Effects of kefir on symptoms, sleep, and gut microbiota in children with ADHD: a randomised controlled trial

Background Evidence indicates the gut microbiome may be altered in ADHD, suggesting that targeting gut bacteria could alleviate symptoms. This study examined the effects of kefir supplementation on ADHD symptoms, sleep, attention, and gut microbiome composition in children diagnosed with ADHD. Methods A six-week, randomised, double-blind, placebo-controlled trial was conducted in UK children aged 8–13 years with ADHD. Participants were assigned either to a daily kefir or placebo drink group. The primary outcome was ADHD symptom severity measured by the Strengths and Weaknesses of ADHD Symptoms and Normal Behaviour (SWAN) scale. Secondary outcomes included gut microbiota composition (analysed using shotgun metagenomic sequencing), gastrointestinal symptoms, sleep (actigraphy, parent/self-report), attention and impulsivity. Results Fifty-three participants (mean age = 10.2 years, SD = 1.7) completed the study. Kefir had no significant overall effect on parent or teacher-rated ADHD symptom severity. A non-significant interaction was observed between baseline symptom severity and group for teacher-rated SWAN scores, with children in the kefir group who had the highest baseline ADHD symptoms showing lower scores at week six (M = 2.03, SE = 0.33 vs. 2.86, SE = 0.34), p = 0.088. Actigraphy revealed the kefir group spent fewer minutes awake during the down period at week six (M = 70.10, SE = 0.09) than the placebo group (M = 89.72, SE = 0.07), p = 0.04. However, the kefir group self-reported more sleep problems post-intervention (M = 39.81, SE = 0.75 vs. 37.40, SE = 0.65), p = 0.02. For Go/NoGo RT variance, a non-significant interaction (p = 0.052) between baseline and post intervention scores was found. No other significant group differences were observed. Kefir supplementation did not significantly affect gut microbiota alpha or beta diversity. However, relative abundance of several species including bifidobacterium adolescentis, B. infantis, and B. longum and Alistipes sp021204515 and A. timonensi increased significantly in the kefir group. Conclusions Kefir supplementation may support modest improvements in sleep quality, in children with ADHD. These findings contribute to our understanding of the potential role of nutrition in ADHD management and may inform clinical guidance for practitioners working with neurodivergent individuals. Ethics Ethical approval for the study was granted by St Mary’s University Ethics Committee. Trial registration The trial protocol has been prospectively registered with ClinicalTrials.gov: NCT05155696. Registered on 13 December 2021.