Does Breastfeeding Protect Against Autism? a Birth Cohort Study

Background:  It is suggested that breastfeeding may protect against autism spectrum disorder. However, to date only a handful of epidemiological studies have examined this relationship and have reported inconsistent findings. All previous studies were based on retrospective maternal recall about breastfeeding, sometimes more than ten years after birth, which left them vulnerable to recall bias. In addition most studies did not make attempts to account for potential confounders. 

Objectives:  To study the associations between prospectively collected information on the intention, initiation and duration of breastfeeding and 1) a diagnosis of autism and 2) symptoms of autism in a large birth cohort study.

Methods:  We used data from the Avon Longitudinal Study of Parents and Children (ALSPAC), a birth cohort study in England which recruited 14,541 pregnant women in the Bristol area who had an expected delivery date between April 1991 and December 1992, resulting in 14062 live births. We used prospectively collected data on the intention to breastfeed (collected at 32 weeks of pregnancy), and the initial and duration of breastfeeding (collected post partum at 6 and 15 months). Using these we classified these variables into no intention, less than one month, more than one month and uncertain from the beginning. Another binary variable was created for ever having breastfed versus never. Finally we used the age in months at which any breastfeeding was stopped, whether partial or exclusive, as a continuous measure of duration to test whether any associations might be cumulative.  Cohort children with an ASD diagnosis were identified by record linkage with health and education records, or maternal report of having being told the child had autism (n=134). Symptoms suggestive of autism were ascertained by 4 scales that combine optimally within ALSPAC to predict ASD: the Children's Communication Checklist (coherence subscale), the Social and Communication Disorders Checklist, a repetitive behaviour measure, and the Emotionality, Activity and Sociability scale (sociability subscale).  These measures were dichotomised, with approximately 10% defined on each scale as having highest autistic traits. 

Results:  There was no evidence for an association of ever being breastfed in relation to a diagnosis of autism (adjusted OR 1.12 [95% CI 0.64 to 1.95]) but some evidence of a protective effect on impairment in autism related measures of coherence (adjusted OR 0.73 [95% CI 0.51-0.91]) and sociability (adjusted OR 0.83 [95% CI 0.70-1.00]). Similar results were found in analyses on intention to breastfeed and the total duration of breastfeeding. 

Conclusions:  In this population-based prospective cohort study, we did not find evidence to support the hypothesis that breastfeeding protects against autism spectrum disorders. We did observe some associations between breastfeeding and lower scores on some autistic traits. Whether this is the result of residual confounding or a truly protective effect, and if so, the pathway of this relationship deserves further investigation.