A federally funded analysis of MRI scans of the aging hearts of nearly 3,000 adults shows significant differences in the way male and female hearts change over time.
In both sexes, the main heart chamber, the left ventricle—which fills with and then forces out blood—gets smaller with time. As a result, less blood enters the heart and less gets pumped out to the rest of the body.
In men, the study reveals, the heart muscle that encircles the chamber grows bigger and thicker with age, increasing by an average of 8 grams. In women, the heart muscle retains its size or decreases by an average of 1.6 grams.
The heart's filling capacity—marked by the amount of blood the left ventricle can hold between heartbeats—declined in both sexes but more precipitously so in women, by about 13 milliliters, compared with just under 10 milliliters in men.
The differences in size, volume and pumping ability occurred independently of other risk factors known to affect heart muscle size and performance, including body weight, blood pressure, cholesterol levels, exercise levels and smoking.
"Thicker heart muscle and smaller heart chamber volume both portend heightened risk of age-related heart failure, but the gender variations we observed mean men and women may develop the disease for different reasons," says lead investigator John Eng, associate professor of radiological science at the Johns Hopkins University School of Medicine.
A condition that affects more than 5 million Americans, heart failure is marked by the gradual weakening of the heart muscle and eventual loss of pumping ability. To lower the risk, cardiologists often prescribe medications designed to reduce the thickness of the heart muscle over time and boost cardiovascular performance. But the finding that, in women, the heart muscle tends to shrink or remain the same size means they may not derive the same benefit from such treatments, researchers say.
The research team cautions that its study was not designed to find what exactly fuels the differences in cardiac physiology between the sexes, but says this "fascinating discrepancy" demands further investigation to figure it out.
The research, published online October 20 in the journal Radiology involved analysis of MRI scans performed on nearly 3,000 older adults, ages 54 to 94, without preexisting heart disease. Participants were followed between 2002 and 2012 at six hospitals across the United States; each of them underwent MRI testing at the beginning of the study and once more after a decade. MRI scans tend to provide more detailed images— and more reliable information— about the structure and function of the heart muscle than ultrasound technology used in other studies.
The study is part of an ongoing long-term project called the Multi-Ethnic Study of Atherosclerosis (MESA), which is following nearly 7,000 men and women of different ethnic backgrounds across the country. Other institutions involved in the study include the University of Washington; the University of California, Los Angeles; Wake Forest Baptist Medical Center; Brigham and Women's Hospital; the National Heart, Lung, and Blood Institute; Vanderbilt University; and Columbia University.Read more from Johns Hopkins Medicine