To see if breastfeeding and its length are linked to a lower risk of low IQ or other neurodevelopmental disorders was the goal of the study.
Researchers performed a secondary analysis of two parallel multicenter, double-blind randomized controlled trials in which people with a singleton pregnancy with either subclinical hypothyroidism or hypothyroxinemia were given thyroxine or a placebo. The main result was a low IQ score (less than 85 on the WPPSI-III [Wechsler Preschool and Primary Scale of Intelligence III] at age 5 years). Performance measures on additional validated neurodevelopmental assessments were used as secondary outcomes. The connection between breastfeeding and neurodevelopmental outcomes was studied using both univariable and multivariable models. The final modified models were created using stepwise backward progressing linear and logistic regression models.
Breastfeeding was reported by 614 (80%) of the 772 participants studied. 31% had been breastfeeding for less than four months, 19% for four to six months, 11% for seven to nine months, 15% for ten to twelve months, and 23 percent for more than twelve months. IQ scores were available for 756 children; mean age-5 scores were higher with any nursing (96.7±15.1) than without (91.2±15.0, 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). Breastfeeding remained related to a lower risk of low IQ score (adjusted odds ratio [aOR] 0.62, 95% CI 0.41–0.93) in adjusted analyses, and each additional month of breastfeeding was associated with a decreased risk of low IQ score (aOR 0.97, 95% CI 0.939–0.996). In adjusted analyses, no significant relationships between breastfeeding and other neurodevelopmental outcomes were found.
Breastfeeding and its duration are connected with a decreased risk of having a low IQ at the age of five.
