Could muscle strength reduce type 2 risk? There could be more to working out than just looking good and feeling good for patients with pre-diabetes.
Muscular strength has been recognized to play an increasing role in the prevention and management of chronic diseases such as some forms of cancers and heart disease. Muscle tissue is responsible for the clearance of glucose from the body in the presence of insulin, indicating its role in the progression of type 2 diabetes mellitus. Previous studies have been published that have already linked physical activity in the form of aerobic exercise and cardiorespiratory fitness to the prevention of type 2 diabetes.
The goal of the study published by several researchers out of the Iowa State University was to determine any association between muscular strength, achieved through resistance exercise, and the incidence of type 2 diabetes, independent of the level of cardiorespiratory fitness achieved within each population subgroup. A total of 4,681 study participants between the ages of 20 and 100 were included in the prospective cohort spanning over the course of 25 years; this excluded patients with prior myocardial infarction, stroke, or cancer, as well as patients who had been diagnosed with clinical type 2 diabetes, per ADA standards, prior to enrollment.
Baseline characteristics of each patient were obtained once they were enrolled into the study in efforts to reduce confounding during statistical analysis; these characteristics included but were not limited to BMI, personal medical, social, and family histories, as well as level of cardiorespiratory fitness. The level of muscular strength was assessed using 1-repetition maximum weight for both upper and lower body resistance exercise machines. Upper body muscular strength was demonstrated through the supine bench press while lower body muscular strength was demonstrated through the seated leg press. Results of muscular strength were categorized into thirds: lower, middle, and upper, relative to the entire study population. In efforts to control the level of cardiorespiratory fitness demonstrated by study participants of varying muscular strengths, results were dichotomized into halves (low and high) which were then included into subgroup analysis.
The primary outcome of this study was overall incidence of type 2 diabetes at follow-up, with day one defined as the day of baseline examination. Secondary outcomes included achieved level of muscular strength and cardiorespiratory fitness. Multiple Cox proportional hazard regression models were used to report incidence of type 2 diabetes throughout multiple exposure categories.
Out of the 4,681 total study participants, 229 had developed type 2 diabetes during a mean follow up of 8.3 years. The lower muscular strength third of participants had the most new cases of type 2 diabetes (88) while the middle muscular strength third of participants had the fewest (63). The lower-third category was used as a reference range and reported an adjusted hazard ratio of 1. The upper muscular strength third of participants had developed 78 new cases of type 2 diabetes.
In a Cox proportional hazards regression model adjusted for level of cardiorespiratory fitness (model 3), participants with the middle level of muscular strength showed a significant 32% reduced risk of developing type 2 diabetes as compared to those participants with a lower level of muscular strength. Participants with the upper level of muscular strength did not show any significant reductions in risk of developing type 2 diabetes. Results were consistent throughout other models of Cox proportional hazard regression conducted that were adjusted for age (model 1) and all baseline characteristics (model 2).
In conclusion, does muscle strength reduce type 2 diabetes incidence? The study found moderate muscular strength is associated with a significant reduction of type 2 diabetes incidence, independent of the level of cardiorespiratory fitness. However, high levels of muscular strength did not show similar risk reductions indicating that extensive regimens of resistance exercise may not be necessary to achieve optimal health benefits.
- In this study, only a moderate level of muscular strength was associated with a reduction in risk of developing type 2 diabetes.
- A majority of participants in this study were middle-aged, white, well educated, and belonged to middle-upper socioeconomic income households
- Further studies should be completed to more accurately define moderate muscular strength and the relationship with level of resistance exercise in order to determine the level of patient generalizability.
Wang Y, Lee D, Brellenthin AG, et al. Association of muscular strength and incidence of type 2 diabetes. Mayo Clin Proc 2019; 94(4):643-51. DOI: 10.1016/j.mayocp.2018.08.037
Wolfe RR. The underappreciated role of muscle in health and disease. Am J Clin Nutr 2006; 84(3):475-482. DOI: 10.1093/ajcn/84.3.475
Adam Chalela, B.S. Doctor of Pharmacy Candidate USF College of Pharmacy
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