Breastfeeding and the Timing of Puberty Onset
by Anne Eglash MD, IBCLC, FABM
The average age of menses onset (menarche) has decreased from age 16 in the 1800s to 13 in the 1960s. According to the authors of this week’s CQW article, children who undergo puberty earlier than their peers are at higher risk for a number of psychosocial and behavioral problems such as depression, eating disorders, substance use, teen pregnancy, and sexual abuse.
Childhood obesity has been associated with earlier puberty, and we know that longer breastfeeding helps to prevent childhood obesity. The authors of this week’s CQW article were interested in whether a history of shorter breastfeeding is associated with earlier puberty.
This study was undertaken within Kaiser Permanente Northern California. They identified 3331 mother-female infant pairs whose medical records could be tracked over time. They were able to harvest infant feeding data, categorized as ‘not breastfed’, ‘breastfed for less than 6 months’ or ‘breastfed for 6 or more months’. The children’s medical records were evaluated for age of onset of early pubertal changes, which was typically documented in the every 1-2 year well-child exams. They also recorded the prepubertal BMI.
They controlled for maternal education and maternal race/ethnicity. They could not track socioeconomic level due to not having this information in the medical record. The population studied were 24% Asian/Pacific Islander, 26% Hispanic, and 8% African American.
- Children not breastfed underwent puberty 2.5 months earlier than those who breastfed longer than 6 months.
- Children who breastfed less than 6 months underwent puberty 1.5 months earlier than those who breastfed longer than 6 months.
- Even when prepuberty BMI was controlled for (taken into account), no breastfeeding was still associated with earlier puberty.
- The trend between less breastfeeding and earlier puberty was similar between all race/ethnicity groups (Asian/Pacific Islander, Hispanic, non-Hispanic whites, and African-American).
- The authors found that higher pre-pubertal obesity partially explained the association between lack of breastfeeding and earlier puberty.
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Early puberty is associated with higher risk of adverse health and behavioral outcomes throughout adolescence and adulthood. US girls are experiencing earlier puberty with substantial racial/ethnic differences. We examined the association between breastfeeding and pubertal timing to identify modifiable risk factors of early puberty and potential sources of racial/ethnic differences in the timing of pubertal development.
A prospective cohort study of 3331 racially/ethnically diverse girls born at Kaiser Permanente Northern California (KPNC) between 2004 and 06. All data were obtained from KPNC electronic clinical and administrative datasets. Mother-reported duration of breastfeeding was obtained from questionnaires administered at each ‘wellbaby’ check-up exam throughout the baby’s first year and categorized as ‘Not breastfed’, ‘Breastfed < 6 months’, and ‘Breastfed ≥ 6 months’. Pubertal development data used Tanner stages assessed by pediatricians during routine pediatric checkups starting at age 6. Pubertal onset was defined as transition from Tanner Stage 1 to Tanner Stage 2+ for breast (thelarche) and pubic hair (pubarche). Weibull regression models accommodating for left, right, and interval censoring were used in all analyses. Models were adjusted for maternal age, education, race/ethnicity, parity and prepubertal body mass index (BMI). We also examined race/ethnicity as a potential effect modifier of these associations.
Not breastfeeding was associated with earlier onset of breast and pubic hair development compared to breastfeeding ≥6 months (adjusted hazard ratio [HR]: 1.25; 95% confidence interval [CI]: 1.07–1.46; HR: 1.24; 95% CI: 1.05–1.46, respectively). Breastfeeding for < 6 months was also associated with the risk of earlier pubic hair development (HR: 1.14; 95% CI: 1.00–1.30, compared to breastfeeding ≥6 months). Inclusion of girls’ prepubertal BMI slightly attenuated the association between breastfeeding and timing of breast onset but remained significant. The association between not breastfeeding and early breast development may be stronger among African American girls (HR: 1.92; 95% CI: 1.01–3.66, no breastfeeding vs. ≥6 months) than other racial/ethnic groups.
Breastfeeding is an independent predictor of pubertal onset in girls, and the strength of the association may vary by race/ethnicity. Providing breastfeeding support and lactation education for high risk mothers may help prevent earlier pubertal onset and promote positive health outcomes later in life.
The authors of this study found that prepubertal obesity partially explained the earlier puberty in female children who were not breastfed, but breastfeeding over 6 months was itself protective of early puberty. Male children were not studied. We don’t have a good explanation for this. According to the authors, psychosocial stress early in life due to insecure parental attachment may play a role in early pubertal onset. Breastfeeding is known to strengthen the parent-child bond.
The authors were not able to measure the association between socioeconomic status, breastfeeding duration, and timing of pubertal onset. I wonder if infants who are breastfed over 6 months have less contact with environmental endocrine disruptors. There is evidence that endocrine disruptors such as Bisphenol A in plastics, various pesticides in foods, and flame retardants in furniture and carpet are associated with earlier pubertal onset. Mothers who breastfeed longer tend to be older, have a higher education and higher income, so may have more resources to avoid these environmental contaminants.