Nationwide twin cohorts in the Netherlands and Sweden suggest antibiotic use in infants is not a risk factor for ADHD

Proper development of the gut biota is important for the health of the brain and nervous system. It has been hypothesized that disturbances of gut bacteria by antibiotics could contribute to the development of neurodevelopmental disorders, including ADHD.

In the case of ADHD, studies to date have produced conflicting results. To tease out any familial confounding reflecting shared environment and genetics, a joint Dutch-Swedish team of researchers further tested the hypothesis through 7- to 12-year-old twins in the Netherlands Twin Register (25,781 twins) and 9-year-old twins in the Swedish Twin Registry (7,946 twins).

ADHD symptoms in the Netherlands cohort were derived from mothers’ answers to the short Conners’ Parental Rating Scale-Revised. For the Swedish cohort, ADHD was determined through the International Classification of Diseases codes for ADHD in the cross-linked National Patient Register.

Exposure to antibiotics during the first two years of childhood was determined by parent reports for the Netherlands twin cohort, and by prescription claims for antibiotics in the Swedish twin cohort.

Covariates were explored in both twin cohorts including educational attainment of parents, gender of the infant, birth weight, delivery mode, and asthma. Breastfeeding was also explored in the Dutch cohort.

In the unmatched analysis, comparing children with ADHD with non-related children without ADHD, early-life antibiotic use was associated with a significant 8% greater odds of ADHD in the Netherlands cohort and a significant 14% greater odds of ADHD in the Swedish cohort.

However, when limiting the analysis to matched monozygotic twins, the association disappeared altogether in both the Dutch and Swedish cohorts. Pooling both cohorts resulted in the same outcome. In all three cases, the odds flipped into a mildly negative association, but with no statistical significance.

Using higher cutoff values for ADHD symptoms made no difference.

The authors concluded, “In this large co-twin study performed in two countries, early-life antibiotic use was associated with increased risk of ADHD and ASD, but the results suggest that the association disappeared when controlled for shared familial environment and genetics, indicating that this association may be susceptible to confounding. … our results indicate that there is no association between ADHD and ASD diagnoses and early antibiotic use when environmental and genetic family factors are taken into account.”

Elise M A Slob, Bronwyn K Brew, Susanne J H Vijverberg,Talitha Dijs, Catharina E M van Beijsterveldt, Gerard H Koppelman, MeikeBartels, Conor V Dolan, Henrik Larsson, Sebastian Lundström, Paul Lichtenstein,Tong Gong, Anke H Maitland-van der Zee, Aletta D Kraneveld, Catarina Almqvist,Dorret I Boomsma, “Early-life antibiotic use and risk of attention-deficithyperactivity disorder and autism spectrum disorder: results of a discordanttwin study,”International Journal of Epidemiology(2020),