In a study of elderly women, administration of omeprazole decreased the absorption of calcium,1 presumably because the drug decreased the stomach's production of hydrochloric acid, which is necessary for calcium absorption. The form of calcium used in the study to test calcium absorption was calcium carbonate. Drugs that reduce stomach acid secretion may not inhibit other forms of calcium, such as calcium citrate.2
Folic acid is needed by the body to utilize vitamin B12. Antacids, including sodium bicarbonate, inhibit folic acid absorption.3 People taking antacids are advised to supplement with folic acid.
Treatment of healthy volunteers with omeprazole for four weeks resulted in a 12.3% decrease in blood levels of vitamin C.5
In a study of nine healthy people, sodium bicarbonate administered with 10 mg of iron led to lower iron levels compared to iron administered alone.6 This interaction may be avoided by taking sodium bicarbonate-containing products two hours before or after iron-containing supplements.
Omeprazole interferes with the absorption of vitamin B12 from food (though not from supplements) in some7 , 8 , 9 , 10 but not all11 , 12 studies. A true deficiency state, resulting in vitamin B12-deficiency anemia, has only been reported in one case.13 The fall in vitamin B12 status may result from the decrease in stomach acid required for vitamin B12 absorption from food caused by the drug.14 This problem may possibly be averted by drinking acidic juices when eating foods containing vitamin B12.15
However, all people taking omeprazole need to either supplement with vitamin B12 or have their vitamin B12 status checked on a yearly basis. Even relatively small amounts of vitamin B12 such as 10–50 mcg per day, are likely to protect against drug induced vitamin depletion.
People taking omeprazole may increase absorption of dietary vitamin B12 by drinking cranberry (Vaccinium marocarpon) juice or other acidic liquids with vitamin B12-containing foods.16
In a study of healthy human volunteers, supplementing with St. John's wort greatly decreased omeprazole blood levels by accelerating the metabolism of the drug.17 Use of St. John's wort may, therefore, interfere with the actions of omeprazole.
1. O'Connell MB, Madden DM, Murray AM, et al. Effects of proton pump inhibitors on calcium carbonate absorption in women: a randomized crossover trial. Am J Med 2005;118:778–81.
2. (Recker RR. Calcium absorption and achlorhydria. N Engl J Med 1985;313:70–3.
3. Russell RM, Golner BB, Krasinski SD, et al. Effect of antacid and H2 receptor antagonists on the intestinal absorption of folic acid. J Lab Clin Med 1988;112:458–63.
4. Russell RM, Golner BB, Krasinski SD, et al. Effect of antacid and H2 receptor antagonists on the intestinal absorption of folic acid. J Lab Clin Med 1988;112:458–63.
5. Henry EB, Carswell A, Wirz A, et al. Proton pump inhibitors reduce the bioavailability of dietary vitamin C. Aliment Pharmacol Ther2005;22:539–5.
6. O’Neil-Cutting MA, Crosby WH. The effect of antacids on the absorption of simultaneously ingested iron. JAMA 1986;255:1468–70.
7. Marcuard SP, Albernaz L, Khazanie PG. Omeprazole therapy causes malabsorption of cyanocobalamin (Vitamin B12). Ann Intern Med 1994;120:211–5.
8. Termanini B, Gibril F, Sutliff VE, et al. Effect of long-term gastric acid suppressive therapy on serum vitamin B12 levels in patients with Zollinger-Ellison syndrome. Am J Med 1998;104:422–30.
9. Koop H. Review article: metabolic consequences of long-term inhibition of acid secretion by omeprazole. Aliment Pharmacol Ther 1992;6:399–406 [review].
10. Bellou A, Aimone-Gastin I, De Korwin JD, et al. Cobalamin deficiency with megaloblastic anaemia in one patient under long-term omeprazole therapy. J Intern Med 1996;240:161–4.
11. Koop H, Bachem MG. Serum iron, ferritin, and vitamin B12 during prolonged omeprazole therapy. J Clin Gastroenterol 1992;14:288–92.
12. Schenk BE, Festen HP, Kuipers EJ, et al. Effect of short-and long-term treatment with omeprazole on the absorption and serum levels of cobalamin. Aliment Pharmacol Ther 1996;10:541–5.
13. Bellou A, Aimone-Gastin I, De Korwin JD, et al. Cobalamin deficiency with megaloblastic anaemia in one patient under long-term omeprazole therapy. J Intern Med 1996;240:161–4.
14. Saltzman JR, Kemp JA, Golner BB, et al. Effect of hypochlorhydria due to omeprazole treatment or atrophic gastritis on protein-bound vitamin B12 absorption. J Am Coll Nutr 1994;13:584–91.
15. Bradford GS, Taylor CT. Omeprazole and vitamin B12 deficiency. Ann Pharmacother 1999;33:641–3 [review].
16. Saltzman JR, Kemp JA, Golner BB, et al. Effect of hypochlorhydria due to omeprazole treatment or atrophic gastritis on protein-bound vitamin B12 absorption. J Am Coll Nutr 1994;13:584–91.
17. Wang LS, Zhou G, Zhu B, et al. St John's wort induces both cytochrome P450 3A4-catalyzed sulfoxidation and 2C19-dependent hydroxylation of omeprazole. Clin Pharmacol Ther 2004;75:191–7.
18. Gau JT, Yang YX, Chen R, Kao TC. Uses of proton pump inhibitors and hypomagnesemia. Pharmacoepidemiol Drug Saf 2012;21:553–9.
19. U.S. Food and Drug Administration. FDA Drug Safety Communication: Low magnesium levels can be associated with long-term use of Proton Pump Inhibitor drugs (PPIs). U.S. Food and Drug Administration Web site. Accessed at http://www.fda.gov/drugs/drugsafety/ucm245011.htm#Additional_Information_for_Patients on September 13, 2011
Last Review: 05-01-2013
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