A new study from the University of Bergen shows an association between breastfeeding up to six months of age and a reduced risk of ADHD symptoms from ages three to eight.
Breast milk is the primary source of nutrition for infants. It is uniquely tailored for the child and contains numerous components beneficial for growth and brain development, including long-chain fatty acids, amino acids, antibodies, and beneficial bacteria.

“It is well established that psychiatric symptoms and disorders can be influenced by both genetic and environmental factors,” says Berit Skretting Solberg, psychiatrist and researcher at the Department of Biomedicine, University of Bergen, and senior consultant at Betanien Hospital.

There has been considerable scientific interest in understanding how breast milk and breastfeeding affect brain development and the infant immune system.
Together with her co-authors, Solberg therefore examined the relationship between the number of months an infant is exclusively breastfed (up to six months of age) and the child’s risk of developing ADHD symptoms.

Less ADHD symptoms at ages three, five, and eight years

The study used data from 37,600 families participating in the Norwegian Mother, Father and Child Cohort Study (MoBa).
Mothers reported, through a questionnaire six months after birth, the duration of exclusive breastfeeding, partial breastfeeding, and the introduction of other liquids or solid foods. These data were used to calculate the number of months each child was exclusively breastfed.

“We found that the longer a child was exclusively breastfed (up to six months), the lower the level of ADHD symptoms at ages three, five, and eight years,” says Solberg.

The association was observed in both boys and girls and was strongest at ages three and five, and somewhat weaker at age eight. All breastfeeding showed an effect, but the effect increased with the duration and intensity of breastfeeding and was strongest with exclusive breastfeeding up to six months.

Clear but moderate effect after adjustments

ADHD is partly explained by genetic factors. For example, it is known that mothers with ADHD symptoms tend to breastfeed less than others and are more likely to have children with ADHD symptoms. At the same time, children with ADHD symptoms may be more difficult to breastfeed.

“This may partly explain the relationship between lower breastfeeding and increased ADHD symptoms in children,” says Solberg.

To better understand possible causal relationships, the study adjusted for known genetic risk of ADHD and sociodemographic factors. Sibling analyses were also conducted, comparing different breastfeeding patterns within the same family.

“Even after these adjustments, there was a clear but moderate protective effect of the duration of exclusive breastfeeding on later ADHD symptoms,” Solberg explains.

More research needed to clarify causality

Solberg notes that the MoBa study is not fully representative of the Norwegian population. Participants tend to have higher education levels and are more likely to breastfeed, and to do so for longer than the general population.
She therefore does not rule out the possibility that the effect could be even greater in groups where breastfeeding is less common.

“As with other observational studies, it is difficult to draw firm conclusions about causality,” says Solberg, emphasizing the need for further research.

At the same time, she notes that the findings suggest that factors beyond genetics may influence ADHD risk:

“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.”