Postnatal Programming of Infant Temperament at 12-Months: A Test of Lactation Programming Theory

The current study examined how maternal cortisol and breastfeeding duration across the first six months postpartum might relate to infant temperament profile membership at 12 months in 322 low-income Mexican American mother-infant dyads (46.3% male). Results revealed that maternal postnatal cortisol levels were significantly moderated by breastfeeding duration to predict infant temperament profile (β = 0.14, p = .030) such that more maternal cortisol was linked to higher likelihood of belonging to a high positive affect, well-regulated profile when mothers breastfed for above average durations. This suggests that while maternal cortisol in breastmilk might initially shape infant negative temperament, there may be a threshold at which the influence of cortisol is overridden by the benefits of extended breastfeeding duration.