Can weight training prevent diabetes?

By Deborah Kotz, Globe Staff

With the booming popularity of weight-lifting DVD’s like P90X and Insanity, many men -- the target audience of these videos -- have made strength training their only form of exercise. As it turns out, working to bulk up those muscles not only helps build strength and prevent age-related muscle loss, but may help ward off type 2 diabetes as well.

In fact, it may work nearly as well as steady aerobic exercise such as walking, swimming, and biking.

That’s what Harvard School of Public Health researchers found when they followed more than 32,000 men for nearly two decades: Those who reported doing 30 minutes a day of resistance training at the beginning of the study had a 34 percent decrease in their diabetes risk compared with those who didn’t exercise. Men who did 30 minutes a day of aerobic activity had a 52 percent lower risk of diabetes compared with couch potatoes, according to the study published Monday in the Archives of Internal Medicine.

The best form of exercise when it comes to diabetes prevention? Doing a combination of steady exercise and weight training for at least 30 minutes a day on most days of the week. Study participants who did both had nearly a 60 percent reduction in their diabetes risk.

(Among all the men, about 7 percent developed diabetes during the study.)

“Our study was the first to look at whether weight training provided benefits long-term in lowering the incidence of diabetes.,” said study co-author Dr. Frank Hu,, a professor of nutrition and epidemiology. “While the study didn’t include women, there’s no reason to believe that the finding doesn’t apply to them as well.”

Another finding published in the same journal analyzed data from five studies and found that diabetics who reported moderate levels of physical activity -- whether hauling lumber on the job or walking regularly with friends -- had a 38 percent lower risk of dying of any cause compared with diabetics who didn’t engage in any exercise.

Strength-training activities trigger muscle cells to utilize more glucose for energy, which can lower blood sugar levels, said Hu. An increase in lean body mass also helps make cells more sensitive to the hormone insulin, helping to reverse insulin resistance, a precursor of diabetes. Aerobic activity, he added, probably works through different mechanisms to help prevent diabetes by encouraging fat loss and insulin sensitivity through calorie burning. Thus, combining the two may be ideal for both preventing and managing diabetes.

“I cannot help but note that none of the time I spend trying to decide whether to increase the dose or add a new medication for my patients with type 2 diabetes is likely to result in a 38 percent reduction in mortality,” wrote Dr. Mitchell Katz, in an editorial that accompanied the study. He urged doctors to write specific exercise prescriptions for patients with diabetes and those at risk of becoming diabetic -- such as 30 minutes of brisk walking three times a week and two days a week of muscle-building activities -- rather than just advising them to do whatever activity they enjoy.

Joslin Diabetes Center provides an exercise program in its on-site gym that includes a strength-training component, often using resistance bands, for diabetic patients who might be reluctant to purchase free weights or join a gym. The specific benefits conferred by strength training are “really newly recognized,” said Jacqueline Shahar, a clinical exercise physiologist at Joslin. “When I first came here 10 years ago, the exercise program we provided was strictly aerobic, but now everyone gets a program that includes resistance training.”

While insurance providers in the state cover the cost of the Josline exercise program -- which run upwards of $100 per session -- for those diagnosed with diabetes, they often don’t cover the program in those who are at risk of becoming diabetic because they have insulin resistance or a strong family history. Joslin’s website offers a few free strengthening videos to learn some basics.

The new Harvard study could provide an impetus for managed care companies to pick up the exercise tab for those who don’t yet have diabetes, to prevent the condition and the long-term complications that go along with it, including heart disease, blindness, and nerve damage. But that may not happen until better-designed studies can demonstrate that exercise itself can prevent diabetes.

“It’s very hard to know for certain from this new study whether it was the weight training that prevented diabetes or whether people who lift weights are healthier than others because of other behaviors they engage in,” said Dr. Vivian Fonseca, president of medicine amd science at the American Diabetes Association. The researchers took into account dietary habits, smoking status, and body weight, but they couldn’t account for other lifestyle habits associated with diabetes such as poor sleep and stress.

Deborah Kotz can be reached at dkotz@globe.com. Follow her on Twitter @debkotz2.