Homocysteine is a naturally occurring amino acid found in the blood and tissues. However, it is not among the twenty amino acids which are the building blocks of proteins and hence is not found in dietary protein. Homocysteine is formed from the amino acid methionine which is a constituent of dietary protein. Homocysteine can also be converted back to methionine by two pathways. One of these pathways requires cobalamin (vitamin B12) and tetrahydrofolate (derived from dietary folic acid) as cofactors. An alternative route for the metabolism of homocysteine is conversion to cystathionine and then to the amino acid cysteine.
This conversion requires pyridoxal phosphate (derived from vitamin B6) as a cofactor. Hence, efficient disposal of homocysteine requires three dietary vitamins namely folic acid, vitamin B12 and vitamin B6. Green vegetables and citrus fruits are excellent sources of folic acid, and vitamins B6 and B12 are found in a wide range of plant and animal foods including whole grain products, bananas, fatty fish, nuts, poultry and red meats. A balanced diet will, therefore, provide adequate intakes of all three vitamins and hence ensure efficient disposal of homocysteine.
Over thirty years have gone by since it was first suggested that elevated levels of homocysteine in the blood are associated with a high risk of cardiovascular disease (1).
However, not all studies have been able to demonstrate this association. After correction for other risk factors, a study of cases and controls from the Atherosclerosis Risk in Communities (ARIC) study was unable to find any association between blood homocysteine levels and risk of coronary heart disease (2). Similarly, after correction for other risk factors, a study of cases and controls from the Caerphilly cohort was unable to show that coronary heart disease risk was associated with serum homocysteine levels (3).
City of Gosford, Australia,
Antigua and Barbuda, St. John’s,
Norfolk, Virginia, USA