Birthweight, lifetime obesity and physical functioning in mid-adulthood: a nationwide birth cohort study

Background: Evidence is scant on long-term implications of childhood obesity and body mass index (BMI) gains over the life-course for poor physical functioning (PF). The objective was to establish whether (i) birthweight and BMI across the life-course, (ii) BMI gains at specific life-stages and (iii) age of obesity onset were associated with PF at 50y. Methods: In the 1958 British birth cohort (n=8674), BMI (kg/m(2)) was calculated using height and weight [measured (7, 11, 16, 33 and 45y); self-reported (23 and 50y)]. PF was assessed at 50y using the validated PF subscale of the Short-form 36 survey; the bottom (gender-specific) 10% was classified as poor PF. Missing data were imputed via multiple imputation. Associations were examined using logistic regression, adjusting for health and social factors. Results: Birthweight was not associated with PF. At each adult age, odds of poor PF were highest for obese (vs normal), e.g. for 23y obesity the odds ratio (OR)(adjusted) for poor PF was 2.28 (1.34, 3.91) and 2.67 (1.72, 4.14) in males and females respectively. BMI gains were associated with poor PF, e.g. for females, ORadjusted per standard deviation (SD) in BMI gain 16-23y was 1.28 (1.13, 1.46); for BMI gains 45-50y it was 1.36 (1.11, 1.65). Longer duration of obesity was associated with poor PF, e.g. in males, ORadjusted was 2.32 (1.26, 4.29) for childhood obesity onset and 1.50 (1.16, 1.96) for mid-adulthood onset (vs never obese, P-trend<0.001). Conclusion: Obesity, BMI gains, and earlier obesity onset were associated with poor PF in mid-adulthood, reinforcing the importance of preventing and delaying obesity onset.