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ACQUIRED HEART DISEASE: CHOLESTEROL CONTROVERSY

In January 1984 the world's media were given a full briefing on the results of an important and expensive heart study organized by the American National Heart, Lung and Blood Institute's Coronary Primary Prevention Trial, which had been begun ten years earlier. The aim of this investigation was to take many of the established findings on cholesterol and CHD one step further than the straightforward (or not so straightforward?) cause-and-effect stage.

The Framingham researchers had shown that heart disease is associated with high cholesterol levels in the blood, a strong indication that the latter was a probable cause of CHD. However, it had been by no means scientifically proven that eating a diet low in cholesterol would actually prevent atherosclerosis. It might seem on the face of it that it must do so, but suspicion, hunch, deduction and inference are not proof. And proof is what the National Heart, Lung and Blood Institute wanted, and was prepared to spend 150 million dollars to acquire.

The evidence

The researchers took 3806 men between the ages of 35 and 59 whom they identified as having higher than average levels of cholesterol in their bloodstream. None had signs of coronary heart disease when the study began. The subjects were split randomly into two groups: one was the test group while the other formed a control group against which the results of the test group could be evaluated.

Next, both groups were put on a low-cholesterol diet, but the test group was also given cholestyramine - a substance known to lower blood-cholesterol levels. The theory was that members of the test group should end up with less incidence of heart disease because, with the cholestyramine advantage, they were being subjected to tighter control over the amount of their cholesterol intake, particularly a type called Low Density Lipoprotein-Cholesterol (LDL-C) that reached and circulated in their bloodstream.

In the event, after nearly seven-and-a-half years on these regimes, this is exactly what happened. Cholesterol levels dropped in both groups, but the test group had 19 percent less heart disease in general (sudden death, coronary, fatal and non-fatal heart attacks) and 24 percent fewer fatal heart attacks. There were benefits in terms of the incidence of angina and the need for coronary bypass operations.

However, we must remember that the volunteers for this trial belonged to a particularly 'at-risk' sector of the community, all having initially high LDL-C levels. In a more normal cross-section of the population it might be enough to use reduced fat diets to produce improvements. But the trial does show that, for those at risk, drugs can improve health and lengthen life. For every 1 percent drop in blood cholesterol the researchers found a 2 percent drop in the risk of heart attack - a very encouraging result. The research team believes that similar results could be expected among other age-groups and among women, although they have not extrapolated their results to consider people with average cholesterol levels.

The verdict

This extensive study, carried out in 12 Lipid Research Clinics, is, according to the researchers, the first to establish conclusively that lowering high blood-cholesterol in humans reduces heart attacks and deaths caused by heart attacks. For years doctors have described how excess cholesterol forms the fatty yellow substance known as 'plaque' which builds up in the cells lining the arteries. They have shown how platelets - the special protective cells that help blood coagulate - seal off these deposits, forming clots that can detach themselves from the blood-vessel wall to block blood-flow and so cause a heart attack or stroke. Now comes proof that you can improve your health by curbing directly the build-up of lipids in the first place, and probably thereby preventing deposits of fat being incorporated in the arterial wall. All very logical, you might say, even obvious - but now we have proof. Now, surely, we can be confident in sentencing cholesterol to exile in order to keep our hearts alive?

Well, confident perhaps, but nothing is ever simple in medicine. For example, there is some evidence that people with relatively low levels of cholesterol may be slightly more prone to cancer than those with higher levels. The issue of the relationship of lipids to malignancies is rather complicated, being tied up with the presence of Vitamin A in ways that are not fully understood.

Nevertheless, this is an interesting finding and one which deserves further study before we start patting ourselves on the back and pretending that now we know it all. We do not.

Another complication is in determining what constitutes a high or low lipid level diet. Even a substance as fat-free as coffee can have cholesterol-related repercussions. There is evidence from studies carried out in Norway by Dr. Dag Thelle and his colleagues that men drinking eight or nine cups of coffee a day have nearly 20 percent higher levels of blood cholesterol than the one-cup-a-day man. In women the lipid-level difference is 12 percent. Could imbibing coffee somehow boost blood-lipid levels? If so, does drinking coffee predispose you to coronary heart disease? The Norwegian work suggests that the answer to both questions is 'yes'.

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CARDIO & BLOOD

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