Physical activity and obesity-related metabolic impairments: estimating interation from an additive model

PhD ceremony: Ms. L. Qin, 13.15 uur, Academiegebouw, Broerstraat 5, Groningen

Title: Physical activity and obesity-related metabolic impairments: estimating interation from an additive model

Promotor(s): prof. R.P. Stolk

Faculty: Medical Sciences

Increased physical activity is associated with a reduced risk of type 2 diabetes. However, physical activity is also the key to treat adiposity, and it therefore may modify the association between adiposity and diabetes. It is unclear whether “fatfit” or “lean-unfit” individuals have an increased diabetes risk, and whether obese individuals could benefit from increased physical activity independent of the changes in body composition.

The main objective of this thesis was to investigate whether physical activity interacts with adiposity in relation to diabetes. We reviewed the epidemiological evidence of the joint effect of obesity and physical inactivity, to discern the additive and multiplicative interactions. The results indicate that increased body weight is a stronger diabetes risk factor than physical inactivity, and that these show additive interaction.

Second, the joint effect of these two factors with fasting glucose was examined in the Guangzhou Biobank Cohort Study (n=28,946). The risk reduction of diabetes due to this combined effect was further quantified in the Finnish Diabetes Prevention Study (n=487), a lifestyle intervention trial. Both studies confirmed the interactive effects. Moreover, we extensively investigated the influence of biological background (like ethnicity, aging), hyperglycemia, the intensity of physical activity, and the different adiposity indices.

Finally, we also investigated several methodological issues involved in etiologic epidemiological research (like interaction models, confounding, mediating, and measurement errors), and the links between pathophysiology, epidemiology and clinical implications.