Breastfeeding, childhood milk consumption, and onset of puberty.

OBJECTIVE Early nutrition has been postulated as programming pubertal timing. Limited observational studies, mainly from Western settings, suggest puberty occurs later with breastfeeding and earlier with higher cow's milk (including infant formula) consumption. However, these observations may be socioeconomically confounded. This study examined whether breastfeeding or childhood milk consumption was associated with pubertal onset in a setting with different associations of breastfeeding and puberty with socioeconomic position. METHODS The adjusted associations of breastfeeding or milk consumption at 6 months, 3 years, and 5 years with clinically assessed age at pubertal onset (Tanner stage II) were assessed by using interval-censored regression in a population-representative Hong Kong Chinese birth cohort, "Children of 1997," with 90% follow-up (N = 7523). RESULTS Compared with never breastfeeding, exclusive breastfeeding for 3+ months was unrelated to age at pubertal onset (time ratio [TR] 1.001, 95% confidence interval [CI] 0.987-1.015), as was partial breastfeeding for any length of time or exclusive breastfeeding for <3 months (TR 1.003, 95% CI 0.996-1.010), adjusted for gender, socioeconomic position, birth weight-for-gestational age, birth order, second-hand smoke exposure, and mother's age and place of birth. Daily milk consumption at 6 months (TR 1.004, 95% CI 0.991-1.018), 3 years (TR 0.995, 95% CI 0.982-1.008), or 5 years (TR 0.998, 95% CI 0.988-1.009) was also unrelated to age at pubertal onset compared with milk consumption for ≤ 1 time per week at the corresponding ages. CONCLUSIONS In a non-Western setting, neither breastfeeding nor childhood milk consumption was associated with age at pubertal onset, suggesting that associations may vary by setting.