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> Nutritional and Dietary Supplements > Methionine
METHIONINEVisit The Healthy Living Bookshelf:
What does it do? 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). People with AIDS have low levels of methionine. Some researchers suggest this may explain some aspects of the disease process,1 2 3 especially the deterioration that occurs in the nervous system that can cause symptoms, including dementia.4 5 A preliminary study has suggested that methionine (6 grams per day) may improve memory recall in people with AIDS-related nervous system degeneration.6 Other preliminary studies have suggested that methionine (5 grams per day) may help treat some symptoms of Parkinson’s disease.7 However, another form of methionine, S-adenosylmethionine, or SAMe, may worsen the symptoms of Parkinson’s disease and should be avoided until more is known.8 9 10 11 12 Methionine (2 grams per day) in combination with several antioxidants, reduced pain and recurrences of attacks of pancreatitis in a small but well-controlled trial.13 Where is it found? 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. Methionine has been used in connection with the following conditions (refer to the individual health concern for complete information):
 Who is likely to be deficient? Most people consume plenty of methionine through a typical diet. Lower intakes during pregnancy have been associated with neural tube defects in newborns, but the significance of this is not yet clear.14 How much is usually taken? 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. Are there any side effects or interactions? 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.15 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.16 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.17 References: 
1. 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;63:242–6. 2. Revillard JP, Vincent CM, Favier AE, et al. Lipid peroxidation in Human Immunodeficiency Virus infection. J Acquir Immune Defic Syndr 1992;5:637–8. 3. Singer P, Katz DP, Dillon L, et al. Nutritional aspects of the Acquired Immunodeficiency Syndrome. Am J Gastroenterol 1992;87:265–73. 4. Tan SV, Guiloff RJ. Hypothesis on the pathogenesis of vacuolar myelopathy, dementia, and peripheral neuropathy in AIDS. J Neurol Neurosurg Psychiatry 1998 65:23–8. 5. 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. 6. 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. 7. Smythies JR, Halsey JH. Treatment of Parkinson’s disease with l-methionine. South Med J 1984;77:1577. 8. Charlton CG, Mack J. Substantia nigra degeneration and tyrosine hydroxylase depletion caused by excess S-adenosylmethionine in the rat brain. Support for an excess methylation hypothesis for parkinsonism. Mol Neurobiol 1994;9:149–61. 9. Crowell BG Jr, Benson R, Shockley D, Charlton CG. S-adenosyl-L-methionine decreases motor activity in the rat: similarity to Parkinson’s disease-like symptoms. Behav Neural Biol 1993;59:186–93. 10. Benson R, Crowell B, Hill B, et al. The effects of L-dopa on the activity of methionine adenosyltransferase: relevance to L-dopa therapy and tolerance. Neurochem Res 1993;18:325–30. 11. Cheng H, Gomes-Trolin C, Aquilonius SM, et al. Levels of L-methionine S-adenosyltransferase activity in erythrocytes and concentrations of S-adenosylmethionine and S-adenosylhomocysteine in whole blood of patients with Parkinson’s disease. Exp Neurol 1997;145:580–5. 12. Charlton CG, Crowell B Jr. Parkinson’s disease-like effects of S-adenosyl-L-methionine: effects of L-dopa. Pharmacol Biochem Behav 1992;43:423–31. 13. Uden S, Bilton D, Nathan L, et al. Antioxidant therapy for recurrent pancreatitis: placebo-controlled trial. Aliment Pharmacol Ther 1990;4:357–71. 14. 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. 15. Toborek M, Hennig B. Is methionine an atherogenic amino acid? J Optimal Nutr 1994;3:80–3. 16. 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. 17. Leach FN, Braganza JM. Methionine is important in treatment of chronic pancreatitis. Br Med J 1998;316:474 [letter]. |
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