ORLANDO, Fla., March 26 -- Motherhood may lead to a more sedentary lifestyle for women that could place them at risk for heart disease, researchers report here today at the American Heart Association's epidemiology and prevention meeting.
A 10-year study of young adult men and women found that parenthood resulted in reduced leisure time physical activities in women, but not in men, says Kathryn Schmitz, Ph.D., postdoctoral fellow, division of epidemiology, University of Minnesota, who presented the study. "This puts women at greater risk for heart disease and other diseases associated with a sedentary lifestyle. To change this trend we need to give moms time to exercise or design programs that allow them to exercise with their children present," she says.
"The biggest difference occurred when they became first-time parents," adds Schmitz. "There wasn't any additional change in physical activity when going from one to two children."
Physical inactivity doubles the risk of coronary heart disease, the cause of heart attacks. The doubling of risk is comparable to the effects of other major risk factors, such as high blood cholesterol, high blood pressure or smoking. According to the American Heart Association as many as 250,000 deaths each year -- about 12 percent of total deaths -- are attributed to a lack of regular physical activity.
"To reverse this trend, moms must take time to exercise and programs should be designed that make it convenient to enjoy an active lifestyle," says Schmitz.
The researchers initially assumed that mothers who were the sole caregivers would have a more dramatic drop in physical activity than married mothers. However, that wasn't the case. "We were thinking if the woman was a single parent there would be just that much more of a load," says Schmitz. "But it didn't matter whether the woman was married or not."
Women may not have the time to exercise. "We can only speculate that the reason women are reporting less leisure-time physical activity overall than men is that they are spending more time caring for children," she says.
The data were derived from the CARDIA (Coronary Artery Risk Development in Young Adults) study, which has followed men and women, ages 18 to 30, for 10 years to track both health and behavioral risk factors of heart disease. The researchers tested whether parenthood resulted in a reduction of self-reported leisure-time physical activity. Leisure-time physical activity and marital and parenting status were self-reported five times during the 10-year period in 3,274 black and white participants. Frequency and intensity of physical activity were used to determine exercise units (EU). For example, 50 EU are the equivalent of jogging two hours or less weekly for six months out of the year. The researchers adjusted for marital and job status, age, education, smoking and body mass index -- an indicator of body fat based on weight and height. Physical activity associated with child care was not considered in this analysis.
The results showed that white women, who averaged about 400 EU annually before parenthood, dropped an average of 56 EU, or 14 percent, after parenthood. Black women, who averaged 278 EU before becoming mothers, dropped 26 EU annually, or 9 percent.
The most commonly reported types of leisure-time physical activity among the study participants were walking, non-strenuous leisure sports and home exercise (calisthenics).
Previous health-related studies have shown that marriage seems to affect leisure-time physical activity in women, but those studies had not looked at the parenthood issue. The larger decrease in white women, compared to black women, is probably attributable to the fact that in population-based samples, black women typically report much less physical activity than white women. Women, in general, are less physically active than men, she says.
"This may place women at increased risk of developing diseases associated with a sedentary lifestyle, says Schmitz. "To change that risk may require something as simple as giving moms time to work out."
The original hypothesis was that lack of time is the most common barrier to physical activity. "We can only speculate that the reason women are reporting less leisure-time physical activity overall than men is that they are spending more time caring for children and don't have time for physical activity.
"Child care availability may be a solution. Perhaps providing child care in gymnasiums or recreation centers where women can work out or creating exercise programs where mothers can bring their young children may be a solution," says Schmitz.
It is hoped that studies like this will spur either some behavioral changes or new policy recommendations for physical activity in women, she says. "This is a topic of considerable emotional depth, for the general public and women in particular."
Co-authors of the study are David R. Jacobs Jr., Ph.D., Pam Schreiner, Ph.D., and Simone French, University of Minnesota, Minneapolis, Cora Lewis, M.D., University of Alabama, Birmingham, Carl Caspersen, Ph.D., U.S. Centers for Disease Control and Prevention, Atlanta, Steve Sidney, M.D., Kaiser Permanente, Oakland, and Barbara Sternfeld, Ph.D., Kaiser Permanente, Oakland.
Media advisory: Dr. Schmitz can be reached at 612-625-8056. (Please do not publish telephone number.)