Introduction With economic development, puberty occurs at younger ages, and may contribute to cardiovascular diseases and hormone-related cancers. Factors determining pubertal timing are poorly understood. The growth axis active during puberty is also active in the first 6 months of life and interacts with the immune system.

Methods The authors examined whether prior infections, proxied by number of hospital episodes for infections at different ages, were associated with age at pubertal onset (Tanner stage II) using interval-censored regression in a population-representative Chinese birth cohort “Children of 1997” (n=7527). Mediation by growth was also examined.

Results Girls, but not boys, hospitalised for infections at least twice in the first 6 months of life had pubertal onset at about 8 months older (mean 10.3 years), time ratio 1.08 (95% CI: 1.04 to 1.12), than those without such hospitalisations (9.6 years) adjusted for infant characteristics and socio-economic position (sex interaction p value 0.02). There were no such associations for infections at 6 months to <8 years. Growth did not mediate the association.

Conclusion Early infectious morbidity in girls may be associated with later puberty, perhaps via suppression of the gonadotropic axis. Fewer infections in early life with economic development may be an additional factor contributing to earlier puberty.