A study of more than 3,500 Japanese-American men over the age of 70 found a steadily increasing death rate from all causes when cholesterol levels drop, reports a group led by Dr. Irwin J. Schatz, a professor of medicine at the University of Hawaii.
"We have been unable to explain our results," they write in the Aug. 4 issue of The Lancet.
One proposed explanation that has to be ruled out is that the finding is somehow linked to this particular ethnic group, Schatz says.
"We think that the risk factors for all-cause mortality are the same the world over," he says. "There is no information that these people are different in terms of susceptibility to any chronic disease. We think it is reasonable to expand the conclusion to all Caucasian men."
The Lancet report comes from the Hawaiian Heart Study, which has been measuring cholesterol levels in a group of Japanese-American men since 1972. After the latest measurements, the researchers reviewed the entire group on the basis of the blood cholesterol levels.
The death rate for those with the highest cholesterol reading was 35 percent lower than for those with the lowest readings, the researchers report: In the highest cholesterol group, there were 43 deaths per 1,000 each year; in the lowest cholesterol group, there were 68 deaths per 1,000 each year.
Schatz says he does have a possible explanation, which he describes as "pure speculation." His explanation is based on the knowledge that high blood cholesterol levels at earlier ages are known to increase the risk of heart disease and stroke.
"I think a selection process takes place," Schatz says. "People with high cholesterol below the ages of 70 and 75 have increased mortality, and those who remain have been selected for survival."
Dr. Richard A. Stein, chief of cardiology at the Brooklyn Medical Center and a spokesman for the American Heart Association, proposes a different explanation. Too-low cholesterol levels could be an indication of an underlying medical problem, he says.
"Cholesterol is produced by the liver, and a variety of conditions in the elderly affect liver metabolism," Stein says. "Any number of illnesses are associated with the geriatric process of failure of liver function."
The frailty of old age alone can affect the liver's ability to produce cholesterol and perform its other vital functions, Stein adds, and there also can be "confounders that have not been identified" that have the same effect.
Schatz says more research is needed to follow up the finding. "The central message is that we need a good, randomized trial of lipid lowering in the elderly," he says.
What To Do
There is no need to change the basic recommendations that older people keep their cholesterol levels in check, Schatz says. But he adds, "I would just suggest to physicians that they might want to be a little less aggressive in efforts to lower cholesterol to very low levels in old people."
And Stein says efforts to reduce heart disease by keeping cholesterol levels low should be pursued with "appropriate moderation" in older people.