Among a group of patients taking part in one of the longest-running
rehabilitation programs for heart patients, Warner and his colleagues found
166 female participants were able to lower their risk of heart attack more
than 553 male participants, the scientists report in the American
Heart Association journal Circulation.
All of the cholesterol levels improved more in the women: (1) HDL, their
"good" cholesterol, increased by 20 percent compared to a five percent
increase in the men; (2) LDL cholesterol, the "bad" form, dropped by 34
percent compared to 15 percent in the men; and (3) women's total cholesterol
decreased overall by 20 percent versus only eight percent in the men.
The 719 men and women, mean ages 57 and 59, respectively, participated in
the Wake Forest Cardiac Rehabilitation Program between Jan. 1, 1988, and
Jan. 1, 1994. They exercised three days a week for up to five years. Each
exercise session involved 10 minutes of stretching followed by 30 to 40
minutes of walking, jogging or riding a stationary bicycle.
All patients were counseled on low-cholesterol and low-fat diets, the
scientists report. The percentage of men and women on cholesterol-lowering
drugs was similar, and only six percent of the women were taking estrogen
The research project is one of the largest "observational" studies to
examine the effects of exercise on HDL-cholesterol and other blood fats in
patients undergoing cardiac rehabilitation and to compare the effects on men
and women, the investigators point out. "A limited number of (earlier)
studies showed a favorable effect of exercise on HDL-cholesterol in cardiac
rehabilitation patients," they say. "However, most of these studies had
small numbers of subjects and short training periods and were conducted
almost exclusively in men." So the researchers designed their study to
compare changes in HDL and other lipids (fats) in a large group of men and
women taking part in a rehab program for five years.
Men in the study showed approximately the same beneficial increase in
HDL-cholesterol as the women during the first year of exercise. "But over
the next four years, there was no further increase" in the men, the authors
report. "It is unclear why HDL-cholesterol remained essentially unchanged
after one year in men and continued to rise over five years in women." "We
were surprised that the men plateaued after one year," says Warner. One
possible factor is that the women started at lower overall fitness levels,
based on measures of aerobic capacity, and thus had "more room for
improvement," he points out.
Even if they don't benefit as much as women do, men should continue to
participate in cardiac rehab programs -- "because if they quit, the
beneficial effects (of past efforts) probably will disappear," Warner says.
Because studies by others have suggested that each one-
milligram-per-deciliter (mg/dl) increase in blood level of HDL-cholesterol
reduces the risk of heart attack by more than two percent, Warner estimates
that the five percent increase in HDL levels in men does represent, at least
in theory, a significant 10 percent decrease in their heart attack risk.
The 20 percent increase in HDL -- and the accompanying theoretical 40
percent decrease in heart attack risk -- seen in the exercising women was as
good a result as they could hope to achieve with the best drug therapies,
says David M. Herrington, M.D., senior author of the study and associate
professor of medicine at Bowman Gray.
But at this point, the researchers have not shown that the improvements they
observed in cholesterol levels actually translate into lower rates of heart
attacks and higher rates of survival. Warner, Herrington and their
co-workers plan to continue to follow the same 719 patients to see which
ones go on to have heart attacks.
Future studies also are needed to clarify the mechanism through which
exercise affects HDL-cholesterol and other lipids in women and men, the
Female hormones including estrogen probably play an important role, notes
Warner, because after menopause, a woman's risk of heart attack rises until
it eventually matches that faced by men. "It's known that until women reach
menopause, they have higher HDL-cholesterol than men," he says.