Children who were fed only breast milk in their first six months showed symptoms of attention deficit hyperactivity disorder (ADHD) less often at ages three, five and eight. This disorder makes it hard for a person to concentrate, and they may be overly active and impulsive. The results were published in the journal Biological Psychiatry. The authors stress that a link exists, but it does not prove that breast milk directly prevents the disorder.
Researchers from the University of Bergen in Norway analyzed data on children born between 1999 and 2009. When the infants were six months old, mothers filled out questionnaires about feeding. The scientists were interested exclusively in breastfeeding - without formula, solid food or even water. Parents then assessed the children's behavior at ages three, five and eight, noting inattention, hyperactivity and impulsivity.
Each additional month of exclusive breastfeeding was associated with a small but measurable reduction in ADHD symptoms at all three ages. The link persisted even when the scientists accounted for the child's genetic predisposition. To do this, they calculated polygenic risk - a conditional measure that estimates the likelihood of a trait developing based on many small variations in DNA.
The researchers then narrowed the sample to families with data on both the mother, the father and the child. They added to the analysis both parents' polygenic risk, as well as the mother's education level, the parents' age when the child was born, the child's birth weight and birth season. Even with adjustment for these factors, the link remained: the longer a child was exclusively breastfed, the fewer ADHD symptoms they had. By age eight the effect weakened somewhat.
The most convincing part was the check on brothers and sisters. The scientists compared pairs of children from the same mother who differed in the duration of exclusive breastfeeding. The child who was breastfed longer, as a rule, had fewer symptoms than their brother or sister. This suggests that the milk itself or the feeding process may be involved, and not only family characteristics. However, when boys and girls were analyzed separately, the effect became weaker.
It is important to understand that this is a correlation - a statistical association that by itself does not prove a cause-and-effect relationship. In addition, the reduction in symptoms was small for each individual child. According to the authors, such changes may be unnoticeable in clinical practice and may appear only at the level of large population groups. The study relied on parent questionnaires rather than medical assessment, which may introduce subjectivity. Participation in the multi-year project was voluntary, so some families dropped out of the follow-up - this is also a limitation.
The scientists plan to find out which biological mechanisms may explain the observed link. Breast milk contains, for example, tryptophan - an amino acid that is broken down in the gut and helps regulate signals between the digestive system and the central nervous system. Milk also contains complex sugars that support beneficial bacteria. In addition, physical contact during feeding is important, which may affect attachment and emotional regulation. But all of this is a direction for future research, not proven causes.