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METIONINA

Also known as: Methionine, Met, L-methionine, DL-methionine, hydroxyl analog of methionine, OH-Met

Overview

Methionine is an essential sulfur-containing amino acid that the human body cannot produce, necessitating its intake through dietary sources like meat, fish, and dairy. It is crucial for protein synthesis and acts as a methyl group donor in various metabolic processes. Methionine also exhibits antioxidant properties and aids in tissue protection and repair. It exists in various forms, including L-methionine, DL-methionine, and hydroxyl analogs, which differ in bioavailability and efficacy. As a dietary supplement, methionine is used for preventing neural tube birth defects during pregnancy, supporting liver function, and potentially as an adjunct in viral infections and cancer. However, the evidence supporting many of these uses is limited or inconclusive. Research on methionine is moderately mature, with substantial animal and human studies, including systematic reviews and meta-analyses, particularly in animal nutrition. Human clinical evidence is less extensive and often preliminary.

Benefits

Methionine is essential for protein deposition and growth, particularly evident in animal models like post-weaning pigs, where supplementation improves average daily gain (ADG) and protein retention efficiency. In humans, adequate methionine intake during pregnancy is associated with a reduced risk of neural tube defects. Additionally, methionine may act as an antioxidant and support tissue repair. It is involved in methylation reactions important for DNA and neurotransmitter synthesis. Pregnant women benefit from methionine intake, which correlates with a lower incidence of neural tube birth defects. Livestock, such as pigs, also benefit from methionine supplementation, which improves growth performance and protein utilization. Animal studies quantify methionine utilization efficiency for protein deposition, showing clear dose-response relationships for growth parameters. Human data on birth defect prevention suggest a protective effect, though precise effect sizes vary and require further high-quality RCTs. Growth benefits in animals are observed over weeks to months of supplementation, while neural tube defect prevention requires adequate methionine intake during early pregnancy.

How it works

Methionine functions as a substrate for protein synthesis and a precursor for S-adenosylmethionine (SAM), a universal methyl donor involved in the methylation of DNA, proteins, and lipids. It provides sulfur for the synthesis of cysteine and glutathione, which are key antioxidants. Methionine metabolism also influences homocysteine levels, which have implications for cardiovascular health. Absorption primarily occurs in the small intestine, with bioavailability varying depending on the chemical form; L-Met is generally more bioavailable than DL-Met or OH-Met.

Side effects

Methionine is generally safe when consumed at dietary levels or under medical supervision, but excessive intake can be harmful. Common side effects are not well-documented at normal doses. Uncommon side effects include elevated homocysteine levels, which may increase cardiovascular risk. Rare side effects include potential neurotoxicity and brain damage with very high doses, and possible tumor growth promotion in some contexts. Methionine may interact with drugs affecting methylation or homocysteine metabolism. It is contraindicated in patients with cardiovascular disease risk due to the potential for homocysteine elevation. Pregnant women should ensure adequate intake but avoid excessive dosing. Caution is advised to avoid homocysteine elevation and potential cardiovascular risks.

Dosage

The minimum effective dose of methionine is not firmly established for humans, but dietary intake recommendations exist (e.g., WHO recommends approximately 13 mg/kg/day). Optimal dosage ranges vary by species and purpose; in animal studies, doses are adjusted to meet standardized ileal digestible methionine requirements. Excessive intake can be toxic, and while no precise upper limit is established, caution is advised to avoid homocysteine elevation. For birth defect prevention, intake during early pregnancy is critical. L-methionine is preferred for bioavailability, while DL-methionine and hydroxyl analogs are used in animal nutrition with varying efficacy. Bioavailability depends on the chemical form and the presence of other amino acids. Adequate levels of vitamins B6, B12, and folate are important for methionine metabolism and homocysteine regulation.

FAQs

Is methionine supplementation safe?

Yes, at recommended doses and under supervision. Excessive intake can cause harm, particularly by elevating homocysteine levels, which may increase cardiovascular risk.

Can methionine prevent birth defects?

Adequate intake during pregnancy is associated with a reduced risk of neural tube defects. It's crucial to maintain sufficient levels, especially during early pregnancy.

Does methionine increase heart disease risk?

High doses may raise homocysteine, a risk factor for cardiovascular disease. Monitoring homocysteine levels is advisable with high-dose supplementation.

Which form of methionine is best?

L-methionine is generally more bioavailable than DL-methionine or hydroxyl analogs, making it a preferred choice for supplementation.

How quickly do benefits appear?

Growth effects in animals appear within weeks. For birth defect prevention, consistent intake during early pregnancy is essential for optimal outcomes.

Research Sources

https://pubmed.ncbi.nlm.nih.gov/37482458/ – This systematic review and meta-analysis, encompassing 24 studies and 208 treatment means in post-weaning pigs, modeled methionine utilization efficiency for protein deposition. The findings indicated that L-methionine and other forms differ in efficacy for growth, and methionine intake below the required level limits growth. This study highlights the importance of adequate methionine levels for optimal growth in animal models.
https://www.mdpi.com/2076-2615/14/12/1771 – This meta-analysis evaluated DL-methionine versus methionine hydroxy analogs in animal feed. The study concluded that DL-methionine can replace MHA at a 65% dose with similar efficacy. This suggests that DL-methionine is a viable alternative to methionine hydroxy analogs in animal nutrition, offering potential cost-saving benefits.
https://www.webmd.com/vitamins/ai/ingredientmono-42/methionine – This systematic review, summarized by WebMD, links methionine intake during pregnancy to a lower risk of neural tube defects. It also notes that there is no strong evidence for methionine's efficacy in treating other conditions and highlights safety concerns with high doses. The review underscores the importance of adequate methionine intake during pregnancy while cautioning against excessive supplementation.