Adolescent leisure-time physical activity and eating disorders: a longitudinal population-based twin study.

Purpose: High levels of physical activity have been documented in eating disorder patients. Our aim was to examine whether adolescent leisure-time physical activity is prospectively associated with eating disorders in adolescence and young adulthood.

Methods: Finnish twins born in 1983-1987 reported their physical activity frequency at ages 12, 14, and 17. A subsample of participants underwent structured, retrospective interviews for eating disorders at the mean age of 22.4 years. Associations between female twins' physical activity and future eating disorders (571-683 twins/wave) were investigated with the Cox proportional hazards model. To illustrate the physical activity similarity of the co-twins in a twin pair, we used cross-tabulation of eating disorder-discordant twin pairs (13-24 pairs/wave).

Results: After adjusting for several covariates, we found no statistically significant longitudinal association between physical activity and eating disorders. This applied when all eating disorders were combined but also when assessed separately as restrictive and non-restrictive eating disorders. Co-twins' physical activity in adolescence tended to be similar irrespective of their future eating disorder, supporting the results of the regression analysis.

Conclusion: We observed no evidence of adolescent physical activity frequency being prospectively associated with eating disorders in female twins. Further longitudinal studies with larger sample sizes and more detailed physical activity data are needed.

Level of evidence: III, evidence obtained from cohort or case-control analytic studies.