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Methionine II

Also known as: Methionine, Met, L-Methionine, DL-Methionine, (2S)-2-amino-4-(methylsulfanyl)butanoic acid

Overview

Methionine is an essential, sulfur-containing amino acid crucial for protein synthesis and various metabolic processes. It's found in protein-rich foods like meat, fish, dairy, nuts, and seeds. As a dietary supplement, it's used to support protein synthesis, methylation reactions, and as a precursor to S-adenosylmethionine (SAMe). Methionine plays a key role in methylation, antioxidant synthesis (specifically glutathione), and homocysteine metabolism. While its fundamental biological functions are well-established, clinical research on its supplemental uses is still evolving, with more robust data from animal studies than human trials. The quality of evidence ranges from moderate to high for basic biological roles, but clinical evidence for specific supplemental benefits remains limited, often lacking large, well-controlled human trials. It is important to note that high doses may be harmful.

Benefits

Methionine's primary benefits include its potential role in neural tube defect prevention during pregnancy, although evidence is primarily observational and not quantified in large randomized controlled trials (RCTs). Animal studies suggest that methionine supplementation can improve growth responses, but human data are limited. As a precursor to SAMe, methionine indirectly supports liver function, but direct methionine supplementation is not typically recommended for liver disease. Population-specific benefits may include neural tube defect prevention during pregnancy and general support for protein synthesis and methylation in the broader population. The effect sizes for neural tube defects are not quantified in RCTs, while growth effects in animals vary by species and diet. Benefits related to methylation and growth accrue over weeks to months.

How it works

Methionine primarily functions through several key biological pathways. It is converted to S-adenosylmethionine (SAMe), a universal methyl donor involved in DNA, RNA, and protein methylation. Methionine also serves as a precursor for glutathione, a major cellular antioxidant. Additionally, it participates in homocysteine metabolism, where it is metabolized to homocysteine, which can then be remethylated or converted to cysteine. These processes affect various body systems, including the liver, where SAMe supports liver function and detoxification, and the nervous system, where it is involved in neurotransmitter synthesis and neural development. Methionine is rapidly absorbed from the gut, exhibiting high bioavailability when taken orally as L-methionine.

Side effects

Methionine is generally considered safe when consumed in dietary amounts. However, supplemental use, especially at high doses, may pose risks and should be medically supervised. Common side effects are not well-documented in clinical trials, but uncommon side effects include acidosis (increased blood acidity) and elevated homocysteine levels, which is a risk factor for cardiovascular disease. Rare side effects, reported in animal models and case reports with excessive intake, include brain damage and death. There are no major drug interactions documented in clinical literature. Contraindications include liver disease (may worsen condition), atherosclerosis (may exacerbate condition), MTHFR deficiency (may worsen disorder), and schizophrenia (high doses may cause confusion and agitation). Pregnant women may benefit from methionine for neural tube defect prevention, but high doses are not recommended. Safety in children is not well established, and use is not recommended without medical supervision.

Dosage

The minimum effective dose of methionine for supplemental use is not well established. Typical dietary intake is around 19 mg/kg body weight per day for adults. In clinical studies, supplemental dosages range from 500 to 1000 mg/day, but this is not universally recommended. The maximum safe dose is also not established, but high doses (above 3 g/day) may be harmful. There are no specific timing recommendations; methionine can be taken with meals. L-methionine is preferred over DL-methionine for human use. It is rapidly absorbed from the gut. Adequate intake of B vitamins (B6, B12, folate) is important for homocysteine metabolism when supplementing with methionine.

FAQs

Who should avoid methionine supplementation?

Individuals with liver disease, atherosclerosis, or MTHFR deficiency should avoid methionine supplementation due to potential worsening of their conditions. High doses can be toxic, so medical supervision is recommended.

When is the best time to take methionine?

There is no specific timing required for methionine supplementation. It can be taken with meals for optimal absorption and to minimize potential gastrointestinal discomfort.

What are the expected benefits of methionine supplementation?

In healthy individuals, dramatic benefits are not expected. Possible benefits may be seen in specific populations, such as pregnant women, for neural tube defect prevention under medical supervision.

Is methionine a cure-all supplement?

No, methionine is not a cure-all. Its benefits are limited to specific contexts and populations, such as supporting liver health as a precursor to SAMe and potentially preventing neural tube defects during pregnancy.

What form of methionine is best?

L-methionine is the preferred form for human use due to its superior bioavailability and utilization compared to the DL-methionine racemic mixture.

Research Sources

https://pubmed.ncbi.nlm.nih.gov/25774783/ – This systematic review examines the use of S-adenosyl-L-methionine (SAMe), a derivative of methionine, for treating chronic liver disease. The review suggests that SAMe may improve liver function and is considered safe for use in these conditions. However, it's important to note that the review focuses on SAMe, not direct methionine supplementation, for liver disease.
https://www.mdpi.com/2076-2615/14/12/1771 – This meta-analysis of animal studies investigates the impact of methionine supplementation on growth responses. The findings indicate that supplementing beyond basal dietary levels improves growth in animals. However, the results are limited to animal models and may not directly translate to human outcomes.
https://www.webmd.com/vitamins/ai/ingredientmono-42/methionine – This review, drawing from peer-reviewed literature, discusses the uses and side effects of methionine. It highlights the potential of methionine to lower the risk of neural tube defects during pregnancy. However, it also cautions that high doses can be harmful, particularly for individuals with specific health conditions.
https://pubmed.ncbi.nlm.nih.gov/32293681/ – This study investigates the effects of methionine restriction on adipose tissue remodeling and metabolic health. The findings suggest that methionine restriction can induce beneficial changes in adipose tissue, potentially improving metabolic health. This research provides insights into the role of methionine in metabolic regulation and its potential therapeutic implications.