Up and down on the lipoprotein seesaw.

Up and down on the lipoprotein seesaw 

Too much fat pumping through your bloodstream is not a pretty thought. But the story of unhealthy lipids and their carriers in the blood isn't as straightfor ward as once believed. Although both lipoproteins carry cholesterol, many studies suggest that high-density lipoprotein (HDL) reduces the cholesterol buildup in blood vessel walls that leads to atherosclerosis, whereas low-density lipoprotein (LDL) contributes to fatty accumulation (SN: 11/30/85, p.343).

There are a number of factors that evidently can influence a person's HDL/LDL ratio. Researchers at the meeting discussed new findings on some of these factors, including alcohol consumption and prescription drugs.

Several studies in recent years had exposed a curious aspect of alcohol's relationship to heart disease: Having one or two alcoholic drinks a day appears to reduce the risk of coronary heart disease (SN:6/1/85, p.345). In an attempt to explain this, a group of researchers at Harvard Medical School and Brigham and Women's Hospital in Boston looked at the interactions among heart attacks, alcohol and specific subgroups of HDL in 789 subjects. Of those, 366 had suffered their first heart attack; the remainder were matched controls who had not had an attack.

Heavy drinking--defined in this study as five or more drinks per day--is "unequivocally' bad in terms of heart disease, says Harvard's Charles H. Hennekens. However, light to moderate drinking--defined here as two beers or glasses of wine, or one liquor-based drink daily--was associated with a 46 percent lower risk of having a heart attack when compared to that of nondrinkers. The only explanation of the finding at this point, says Hennekens, is that alcohol apparently changes the levels of HDL. The group found that both major HDL components, HDL2 and HDL3, are elevated in those who drink conservatively.

Another study supports the observation that small amounts of alcohol help protect against heart disease by altering HDL concentrations. Using squirrel monkeys fed diets in which alcohol ranged from 0 to 36 percent of the total calories, researchers of the University of Lowell (Mass.) and the Zablocki Veterans Administration Center in Wood, Wis., found that a little goes a long way. The lowest LDL levels and highest proportion of HDL2 occurred in animals fed diets of 12 percent alcohol, a dose consistent with that seen in nutritional surveys of nondrinkers, say the scientists. But a small increase to 18 percent, although it further raised HDL, also caused a significant elevation in the levels of LDL constituents linked to atherosclerosis.

Despite these findings, the scientists do not recommend that nondrinkers begin consuming alcohol, which can lead to its own set of health problems. A more logical approach, says Hennekens, would be to design drugs that duplicate alcohol's boosting effect on HDL components.

Researchers have been searching for ways to increase HDL levels in an effort to undermine lipid profiles that might lead to heart disease. For example, one of the latest in cholesterollowering drugs, called gemfibrozil, appears to reduce by 34 percent the incidence of coronary heart disease, according to a report in the Nov. 12 NEW ENGLAND JOURNAL OF MEDICINE. The Swedish study concludes that gemfibrozil increases HDL and decreases LDL levels.

Tinkering with HDL levels, however, may prove unwise; new results from a joint Soviet/U.S. study may reverse the general opinion that HDL is advantageous. Scientists at Columbia University in New York City and the Academy of Medical Sciences in Leningrad found that in nearly 8,000 Soviet men, higher levels of one type of HDL are associated with higher mortality from coronary heart disease.