Before menopause, women suffer only about half as many heart attacks as men of similar age do. But after menopause the statistics even out. Many medical researchers suspect that because estrogen production drops sharply after menopause, the hormone might somehow help ward off heart disease. But a recent study suggests that in addition to estrogen, the monthly loss of blood may protect women from heart disease, and that men might benefit by regularly donating blood.
David Meyers, a cardiologist at Kansas University Medical Center, became interested in a possible link between blood loss and heart disease after reading about a Finnish study that found that men with high levels of iron in their blood had more than twice the risk of heart attacks than men with lower levels. He wondered whether the regular loss of blood, by depleting the body’s iron reserves, might reduce that risk.
To find out, Meyers studied a group of Nebraskans who had participated in a health survey ten years ago. He followed up on 3,855 men and women in the original survey, all of whom are now over 40, and noted how many went on to develop heart disease and how many had donated blood in the past decade. Meyers found that men who had donated blood at least once in the last three years were 30 percent less likely to have developed heart disease. He found no difference for women between donors and nondonors.
What causes the effect? When women menstruate, the blood loss also reduces their stores of iron. Women typically have about half as much iron as men. Iron, researchers believe, acts as a catalyst in cholesterol oxidation, transforming cholesterol into a more dangerous molecule. Cholesterol is kind of a mild irritant, but oxidized cholesterol is just a really nasty irritant, he says. It causes lots of scar formation in the arteries, hardening them.
Meyers believes that more studies are necessary to make sure that blood loss does indeed lower the risk of heart disease. It’s possible, he says, that the earlier studies may just reflect that blood donors tend to be healthier than nondonors. To answer that question, it’s going to take another decade of trials where we randomly decide who will and who will not donate blood, says Meyers. Then we’ll see what happens.