Men who give blood reduce the amount of iron in their bodies, but that does not result in a reduction in their risk of coronary heart disease (CHD) and heart attack. Iron levels in the body had once been thought to explain the difference in CHD rates among men and women. “The results of this study throw cold water on the 20-year-old hypothesis that reduced iron levels decrease the risk of coronary heart disease,” said Alberto Ascherio, associate professor of nutrition and epidemiology at the Harvard School of Public Health. Previous studies hypothesized that women have lower incidences of coronary heart disease than men because of a loss of iron in the blood through menstruation. Men can cut their iron level stores in half by donating one unit of blood per year and can further lower the level to that of premenopausal women by donating two or three units per year. The contrast between U.S. men who donate blood, and those who do not, provided a test for the hypothesis.