Puberty timing and adiposity change across childhood and adolescence: disentangling cause and consequence

Objective: To better understand if earlier puberty is more likely a result of adiposity gain in childhood than a cause of adiposity gain in adulthood. Design: Prospective birth cohort study. Setting: Population based study of children born in 1991/1992 in Bristol UK (Avon Longitudinal Study of Parents and Children (ALSPAC)). Participants: 4,186 participants (2,176 female and 1,990 male) of predominantly White ethnicity with 18,232 repeated measures throughout follow-up. Exposures & outcomes: Repeated measures of height from 5y to 20y to identify puberty timing (age at peak height velocity) and repeated measures of dual-energy X-ray absorptiometry-derived fat mass from age 9y to 18y, modelled separately in females and males using models based on chronological age and time before and after puberty onset. Results: Mean age at peak height velocity was 11.7y (standard deviation (SD)=0.8y) for females and 13.6y (SD=0.9y) for males. In adjusted models of fat mass by chronological age, a one-year later age at peak height velocity was associated with 20.4% (95% Confidence Interval (CI): 18.5% to 22.3%) and 22.8% (95% (CI): 20.7% to 24.8%) lower fat mass in females and males respectively at 9y. These differences were smaller at age 18y: 7.8% (95% (CI):5.9% to 9.6%) and 11.9% (95% (CI): 9.1%, to 14.7%) lower fat mass in females and males respectively per year later age at peak height velocity. Trajectories of fat mass by time before and after puberty onset provided strong evidence for an association of pre-pubertal fat mass with puberty timing, and little evidence of an association of puberty timing with post-pubertal changes in fat mass in females. In males, findings were less clear before puberty though there was some evidence for an association of earlier puberty timing with great post-pubertal gain in fat mass. Conclusions: Earlier puberty is more likely a result of adiposity gain in childhood than a cause of adiposity gain in adulthood in females. In males early to puberty, differences in fat mass after puberty are driven partially by tracking of adiposity from early childhood but also greater gains in post-pubertal adiposity. Reducing levels of childhood adiposity may help prevent both earlier puberty, later life adiposity and their associated adverse social, mental and physical health sequelae.