Prolonged, Exclusive Breast-Feeding Linked to Improved Cognitive Development
News Author: Laurie Barclay, MD
CME Author: Désirée Lie, MD, MSEd
Observational studies of breast-feeding have consistently demonstrated a positive effect of breast-feeding on infant cognitive development using IQ measures compared with formula-feeding and a dose-response association with larger differences for longer duration of breast-feeding. Randomization to breast-feeding vs formula-feeding is unfeasible, but randomization to a strategy to promote breast-feeding among mothers who have already decided to initiate breast-feeding can be performed.
PROBIT is the largest randomized trial of human lactation ever conducted and used a cluster randomization design to randomize hospitals and clinics in Belarus to an intervention to promote breast-feeding using the Baby-Friendly Hospital Initiative of WHO and UNICEF. In this study, the WASI IQ measures and teacher evaluations of academic performance in children at 6.5 years were linked to breast-feeding in infancy.
Included were participants in the PROBIT study consisting of 17,046 healthy term infants weighing at least 2500 g at birth, from 31 maternity hospitals and their associated polyclinics in 1 country.
Sites were randomized to either an intervention to promote breast-feeding or usual policy.
The 2 types of cluster groups were matched for maternal age, education, previous breast-feeding, and number of other children.
The experimental intervention led to a significant increase in duration of any breast-feeding up to 12 months and also of exclusive breast-feeding up to 6 months.
Follow-up interviews and examinations were conducted at 6.5 years by pediatricians, 1 to 2 for each site, using the WASI scale.
The WASI consisted of 4 subsets testing vocabulary, similarities, block design, and matrices and took 30 minutes to administer.
It was translated to Russian and back translated to ensure comparability of the Russian version.
Children who had begun school by the 6.5 year follow-up were evaluated by their teachers in 4 components: reading, writing, mathematics, and other subjects.
The child was rated using a 5-point scale as "far below," "somewhat below," "at somewhat above," or "far above" his or her grade level.
5 children were randomly selected for audit for each pediatrician to assess inter-rater reliability and consistency of WASI testing.
More than 80% of mothers were aged 20 to 34 years, half had completed secondary education, more than half had no other children at home, and fewer than 3% smoked during pregnancy.
Mean birth weight was 3440 g.
The 2 randomized groups were similar in demographics.
Follow-up at 6.5 years was 81.5% with similar rates in the 2 groups.
The cluster-adjusted mean difference in IQ was greatest for verbal IQ.
The verbal IQ was +7.5 points higher; the performance IQ, +2.9 points higher; and the full-scale IQ, +5.9 points higher in the breast-feeding intervention vs the no intervention group.
The results of the WASI demonstrated a high degree of clustering and large confidence intervals.
After adjusting for the cluster randomization, differences in mean scores for the WASI were +2.8 for verbal IQ, +2.9 for performance IQ, and +3.1 for full-scale IQ.
After carrying out sensitivity analyses to account for the large site variations, the differences were +4.7, +4.0, and +4.9, respectively.
There was a slightly greater mean difference in verbal IQ for boys (8 points higher for boys and 7 points higher for girls) in the breast-feeding vs the control group.
Higher WASI scores were seen with greater duration of breast-feeding and of exclusive breast-feeding.
Exclusive breast-feeding for 6 months or more was associated with an increase in verbal IQ score of +5.2 points vs exclusive breast-feeding for less than 3 months.
Similar dose-response associations were seen for teacher ratings for all 4 subject areas, but the increases were not significant for breast-feeding duration of 6 months or more.
The findings were robust in the direction of benefit for breast-feeding.
The authors concluded that breast-feeding improved children’s cognitive development.
Pearls for Practice
A breast-feeding intervention vs no intervention is associated with higher WASI IQ scores, which are greater for verbal IQ but also indicated for the performance and overall IQ scores, in children age 6.5 years old.
Improved IQ scores and teacher evaluations for 6.5-year-old children associated with increased breast-feeding are greater with longer duration of exclusive breast-feeding.