The most obvious difference between heart disease rates in men and women-the
coronary "grace period" women enjoy prior to menopause-may also be the
source of the greatest misunderstanding. Noting the spike in heart disease
rates after menopause, researchers have assumed, logically enough, that the
dropoff in circulating estrogen levels was responsible.
But logic can be a most unreliable guide to human physiology. Can women
indeed thank estrogen for their youthful immunity to heart disease, or is it
some chemical component of the hormone that deserves credit?
The case for estrogen is compelling, but not yet complete. Nearly every
study done to date-most notably, a Harvard Public Health Study indicates
supplemental estrogen protects postmenopausal women against coronary heart
disease, but none of these studies was the kind of randomized, controlled
trial that is the scientific gold standard. Estrogen is believed to boost a
woman's levels of HDL (the so-called "good" cholesterol) and lower her
levels of LDL (the "bad" cholesterol), slowing the process of
atherosclerosis. It is also thought to make blood-vessel walls dilate more
easily, so blockages are less common.
Among the researchers exploring the artery-friendly powers of estrogen is
Frank Sacks, associate professor in the Department of Nutrition. "Estrogen
increases the rate at which LDL is removed from the bloodstream," says
Sacks. "Our work is focused on the basic, metabolic process by which this
happens."
Previous research has found that estrogen increases the number of LDL
"receptors" deployed on the surface of liver cells. These receptors, which
bind specifically to LDL molecules, enable the liver to filter LDL out of
the blood. Sacks has built on this work by showing that estrogen also
increases the body's production of HDL, thereby preventing cholesterol
buildup in arteries. "A better understanding of this process may one day
lead to estrogen-based treatments for lowering high cholesterol counts,"
Sacks comments.
Has evolution rigged the heart disease equation against men-endowing women
with heart-healthy estrogen and men with testosterone, which has been shown
to lower levels of beneficial HDL. "Heart disease was irrelevant in
evolution," Sacks remarks. "Few people lived long enough to be affected by
it. Testosterone helps build muscles; the fact that it could promote heart
disease later in life didn't matter much." Estrogen, on the other hand,
"plays a beneficial role during pregnancy by stimulating fat metabolism and
helping women put on weight."