Breastfeeding in infancy was linked to fewer attention-deficit/hyperactivity disorder symptoms later in childhood in a large Norwegian study, even after researchers accounted for genetic and family-related factors.
The study, published in Biological Psychiatry, followed data from 37,600 families in the Norwegian Mother, Father and Child Cohort Study. Researchers looked at how long infants were exclusively breastfed up to 6 months of age, then examined ADHD symptoms at ages 3, 5 and 8. The findings suggest early infant feeding may play a small role in later ADHD-related behaviors, but they do not show that breastfeeding prevents ADHD or that formula feeding causes ADHD.
“It is well established that psychiatric symptoms and disorders can be influenced by both genetic and environmental factors,” said Berit Skretting Solberg, a psychiatrist and researcher at the Department of Biomedicine at the University of Bergen and senior consultant at Betanien Hospital.
Breast milk contains nutrients and biological components involved in growth, immune development and brain development, including long-chain fatty acids, amino acids, antibodies and beneficial bacteria. Because ADHD is influenced by both inherited and environmental factors, researchers have been interested in whether early nutrition may be part of that larger picture.
In this study, mothers reported infant feeding practices through questionnaires when their babies were 6 months old. The researchers used those responses to calculate how many months each child was exclusively breastfed, along with partial breastfeeding and the introduction of other liquids or solid foods.
“We found that the longer a child was exclusively breastfed (up to 6 months), the lower the level of ADHD symptoms at ages three, five, and eight years,” Solberg said.
The association was seen in both boys and girls. According to the University of Bergen, it was strongest at ages 3 and 5 and somewhat weaker by age 8. The researchers also reported that the association grew stronger with longer duration and greater intensity of breastfeeding, with the strongest pattern seen for exclusive breastfeeding up to 6 months.
That does not make the finding simple. ADHD has a strong genetic component, and the relationship between breastfeeding and ADHD symptoms can be shaped by many overlapping factors. Mothers with ADHD symptoms may be less likely to breastfeed for longer, and children who later show ADHD symptoms may also have been harder to breastfeed as infants. Family stress, sleep, parental mental health, socioeconomic factors and other early-life experiences can also complicate the picture.
“This may partly explain the relationship between lower breastfeeding and increased ADHD symptoms in children,” Solberg said.
To address that issue, the researchers adjusted for known genetic risk for ADHD and sociodemographic factors. They also conducted sibling analyses, comparing children within the same family who had different breastfeeding patterns. Those methods help reduce some forms of confounding, but they cannot eliminate every possible explanation.
“Even after these adjustments, there was a clear but moderate protective effect of the duration of exclusive breastfeeding on later ADHD symptoms,” Solberg said.
The word “moderate” matters. This study does not suggest that infant feeding choices determine whether a child will have ADHD. It also should not be read as a judgment on parents who could not breastfeed, chose not to breastfeed or used formula for medical, work-related, adoption, supply or personal reasons.
ADHD is a neurodevelopmental condition shaped by many factors. Breastfeeding may be one part of the early-life environment, but it is not the whole story.
The study also has limits. The Norwegian cohort is not fully representative of the general population. Participants tend to have higher education levels and are more likely to breastfeed, and to breastfeed for longer, than the broader Norwegian population. The study also relied on parent-reported breastfeeding and ADHD symptoms, and as an observational study, it cannot prove cause and effect.
“As with other observational studies, it is difficult to draw firm conclusions about causality,” Solberg said.
Still, the findings add to research exploring how early nutrition, genetics and child development may interact. They also offer a more careful way to talk about breastfeeding and brain health: not as a guarantee, not as a test of good parenting and not as a single answer to ADHD, but as one possible influence among many.
“In our society, heredity is likely the strongest risk factor for ADHD. However, since ADHD — like other neurodevelopmental disorders — is influenced by multiple factors, our study suggests that the extent of breastfeeding may also help protect against the development of ADHD symptoms in young children,” Solberg said.
This project received funding from the European Union’s Horizon 2020 research and innovation program. The Norwegian Mother, Father and Child Cohort Study is supported by the Norwegian Ministry of Health and Care Services and the Ministry of Education and Research. The researchers also acknowledged support from Stiftelsen KG Jebsen and several research institutions, foundations and public research funders involved in genomic data generation. Some authors reported outside funding, speaker fees or honoraria from organizations including Takeda, Shire Pharmaceuticals, Medice and Evolan Pharma AB, all outside the submitted work.