Background
Breastfeeding may protect against infections, but its optimal duration remains controversial. We aimed to study the association of the duration of full and any breastfeeding with infections the first 18 months of life.
Methods
The Norwegian Mother and Child study (MoBa) is a prospective birth cohort which recruited expecting mothers giving birth from 2000–2009. We analyzed data from the full cohort (n=70 511) and sibling sets (n=21 220) with parental report of breastfeeding and infections. The main outcome measures were the relative risks for hospitalisation for infections from 0–18 months by age at introduction of complementary foods and duration of any breastfeeding.
Results
While we found some evidence for an overall association between longer duration of full breastfeeding and lower risk of hospitalisations for infections, 7.3% of breastfed children who received complementary foods at 4–6 months of age compared to 7.7% of those receiving complementary foods after 6 months were hospitalised (adjusted relative risk [RR] 0.95, 95% CI 0.88–1.03). Higher risk of hospitalisation was observed in those breastfed six months or less (10.0%) compared to ≥12 months (7.6%, adjusted RR 1.22, 95% CI 1.14–1.31), but with similar risks for 6–11 months versus ≥12 months. Matched sibling analyses, minimising the confounding from shared maternal factors, showed non-significant associations and were generally weaker compared with the cohort analyses.
Conclusions
Our results support the recommendation to fully breastfeed for 4 months and to continue breastfeeding beyond 6 months, and suggest that protection against infections is limited to the first 12 months.