"Good" v. "Bad" Cholesterol

At last, a fatty molecule that may help your heart

Cholesterol has been portrayed as a kind of coronary time bomb. One study after another has shown that people with the highest concentration of the fatty molecule in their bloodstreams run the greatest risk of atherosclerosis. This is the buildup of fibrous fatty plaques in the blood vessels and a precursor of heart disease--the leading cause of death in the U.S. Hence, the reduction of blood (or serum) cholesterol has become a prime goal of doctors and patients alike. Still, physicians have been puzzled by one observation: though some patients show a seemingly dangerous level of serum cholesterol, they somehow remain immune to coronary disease.

Now this paradox is being explained. Pondering data from a massive study of coronary problems in five different areas--Framingham, Mass., Honolulu, San Francisco, Evans County, Ga., and Albany, N.Y.--Statistician Tavia Gordon of the National Institutes of Health in Bethesda, Md., noticed an unusual correlation. Virtually all those with heart disease--regardless of age, sex or racial background--also had reduced levels of a substance called high-density lipoprotein (HDL) in their blood. By contrast, those free of atherosclerosis showed remarkably elevated HDL counts.

Consisting of molecules of fat, including cholesterol, and protein tightly bound together into a single chemical complex, the lipoproteins are part of an intricate transport system. Among the largest and lightest of these globules are the very-low-density lipoproteins (VLDL). They carry some cholesterol but mainly other fats to various parts of the body. The slightly heavier low-density lipoproteins (LDL) move cholesterol from cell to cell, where it is used to produce sex hormones, among other things. Any excess cholesterol is picked up by the heaviest lipoproteins, HDL, which, like garbage trucks, haul it off to the liver for disposal.

Because HDL usually accounts for only a small portion of the blood's store of lipoproteins--perhaps no more than 20% in most adults (but as much as 50% in infants)--doctors long felt that it could not have any really significant effect on total cholesterol levels. Now they are being forced to reconsider that view. Some researchers believe lipoproteins not only carry off cholesterol but may actually help flush away fatty deposits from plaque on arterial walls.

If these ideas are indeed correct, any cholesterol program should be directed, at least in part, toward raising the supply of these "good" cholesterol-disposing HDLs in the bloodstream, as opposed to the "bad" cholesterol-depositing LDLs. Some tactics for doing that are already available. At Stanford University, researchers have discovered that middle-aged male runners have HDL levels nearly 50% higher than their peers; their levels might be mistaken for those of young women, who are naturally endowed with more HDL and seldom have heart attacks. Other studies have shown that shedding flab and following a diet rich in vegetables and vegetable oils, but low in red meat and dairy products--along with moderate drinking (a cocktail or two a day)--can also elevate HDL. In the future, drugs may also be used; a compound known as PHB (for sodium para-hexadecylaminobenzoate) has been shown by Boston University's Dr. William Hollander to raise HDL levels in monkeys.

Such measures will not by themselves provide foolproof insurance against atherosclerosis. Dr. William P. Castelli, director of laboratories for the Framingham Heart Studies, advises people to keep a tight rein on their consumption of such cholesterol-rich foods as meat, hard cheese, eggs and cream.

Castelli also has advice for doctors: instead of relying only on total cholesterol counts, they should also measure the ratio of HDL to other lipoproteins. If it is sufficiently high--and there are no other untoward signs--the patient probably runs little risk of heart disease.

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