Methionine

Methionine is an essential sulphur-containing amino acid, meaning the body cannot synthesise it on its own and must obtain it exclusively through diet. It is found primarily in animal proteins — meat, fish, eggs and dairy products — as well as in certain legumes and seeds. Its sulphur content gives it a key structural role in the formation of keratin, the fibrous protein that makes up hair, nails and the epidermis. Beyond its structural role, methionine contributes to the synthesis of cysteine and glutathione, two molecules involved in the body's antioxidant defences. It also participates in methylation reactions, essential biochemical processes related to gene expression, creatine production and hepatic lipid metabolism. Methionine requirements can be difficult to meet through strict vegetarian or vegan diets, as plant-based sources generally provide lower amounts. Targeted supplementation may therefore help maintain adequate intakes, particularly to support the quality of hair and nails and the proper functioning of sulphur metabolism.