Homocysteine is a sulphur-containing amino acid formed during the metabolism of methionine — an essential amino acid obtained from dietary protein. It is normally converted to cysteine or remethylated back to methionine through pathways that require vitamins B6, B12, and folate as cofactors.

Elevated homocysteine (hyperhomocysteinaemia) damages the endothelium (the inner lining of blood vessels), promotes oxidative stress, impairs nitric oxide function, and increases platelet aggregation — all contributing to cardiovascular disease. Elevated homocysteine is an independent risk factor for heart attack, stroke, and peripheral artery disease, yet is routinely missed in standard cardiovascular assessments. It is also associated with MTHFR gene variants, B12 and folate deficiency, kidney disease, and hypothyroidism.