Children who were fully breastfed for longer periods showed modestly fewer ADHD symptoms from ages 3 to 8, even after researchers accounted for genetic and family-related factors, suggesting early feeding patterns may play a small but meaningful role in neurodevelopment.
Study: Breastfeeding and Development of Attention-Deficit/Hyperactivity Disorder Symptoms Across Childhood. Image credit: Pixel-Shot/Shutterstock.com
According to a recent study published in Biological Psychiatry, breastfeeding was associated with modestly lower symptoms of attention-deficit/hyperactivity disorder (ADHD) during childhood.
Breastfeeding emerges as a potential ADHD modifier
ADHD is one of the most common neurodevelopmental disorders in children and is characterized by persistent inattention, hyperactivity, and impulsivity. About two-thirds of children with ADHD grow up to have ADHD as adults. It is also linked to multiple psychiatric and somatic illnesses such as autism, depression, obsessive-compulsive disorder (OCD), and substance abuse.
While genetics plays a major role, with an estimated 70%-80% heritability, early-life environmental factors, including infant feeding practices, may also influence brain development. The environmental factors are less well established, but may include dietary exposures before and after birth. However, it is important to understand their contribution as they are potentially modifiable.
Breastfeeding is an important source of dietary exposure for most infants in the first few months of life. In Norway, where this study was conducted, most mothers breastfeed for at least six months, but almost all begin solid foods at 4-5 months.
Previous studies have reported inconsistent findings on whether breastfeeding protects against ADHD. Breastfeeding in high-income countries is a marker of healthy behaviors, which may confound the association with ADHD. Other confounders include maternal ADHD traits, which may reduce the odds of breastfeeding while increasing the risk of ADHD in the infant. Infants with ADHD traits may be more difficult to breastfeed, potentially contributing to the association between less breastfeeding and higher ADHD risk.
Conversely, a prior study using Mendelian randomization (MR) supported the protective effect of breastfeeding against ADHD.
In the current study, researchers conducted a prospective follow-up on a large family cohort, using polygenic risk scores (PRS) and ADHD assessments repeated throughout childhood. They aimed to examine how full breastfeeding correlated with mother-reported ADHD symptoms at 3,5 and 8 years.
Combining symptom tracking with genetic risk
The data in this study were taken from the Norwegian Mother, Father and Child Cohort Study (MoBa) and the Medical Birth Registry of Norway (MBRN). The genotypic data were obtained using MoBaPsychGen.
Researchers followed a birth cohort of 37,643 children and 18,349 complete family units (father, mother, and child). The mothers completed standardized questionnaires from which ADHD scores were calculated for each child at each time point. The researchers adjusted for socioeconomic factors, perinatal factors, and child ADHD PRS in the main analyses, with maternal and paternal ADHD PRSs included in a smaller trio-based analysis.
Information on breastfeeding was self-reported at six months. Full breastfeeding refers to exclusive or predominant breastfeeding (only or mostly breastmilk feeding, with, in the latter case, less than weekly use of water-based drinks or fruit juices). The study captured both the type of breastfeeding (full versus partial, when solid or semi-solid foods or formula were also given) and the duration (from no breastfeeding to full breastfeeding for 6 months or longer).
Longer full breastfeeding linked to fewer symptoms
For each month of full breastfeeding, the ADHD scores in the child were 0.06-0.08 lower at all ages. With the addition of the ADHD PRSs of the child and both parents to the model, the associations were slightly weakened. With the fully adjusted model, similar associations persisted at all ages. The model explained approximately 4% to 7% of the total variance in ADHD symptoms.
In the category-wise analysis, using infants who were fully breastfed for six months as the reference group, the investigators found higher ADHD symptom scores with shorter durations of full breastfeeding at all three time points. The difference in score ranged from 0.33 to 0.55 higher at age 3 and from 0.21 to 0.46 higher at age 8, indicating smaller associations over time.
The greatest increase in ADHD scores was seen with less breastfeeding (only partial breastfeeding for <4 months) compared to the reference. Inconsistent results were obtained across all three ages in the no-breastfeeding analysis, perhaps because the group was small and may have included infants who were not breastfed for various reasons, including serious maternal or infant illness and other heterogeneous factors.
Taken together, children who had been fully breastfed for longer durations showed fewer ADHD symptoms at all ages compared with those who were partially or fully breastfed for shorter durations.
Notably, similar results were obtained from sibling-pair analyses with different breastfeeding exposures between siblings, supporting the main finding. However, weaker associations were obtained when stratified by sex. Earlier studies in preterm infants have shown lower ADHD symptom scores at age 7 when the infants were fed more maternal milk while in the neonatal intensive care unit.
The differences were relatively small, similar to the effect size for multiple environmental toxins and chemicals that increase ADHD risk in childhood.
The current study builds on the previous MR study by adjusting for PRS and other confounders when estimating the effect on the outcome. While these findings do not demonstrate a protective effect at the individual level, even a small population-level reduction in ADHD symptoms could reduce the proportion of individuals who develop clinically relevant ADHD.
Possible explanations
Breastfeeding may support brain development through several mechanisms. These could include nutrients such as tryptophan, vitamins, pre- and probiotics, and other bioactive compounds that influence neural development directly, through gut-brain signaling, and via their effects on the gut microbiota. Breastfeeding may also promote mother-infant skin-to-skin contact, which can enhance attachment security and potentially 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 breastmilk may help protect against pathogens, while immune-related signaling pathways could also influence neurodevelopment.
Strength and limitations
This prospective study with a large number of participants included both genetic and phenotypic data and accounted for genetic liability using PRSs. The sibling comparison analysis also supported the main finding and strengthened the possibility of a causal relationship.
Other strengths include repeated ADHD symptom assessment over time, the inclusion of confounding factors such as parity and socioeconomic environment, and the use of breastfeeding categories that incorporated both the intensity and duration of breastfeeding, which also helped support the study findings.
However, the study was observational and cannot establish causation. The ADHD PRS may not account for all genetic risk, though the sibling analysis helped to control for unmeasured genetic and environmental confounding.
ADHD symptoms were measured using questionnaires rather than clinical diagnoses. However, the researchers point out that this may be an advantage as diagnostic patterns across Norway remain inconsistent. About one-third of participants dropped out by the last assessment, but this did not significantly affect the results, though it may have introduced selection bias.
Six months of full breastfeeding supports healthy neurodevelopment
The findings suggest that longer durations of full breastfeeding, up to 6 months, were associated with fewer ADHD symptoms throughout childhood, with a dose-response relationship, after adjusting for genetic, socioeconomic, and perinatal factors that could have influenced the outcome.
Despite the small effect sizes, the findings suggest that longer full breastfeeding may contribute to healthy neurodevelopment, although the observational nature of the study precludes confirmation of causality.
Download your PDF copy now!
Childhood lead exposure declines but disparities persist nationwide