Originally published 8/26/2004
L-methionine is an essential sulfur-containing amino acid that is soluble in water. It is a powerful antioxidant, assists in the breakdown of fats, and helps inactivate free radicals. Because it is an essential amino acid, it must be supplied in the diet.
The recommended daily intake is 13 mg per kg or about one gram daily for adults. The actual intake is higher due to the fact that it is principally derived from dietary proteins. Cheese, eggs, fish, meat and poultry are all rich sources of L-methionine. It can also be found in fruits and vegetables, but not as abundantly.
L-methionine is part of many biochemical reactions, including the production of S-adenosylmethionine (SAM or SAMe), L-cysteine, gluthione, taurine, and sulfate. SAM is involved in the synthesis of creatine, epinephrine, melatonin and the polymines spermine and spermidine, among several other substances.
Since L-methionine is a glycogenic amino acid, it may participate in the formation of D-glucose and glycogen. It can help reduce the liver-toxic effects of such hepatotoxins as acetaminophen and methotrexate. Some suggest that acetaminophen products should contain L-methionine. Not enough tests have been performed to determine whether or not this would be beneficial.
It is not recommended that you supplement methionine unless directed by a professional physician. It can be used as an effective antidote in some cases of acetaminophen poisoning. Some research suggest that it may promote some cancers, and the use as a supplement is inadvisable.
L-methionine should be avoided by pregnant and nursing women unless otherwise prescribed by a physician. Basically, supplemental L-methionine should only be used if it is recommended and monitored by a physician.
Dietary supplementation with L-methionine was found to decrease glycine levels when given to healthy women on a low-protein diet. High L-methionine intake in a diet high in salt and nitrites/nitrates may increase the risk of stomach cancer.
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