Breastfeeding and Child IQ at Age 5
by Anne Eglash MD, IBCLC, FABM
Nature vs nurture. Despite a wealth of research associating breastfeeding and a more favorable IQ over the last few decades, many people still question whether the association is due to parents’ higher education and/or higher socioeconomic status (associated with better quality schooling/access to enriching experiences), since people of these demographics are more likely to breast/chestfeed.
The good news is that many studies done among different countries that have controlled for multiple demographic factors, such as parental age, education, socioeconomic status, etc. have demonstrated a persistent association between child IQ and breastfeeding.
The more data the better, right? The article for this week is secondary analysis of data that was collected for a randomized controlled trial ‘Treatment of Subclinical Hypothyroidism or Hypothyroxinemia in Pregnancy’. The original trial included 772 pregnant patients under 20 weeks gestation from 33 hospitals in the USA who had subclinical hypothyroidism, and randomized them to received levothyroxine or placebo. They found no association between treatment with levothyroxine and child IQ thru 5 years of age.
The researchers decided to re-look at this data to find any association between breastfeeding and low IQ (under 85 on the Weschler Preschool and Primary Scale of Intelligence III). They also evaluated other cognitive and behavioral scores in these children between ages 3-5 years, including scores for attention deficit and hyperactivity disorder (ADHD). Categories of breastfeeding included less than 4 months (31%), 4-6 months (19%), 7-9 months (11%), 10-12 months (15%), and more than 12 months (23%). After adjusting for multiple confounding variables, the researchers found that breastfeeding is associated with a lower risk of low IQ.
- The mean IQ among breastfed infants was higher than the mean IQ among those not breastfed.
- The longer a child was breastfed, the higher the IQ.
- The longer a child was breastfed, the lower the risk of a low IQ.
- The longer a child was breastfed, the lower the risk of attention deficit and hyperactivity disorder (ADHD).
See the Answer
To evaluate whether breastfeeding and its duration are associated with a reduced risk of low IQ scores or other neurodevelopmental problems.
We conducted a secondary analysis of two parallel multicenter, double-blinded randomized controlled trials in which participants with a singleton pregnancy and either subclinical hypothyroidism or hypothyroxinemia were treated with thyroxine or placebo. Our primary outcome was a low IQ score (less than 85 on the WPPSI-III [Wechsler Preschool and Primary Scale of Intelligence III] at age 5 years). Secondary outcomes included performance measures on other validated neurodevelopmental tests. Univariable and multivariable analyses were performed to evaluate the association between breastfeeding and neurodevelopmental outcomes. Stepwise backward proceeding linear and logistic regression models were used to develop the final adjusted models.
Of the 772 participants studied, 614 (80%) reported breastfeeding. Of these, 31% reported breastfeeding for less than 4 months, 19% for 4–6 months, 11% for 7–9 months, 15% for 10–12 months and 23% for more than 12 months. IQ scores were available for 756 children; mean age-5 scores were higher with any breastfeeding (96.7615.1) than without (91.2615.0, mean difference 5.5, 95% CI 2.8–8.2), and low IQ scores were less frequent with any breastfeeding (21.5%) than with no breastfeeding (36.2%, odds ratio 0.48, 95% CI 0.33–0.71). In adjusted analyses, breastfeeding remained associated with reduced odds of low IQ score (adjusted odds ratio [aOR] 0.62, 95% CI 0.41–0.93), and each additional month of breastfeeding was associated with lower odds of a low IQ scores (aOR 0.97, 95% CI 0.939–0.996). No significant associations between breastfeeding and other neurodevelopmental outcomes were identified in adjusted analyses.
Breastfeeding and its duration are associated with lower odds of low IQ score at age 5 years.
The researchers found that the longer a child was breastfed, the lower the odds of an IQ at 85 or lower. However, they did not see a dose response relationship between duration of breastfeeding and higher IQ, and the mean IQ was not higher in breastfed vs non breastfed children. They also found no association between breastfeeding and lower risk of ADHD.
In having conversations with families about the importance of breastfeeding for brain development, it is safe to advise that breast/chestfeeding protects the infant from a low IQ. This may be mediated by the abundance of appropriate long-chain polyunsaturated fatty acids in human milk that are essential for the development of myelin.