The big picture: Homocysteine is a sulfur-containing amino acid that is produced by the body during the metabolism of methionine, an essential amino acid. Its levels are a modifiable independent risk factor for heart disease, stroke, and dementia, and are influenced by the intake of vitamins B6, B9 and B12.

Methionine’s role: Methionine is an essential amino acid, meaning the body cannot produce it on its own, and it must be obtained through diet. Sources include meat, fish, dairy products, and some nuts and seeds. It's vital for building proteins, regulating metabolism, aiding detoxification, and producing antioxidants, but its balance is key as excessive intake can increase health risks while deficiency can impair bodily functions.

From methionine to homocysteine: The body's conversion of methionine to homocysteine and subsequently to other useful compounds is a process heavily reliant on B vitamins, specifically B6, B9 (folate), and B12. This conversion is vital for maintaining low homocysteine levels. Elevated levels can indicate either a dietary deficiency in these vitamins or a genetic condition that impedes the efficient metabolism of homocysteine.

Dietary impact: Diets lacking in B vitamins, often seen in vegans and vegetarians, can lead to increased levels of homocysteine. This elevation is significant because it has been consistently linked to an increased risk of cardiovascular diseases and neurological disorders.

Cardiovascular risks: High homocysteine is independently associated with cardiovascular issues, believed to cause heart disease by promoting oxidative stress, damaging arteries, and encouraging clot formation. Research shows that a reduction in homocysteine levels is associated with a decreased risk of ischemic heart disease and stroke. Specifically, lowering homocysteine by 25% or 3 μmol/L correlates with an 11% lower risk of ischemic heart disease and a 19% reduction in stroke risk.

Neurological implications: Homocysteine levels have also been linked to an increased risk of dementia, including Alzheimer’s disease. Individuals with moderately raised levels of homocysteine are up to 2.5 times more likely to develop dementia. It has been estimated that lowering homocysteine through supplementation with vitamins, especially B12, could prevent 12-31% of dementia cases.