Getting regular, moderate-intensity exercise may be critically important for post- menopausal women who want to reduce their risk of cancer, heart disease and other chronic diseases.
The reason: exercise effectively reduces intra-abdominal fat, a hidden risk factor for many chronic illnesses.
That's the result of a study published Wednesday and led by researchers in the Public Health Sciences Division.
Lead investigator Dr. Anne McTiernan and colleagues reported the results of the largest randomized clinical trial to assess the effect of exercise on overall and intra-abdominal obesity in postmenopausal women in the Jan. 15 edition of the Journal of the American Medical Association.
Drs. Yutaka Yasui, Neli Ulrich, Deb Bowen, Rebecca Rudolph, Erin Aeillo and John Potter, also from PHS, were co-authors, as were collaborators at the University of Washington, Yale University and the University of Colorado.
'Most dangerous type of fat'
"Even if a woman who exercises regularly doesn't see the benefits of dramatic weight loss on her scale, our results indicate that she can feel confident that she is improving her health," McTiernan said. "Regardless of the amount of weight lost, we now know that exercise reduces hidden intra-abdominal fat, the most dangerous type of fat."
McTiernan, director of Fred Hutchinson's Prevention Center, where PHS conducts its fitness research, and an international expert on the impact of physical activity on cancer prevention, underscored the importance of the results.
"This study gives us direct evidence that exercise can affect biology related to cancer and other chronic diseases in older women," she said.
Reducing intra-abdominal, or visceral, fat is important because in addition to increasing the risk of cardiovascular disease, diabetes and other conditions, such fat can raise insulin levels, which promotes the growth of cancer cells.
People with high levels of intra-abdominal fat may not even know it, McTiernan said, because it is hidden, deposited around the internal organs within the abdomen.
"Most women don't know about intra-abdominal fat, but they should, since it is the most clinically significant type of fat and it's where women tend to store fat after menopause," she said.
Not linked to body shape
Although it is known that so-called "apple-shaped" people who store their fat around the stomach are at higher risk for conditions such as diabetes, hypertension and stroke than "pear-shaped" people who store their fat in their buttocks and thighs, visceral obesity is not necessarily correlated with body shape, McTiernan said.
The only accurate way to determine the presence and extent of intra-abdominal fat, she said, is with imaging procedures such as CT or MRI scans.
"Because it is so costly to measure intra-abdominal obesity, until now very little data have existed on the impact of exercise on this dangerous, hidden health risk," she said.
The year-long study involved more than 170 previously sedentary, overweight, postmenopausal Seattle-area women. None took hormone-replacement therapy. Half were randomly assigned to a moderate-intensity, aerobic-exercise group, and half, who served as a comparison group, attended a weekly hour-long stretching class.
Those in the exercise group, who worked out at home and at a gym for at least 45 minutes five days a week - an amount similar to current national recommendations - achieved significant reductions in weight, total body fat and intra-abdominal fat.
After a year on the program, while the amount of body weight lost was modest yet statistically significant, the exercisers lost between 3.4 percent and 6.9 percent intra-abdominal fat while maintaining their calorie intake.
Women who had the highest adherence to the program experienced the largest decreases in weight, total and intra-abdominal fat. The women in the stretching group, in contrast, experienced a slight gain in intra-abdominal fat.
"The beauty of exercise as a method to reduce total and intra-abdominal fat - and therefore chronic disease - is that it can be done by most women at low cost and with low risk of side effects," McTiernan said.
"In addition, exercise has many other health benefits. The good news is that it is never too late to enjoy the health benefits of exercise."
The results of the study, funded by the National Cancer Institute, are significant for older women who seek a natural way to reduce their risk of chronic disease, said McTiernan, who is also a research associate professor at UW School of Medicine and School of Public Health and Community Medicine.
"Most American women gain one to two pounds on average every year, and that adds up to dangerous levels over a lifetime. All women - especially those at risk for diabetes, cardiovascular disease, cancer or high cholesterol - need to stop gaining weight," she said.
"Regular, moderate-intensity exercise can help keep the weight from creeping on, which can translate to improved health in the long run."
Strengths of the study
Compared to two other trials that looked at the impact of activity on intra-abdominal obesity, the strengths of the PHS study include its large sample (173 vs. fewer than 25 subjects), the length of the exercise (one year vs. less than six months), and its high adherence rates (81 percent of exercisers completed 80 percent or more of 225 minutes per week of exercise).
Another strength was its randomized, controlled, clinical-trial design, the gold standard of medical-study designs. Participants met three times weekly with a physiologist at an exercise facility, where they walked treadmills and rode stationary bikes. They also exercised two days a week at home, doing exercises of their own choosing, mostly walking. "In this type of study, we can directly control for extraneous factors and observe what the women are doing rather than just relying on what they report on questionnaires," said Dr. Anne McTiernan. "Therefore, we have more confidence in the results."