Men who do weight training or resistance training on a regular basis may be able to lower their risk of developing type 2 diabetes, according to a new study published online this week.

Weight training is a form of resistance training, where the aim is to develop strength in the skeletal muscles by resisting force through the use of free weights, for example dumbbells and barbells.

Writing in the 6 August online-first issue of the Archives of Internal Medicine, researchers from the Harvard School of Public Health (HSPH) and the University of Southern Denmark, describe how they found men who practise weight training about 30 minutes a day on 5 days a week may be able to lower their risk for type 2 diabetes by up to 34%.

And they show how men may be able to lower their risk further, by 59%, if they combine weight training with aerobic exercise like brisk walking or running.

The researchers wanted to do the study because while we already know there is a strong link between aerobic exercise and reduced risk for type 2 diabetes, the link with weight training on its own was not so clear.

Evidence from recent trials has shown that resistance training can improve glycemic control in patients with type 2 diabetes, even without aerobic training, and in fact this has led to the recommendation that people with type 2 diabetes incorporate resistance training into their exercise schedule three times a week.

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But this is the first study to show that weight training on its own may prevent type 2 diabetes.

This could be an important finding, as lead author Anders Grøntved, a visiting researcher in the Department of Nutrition at HSPH and a doctoral student in exercise epidemiology at the University of Southern Denmark, told the press, because "many people have difficulty engaging in or adhering to aerobic exercise".

Senior author Frank Hu, professor of nutrition and epidemiology at HSPH, said:

"This study provides clear evidence that weight training has beneficial effects on diabetes risk over and above aerobic exercise."

He said the effects are probably due to increased muscle mass and improved insulin sensitivity.

"To achieve the best results for diabetes prevention, resistance training can be incorporated with aerobic exercise," he added.

For the study, Grøntved and colleagues used data on 32,002 men who took part in the Health Professionals Follow-up Study from 1990 to 2008.

The data included questionnaires that the men had filled in every two years and answered questions about how much time they spent every week doing weight training and aerobic exercise.

Over the study period, 2,278 of the men were newly diagnosed with type 2 diabetes.

After adjusting for possible influencing factors, such as other types of physical activity, watching TV, coffee, alcohol, smoking, family history of diabetes and ethnicity, plus a number of dietary factors, the researchers found a "dose-response" relationship between weight training and reduced risk of type 2 diabetes, in that even a modest amount of weight training appeared to help lower the risk of type 2 diabetes a bit.

Compared with men who did no weight training, the ones who did up to 59 minutes a week had a 12% reduced risk for type 2 diabetes.

And doing between 60 and 149 minutes of weight training a week reduced the risk of type 2 diabetes by 25%, and doing at least 150 minutes a week reduced it by 34%.

When they looked at aerobic exercise, the researchers found, as expected, a similar dose-response relationship.

Up to 59 minutes a week of aerobic exercise reduced the risk for type 2 diabetes by 7%, compared to not doing it at all.

And doing 60 to 149 minutes of aerobic exercise reduced the risk of type 2 diabetes by 31%, while doing at least 150 minutes a week reduced it by 52%.

Grøntved and colleagues also found that weight training and aerobic exercise together had the greatest effect: men who did more than 150 minutes of aerobic exercise, and also at least 150 minutes of weight training every week had a 59% reduced risk of type 2 diabetes.

Grøntved said there now need to be more studies to confirm these findings, and also to find out if the same is true for women.

Type 2 diabetes is a major health problem throughout the world and it is rising.

The World Health Organization estimates that 346 million people have the disease, and deaths related to it are expected to double between 2005 and 2030, with more than 80% of them occuring in low and middle income countries.

Some of the researchers on the study were supported by grants from the National Institutes of Health in the US.

Written by Catharine Paddock PhD