Each year more than half a million Americans die from coronary heart disease (CHD), making it the nation's leading cause of death. For the last two decades, many of us in the fields of nutrition and health have been advocating a reduction both in total fat -- particularly the saturated kind -- and in cholesterol consumption, in an effort to lower serum cholesterol and cut the risk of CHD.

Now a consensus conference sponsored by the National Institutes of Health and attended by experts in cardiology, epidemiology, statistics, primary care and preventive medicine has reaffirmed this recommendation. The conference report represents the strongest statement to date by leaders in the medical and research communities on the cause-and-effect relationship between elevated serum-cholesterol levels and CHD.

More important, the report emphasizes the potential benefits to be gained from decreasing serum-cholestrol levels, not only for those at high risk, but among the general population as well. After examining all available evidence, the panel agreed on a number of questions central to the heart-disease story.

First, to what extent are blood-cholesterol levels really related to CHD? The members of the committee, citing a wealth of data from experimental, clinical and epidemiological studies, conclude that "beyond a reasonable doubt there is a close relationship between elevated blood-cholesterol levels and coronary heart disease."

Given this link, the more important question becomes whether CHD development can be slowed or prevented by reducing already high cholesterol levels. Many clinical trails have shown that serum cholesterol can be lowered by dietary changes and/or drug therapy. It has been more difficult to demonstrate a significant effect of these treatments on CHD.

This apparent lack of effect has been cited by skeptics as reason enough to discourage across-the-board cholesterol-lowering for all Americans. But after reviewing three recent studies, including the much-publicized National Heart, Lung and Blood Institute Intervention trial, the panel found considerable evidence of decreases in the progression and/or incidence of CHD in men on cholesterol-lowering therapy.

The participants in those studies were judged "high risk." But what does this mean? The conference adopted guidelines based on age to help standardize risk classification. For those 40 and over, a fasting serum cholesterol greater than 240 milligrams per deciliter puts them at moderate risk for CHD. Levels greater than 260 for the same age group are considered at high risk. Goals of approximately 180 and 200 for adults under and over 30 respectively are advised. The report notes that about half of the U.S. population is at some increased risk for CHD based on serum-cholesterol levels -- quite a sobering thought.

How should those at moderate and high risk be treated? The panel recommends trying aggressive diet therapy before any drugs are used. Weight reduction, if necessary, is also advised, because obesity is known to increase cholesterol levels. Dietary changes include lowering total fat intake by about 10 percent to account for a total of 30 percent of the day's calories. Particular attention should be directed toward decreasing saturated-fat intake to less than 10 percent, down from the current level of 15 percent. And polyunsaturated fat should be increased to 10 percent. Cholesterol intake should be limited to 250 to 300 milligrams a day.

If all this sounds familiar, it's because it is essentially the same "prudent diet" the American Heart Association has been advocating for years for those at risk for CHD.

In recommending that the regimen be adopted even by those with relatively low cholesterol levels, the NIH panel goes one step further. The report notes that "the relationship between level of cholesterol and level of risk for CHD covers virtually the entire cholesterol distribution." Since following the diet has no adverse effect, it seems a wise precaution.

It should be remembered that there are other risk factors for CHD besides cholesterol levels. These include hypertension, diabetes and a sedentary life style. But a recent report by researchers at Harvard Medical School has quantified the impact of lowering serum cholesterol on CHD incidence.

The investigators analyzed the relative effects of medical intervention -- such as bypass surgery and life style changes, including dietary modifications to reduce cholesterol -- on the well-documented decline in CHD mortality that has been occurring since the late 1960s. They estimated that lowered serum-cholesterol levels account for about 30 percent of the decrease in CHD-related deaths -- a significant contribution.

Some risk factors, such as a family history of CHD, are not subject to change. But your diet is one factor you can, and should, control.

Copyright (c) 1985, Washington Post Writers Group