Homocysteine and heart disease

Studies have shown that high levels of the amino acid, homocysteine, in the blood is linked to a higher risk of coronary heart disease, stroke and peripheral vascular disease.

Other studies suggest that homocysteine may damage the inner lining of arteries and promote blood clots.

In 1998 The American Journal of Medical Science published a review of eight studies totalling 2,400 patients, in which it was reported that the risk of developing thrombosis (blood clots) was up to 13 times greater in people with elevated homocysteine levels.

The connection between homocysteine and cardiovascular disease was suspected about 25 years ago when it was found that people with a rare condition called homocystinuria have a tendency to develop severe cardiovascular disease in their teens and twenties.

What is the normal homocysteine level?

Levels between 5 and 15 micromoles per litre (µmol/L) are classified as normal. Abnormal concentrations are classified as moderate (16-30), intermediate (31-100), and severe (greater than 100 µmol/L).

Yet, despite these classifications, researchers in the Physicians' Health Study, a Harvard-based study that tracked nearly 15,000 male doctors, found that men with the highest homocysteine levels (15 micromoles or higher) were three times as likely to experience a heart attack as those with the lowest homocysteine levels.

How do folic acid and other B vitamins affect homocysteine levels?

Homocysteine levels are strongly influenced by diet. The most helpful dietary nutrients are folic acid and vitamins B6 and B12, which help reduce levels of homocysteine in the body.

Several studies have found that higher blood levels of B vitamins are linked to lower levels of homocysteine. In addition, low blood levels of folic acid have been linked to a higher risk of fatal coronary heart disease and stroke.

How is homocysteine related to cardiovascular risk?

Recent studies suggest that blood tests to detect high homocysteine levels can better assess a patient's risk of heart disease. Testing can be especially useful in patients in whom the usual risk factors (high blood cholesterol, high blood pressure, smoking) do not exist.

Several clinical trials are currently testing whether lowering homocysteine levels will reduce a patient's coronary heart disease risk.

Studies have found that folic acid, in combination with vitamin B6, may reduce the rate of restenosis (renarrowing of the coronary artery) in patients undergoing coronary angioplasty (mechanically widening blood vessels), but it may also increase the rate after coronary stenting (using wire mesh to prop open arteries).

Results from several studies suggest that treatment with B vitamins alone has no effect on stroke recurrence or on complications and death from cardiovascular causes.

What are the recommendations?

If tests reveal that your homocysteine levels are high and you fall into a high risk category for heart disease, you need to ensure you have enough folic acid and vitamins B6 and B12 in your diet.

The recommended daily amount of folic acid is 400mcg. Good sources of folic acid include green vegetables, grain products, citrus fruit and tomatoes. A healthy, balanced diet that's rich in fruit and vegetables, whole grains, and fat-free or low-fat dairy products is advisable.

Dr Rajesh Raipancholia MBBS, MD, FRCP, FACC (USA), Consultant Interventional Cardiologist.

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