Methionine is one of the essential amino acids (building blocks of protein), meaning that it cannot be produced by the body, and must be provided by the diet. It supplies sulfur and other compounds required by the body for normal metabolism and growth. Methionine also belongs to a group of compounds called lipotropics, or chemicals that help the liver process fats (lipids). Others in this group include choline, inositol, and betaine (trimethylglycine).
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2,000 mg daily
5 grams per day
Preliminary trials have suggested that the amino acid methionine may effectively treat some symptoms of Parkinson’s disease.
HIV and AIDS Support
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One trial found that methionine may improve memory recall in people with AIDS-related nervous system degeneration.
People with AIDS have low levels of methionine. Some researchers suggest that these low methionine levels may explain some aspects of the disease process,2 , 3 , 4 especially the deterioration that occurs in the nervous system and is responsible for symptoms such as dementia.5 , 6 A preliminary trial found that methionine (6 grams per day) may improve memory recall in people with AIDS-related nervous system degeneration.7
In a preliminary trial, a thymus extract known as Thymomodulin® improved several immune parameters among people with early HIV infection, including an increase in the number of T-helper cells.8
Amino acid requirements vary according to body weight. However, average-size adults require approximately 800–1,000 mg of methionine per day—an amount easily obtained or even exceeded by most Western diets.
Meat, fish, and dairy are all good sources of methionine. Vegetarians can obtain methionine from whole grains, but beans are a relatively poor source of this amino acid.
Animal studies suggest that diets high in methionine, in the presence of B-vitamin deficiencies, may increase the risk for atherosclerosis (hardening of the arteries) by increasing blood levels of cholesterol and a compound called homocysteine.10 This idea has not yet been tested in humans. Excessive methionine intake, together with inadequate intake of folic acid, vitamin B6, and vitamin B12, can increase the conversion of methionine to homocysteine—a substance linked to heart disease and stroke. Even in the absence of a deficiency of folic acid, B6, or B12, megadoses of methionine (7 grams per day) have been found to cause elevations in blood levels of homocysteine.11 Whether such an increase would create a significant hazard for humans taking supplemental methionine has not been established. Supplementation of up to 2 grams of methionine daily for long periods of time has not been reported to cause any serious side effects.12
1. Smythies JR, Halsey JH. Treatment of Parkinson's disease with l-methionine. South Med J 1984;77:1577.
2. Muller F, Svardal AM, Aukrust P, et al. Elevated plasma concentration of reduced homocysteine in patients with human immunodeficiency virus infection. Am J Clin Nutr 1996;242-6.
3. Revillard JP. Lipid peroxidation in Human Immunodeficiency Virus infection. J Acquired Immunodef Synd 1992;5:637-8.
4. Singer P, Katz DP, Dillon L, et al. Nutritional aspects of the acquired immunodeficiency syndrome. Am J Gastroenterol 1992;87:265-73.
5. Tan SV, Guiloff RJ. Hypothesis on the pathogenesis of vacuolar myelopathy, dementia, and peripheral neuropathy in AIDS. J Neurol Neurosurg Psychiat 1998;65:23-8.
6. Keating JN, Trimble KC, Mulcahy F, et al. Evidence of brain methyltransferase inhibition and early brain involvement in HIV-positive patients. Lancet 1991;337:935-9.
7. Dorfman D, DiRocco A, Simpson D, et al. Oral methionine may improve neuropsychological function in patients with AIDS myelopathy: results of an open-label trial. AIDS 1997;11:1066-7.
8. Valesini G, Barnaba V, Benvenuto R, et al. A calf thymus lysate improves clinical symptoms and T-cell defects in the early stages of HIV infection: Second report. Eur J Cancer Clin Oncol 1987;23:1915-9.
9. Shaw GM, Velie EM, Schaffer DM. Is dietary intake of methionine associated with a reduction in risk for neural tube defect-associated pregnancies? Teratology 1997;56:295-9.
10. Toborek M, Hennig B. Is methionine an atherogenic amino acid? J Optimal Nutr 1994;3:80-3.
11. McAuley DF, Hanratty CG, McGurk C, et al. Effect of methionine supplementation on endothelial function, plasma homocysteine, and lipid peroxidation. J Toxicol Clin Toxicol 1999;37:435-40.
12. Leach FN, Braganza JM. Methionine is important in treatment of chronic pancreatitis. Br Med J 1998;316:474 [letter].
Last Review: 07-22-2014
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