Moderate amounts of muscle strength, but not beyond that, were associated with a 32% reduced risk of developing Type 2 diabetes in the study, published in the journal Mayo Clinic Proceedings
"While it’s not entirely clear why higher strength did not protect against diabetes, it’s possible that higher aerobic fitness, higher amounts of physical activity and lower body mass indexes that were present in this higher-strength group were also affecting the relationship between strength and diabetes," said Angelique Brellenthin, a postdoctoral research associate in Iowa State University’s College of Human Sciences
, who was an author of the study.
"This is also the first study to investigate the relationship between muscular strength and risk of developing diabetes later in life," she said.
More than 30 million Americans, or about 1 in 10, have diabetes -- and 90% to 95% of them have Type 2 diabetes, according to the US Centers for Disease Control and Prevention
Globally, the prevalence of diabetes continues to rise. The number of people with diabetes has risen from 108 million in 1980 to 422 million in 2014, according to the World Health Organization
The new study involved 4,681 people 20 and older who had no Type 2 diabetes at the start of the research.
Between 1981 and 2006, the adults underwent muscular strength tests and treadmill exercise tests as part of medical examinations at the Cooper Clinic in Dallas.
The strength tests assessed strength in the upper and lower body using resistance weight machines, while the treadmill exercise tests assessed cardiorespiratory fitness.
During that same period, the researchers took a close look at whether any of the adults developed Type 2 diabetes; 229 developed the disease.
After dividing the adults’ muscular strength tests into thirds, the researchers found that those in the middle level had a 32% reduced risk of Type 2 diabetes compared with the lower third.
Yet there was no significant association between incidents of Type 2 diabetes and the upper level of muscular strength compared with the lower level, the researchers found.
They came to their findings after taking into account other factors that may influence Type 2 diabetes risk, including cardiorespiratory fitness level.
"While we adjusted for these other healthy factors in the study, it doesn’t completely take away their potential confounding effects, particularly in the higher-strength group," Brellenthin said. "Future studies will have to consider these to fully understand the relationship between strength and diabetes."
The study had some limitations, including that the sample size was small, and the adults were mostly white and in a middle to upper socioeconomic status. More research is needed to determine whether similar findings would emerge among a more diverse group.
The study also did not take into account each adult’s diet, which can influence diabetes risk.
The study’s findings point to how important both muscle strength and cardiorespiratory fitness are for having a lower diabetes risk, said Dr. Monique Tello, a practicing physician at Massachusetts General Hospital
and clinical instructor at Harvard Medical School, who was not involved in the study.
"People in the medium strength group tended to also have good cardiorespiratory fitness," Tello said about the study. "There was a good correlation."
Whereas, "in the low strength group, there were people who had high cardiorespiratory fitness, and then in the high strength group there were people with low cardiorespiratory fitness. The correlation was not as clear, so that may have washed out some of the significant findings," she said. "We know from prior studies that combining aerobic exercise and resistance training particularly improves blood sugars in people who have diabetes, and can also prevent diabetes from developing."