Can you reduce your risk of heart attack even if your total cholesterol is low?

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24 March 2008
The cholesterol in blood plasma is carried to the tissues in low-density lipoprotein (LDL) and back to the liver in high-density lipoprotein (HDL) where it is recycled or excreted in the bile. HDL's reverse transport is the only way cells can get rid of cholesterol. LDL cholesterol is called 'bad' cholesterol because, if levels are high, cholesterol is deposited in the lining of arteries in plaques of atheroma, narrowing blood vessels and causing coronary artery disease, angina, heart attacks and strokes. HDL cholesterol is called 'good' cholesterol because HDL helps to protect the arteries from atheroma and, if there is enough HDL, can even reverse it.

It has been known for some time that patients who have normal or high levels of LDL cholesterol have a greater risk of heart attacks and strokes if their HDL cholesterol is low. Two independent groups of workers have recently investigated for the first time whether a low HDL cholesterol is a risk factor for heart attacks even in patients who have the very low LDL cholesterol levels that can be achieved by treatment with drugs (statins).

The first report was published in The New England Journal of Medicine on 27 September 2007. This study by Dr Philip Barter of Camperdown in Australia and colleagues was conducted on behalf of a large international group of investigators who took part in the ‘Treating to New Targets’ study. The group analysed the results obtained in 9770 mostly male patients with coronary artery disease treated with the cholesterol lowering drug atorvastatin, of whom 2661 achieved very low LDL cholesterol levels (less than 1.8 mmol/L).

The second report was published in The Journal of the American College of Cardiology on 1 January 2008 by Dr Emil deGoma and colleagues from Stanford University Hospital, California. This study was of 4118 male patients who had very low LDL cholesterol levels (less than 1.6 mmol/L) following either treatment with a statin drug or occurring naturally.

Both studies found that the patients with very low LDL cholesterols with the highest HDL cholesterol levels had only 60% of the risk of having a major cardiovascular event compared with those with the lowest levels.

Raising HDL cholesterol levels has been shown to improve outcomes in patients with normal or high LDL cholesterols. Although this has not yet been proved for those with very low HDL cholesterol levels, it would be prudent for everyone to adopt life style factors that have a beneficial effect on the level of LDL cholesterol: not smoking, maintaining a normal body weight and taking regular exercise.

The question of adopting moderate alcohol consumption (one or two drinks a day) remains controversial. A new study of 6075 middle-aged men and women by Dana King and colleagues from the Medical University of South Carolina was published on-line in The American Journal of Medicine on 4 March 2008. New moderate drinkers had higher HDL cholesterol levels and lower LDL cholesterol levels than non-drinkers. During a four-year follow-up period moderate drinkers were 38% less likely to suffer a cardiovascular event than non-drinkers, but the death rates from all causes did not differ.