Methionine
Synonym: L-methionine

Characteristics: It is an essential amino acid found in food sources of protein such as meat and dairy products, which the body cannot produce, so it must be obtained from food or dietary supplements. There are two types of methionine: L-methionine (which occurs naturally and is usually found in supplements) and D-methionine. Both have the same chemical composition, but the molecules are mirror images. A mixture of the two is called DL-methionine. Methionine is a sulfur-containing amino acid with biological functions in the initiation and prolongation step of protein synthesis, transmethylation reactions, cysteine and cystine synthesis, which plays a decisive role in the breakdown of fats, heavy metals, and as a component of antioxidant systems. It helps break down fat by preventing it from building up in the arteries and is also one of the three amino acids the body needs to produce creatine, a compound essential for energy production and muscle building. Products with methionine are recommended for healthy hair, nails, and skin. Metabolism of methionine begins with its conversion to homocysteine (Hcy) via its intermediate, S-adenosyl-methionine (SAM). This sequence of reactions is called transmethylation and occurs ubiquitously in mammalian cells. Hcy is then removed by combining with serine to form cystathionine, which is cleaved to form α-ketobutyrate and cysteine. Homocysteine can be methylated back to methionine-by-methionine synthase. High levels of homocysteine are associated with various diseases such as cardiovascular and cerebrovascular disease, renal dysfunction, and dementia. Several researchers have linked consumption of both unprocessed and processed red meat to a higher risk of type 2 diabetes, heart disease, and some types of cancer.

Absorption: Comparative studies have shown that methionine is absorbed at the highest rate of all proteinogenic amino acids. The primary site of absorption is the small intestine.

Dietary supplements: As L-methionine, usually in a dose of 500 mg 1‒2x a day, or SAM in a dose of 200 mg 2‒4x a day.

Natural sources: Methionine is found in animal foods such as beef and pork, poultry, eggs, and seafood. Plant-based foods include nuts, seeds, soy, beans, and some vegetables.

Effect: One of the main uses of methionine is the treatment of overdose with paracetamol, which is contained in over-the-counter pain relievers. Methionine is thought to prevent paracetamol metabolites from damaging the liver. Methionine supplementation may help reduce the risk of liver damage as it aids in the detoxification of heavy metals, including lead and mercury. Other beneficial effects of methionine include nourishing hair, skin, and nails, slowing cell aging and protecting them from pollutants, and aiding the absorption of other nutrients such as selenium and zinc.

Deficiency: Methionine deficiency can cause fatty liver, slow growth, weakness, swelling and skin lesions. Severe methionine deficiency can cause dementia. Loss of methionine is associated with senile graying of hair because hydrogen peroxide builds up in hair follicles, reducing the effectiveness of tyrosinase and gradually losing hair color.

Recommended daily dose: 14 mg per kg of body weight per day.

Side Effects: Mild side effects include nausea, vomiting, drowsiness, and irritability. In general, methionine is considered safe. However, if used incorrectly, serious side effects can also occur. These can include changes in blood pressure, disorientation, and increased heart rate.

Interaction: Not recorded.

Pregnancy: Contraindicated due to lack of information.

Breastfeeding: Contraindicated due to lack of information.

Warning: People with methylenetetrahydrofolate reductase (MTHFR) deficiency, an inherited condition, should avoid taking methionine. Similarly, people with high blood levels of homocysteine should avoid taking methionine supplements. High levels of homocysteine in the blood can lead to heart disease and other complications. Caution is also for patients with schizophrenia, in whom it is suspected that methionine can induce psychotic symptoms, confusion, restlessness and generally worsen the disease.

Toxicity: High doses cause heart failure or even death.