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Three short walks after eating worked better to control blood sugar levels than one 45-minute walk in the morning or evening, said lead researcher Loretta DiPietro, chairwoman of the George Washington University School of Public Health and Health Services in Washington, D.C.
The after-dinner period is an especially vulnerable time for older people at risk of diabetes, DiPietro said. Insulin production decreases, and they may go to bed with extremely high blood glucose levels, increasing their chances of diabetes.
About 79 million Americans are at risk for type 2 diabetes, in which the body doesn't make enough insulin or doesn't use it effectively. Being overweight and sedentary increases the risk. DiPietro's new research, although tested in only 10 people, suggests that brief walks can lower that risk if they are taken at the right times.
The study did not, however, prove that it was the walks causing the improved blood sugar levels.
"This is among the first studies to really address the timing of the exercise with regard to its benefit for blood sugar control," she said. In the study, the walks began a half hour after finishing each meal.
The research is published June 12 in the journal Diabetes Care.
For the study, DiPietro and her colleagues asked the 10 older adults, who were 70 years old on average, to complete three different exercise routines spaced four weeks apart. At the study's start, the men and women had fasting blood sugar levels of between 105 and 125 milligrams per deciliter. A fasting blood glucose level of 70 to 100 is considered normal, according to the U.S. National Institutes of Health.
The men and women stayed at the research facility and were supervised closely. Their blood sugar levels were monitored the entire 48 hours.
On the first day, the men and women did not exercise. On the second day, they did, and those blood sugar levels were compared to those on the first day.
The men and women were classified as obese, on average, with a body-mass index (BMI) of 30. The men and women walked on a treadmill at a speed of about three miles an hour (a 20-minute mile, which DiPietro described as the lower end of moderate).
The walks after meals reduced the 24-hour glucose levels the most when comparing the sedentary day with the exercise day.
A 45-minute morning walk was next best.
Walking after dinner was much better in reducing blood glucose levels than the morning or afternoon walking, DiPietro found.
Walking a half hour after eating gives time for digestion first, DiPietro said. Within that half hour, she said, "the glucose starts flooding the blood. You are using the working muscles to help clear the glucose from the blood stream." The exercise "is helping a sluggish pancreas do its job, to secrete insulin to clear the glucose," she said.
The briefer, more frequent exercise may also sound more doable to sedentary older adults, she said. "Committing to do this with someone would work best," DiPietro said. "It can be coupled with things like walking the dog or running errands."
The findings make physiological sense, said Dr. Stephen Ross, attending physician at UCLA Medical Center in Santa Monica, Calif.
"If you are exercising right after you eat, that would cause blood sugar to decrease because more of the glucose would go to the muscles to help the muscles with their metabolism," he said.
The brief walks, Ross said, may also fit a person's schedule better.
DiPietro cautioned, however, that "you have to do it every day" to get the benefit. It's not a prescription for fitness, she said, but simply to reduce diabetes risk.
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