Health Benefits Of Methionine

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Methionine is an essential amino acid with numerous important roles in human cellular metabolism; it participates, for example, in the synthesis of proteins and polyamines and in the methylation of DNA. Along with cysteine, it is the only amino acid to contain sulfur in its structure. L-Methionine is a natural chelating agent for heavy metals; moreover, it regulates ammonia formation in the urine and aids in the control of cholesterol levels by increasing the liver’s production of lecithin. ^[1] Our body cannot naturally synthesize methionine, making the adequate consumption of methionine-rich food items vital to health. Good amounts of methionine can be obtained from fish, chicken, pork, cheese, beef, soy meal, nuts, and beans. ^[2]

Methionine and Depression

S-adenosyl-L-methionine (SAMe), a naturally occurring methyl group donor derived from L-methionine and involved in the synthesis of a number of brain neurotransmitters, has been progressively reported to be an effective, well-tolerated, and safe treatment of major depressive disorder. A review of accumulated clinical trial evidence by Mischoulon and Fava (2002) reveal that 200-1600 mg/day of SAMe appears superior than placebo and as efficacious as any tricyclic antidepressant in terms of improving depression. SAMe has also been demonstrated to possess a faster onset of action than conventional antidepressants, to counteract the deleterious effects of Alzheimer disease, and to potentiate the effects of tricyclic antidepressants without causing serious adverse effects. ^[3] Similar findings have been obtained by the study of Papakostas et al. (2010), whose preliminary results indicated the efficacy and safety of SAMe as an adjunctive treatment strategy for patients diagnosed with major depressive disorder but not responding to serotonin reuptake inhibitors (SRI). In this double-blind, randomized clinical trial involving 73 SRI nonresponders, the response rates of patients on SAMe were higher than those on adjunctive placebo according to the 17-item Hamilton Depression Rating Scale, which was the primary outcome measure of the study. Likewise, the remission rates of patients treated with adjunctive SAMe fared better than the group on placebo only. ^[4]

Methionine and Graying Hair

According to a 2009 study from the University of Bradford, UK, hydrogen peroxide accumulates in the shafts of human gray or white hairs in millimolar concentrations, causing oxidative damage in the hair follicles and serving as a key element in senile hair graying. Since such hydrogen peroxide buildup has been linked to a lack in methionine, under in vitro conditions, L-methionine may slow down the gradual loss of hair color by preventing the oxidation mediated by hydrogen peroxide, which methionine effectively scavenges. ^[5]

Methionine as Paracetamol or Acetaminophen Antidote

Similar to acetylcysteine, which is the commonly administered antidote for paracetamol overdose, oral methionine manages paracetamol toxicity effectively when given within ten hours after paracetamol ingestion. Interestingly, oral methionine therapy is completed within 12 hours in comparison to the three days and 20 hours required for oral and intravenous acetylcysteine treatment, respectively, and is equal to acetylcysteine with respect to efficacy in preventing severe liver damage. ^[6]

Methionine Restriction and Cancer

In recent years, considerable amount of scientific attention has been put on the limitation of methionine in the diet as a key preventive approach against cancer development. This has stemmed from the fact that some forms of cancers are dependant on methionine for proliferation and survival. A diet low in methionine, especially a vegan diet, has been found to help control cancer growth and has been associated with an extended life span in experimental rodents. ^[7] Additionally, methioninase, the enzyme that cleaves methionine and therefore depletes this amino acid, works in a similar fashion, completely slowing down the growth of methionine-dependent tumor cells in vivo and inducing tumor-specific late cell-cycle block. ^[8]

Methionine and Neural Tube Defects

Methionine has been reported to favorably interact with folic acid and vitamin B12, nutrients that have known preventive action against the development of neural tube defects. Along with the aforementioned vitamins, methionine seems to be involved in the methylation of contractile proteins associated with closing the neural folds. The findings of a case-control study by Graham et al. (2010) of Mexican American women with normal pregnancies and women with offspring suffering from neural tube defects demonstrated the interaction between dietary methionine and serum vitamin B12 at higher levels of both components and the potential protective action of an increased methionine intake by the mother against neural tube defects. ^[9]