Even after the researchers took into account genetic and family-related factors, children who were exclusively breastfed for long periods of time showed slightly fewer symptoms of ADHD from ages 3 to 8, suggesting that early breastfeeding patterns may play a small but meaningful role in neurodevelopment.
Study: Breastfeeding and the development of attention-deficit/hyperactivity disorder symptoms across childhood. Image credit: Pixel-Shot/Shutterstock.com
According to a recent study published in biological psychiatrybreastfeeding was associated with a modest reduction in symptoms of childhood attention-deficit/hyperactivity disorder (ADHD).
It turns out that breastfeeding may improve ADHD
ADHD is one of the most common neurodevelopmental disorders in children and is characterized by persistent inattention, hyperactivity, and impulsivity. Approximately two-thirds of children with ADHD will continue to have ADHD as adults. It is also associated with multiple mental and physical illnesses, including autism, depression, obsessive-compulsive disorder (OCD), and substance abuse.
Genetics plays a large role, with heritability estimated at 70% to 80%, but early childhood environmental factors, such as infant feeding habits, can also influence brain development. Environmental factors are less well established but may include prenatal and postnatal dietary exposures. However, it is important to understand its contribution, as it is subject to change.
Breastfeeding is an important source of dietary intake for most infants during the first few months of life. In Norway, where this study was conducted, most mothers breastfeed for at least 6 months, but almost all mothers start eating solid foods at 4 to 5 months.
Previous studies have reported inconsistent results on whether breastfeeding protects against ADHD. Breastfeeding in high-income countries is an indicator of healthy behavior and may confound its association with ADHD. Other confounding factors include maternal ADHD characteristics. This may increase the infant’s risk of ADHD while decreasing the likelihood of breastfeeding. Infants with ADHD characteristics may have more difficulty breastfeeding, which may contribute to the association between reduced breastfeeding and increased ADHD risk.
Conversely, previous studies using Mendelian randomization (MR) supported the protective effect of breastfeeding on ADHD.
In the current study, researchers conducted a prospective follow-up of a large family cohort using a polygenic risk score (PRS) and repeated ADHD assessments throughout childhood. They aimed to find out how exclusive breastfeeding was associated with mother-reported ADHD symptoms at ages 3, 5, and 8.
Combining symptom tracking and genetic risk
Data for this study were obtained from the Norwegian Mother and Child Cohort Study (MoBa) and the Norwegian Medical Birth Register (MBRN). Genotypic data were obtained using MoBaPsychGen.
The researchers followed a birth cohort of 37,643 children and 18,349 complete family units (father, mother, child). Mothers completed a standardized questionnaire from which each child’s ADHD score was calculated at each time point. The researchers adjusted for socioeconomic factors, perinatal factors, and child ADHD PRS in the main analysis, and included maternal and paternal ADHD PRS in smaller trio-based analyses.
Breastfeeding information was self-reported at 6 months. Exclusive breastfeeding refers to exclusive or breastfeeding (only or mostly breastfeeding, with the latter using water-based drinks or fruit juices less than once a week). In this study, both the type of breastfeeding (exclusive vs. partial breastfeeding, if solid or semi-solid food or formula was also given) and duration (from no exclusive breastfeeding to >6 months) were recorded.
Symptoms decrease with prolonged exclusive breastfeeding
For each month of exclusive breastfeeding, children’s ADHD scores were 0.06 to 0.08 lower at all ages. Adding child and parent ADHD PRS to the model slightly attenuated the association. Similar associations persisted at all ages in fully adjusted models. This model explained approximately 4% to 7% of the total variance in ADHD symptoms.
In a categorical analysis using infants who were exclusively breastfed for 6 months as a reference group, the researchers found that shorter durations of exclusive breastfeeding were associated with higher ADHD symptom scores at all three time points. Differences in scores were 0.33–0.55 higher for 3-year-olds and 0.21–0.46 higher for 8-year-olds, indicating smaller associations over time.
The greatest increase in ADHD scores was seen with less breastfeeding (only partial breastfeeding for less than 4 months) compared to the reference. Non-breastfeeding analyzes yielded inconsistent results across all three ages. This is probably because the group was small and included infants who were not breastfed for a variety of reasons, including serious maternal morbidity and other heterogeneous factors.
Overall, children who were exclusively breastfed for longer periods of time had fewer symptoms of ADHD at all ages compared to children who were partially or exclusively breastfed for shorter periods of time.
Of note, similar results were obtained from sibling pair analyzes in which siblings differed in breastfeeding exposure, supporting our main findings. However, stratifying by gender yielded weaker associations. Previous studies in preterm infants have shown that infants who receive more breast milk while in the neonatal intensive care unit have lower ADHD symptom scores at age 7.
The differences were relatively small and similar to the effect sizes of several environmental toxins and chemicals that increase the risk of childhood ADHD.
The current study builds on previous MR studies by adjusting for PRS and other confounders when estimating their impact on outcome. Although these findings do not prove a protective effect at the individual level, even small reductions in ADHD symptoms at the population level may reduce the proportion of individuals who develop clinically relevant ADHD.
possible explanation
Breastfeeding may support brain development through several mechanisms. These may include nutrients such as tryptophan, vitamins, prebiotics and probiotics, and other bioactive compounds that directly influence neurodevelopment through effects on gut-brain signaling and the gut microbiome. Breastfeeding may also promote skin-to-skin contact between mother and child, which may increase attachment security and reduce externalizing ADHD symptoms.
Additional biological pathways may involve interactions between the immune system, metabolic regulation, and brain development. Maternal immune cells, stem cells, and antibodies present in breast milk may help protect against pathogens, while immune-related signaling pathways can also influence neurodevelopment.
strength and limits
This prospective study with a large number of participants included both genetic and phenotypic data and used PRS to account for genetic liability. Sibling comparison analyzes also supported the main findings; The possibility of a causal relationship has been strengthened.
Other strengths included repeated assessment of ADHD symptoms over time, inclusion of confounders such as parity and socio-economic environment, and use of breastfeeding categories that incorporated both breastfeeding intensity and duration, which also helped support the study findings.
However, this study is observational and cannot prove cause and effect. Although the ADHD PRS cannot account for all genetic risk, sibling analyzes helped control for unmeasured genetic and environmental confounding.
ADHD symptoms were measured using a questionnaire rather than a clinical diagnosis. However, researchers note that this could be an advantage, as diagnostic patterns across Norway remain inconsistent. Approximately one-third of participants dropped out by the final assessment, which did not significantly affect the results, although selection bias may have occurred.
Exclusive breastfeeding for 6 months supports healthy neurodevelopment
The results of this study suggest that longer durations of exclusive breastfeeding, up to 6 months, are associated with reduced ADHD symptoms throughout childhood in a dose-response relationship, after adjusting for genetic, socioeconomic, and perinatal factors that may have influenced outcomes.
Despite the small effect size, the results of this study suggest that longer periods of exclusive breastfeeding may contribute to healthy neurodevelopment, although the observational nature of the study precludes confirmation of causality.
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