Homocysteine

Homocysteine is an amino acid produced naturally in the human body during the metabolism of methionine, an essential amino acid found in dietary protein. Elevated levels of homocysteine in the blood are considered a risk factor for cardiovascular disease, stroke, and cognitive decline. Readers typically encounter homocysteine in discussions about heart health, blood tests for cardiovascular risk assessment, and nutritional advice regarding B vitamins.

In practice, homocysteine levels rise when the body lacks sufficient vitamin B12, folate (vitamin B9), or vitamin B6, which are required to convert homocysteine into other beneficial substances like methionine or cysteine. A standard blood test measures total homocysteine, with normal levels generally between 5 and 15 micromoles per liter. Diets low in these B vitamins—common in some plant-based eating patterns—can lead to elevated homocysteine, though fortified foods and supplements can mitigate this risk.

For someone eating a plant-based diet, monitoring homocysteine is important because vitamin B12 is not naturally present in plants, and folate can be abundant. Elevated homocysteine may increase cardiovascular risk, but this can be managed by ensuring adequate intake of B12 through fortified foods or supplements, and consuming folate-rich foods like leafy greens and legumes. However, homocysteine is just one of many risk factors, and its direct causal role in heart disease remains debated among researchers.