers found that the combination of vitamin E, vitamin C, and N-acetyl cysteine (NAC)—all antioxidants—protected against chemotherapy-induced heart damage without interfering with the action of the chemotherapy.135

    A comprehensive review of antioxidants and chemotherapy leaves open the question of whether supplemental antioxidants definitely help people with chemotherapy side effects, but neither does it show that antioxidants should be avoided for fear that the actions of chemotherapy are interfered with.136 Although research remains incomplete, the idea that people taking chemotherapy should avoid antioxidants is not supported by scientific research.

    The interaction is supported by preliminary, weak, fragmentary, and/or contradictory scientific evidence.
  • Lomustine

    Chemotherapy can injure cancer cells by creating oxidative damage. As a result, some oncologists recommend that patients avoid supplementing antioxidants if they are undergoing chemotherapy. Limited test tube research occasionally does support the idea that an antioxidant can interfere with oxidative damage to cancer cells.153 However, most scientific research does not support this supposition.

    A modified form of vitamin A has been reported to work synergistically with chemotherapy in test tube research.154 Vitamin C appears to increase the effectiveness of chemotherapy in animals155 and with human breast cancer cells in test tube research.156 In a double-blind study, Japanese researchers found that the combination of vitamin E, vitamin C, and N-acetyl cysteine (NAC)—all antioxidants—protected against chemotherapy-induced heart damage without interfering with the action of the chemotherapy.157

    A comprehensive review of antioxidants and chemotherapy leaves open the question of whether supplemental antioxidants definitely help people with chemotherapy side effects, but neither does it show that antioxidants should be avoided for fear that the actions of chemotherapy are interfered with.158 Although research remains incomplete, the idea that people taking chemotherapy should avoid antioxidants is not supported by scientific research.

    The interaction is supported by preliminary, weak, fragmentary, and/or contradictory scientific evidence.
  • Mechlorethamine

    Chemotherapy can injure cancer cells by creating oxidative damage. As a result, some oncologists recommend that patients avoid supplementing antioxidants if they are undergoing chemotherapy. Limited test tube research occasionally does support the idea that an antioxidant can interfere with oxidative damage to cancer cells.159 However, most scientific research does not support this supposition.

    A modified form of vitamin A has been reported to work synergistically with chemotherapy in test tube research.160 Vitamin C appears to increase the effectiveness of chemotherapy in animals161 and with human breast cancer cells in test tube research.162 In a double-blind study, Japanese researchers found that the combination of vitamin E, vitamin C, and N-acetyl cysteine (NAC)—all antioxidants—protected against chemotherapy-induced heart damage without interfering with the action of the chemotherapy.163

    A comprehensive review of antioxidants and chemotherapy leaves open the question of whether supplemental antioxidants definitely help people with chemotherapy side effects, but neither does it show that antioxidants should be avoided for fear that the actions of chemotherapy are interfered with.164 Although research remains incomplete, the idea that people taking chemotherapy should avoid antioxidants is not supported by scientific research.

    The interaction is supported by preliminary, weak, fragmentary, and/or contradictory scientific evidence.
  • Melphalan

    Chemotherapy can injure cancer cells by creating oxidative damage. As a result, some oncologists recommend that patients avoid supplementing antioxidants if they are undergoing chemotherapy. Limited test tube research occasionally does support the idea that an antioxidant can interfere with oxidative damage to cancer cells.165 However, most scientific research does not support this supposition.

    A modified form of vitamin A has been reported to work synergistically with chemotherapy in test tube research.166 Vitamin C appears to increase the effectiveness of chemotherapy in animals167 and with human breast cancer cells in test tube research.168 In a double-blind study, Japanese researchers found that the combination of vitamin E, vitamin C, and N-acetyl cysteine (NAC)—all antioxidants—protected against chemotherapy-induced heart damage without interfering with the action of the chemotherapy.169

    A comprehensive review of antioxidants and chemotherapy leaves open the question of whether supplemental antioxidants definitely help people with chemotherapy side effects, but neither does it show that antioxidants should be avoided for fear that the actions of chemotherapy are interfered with.170 Although research remains incomplete, the idea that people taking chemotherapy should avoid antioxidants is not supported by scientific research.

  • Mercaptopurine

    Chemotherapy can injure cancer cells by creating oxidative damage. As a result, some oncologists recommend that patients avoid supplementing antioxidants if they are undergoing chemotherapy. Limited test tube research occasionally does support the idea that an antioxidant can interfere with oxidative damage to cancer cells.171 However, most scientific research does not support this supposition.

    A modified form of vitamin A has been reported to work synergistically with chemotherapy in test tube research.172 Vitamin C appears to increase the effectiveness of chemotherapy in animals173 and with human breast cancer cells in test tube research.174 In a double-blind study, Japanese researchers found that the combination of vitamin E, vitamin C, and N-acetyl cysteine (NAC)—all antioxidants—protected against chemotherapy-induced heart damage without interfering with the action of the chemotherapy.175

    A comprehensive review of antioxidants and chemotherapy leaves open the question of whether supplemental antioxidants definitely help people with chemotherapy side effects, but neither does it show that antioxidants should be avoided for fear that the actions of chemotherapy are interfered with.176 Although research remains incomplete, the idea that people taking chemotherapy should avoid antioxidants is not supported by scientific research.

    The interaction is supported by preliminary, weak, fragmentary, and/or contradictory scientific evidence.
  • Minocycline

    Tooth discoloration is a side effect of minocycline observed primarily in young children, but it may occur in adults as well. Vitamin C supplementation may prevent staining in adults taking minocycline.184

  • Polifeprosan 20 with Carmustine

    Chemotherapy can injure cancer cells by creating oxidative damage. As a result, some oncologists recommend that patients avoid supplementing antioxidants if they are undergoing chemotherapy. Limited test tube research occasionally does support the idea that an antioxidant can interfere with oxidative damage to cancer cells.195 However, most scientific research does not support this supposition.

    A modified form of vitamin A has been reported to work synergistically with chemotherapy in test tube research.196 Vitamin C appears to increase the effectiveness of chemotherapy in animals197 and with human breast cancer cells in test tube research.198 In a double-blind study, Japanese researchers found that the combination of vitamin E, vitamin C, and N-acetyl cysteine (NAC)—all antioxidants—protected against chemotherapy-induced heart damage without interfering with the action of the chemotherapy.199

    A comprehensive review of antioxidants and chemotherapy leaves open the question of whether supplemental antioxidants definitely help people with chemotherapy side effects, but neither does it show that antioxidants should be avoided for fear that the actions of chemotherapy are interfered with.200 Although research remains incomplete, the idea that people taking chemotherapy should avoid antioxidants is not supported by scientific research.

    The interaction is supported by preliminary, weak, fragmentary, and/or contradictory scientific evidence.
  • Thioguanine

    Chemotherapy can injure cancer cells by creating oxidative damage. As a result, some oncologists recommend that patients avoid supplementing antioxidants if they are undergoing chemotherapy. Limited test tube research occasionally does support the idea that an antioxidant can interfere with oxidative damage to cancer cells.202 However, most scientific research does not support this supposition.

    A modified form of vitamin A has been reported to work synergistically with chemotherapy in test tube research.203 Vitamin C appears to increase the effectiveness of chemotherapy in animals204 and with human breast cancer cells in test tube research.205 In a double-blind study, Japanese researchers found that the combination of vitamin E, vitamin C, and N-acetyl cysteine (NAC)—all antioxidants—protected against chemotherapy-induced heart damage without interfering with the action of the chemotherapy.206

    A comprehensive review of antioxidants and chemotherapy leaves open the question of whether supplemental antioxidants definitely help people with chemotherapy side effects, but neither does it show that antioxidants should be avoided for fear that the actions of chemotherapy are interfered with.207 Although research remains incomplete, the idea that people taking chemotherapy should avoid antioxidants is not supported by scientific research.

    The interaction is supported by preliminary, weak, fragmentary, and/or contradictory scientific evidence.
  • Thiotepa

    Chemotherapy can injure cancer cells by creating oxidative damage. As a result, some oncologists recommend that patients avoid supplementing antioxidants if they are undergoing chemotherapy. Limited test tube research occasionally does support the idea that an antioxidant can interfere with oxidative damage to cancer cells.208 However, most scientific research does not support this supposition.

    A modified form of vitamin A has been reported to work synergistically with chemotherapy in test tube research.209 Vitamin C appears to increase the effectiveness of chemotherapy in animals210 and with human breast cancer cells in test tube research.211 In a double-blind study, Japanese researchers found that the combination of vitamin E, vitamin C, and N-acetyl cysteine (NAC)—all antioxidants—protected against chemotherapy-induced heart damage without interfering with the action of the chemotherapy.212

    A comprehensive review of antioxidants and chemotherapy leaves open the question of whether supplemental antioxidants definitely help people with chemotherapy side effects, but neither does it show that antioxidants should be avoided for fear that the actions of chemotherapy are interfered with.213 Although research remains incomplete, the idea that people taking chemotherapy should avoid antioxidants is not supported by scientific research.

    The interaction is supported by preliminary, weak, fragmentary, and/or contradictory scientific evidence.
  • Uracil Mustard

    Chemotherapy can injure cancer cells by creating oxidative damage. As a result, some oncologists recommend that patients avoid supplementing antioxidants if they are undergoing chemotherapy. Limited test tube research occasionally does support the idea that an antioxidant can interfere with oxidative damage to cancer cells.214 However, most scientific research does not support this supposition.

    A modified form of vitamin A has been reported to work synergistically with chemotherapy in test tube research.215 Vitamin C appears to increase the effectiveness of chemotherapy in animals216 and with human breast cancer cells in test tube research.217 In a double-blind study, Japanese researchers found that the combination of vitamin E, vitamin C, and N-acetyl cysteine (NAC)—all antioxidants—protected against chemotherapy-induced heart damage without interfering with the action of the chemotherapy.218

    A comprehensive review of antioxidants and chemotherapy leaves open the question of whether supplemental antioxidants definitely help people with chemotherapy side effects, but neither does it show that antioxidants should be avoided for fear that the actions of chemotherapy are interfered with.219 Although research remains incomplete, the idea that people taking chemotherapy should avoid antioxidants is not supported by scientific research.

    The interaction is supported by preliminary, weak, fragmentary, and/or contradictory scientific evidence.
  • Vincristine

    Chemotherapy can injure cancer cells by creating oxidative damage. As a result, some oncologists recommend that patients avoid supplementing antioxidants if they are undergoing chemotherapy. Limited test tube research occasionally does support the idea that an antioxidant can interfere with oxidative damage to cancer cells.220 However, most scientific research does not support this supposition.

    A modified form of vitamin A has been reported to work synergistically with chemotherapy in test tube research.221 Vitamin C appears to increase the effectiveness of chemotherapy in animals222 and with human breast cancer cells in test tube research.223 In a double-blind study, Japanese researchers found that the combination of vitamin E, vitamin C, and N-acetyl cysteine (NAC)—all antioxidants—protected against chemotherapy-induced heart damage without interfering with the action of the chemotherapy.224

    A comprehensive review of antioxidants and chemotherapy leaves open the question of whether supplemental antioxidants definitely help people with chemotherapy side effects, but neither does it show that antioxidants should be avoided for fear that the actions of chemotherapy are interfered with.225 Although research remains incomplete, the idea that people taking chemotherapy should avoid antioxidants is not supported by scientific research.

    The interaction is supported by preliminary, weak, fragmentary, and/or contradictory scientific evidence.

Support Medicine

  • Carbidopa

    A combination of levodopa/carbidopa and vitamin C may be useful for people with Parkinson’s disease whose motor complications are not effectively managed with conventional drug treatment. This combination was administered to people with Parkinson’s disease for 16.8 months in an unblinded, uncontrolled study.34 The researchers reported that participants who completed the study experienced substantial increases in the number of hours with good functional capacity and were able to reduce their intake of other anti-Parkinsonian drugs. However, 62% of the participants withdrew from the study, citing difficulty in performing voluntary movements as the main reason. Until more research is performed, this drug-nutrient combination must be viewed as preliminary.

    The interaction is supported by preliminary, weak, fragmentary, and/or contradictory scientific evidence.
  • Carbidopa-Levodopa

    Combining levodopa-carbidopa and vitamin C may be useful for people with Parkinson’s disease whose motor complications are not effectively managed with conventional drug treatment. This combination was administered to people with Parkinson’s disease in a preliminary study.35 The researchers reported several improvements in participants who completed the study; however, 62% of the participants withdrew from the study, most citing difficulty in performing normal movements. Until more research is performed, this drug-nutrient combination must be viewed as experimental.

    The interaction is supported by preliminary, weak, fragmentary, and/or contradictory scientific evidence.
  • Docetaxel

    Chemotherapy can injure cancer cells by creating oxidative damage. As a result, some oncologists recommend that patients avoid supplementing antioxidants if they are undergoing chemotherapy. Limited test tube research occasionally does support the idea that an antioxidant can interfere with oxidative damage to cancer cells.69 However, most scientific research does not support this supposition.

    A modified form of vitamin A has been reported to work synergistically with chemotherapy in test tube research.70 Vitamin C appears to increase the effectiveness of chemotherapy in animals71 and with human breast cancer cells in test tube research.72 In a double-blind study, Japanese researchers found that the combination of vitamin E, vitamin C, and N-acetyl cysteine (NAC)—all antioxidants—protected against chemotherapy-induced heart damage without interfering with the action of the chemotherapy.73

    A comprehensive review of antioxidants and chemotherapy leaves open the question of whether supplemental antioxidants definitely help people with chemotherapy side effects, but it clearly shows that antioxidants need not be avoided for fear that the actions of chemotherapy are interfered with.74 Although research remains incomplete, the idea that people taking chemotherapy should avoid antioxidants is not supported by scientific research.

    A new formulation of selenium (Seleno-Kappacarrageenan) was found to reduce kidney damage and white blood cell–lowering effects of cisplatin in one human study. However, the level used in this study (4,000 mcg per day) is potentially toxic and should only be used under the supervision of a doctor.75

    The interaction is supported by preliminary, weak, fragmentary, and/or contradictory scientific evidence.
  • Isosorbide Mononitrate

    Some persons taking nitroglycerin or isosorbide mononitrate may find that it loses efficacy over time. This is because the body adapts to the drug, a process known as developing tolerance. One study found that taking 2 grams three times daily of vitamin C can decrease this effect when nitroglycerin patches are simultaneously used.137 Similar benefits have been confirmed in another study.138 However, it should be noted that it is also possible to avoid tolerance to these drugs by simply changing the dosing schedule. People taking ISMN or nitroglycerin should talk with their pharmacists about avoiding drug tolerance.

  • Nitroglycerin

    Vitamin C may help maintain the blood vessel dilation response to nitroglycerin. A double-blind study found that individuals taking 2 grams of vitamin C three times per day did not tend to develop nitroglycerin tolerance over time compared to those taking placebo.185 In another controlled clinical trial, similar protection was achieved with 500 mg three times daily.186

    People using long-acting nitroglycerin can avoid tolerance with a ten- to twelve-hour hour nitroglycerin-free period every day. People taking long-acting nitroglycerin should ask their prescribing doctor or pharmacist about preventing nitroglycerin tolerance.

Reduces Effectiveness

  • none

Potential Negative Interaction

  • none

Explanation Required

  • Acetaminophen

    Taking 3 grams vitamin C with acetaminophen has been shown to prolong the amount of time acetaminophen stays in the body.226 This theoretically might allow people to use less acetaminophen, thereby reducing the risk of side effects. Consult with a doctor about this potential before reducing the amount of acetaminophen. However, increasing the time acetaminophen is in the body might also theoretically increase its toxicity. Consult with a doctor before taking vitamin C along with acetaminophen.227

    The interaction is supported by preliminary, weak, fragmentary, and/or contradictory scientific evidence.
  • Capecitabine

    Chemotherapy can injure cancer cells by creating oxidative damage. As a result, some oncologists recommend that patients avoid supplementing antioxidants if they are undergoing chemotherapy. Limited test tube research occasionally does support the idea that an antioxidant can interfere with oxidative damage to cancer cells.228 However, most scientific research does not support this supposition.

    A modified form of vitamin A has been reported to work synergistically with chemotherapy in test tube research.229 Vitamin C appears to increase the effectiveness of chemotherapy in animals230 and with human breast cancer cells in test tube research.231 In a double-blind study, Japanese researchers found that the combination of vitamin E, vitamin C, and N-acetyl cysteine (NAC)—all antioxidants—protected against chemotherapy-induced heart damage without interfering with the action of the chemotherapy.232

    A comprehensive review of antioxidants and chemotherapy leaves open the question of whether supplemental antioxidants definitely help people with chemotherapy side effects, but neither does it show that antioxidants should be avoided for fear that the actions of chemotherapy are interfered with.233 Although research remains incomplete, the idea that people taking chemotherapy should avoid antioxidants is not supported by scientific research.

    The interaction is supported by preliminary, weak, fragmentary, and/or contradictory scientific evidence.
  • Cisplatin

    Chemotherapy can injure cancer cells by creating oxidative damage. As a result, some oncologists recommend that patients avoid supplementing antioxidants if they are undergoing chemotherapy. Limited test tube research occasionally does support the idea that an antioxidant can interfere with oxidative damage to cancer cells.234 However, most scientific research does not support this supposition.

    A modified form of vitamin A has been reported to work synergistically with chemotherapy in test tube research. Vitamin C combined with Vitamin K3 appears to increase the effectiveness of chemotherapy in animals235 and with human breast cancer cells in test tube research.236 In a double-blind study, Japanese researchers found that the combination of vitamin E, vitamin C, and N-acetyl cysteine (NAC)—all antioxidants—protected against chemotherapy-induced heart damage without interfering with the action of the chemotherapy.237

    A comprehensive review of antioxidants and chemotherapy leaves open the question of whether supplemental antioxidants definitely help people with chemotherapy side effects, but neither does it show that antioxidants should be avoided for fear that the actions of chemotherapy are interfered with.238 Although research remains incomplete, the idea that people taking chemotherapy should avoid antioxidants is not supported by scientific research.

    The interaction is supported by preliminary, weak, fragmentary, and/or contradictory scientific evidence.
  • Cyclophosphamide

    Chemotherapy can injure cancer cells by creating oxidative damage. As a result, some oncologists recommend that patients avoid supplementing antioxidants if they are undergoing chemotherapy. Limited test tube research occasionally does support the idea that an antioxidant can interfere with oxidative damage to cancer cells.239 However, most scientific research does not support this supposition.

    Cyclophosphamide requires activation by the liver through a process called oxidation. In theory, antioxidant nutrients (vitamin A, vitamin E, beta-carotene and others) might interfere with the activation of cyclophosphamide. There is no published research linking antioxidant vitamins to reduced cyclophosphamide effectiveness in cancer treatment. Another animal research report indicated that vitamin C may increase the effectiveness of cyclophosphamide without producing new side effects.240 Preliminary human research found that adding antioxidants (beta-carotene, vitamin A, and vitamin E) to cyclophosphamide therapy increased the survival of people with small-cell lung cancer treated with cyclophosphamide.241 It is too early to know if adding antioxidants to cyclophosphamide for cancer treatment is better than cyclophosphamide alone. Vitamin A can be toxic in high amounts.

    The interaction is supported by preliminary, weak, fragmentary, and/or contradictory scientific evidence.
  • Cytarabine

    Chemotherapy can injure cancer cells by creating oxidative damage. As a result, some oncologists recommend that patients avoid supplementing antioxidants if they are undergoing chemotherapy. Limited test tube research occasionally does support the idea that an antioxidant can interfere with oxidative damage to cancer cells.242 However, most scientific research does not support this supposition.

    A modified form of vitamin A has been reported to work synergistically with chemotherapy in test tube research.243 Vitamin C appears to increase the effectiveness of chemotherapy in animals244 and with human breast cancer cells in test tube research.245 In a double-blind study, Japanese researchers found that the combination of vitamin E, vitamin C, and N-acetyl cysteine (NAC)—all antioxidants—protected against chemotherapy-induced heart damage without interfering with the action of the chemotherapy.246

    A comprehensive review of antioxidants and chemotherapy leaves open the question of whether supplemental antioxidants definitely help people with chemotherapy side effects, but neither does it show that antioxidants should be avoided for fear that the actions of chemotherapy are interfered with.247 Although research remains incomplete, the idea that people taking chemotherapy should avoid antioxidants is not supported by scientific research.

    The interaction is supported by preliminary, weak, fragmentary, and/or contradictory scientific evidence.
  • Epinephrine

    Intravenous administration of epinephrine to human volunteers reduced plasma concentrations of vitamin C.248 Epinephrine and other “stress hormones” may reduce intracellular concentrations of potassium and magnesium.249 Although there are no clinical studies in humans, it seems reasonable that individuals using epinephrine should consume a diet high in vitamin C, potassium, and magnesium, or should consider supplementing with these nutrients.

  • Etoposide

    The chemotherapy drug cisplatin may cause kidney damage, resulting in depletion of calcium and phosphate.256

    The interaction is supported by preliminary, weak, fragmentary, and/or contradictory scientific evidence.
  • Fluorouracil

    Chemotherapy can injure cancer cells by creating oxidative damage. As a result, some oncologists recommend that patients avoid supplementing antioxidants if they are undergoing chemotherapy. Limited test tube research occasionally does support the idea that an antioxidant can interfere with oxidative damage to cancer cells.263 However, most scientific research does not support this supposition.

    A modified form of vitamin A has been reported to work synergistically with chemotherapy in test tube research.264 Vitamin C appears to increase the effectiveness of chemotherapy in animals265 and with human breast cancer cells in test tube research.266 In a double-blind study, Japanese researchers found that the combination of vitamin E, vitamin C, and N-acetyl cysteine (NAC)—all antioxidants—protected against chemotherapy-induced heart damage without interfering with the action of the chemotherapy.267

    A comprehensive review of antioxidants and chemotherapy leaves open the question of whether supplemental antioxidants definitely help people with chemotherapy side effects, but the article strongly suggests that antioxidants need not be avoided for fear that the actions of chemotherapy would be interfered with.268

    A new formulation of selenium (Seleno-Kappacarrageenan) was found to reduce kidney damage and white blood cell–lowering effects of cisplatin in one human study. However, the level used in this study (4,000 mcg per day) is potentially toxic and should only be used under the supervision of a doctor.269

    The interaction is supported by preliminary, weak, fragmentary, and/or contradictory scientific evidence.
  • Hydrocodone-Acetaminophen

    Taking 3 grams vitamin C with acetaminophen has been shown to prolong the amount of time acetaminophen stays in the body.270 This theoretically might allow people to use less acetaminophen, thereby reducing the risk of side effects. Consult with a doctor about this potential before reducing the amount of acetaminophen. However, increasing the time acetaminophen is in the body might also theoretically increase its toxicity. Consult with a doctor before taking vitamin C along with acetaminophen.271

    The interaction is supported by preliminary, weak, fragmentary, and/or contradictory scientific evidence.
  • Hydroxyurea

    Chemotherapy can injure cancer cells by creating oxidative damage. As a result, some oncologists recommend that patients avoid supplementing antioxidants if they are undergoing chemotherapy. Limited test tube research occasionally does support the idea that an antioxidant can interfere with oxidative damage to cancer cells.272 However, most scientific research does not support this supposition.

    A modified form of vitamin A has been reported to work synergistically with chemotherapy in test tube research.273 Vitamin C appears to increase the effectiveness of chemotherapy in animals274 and with human breast cancer cells in test tube research.275 In a double-blind study, Japanese researchers found that the combination of vitamin E, vitamin C, and N-acetyl cysteine (NAC)—all antioxidants—protected against chemotherapy-induced heart damage without interfering with the action of the chemotherapy.276

    A comprehensive review of antioxidants and chemotherapy leaves open the question of whether supplemental antioxidants definitely help people with chemotherapy side effects, but neither does it show that antioxidants should be avoided for fear that the actions of chemotherapy are interfered with.277 Although research remains incomplete, the idea that people taking chemotherapy should avoid antioxidants is not supported by scientific research.

    The interaction is supported by preliminary, weak, fragmentary, and/or contradictory scientific evidence.
  • Irinotecan

    The chemotherapy drug cisplatin may cause kidney damage, resulting in depletion of calcium and phosphate.278

    The interaction is supported by preliminary, weak, fragmentary, and/or contradictory scientific evidence.
  • Methotrexate

    Chemotherapy can injure cancer cells by creating oxidative damage. As a result, some oncologists recommend that patients avoid supplementing antioxidants if they are undergoing chemotherapy. Limited test tube research occasionally does support the idea that an antioxidant can interfere with oxidative damage to cancer cells.279 However, most scientific research does not support this supposition.

    A modified form of vitamin A has been reported to work synergistically with chemotherapy in test tube research. Vitamin C combined with Vitamin K3 appears to increase the effectiveness of chemotherapy in animals280 and with human breast cancer cells in test tube research.281 In a double-blind study, Japanese researchers found that the combination of vitamin E, vitamin C, and N-acetyl cysteine (NAC)—all antioxidants—protected against chemotherapy-induced heart damage without interfering with the action of the chemotherapy.282

    A comprehensive review of antioxidants and chemotherapy leaves open the question of whether supplemental antioxidants definitely help people with chemotherapy side effects, but it clearly shows that antioxidants need not be avoided for fear that the actions of chemotherapy are interfered with.283 Although research remains incomplete, the idea that people taking chemotherapy should avoid antioxidants is not supported by scientific research.

    The interaction is supported by preliminary, weak, fragmentary, and/or contradictory scientific evidence.
  • Methylprednisolone

    Oral corticosteroids have been found to increase urinary loss of vitamin K, vitamin C, selenium, and zinc.284 The importance of these losses is unknown.

    The interaction is supported by preliminary, weak, fragmentary, and/or contradictory scientific evidence.
  • Paclitaxel

    Chemotherapy can injure cancer cells by creating oxidative damage. As a result, some oncologists recommend that patients avoid supplementing antioxidants if they are undergoing chemotherapy. Limited test tube research occasionally does support the idea that an antioxidant can interfere with oxidative damage to cancer cells.285 However, most scientific research does not support this supposition.

    A modified form of vitamin A has been reported to work synergistically with chemotherapy in test tube research.286 Vitamin C appears to increase the effectiveness of chemotherapy in animals287 and with human breast cancer cells in test tube research.288

    A comprehensive review of antioxidants and chemotherapy leaves open the question of whether supplemental antioxidants definitely help people with chemotherapy side effects, but the article strongly suggests that antioxidants need not be avoided for fear that the actions of chemotherapy would be interfered with.289

    A new formulation of selenium (Seleno-Kappacarrageenan) was found to reduce kidney damage and white blood cell–lowering effects of cisplatin in one human study. However, the level used in this study (4,000 mcg per day) is potentially toxic and should only be used under the supervision of a doctor.290

    The interaction is supported by preliminary, weak, fragmentary, and/or contradictory scientific evidence.
  • Perphenazine

    Taking phenothiazine drugs can stop menstruation in some women. Two women taking phenothiazines similar to perphenazine began menstruating following supplementation with 6 grams of vitamin C each day.291 Controlled studies are needed to determine whether vitamin C supplementation might benefit women specifically taking perphenazine who are experiencing menstrual changes. Some health practitioners recommend vitamin C supplementation to women who stop menstruating while taking perphenazine. Vitamin C might also enhance the effectiveness of neuroleptic drugs such as perphenazine in the treatment of schizophrenia. One uncontrolled study showed that 10 of 13 individuals experienced a reduction in disorganized thoughts, hallucinations, and suspicious thoughts when 8 grams of vitamin C was added to their daily drug therapy.292 Controlled studies are needed to show whether people taking perphenazine for schizophrenia might benefit from vitamin C supplementation.

    The interaction is supported by preliminary, weak, fragmentary, and/or contradictory scientific evidence.
  • Prednisolone

    Oral corticosteroids have been found to increase urinary loss of vitamin K, vitamin C, selenium, and zinc.293 The importance of these losses is unknown.

    The interaction is supported by preliminary, weak, fragmentary, and/or contradictory scientific evidence.
  • Prednisone

    Oral corticosteroids have been found to increase urinary loss of vitamin K, vitamin C, selenium, and zinc.294 The importance of these losses is unknown.

    The interaction is supported by preliminary, weak, fragmentary, and/or contradictory scientific evidence.
  • Thioridazine

    Taking phenothiazine drugs can stop menstruation in some women. A 45-year-old woman taking thioridazine started menstruating once she began supplementing with 6 grams of vitamin C daily.295 Controlled studies are needed to determine whether women taking thioridazine, who are experiencing menstrual changes, might benefit from supplemental vitamin C. Vitamin C might also enhance the effectiveness of neuroleptic drugs, such as thioridazine, in the treatment of schizophrenia. One uncontrolled study showed that 10 of 13 individuals experienced a reduction in disorganized thoughts, hallucinations, and suspicious thoughts when 8 grams of vitamin C was added to their daily drug therapy.296 Controlled studies are needed to determine whether people taking thioridazine for schizophrenia might benefit from vitamin C supplementation.

    The interaction is supported by preliminary, weak, fragmentary, and/or contradictory scientific evidence.
  • Vinblastine

    Chemotherapy can injure cancer cells by creating oxidative damage. As a result, some oncologists recommend that patients avoid supplementing antioxidants if they are undergoing chemotherapy. Limited test tube research occasionally does support the idea that an antioxidant can interfere with oxidative damage to cancer cells.297 However, most scientific research does not support this supposition.

    A modified form of vitamin A has been reported to work synergistically with chemotherapy in test tube research.298 Vitamin C appears to increase the effectiveness of chemotherapy in animals299 and with human breast cancer cells in test tube research.300 In a double-blind study, Japanese researchers found that the combination of vitamin E, vitamin C, and N-acetyl cysteine (NAC)—all antioxidants—protected against chemotherapy-induced heart damage without interfering with the action of the chemotherapy.301

    A comprehensive review of antioxidants and chemotherapy leaves open the question of whether supplemental antioxidants definitely help people with chemotherapy side effects, but neither does it show that antioxidants should be avoided for fear that the actions of chemotherapy are interfered with.302 Although research remains incomplete, the idea that people taking chemotherapy should avoid antioxidants is not supported by scientific research.

    The interaction is supported by preliminary, weak, fragmentary, and/or contradictory scientific evidence.
  • Warfarin

    Although case reports have suggested that vitamin C might increase the activity of anticoagulants in a potentially dangerous way, this interaction has not been confirmed in research studies.303 In fact, a possible interference by vitamin C with the effect of anticoagulants has also been reported.304 A 52-year-old woman maintained on 7.5 mg of warfarin per day had a shortening of the blood clotting time which was not corrected by increasing warfarin up to 20 mg per day. Further questioning revealed she had begun taking an unspecified amount of vitamin C each morning. After stopping vitamin C, the blood clotting time returned to desired levels. Based on this and other case reports, people taking warfarin should consult with their physician before taking vitamin C supplements.

More Resources

Vitamin C

Where to Find It

Broccoli, red peppers, currants, Brussels sprouts, parsley, potatoes, citrus fruit, and strawberries are good sources of vitamin C.  Rose hips, harvested from rose bushes and sold as a supplement, are particularly high in vitamin C.

Resources

See a list of books, periodicals, and other resources for this and related topics.

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