Objective: Body mass index (BMI) has shown moderate to strong stability through childhood into adulthood, while physical activity (PA) tracks less well. Tracking studies have often had limited follow-up lengths. The aim was to investigate BMI and PA tracking over 22 years from youth to adulthood.
Methods: Subjects included 374 participants aged 7 to 18 years in the 1981 Canada Fitness Survey, who were re-evaluated in 2002-04. The stability of BMI and leisure-time PA energy expenditure (AEE) was assessed by inter-age correlations, maintenance of extreme quintiles and BMI status, and the prediction of adult overweight from youth BMI.
Results: BMI tracking was moderate to strong (r=0.42-0.65) in females, and moderate (r=0.29-0.53) in males. Approximately 38% and 42% of youth in the highest and lowest BMI quintiles, respectively, remained in these quintiles as adults. About 83% of overweight youth remained overweight as adults, while 85% of overweight adults were not overweight youth. Almost all healthy weight adults had been healthy weight youth. The odds of being overweight in adulthood was 6.2 times greater (95% CI: 2.2-17.2) in overweight compared with healthy weight youth. PA tracking over 22 years was low and non-significant, but moderate over the final 15 years. Only 16% and 18% of youth in the highest and lowest PA quintiles, respectively, remained in these quintiles as adults.
Conclusions: BMI, but not PA, tracked well over 22 years in this sample. The majority of overweight youth remained overweight as adults; however, the majority of overweight adults were not overweight youth.