Breast-feeding and Infant Hospitalization for Infections: Large Cohort and Sibling Analysis

Abstract

Objectives: Breast-feeding may protect against infections, but its optimal duration remains controversial. We aimed to study the association of the duration of full and any breast-feeding 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 to 2009. We analyzed data from the full cohort (n = 70,511) and sibling sets (n = 21,220) with parental report of breast-feeding and infections. The main outcome measures were the relative risks (RRs) for hospitalization for infections from 0 to 18 months by age at introduction of complementary foods and duration of any breast-feeding.

Results: Although we found some evidence for an overall association between longer duration of full breast-feeding and lower risk of hospitalizations for infections, 7.3% of breast-fed children who received complementary foods at 4 to 6 months of age compared to 7.7% of those receiving complementary foods after 6 months were hospitalized (adjusted RR 0.95, 95% confidence interval 0.88-1.03). Higher risk of hospitalization was observed in those breast-fed 6 months or less (10.0%) compared to ≥12 months (7.6%, adjusted RR 1.22, 95% confidence interval 1.14-1.31), but with similar risks for 6 to 11 months versus ≥12 months. Matched sibling analyses, minimizing the confounding from shared maternal factors, showed nonsignificant associations and were generally weaker compared with the cohort analyses.

Conclusions: Our results support the recommendation to fully breast-feed for 4 months and to continue breast-feeding beyond 6 months, and suggest that protection against infections is limited to the first 12 months.

Figure 1. Subjects included in the analyses. Siblings were part of the full cohort and also included in sibling analyses

Abbreviation: MBR, Medical Birth Registry. ^a 225 of the 13 384 were lost due to deaths in the observation period. ^b 21 of the 14 983 were lost due to deaths in the observation period.

Figure 2. Relative risk of hospital admission for infections the first 18 months of life by age at introduction of complementary foods, solid foods and formula in infants breastfed > 6 months age (n=57 007).)

Relative risks were adjusted for maternal age and parity (three categories), caesarean section, maternal smoking, education, birthweight (< 2500 g, 2500–3499, 3500–4499, >4500 g), gestational age ( 37 weeks), gender, day-care outside home and duration of any breastfeeding. Adj.RR=adjusted relative risk, CI=Confidence interval

Figure 3. Relative risk of a) hospital admission for infection and b) any infection from 0–18 months by duration of any breastfeeding (n=70 511)

Relative risks were adjusted for maternal age and parity (three categories), caesarean section, maternal smoking, education, birthweight (< 2500 g, 2500–3499g, 3500–4500g, >4500 g), gestational age ( 37 weeks), gender and day-care outside home. Adj.RR=adjusted relative risk, CI=Confidence interval, LRTI=Lower respiratory tract infection.