Now, a new systematic review shows that exercise helps regulate blood glucose (sugar) levels, increases the body's sensitivity to insulin, and decreases blood lipids (fats) while also helping to burn body fat.
"Type 2 diabetes is an increasing problem in Western societies and is associated with increased rates of overweight and obesity," said review co-author Elizabeth Elliott, M.D., of the University of Sydney and Children's Hospital at Westmead, in Australia. "In this study, we wanted to determine if there was an independent effect of exercise — separate from dietary modification and medications — in improving outcomes in patients with type 2 diabetes."
The review appears in the current issue of The Cochrane Library, a publication of The Cochrane Collaboration, an international organization that evaluates research in all aspects of health care. Systematic reviews draw evidence-based conclusions about medical practice after considering both the content and quality of existing trials on a topic.
The study, which reviewed data from 14 randomized controlled trials, included a total of 377 participants. The average age range in studies was 45 to 65 years with slightly more men than women. All participants had type 2 diabetes and the only difference between groups was that they were assigned to either no exercise or to a prescribed exercise regime.
The types of exercise programs in each study varied widely. Resistance training and aerobic workouts were the most common, although one study involved qi gong.
Exercise sessions varied from one to seven times a week, with most studies involving three sessions a week. Sessions lasted from 30 minutes to two hours, with half the studies using hour-long sessions. The studies were short term, ranging from eight weeks to 12 months with most lasting less than six months.
"We were interested in whether a prescribed exercise regime versus no exercise regime would actually improve blood sugar control, and it did," said Elliott. The researchers determined this by looking at the percent of glycated hemoglobin in the blood, also known as an A1C test. The American Diabetes Association considers A1C values to be the best indicator of long-term blood glucose control.
Participants who exercised had an overall decrease of 0.6 percent of A1C levels. While that may not sound like much, it represents a 30 percent improvement towards the goal of attaining an A1C of 7 percent, and a 20 percent improvement towards a normal A1C of 6 percent.
"This was a both a statistically and clinically significant drop," said Elliott. "It's comparable to the drop that clinicians would like to see if prescribing medication" to regulate blood sugar, she said.
"Many people with type 2 diabetes find when they start walking daily, for example, that blood sugar control becomes much easier. That's been known anecdotally for a long time," Elliott said. "Our study gives justification to the recommendation that exercise is important."
Participants enrolled in an exercise program also lost significantly more fat around the abdominal organs and under the skin, compared to those who didn't exercise.
Exercising participants didn't actually lose any weight, however — probably because exercise helps replace fat with heavier muscle tissue, researchers said, and because the average length of the studies was too short to show weight loss. Muscle tissue helps in the metabolism of insulin and blood sugar regulation.
Participants who exercised also experienced a significant lowering of blood triglycerides, which are often elevated in patients with diabetes. Excess triglycerides have been linked to coronary artery disease.
"Our review shows that diabetes management can be enhanced by nonmedical measures such as exercise," Elliot says. "All patients with diabetes would probably benefit from a consultation not only with a dietitian but also a physiotherapist, exercise physiologist or sports medicine physician who can create for them a sustainable exercise program."
Neal Kohatsu, M.D., president of the American College of Preventive Medicine, concurs. "There is a strong body of evidence that exercise in partnership with other healthy lifestyle and medical interventions does have benefit" for patients with type 2 diabetes, he said. "People often think that you have to be a triathlon competitor to get benefits from exercise. In fact there is substantial benefit going from couch potato to being even modestly active."
While there were no documented adverse effects from any of the exercise regimes in studied, Kohatsu says that patients with type 2 diabetes should consult with their physician before starting or changing an exercise program. "There are issues related to diabetes and exercise that one has to be cautious about. For example, good foot care is important because of potential problems with circulation and neuropathy," he said.
In addition, he said that insulin-dependent diabetic patients may be at risk for hypoglycemia, or low blood sugar, when exercising and need to know how to monitor and treat themselves if they should become hypoglycemic.
Age, cardiovascular status, and other factors may also influence what kind of exercise is best for an individual patient with type 2 diabetes.