Breast feeding and timing of puberty in boys and girls: A nationwide cohort study

Background: Breast feeding has been associated with improved infant health, but its impact on pubertal timing remains uncertain, particularly in boys. Objective: The objective of this study was to investigate the association between duration of breast feeding and pubertal timing in boys and girls. Methods: This population-based cohort study included 13 511 boys and girls from the Puberty Cohort nested within the Danish National Birth Cohort. The children gave half-yearly, self-reported information on pubertal development through questionnaires (Tanner stages, age at menarche, first ejaculation, voice break, axillary hair growth, and acne). Information on breast feeding was provided by the mothers when the children were 6 months of age. We estimated mean differences (in months) in age at attaining each pubertal marker and for overall timing of puberty (combined estimate) for every additional month of exclusive breast feeding. Furthermore, we estimated differences in pubertal age when comparing children never exclusively breastfed and exclusively breastfed