Physical activity and health: Findings from Finnish monozygotic twin pairs discordant for physical activity

Abstract

AbstractGenetic and early environmental differences including early health habits associate with future health. To provide insight on the causal nature of these associations, monozygotic (MZ) twin pairs discordant for health habits provide an interesting natural experiment. Twin pairs discordant for leisure-time physical activity (LTPA) in early adult life are thus a powerful study design to investigate the associations between long-term LTPA and indicators of health and wellbeing. We have used this study design by identifying 17 LTPA discordant twin pairs from two Finnish twin cohorts and summarize key findings of these studies in this paper. The carefully characterized rare long-term LTPA discordant MZ twin pairs have participated in multi-dimensional clinical examinations. The occurrence of type 2 diabetes and death has been evaluated on the basis of prospective questionnaire data and register follow-up among a larger number of twin pairs. Key findings highlight that, compared to less active twins in such MZ twin pairs, the twins with higher long-term LTPA have higher physical fitness, reduced body fat, reduced visceral fat, reduced liver fat, increased lumen diameters of conduit arteries to the lower limbs, increased bone mineral density in loaded bone areas, increased high-density lipoprotein cholesterol levels and reduced occurrence of type 2 diabetes. However, we have not been able to document differences in the life expectancy between the less and more active twin siblings of the LTPA discordant MZ twin pairs. The findings are in agreement with intervention studies but not with all observational studies in which genetic factors are not controlled for.