Low physical activity is a predictor of thinness and low self-rated health: gender differences in a Swedish cohort.

Purpose: To examine the relationship between leisure time physical activity in 15-year-old students, and weight status and self-rated health 3 years later.

Methods: Data were used from two follow-up waves, one in 2002 (grade 9, age 15 years) and one in 2005 (grade 12, age 18 years) of a cohort of approximately 2,500 adolescents. Adolescents reported height and weight, health behaviors, and self-rated health by a questionnaire at both occasions. Age and gender-specific body mass index cut-off points for thinness, overweight, and obesity were used to assess weight status. Logistic regression analyses were performed with weight status and self-rated health as the outcomes and level of leisure time physical activity as the independent variable. Adjustments were made for parental years of education, student's current smoking habits, and baseline body mass index.

Results: As compared with students who were active for more than 4 hours per week during leisure time, being active 2-4 hours (odds ratio [OR]: 4.15, confidence interval [CI]: 1.62-10.60) and <2 hours (OR: 3.92, CI: 1.30-11.78) predicted thinness in boys. In girls, the risk was smaller and became significant at <2 hours per week (OR: 2.57, CI: 1.38-4.77). Overweight or obesity was not significantly predicted by physical activity. A significant risk of low self-rated health was found at follow-up in boys active for <4 hours per week compared with those active for >4 hours per week.

Conclusion: Physical activity is important to maintain a healthy body weight and for future self-rated health in boys.