Photo by Todd McNaught
Postmenopausal women who exercised for 30 or more minutes per day significantly lowered their blood levels of markers associated with diabetes and heart disease, according to a new Public Health Sciences Division study published in the March issue of Obesity Research.
The research, conducted by affiliate investigator Dr. Laura Frank during her postdoctoral work at the Hutchinson Center, found that regular, moderate-intensity exercise lowered levels of hormones that help the body use sugar and regulate weight, even when the study participants gained overall body fat. "Our study suggests that we can change metabolic risk factors through regular, moderate-intensity exercise, even among women who gained overall body fat," Frank said. "That's good news."
Principal investigator Dr. Anne McTiernan led the yearlong study of 173 women, 50 to 75 years old, to examine metabolic differences between women who exercised regularly compared with women who limited their activity to stretching. The study targeted postmenopausal women who were sedentary and overweight or obese at the beginning of the trial.
More than 60 percent of postmenopausal women in the United States are overweight or obese, which increases levels of metabolic factors such as insulin (a hormone that helps the body use sugar and carbohydrates), glucose (blood sugar), triglycerides (blood fats) and leptin (a hormone that regulates weight and metabolism). Obesity, especially abdominal fat, is associated with increased risk of type 2 diabetes, heart disease, stroke and several cancers.
Participants in the National Cancer Institute-sponsored study exercised using treadmills and stationary bicycles, as well as by walking. All study members were asked to maintain their usual diet.
The researchers found that after 12 months of routine exercise, the active women had a 4 percent decrease in insulin levels compared to a 12 percent increase in the sedentary control group. Over the same period, leptin concentrations decreased by 7 percent among exercisers while remaining constant in the inactive women. Homeostasis model assessment scores (a marker of insulin resistance) decreased by 2 percent in the active group but increased by 14 percent in the sedentary group. There were not significant changes in glucose or triglyceride levels between the two groups.
Data proves exercise works
In the exercise group, women who gained body fat during the study did not have increased insulin levels, which may rise along with increases in overall fat mass. "Even if they didn't lose fat mass while they were exercising, they still benefited," Frank said.
Women tend to gain abdominal weight — the so-called "menopot" — during their postmenopausal years. Abdominal fat is especially associated with diabetes and heart disease, but Frank found that changing overall body fat was more important for decreasing insulin levels. "It was overall fat that made the difference," she said. Exercise participants who were active for 131 to 190 minutes per week experienced the most benefit compared to women who exercised the least (130 minutes or less per week). However, there was no additional benefit for participants who exercised more than 190 minutes weekly.
The Centers for Disease Control and Prevention and the American College of Sports Medicine recommend that adults exercise for 30 or more minutes on five or more days per week. "Our data shows that it actually works!" Frank said. "We showed that approximately 30 minutes of moderate-intensity exercise on most days of the week improved insulin levels. If we can improve that, we can decrease the risk of obesity-related diseases like insulin resistance, type 2 diabetes and cardiovascular risk factors."
Frank hopes the study results will encourage more women to exercise daily, even for a half-hour. "I worry when the public health officials say, 'Well, 30 minutes wasn't good enough, so now we're going to recommend 60 minutes,'" she said. "So what do you do with the people who haven't reached that 30-minute goal yet? If we want to work on obesity in America, we have to have realistic goals for everybody."
Co-authors included Bess Sorensen and Drs. Yutaka Yasui, Neli Ulrich, Rebecca Rudolph, Kumar Rajan, Frank Stanczyk, Deborah Bowen, John Potter and Anne McTiernan, of the Hutchinson Center; Dr. David Weigle, University of Washington; Dr. Shelley Tworoger, Harvard University; Dr. Robert Schwartz, University of Colorado; and Dr. Melinda Irwin, Yale University.