A new study shows relative benefits are greatest for those starting from low levels of exercise, but even active people will see benefits by further increasing their activity levels.
Exercise has long been recognized as one factor that can help reduce the risk of developing type 2 diabetes. However, the extent to which different levels of exercise may reduce that risk – known as the dose-response relationship – is less well understood.
A study recently published in Diabetologia has reviewed the existing literature documenting prospective cohort studies in which the association between physical activity and type 2 diabetes was examined. In all, 28 studies found on PubMed and EMBASE were included in the review. Eligible studies had to have been conducted on adults, and involve participants who were not diagnosed with type 2 diabetes at baseline. They also had to provide data about activity levels of participants at baseline, and risk ratios for development of diabetes at the conclusion of the study.
Taken together, the 28 studies covered 1,261,991 individuals, and 84,134 cases of type 2 diabetes. Most studies (24 of them) provided data about the association between type 2 diabetes and physical activity undertaken in leisure time; however, four of the studies looked at total overall physical activity.
Results of the literature review confirm that exercise clearly has a positive impact in reducing the risk of type 2 diabetes. More interestingly, however, analysis of the combined data from the 28 studies indicates that the relationship between levels of activity and reduction in the risk of developing type 2 diabetes is not linear, but curvilinear. Essentially, the analysis showed that while the largest reduction in risk levels occurs among individuals adopting a regime of moderate exercise (compared with sedentary individuals), additional reductions in risk continue to occur as activity levels increase, even among people who are already highly active.
To conduct their analysis, researchers converted the data about physical activity levels drawn from the 28 studies into units called metabolic equivalent of task (MET) hours/week. They then applied a cubic spline model of analysis to the data to evaluate the relationship between physical activity levels and risk of developing type 2 diabetes.
The results of this analysis showed a risk reduction of 26% for type 2 diabetes among those who engaged in 11.25 MET-hours/week (which is roughly equivalent to 150 min/week of moderate activity) relative to inactive individuals. Individuals who engaged in double that amount of activity were found to have a 36% reduced their risk. The reduction of risk continued even at higher levels of activity; individuals who engaged in 60 MET hours/week showed a risk reduction of 53%.
Based on these results, researchers conclude that there is no clear point at which additional exercise ceases to be associated with a reduction in the risk of developing type 2 diabetes. Rather, they suggest that the data supports a philosophy of “some is good but more is better” when it comes to recommendations about the benefits that may be derived from physical activity. They suggest that this information could be an important tool informing public health initiatives aimed at combating the prevalence of obesity and diabetes among the general population.
Written By: Linda Jensen