Predictors and Tracking of Body Mass Index from Adolescence into Adulthood: Follow-up of 18 to 20 Years in the Oslo Youth Study

Objectives: To examine tracking of body mass index (BMI) (weight in kilograms divided by the square of height in meters) from age 15 to 33 years, to examine the effect of adolescent and adult health-related behavior and parents' BMI and education on adult BMI; and to examine changes in lifestyle factors as predictors of adult overweight and obesity.

Methods: A longitudinal study with 18 to 20 years of follow-up in a cohort from Oslo, Norway (N = 485); mean age was 15 years at baseline. Weight, height, physical fitness, leisure time physical activity (LTPA), smoking, and education were assessed at baseline and follow-up. Parents' height, weight, and education were assessed at baseline.

Results: Tracking of BMI from age 15 to 33 years was high (r = 0.54). Adolescent BMI, father's BMI, the subject's own LTPA, adult smoking, and sex explained 44.1% of the variation in adult BMI. The odds ratio (95% confidence interval) of having a BMI of 25 or more as an adult was 0.07 (0.03-0.14) for lowest vs highest quartile of adolescent BMI. The corresponding odds ratio of having a BMI of 30 or more was 0.02 (0.002-0.14). Those who increased their LTPA level between adolescence and adulthood had a lower risk of adult overweight than those with a stable low LTPA level.

Conclusions: Tracking of BMI from adolescence into adulthood was substantial. Changes in LTPA between adolescence and adulthood predicted the risk of adult overweight, suggesting that the foundation for adult body weight is laid during adolescence. Implications of this would be to emphasize physical activity among youths.