Epidemiological studies of physical activity and diabetes risk, and implications for diabetes prevention

The evidence linking physical inactivity to the future risk of type 2 diabetes is strong, and modification of behaviour is a critical and effective element of strategies aimed at the prevention of this increasingly prevalent disorder. Two key unresolved epidemiologic issues relate to the type of activity that is likely to be maximally effective in preventing diabetes and the amount of activity that is required. Resolution of both these issues is likely to require a change in the way activity is measured, with a move away from self-report instruments, toward objective assessment of activity and the pattern and overall level of energy expenditure. It is also unclear whether the impact of physical activity on metabolic risk is homogenous across the population. Subgroups that might respond differently could be defined on the basis of characteristics such as age, degree of obesity, family history, ethnicity, and genetic risk, but the literature on effect modification is limited by study design issues. The identification of such subgroups could aid in the targeting of preventive interventions. An appropriate balance between individually tailored approaches aimed at those at high risk and interventions aimed at trying to shift physical activity levels in entire populations remains to be determined.