A once-obscure molecule called homocysteine has turned out to be a significant risk factor for heart disease and stroke for a significant number of people.
Homocysteine, found in the blood, is a breakdown product of dietary methionine. A number of studies have shown that high blood levels of homocysteine are associated with a high incidence of heart attack and stroke.Most people with homocystinuria - high blood levels of homocysteine - have it because they are deficient in one of three vitamins - vitamin B-12, vitamin B-6 or folic acid, which are needed to metabolize homocysteine.
There are a few hereditary forms of homocystinuria. These disorders are caused by the deficiency or absence of enzymes necessary for metabolism of homocysteine and methionine.
People with these genetic disorders have an increased likelihood of strokes and heart attacks in the second or third decade of life.
High blood homocysteine also helps to explain the elevated incidence of cardiovascular disease in people who have kidney failure, which interferes with the metabolism of the molecule.
Homocysteine causes cardiovascular disease because it causes platelets to become more sticky. These sticky platelets adhere to the lining of blood vessels leading to blockages.
High blood homocysteine is common among the elderly, largely because of a high incidence of vitamin B-12 deficiency. Perhaps one of every 12 older people is somewhat B-12 deficient. Many older people lack enough stomach acid, which is needed to split vitamin B-12 from food.