Autism spectrum disorder (ASD) is a complex developmental condition characterized by challenges with social skills, communication, and restricted or repetitive behaviors. The causes of autism are still not fully understood, but both genetic and environmental factors are thought to play a role. One area of interest has been whether breastfeeding may help reduce the risk of a child developing autism. Here we review the current research on breastfeeding and autism and discuss some of the potential mechanisms by which breastfeeding could influence autism risk.
Key Questions
Some key questions around breastfeeding and autism include:
- Does breastfeeding reduce the risk of autism compared to formula feeding?
- How long should a mother breastfeed to see protective benefits against autism?
- Are there components in breastmilk like antibodies or fatty acids that may support brain development?
- Could factors associated with bottle feeding like lack of skin-to-skin contact affect autism risk?
- Do any benefits of breastfeeding persist after breastfeeding stops?
Examining these types of questions through epidemiological studies and clinical research can help shed light on the potential links between breastfeeding and autism.
Overview of Research
Several studies over the past two decades have examined whether breastfeeding is associated with a lower risk of autism compared to formula feeding. However, the findings have been mixed. Some studies have found protective effects of breastfeeding while others have found no significant associations. Here is a brief overview of some of the key studies in this area:
Studies Finding Protective Effects of Breastfeeding
- A 2016 meta-analysis combined results from 18 studies on breastfeeding and autism involving over 200,000 children. They found children who were breastfed for any duration of time had a 15% lower risk of autism compared to those who were formula-fed.
- A large 2013 study of over 1,700 children in the Nurses’ Health Study II found that children who were breastfed for at least 6 months had a 39% lower risk of developing autism compared to those breastfed for a shorter duration.
- A smaller study from Egypt in 2015 found that children who were exclusively breastfed for 6 months or more had an 89% lower risk of autism than non-breastfed children.
Studies Finding No Protective Effects
- A 2021 study in Australia examined infant feeding practices and autism diagnoses in over 4000 children. They found no significant association between breastfeeding duration and autism risk.
- A small 2018 study followed 180 infants with high autism risk based on having an older sibling with autism. Rates of autism at 36 months were similar between those who were breastfed versus formula fed.
- A large 2013 cohort study of over 13,000 children in Norway found no link between duration of breastfeeding and autism risk after adjusting for confounding factors.
As you can see the research has been contradictory so far. Next we’ll discuss some of the challenges and limitations faced by these types of studies.
Challenges in Studies on Breastfeeding and Autism
Studying the relationship between breastfeeding and autism risk comes with several inherent challenges:
- Retrospective design – Many studies are retrospective, meaning they gather data about breastfeeding after signs of autism have already appeared. This makes it difficult to establish cause-and-effect.
- Confounding factors – Breastfeeding mothers often differ from formula feeding mothers in many ways like income, education, and mental health. These other factors could influence any links seen with autism.
- Recall bias – In retrospective studies, parents are relied upon to accurately remember duration and exclusivity of breastfeeding often years later. Their recollections could be faulty.
- Reverse causality – Some infants may show early signs of autism that lead mothers to breastfeed for a shorter duration.
- Small sample sizes – Many studies, especially clinical trials, have included only a small number of children which limits their ability to detect small effects.
Researchers attempt to account for these limitations but they make studying breastfeeding and autism complex. Larger prospective studies tracking infants from birth are needed to better evaluate the links.
Potential Biological Mechanisms
Although the epidemiological evidence is unclear, there are some plausible biological mechanisms through which breastfeeding could hypothetically reduce autism risk including:
Passive Immunity
Breastmilk provides antibodies and other immune factors that protect babies from infections early in life. Since prenatal and postnatal infections have been linked to increased autism risk, the immune protection from breastfeeding could reduce this risk.
Gut Microbiome
Breastfeeding plays an important role in developing a healthy infant gut microbiome. Disruptions to the natural development of gut bacteria have been associated with autism in some children. Breastmilk contains beneficial bacteria and nutrients for healthy microbial growth.
Essential Fatty Acids
The long-chain polyunsaturated fatty acids (LCPUFAs) in breastmilk, especially DHA and ARA, are important for brain development and function. Some studies have found lower levels of these fatty acids in children with autism.
Oxytocin
Breastfeeding mothers release oxytocin during nursing sessions. This hormone is thought to promote social bonding between mother and infant which could influence social communication abilities.
Sensory Stimulation
The skin-to-skin contact and mutual gaze experienced during breastfeeding provides sensory stimulation that may support brain development related to sensory processing issues seen in some autistic children.
However, these potential mechanisms remain speculative. More research is needed to understand if they underlie any connection between breastfeeding and autism risk.
Review of Key Research Findings
To summarize the key research covered so far:
- Some large studies have found an association between longer durations of breastfeeding (typically at least 6 months) and a lower risk of autism by around 15-40%.
- However, other well-designed studies have not found breastfeeding to be protective against autism.
- Methodological limitations like confounding factors, recall bias, and reverse causation make these epidemiological findings difficult to interpret.
- Potential biological mechanisms exist but have not been firmly established as underlying any breastfeeding-autism link.
Based on the totality of evidence so far, there is mixed support for the hypothesis that breastfeeding reduces autism risk. Higher quality research is still needed to provide more definitive answers. Next we will cover some recommendations for mothers when it comes to breastfeeding and autism.
Recommendations for Mothers
Based on the current state of evidence, here are some recommendations for mothers concerned about breastfeeding and autism:
- Women should feel comfortable choosing the best infant feeding method for their family and situation, whether that be breastfeeding or formula feeding.
- Exclusive breastfeeding is recommended for at least the first 4-6 months whenever possible for general health benefits.
- Mothers who want to breastfeed may consider setting goals like breastfeeding for at least 6-12 months as some studies suggest this duration could be important for autism risk.
- However, no firm breastfeeding duration has been proven to prevent autism, so mothers should not feel pressured.
- Mothers unable to breastfeed or who choose not to breastfeed should not feel guilty, as evidence for meaningful impacts on autism risk remains inconclusive.
- All mothers should discuss any concerns about their child’s development with their pediatrician and seek evaluation if signs of autism arise.
The decision of how to feed one’s baby is a personal one, and mothers should not be made to feel undue anxiety about breastfeeding duration and autism. Continued research and improved understanding of any breastfeeding benefits on autism risk will help guide mothers in the future.
Conclusion
The potential connections between breastfeeding and autism risk are complex. While some studies suggest breastfeeding, especially for 6 months or longer, could offer protection against autism, other quality research has not found this effect. Methodological issues continue to limit the strength of evidence available. Potential biological mechanisms like passive immunity and brain development exist, but have not been firmly proven. More prospective research controlling for confounding factors is key to clarifying whether breastfeeding can provide meaningful protection against autism in the future. Currently, mothers should be supported in their infant feeding choices and not made to feel pressure when it comes to breastfeeding duration and autism prevention. Continued work understanding the causes of autism will help inform new parents about how to best support the neurodevelopmental health of their children.
