Getting Active, Staying Healthy
Can aerobic exercise improve beta cell function—and stave off type 2 diabetes?
Researcher: Anne Chang, MD
Occupation: Assistant Professor of Internal Medicine, University of Michigan
Research Funding: Clinical/Translational Research Award
It's a stunning statistic: Nearly a quarter of Americans over 60 have type 2 diabetes, and that number is bound to grow in the future. When it comes to diabetes, it turns out that getting older is a risk factor all by itself. There's ample evidence that our bodies serve up an insulin double whammy as we age: The beta cells in the pancreas stop producing enough insulin, and at the same time aging increases resistance to the insulin the body manages to make. The combination of decreased insulin production and increased insulin resistance, on top of the other factors that come into play later in life—weight gain and lack of exercise both being high on the list—turns type 2 diabetes into a major threat.
The consequences for this country alone could be dramatic. In an article in the December 2009 issue of Diabetes Care, University of Chicago epidemiologist Elbert Huang estimates that the number of people with diabetes is set to double in the next 25 years and that the cost of caring for them will triple. One of the most important factors behind the increase, Huang writes, is the aging of the baby boom generation, a massive cohort of Americans born between 1946 and 1964 that represents a quarter of the U.S. population.
The oldest baby boomers started turning 60 in 2006. Since then, the Census Bureau estimates, nearly 8,000 Americans have turned 60 each day. That's roughly 330 an hour, 165 of whom will probably eventually develop type 2 diabetes. When Anne Chang, an endocrinologist at the University of Michigan whose mother, grandmother, and sister all have type 2 diabetes, first learned of these stats, she was amazed. "I was surprised there were such tremendous rates of diabetes in people 60 or older," Chang says.
Fortunately, the solution for some at risk may be as simple as regular exercise. "Lifestyle intervention with diet and exercise is tremendously effective, particularly in people over 60," Chang says. In a 2008 study, she measured the effects of seven straight days of aerobic exercise on beta cells. Though the study was small, the results were encouraging: The people in the study had improved beta cell function and were more sensitive to insulin when they were tested at the end of the week.
"It's exciting to see those results after just one week," Chang says. The promising results encouraged her to design a more complete study looking at the links between exercise and insulin production, to see if the initial study could be confirmed on a wider scale. Says Chang: "It's a proof of principle. Does aerobic exercise training improve beta cell function?"
The expanded study involves bringing in older people from the Ann Arbor, Mich., area four times a week for 45-minute exercise sessions. Chang is focusing on people who are at risk of developing type 2 diabetes, for whom an intervention might make a difference. "These are sedentary people who don't exercise regularly," she says. "All of them have pre-diabetes."
Chang's team measured indicators like insulin secretion, insulin sensitivity, and body composition, to see how the exercise changed people's bodies. But because the study was focused on how exercise—not weight loss—affected beta cell function, Chang made sure to compensate for the calories burned by exercise with post-workout snacks. "We wanted a weight-maintenance diet to eliminate weight loss as a variable," she says.
She tested the study participants before their first session, to get a baseline for later comparisons. "They're very comprehensive, dynamic tests of insulin secretion, including having glucose infused through IV lines and seeing how much insulin is produced," she says. Participants work with physical trainers on a specially tailored aerobic exercise program that includes time on treadmills and stationary bikes. Chang tests them again after the first exercise session, then after three months of regular exercise, and one last time a little less than a week after they stop the organized exercise program to see if the results hold steady.
Though she estimates it will be another year before she's done with testing and analysis, Chang says that so far what she's seeing matches what she expected from her initial research. "The results are pretty encouraging," she says. "There seems to be a decrease in central fat and an improvement in insulin sensitivity and beta cell function."
It's no cure, but it is a good sign that the benefits of exercise go beyond weight loss and reach deep into the body, helping reverse some of the effects of aging when it comes to insulin production and resistance. And, of course, there are benefits no tests can measure. "Everybody has really enjoyed the exercise program," Chang says. "Most have said they've never felt so good."
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