Tracking of body mass index during childhood: a 15-year prospective population-based family study in eastern Finland

OBJECTIVES: To investigate the tracking of body mass index (BMI) during childhood. The effect of birth weight and family history of obesity on BMI development during childhood was also evaluated. METHODS: All children born during 1981-1982 in a rural community of eastern Finland were followed at ages 6 months, 7 and 15 y (-6m, -7y, -15y). Out of 205 children, 138 completed the full follow-up period, of which 100 (45 girls) were included in the analysis with complete data. RESULTS: BMI-6 m was significantly associated with BMI-7y (r=0.320; P-value=0.001), but no longer with BMI-15y. BMI-7y was significantly associated with BMI-15y (r=0.686; P-value <0.001). Children in the highest tertile of BMI-6 m did not have a higher risk of being in the highest tertile of either BMI-7y or BMI-15y compared with children in other tertiles of BMI-6 m. Children in the highest tertile of BMI-7y had a significantly higher risk of being in the highest tertile of BMI-15y (relative risk=3.6 (2.0-6.3)) compared with children in other tertiles of BMI-7y. BMI-7y was predicted negatively by parents' education and male gender and positively by BMI-6 m. BMI-15y was predicted positively by BMI-7y, the difference in BMI between ages 7y and 6 months and the mean of BMI between ages 6 months and 7y. Birth weight was not a good predictor of BMI during childhood. Children with at least one obese parent seemed to have higher BMI during childhood; however, this association did not reach a significant level. CONCLUSION: The study confirmed the tracking of BMI during childhood. Neither birth weight nor family history of obesity was found a good predictor of BMI during childhood. The risk of obesity in adolescence can be determined during middle childhood and obese children may be targeted in lifestyle advice to reverse this trend. Parental education may have a key role in the prevention of obesity during childhood.