Vitamin D and ADHD
Attention deficit hyperactivity disorder (ADHD) affects an estimated 5% of children and 2.5% of adults. Vitamin D deficiency is more common in ADHD children than in matched controls. Whether correcting it changes ADHD symptoms is less clear.
The deficiency association
A 2020 meta-analysis (Khoshbakht) of 13 studies found ADHD children had mean 25(OH)D ~4.6 ng/mL lower than controls, and the odds of deficiency were roughly doubled. Prenatal maternal 25(OH)D has also been linked with later childhood ADHD risk (Bekkhus 2020) — a causal interpretation would need better evidence.
Supplementation trials
- Elshorbagy 2018 — 62 ADHD children (deficient); adjunctive cholecalciferol 2,000 IU/day for 3 months plus methylphenidate improved cognitive function and behaviour vs methylphenidate alone.
- Naeini 2019 — 96 ADHD children; 50,000 IU weekly × 6 weeks: significant improvement in Conners rating scale total, hyperactivity, and inattention scores vs placebo.
- Mohammadpour 2018 — 96 children (deficient), 50,000 IU weekly × 8 weeks: improved evening (but not morning) parent- and teacher-rated ADHD scores.
- 2019 meta-analysis (4 RCTs) — significant reduction in ADHD symptom scores favouring vitamin D adjunct; sample sizes small, replication needed.
Where to be sceptical
Trials to date are small, mostly single-country, and use variable ADHD assessment tools. Effect sizes are modest. The intervention is safe and cheap, so correcting deficiency in an ADHD child who happens to be deficient is reasonable — but do not expect it to replace stimulants or behavioural interventions in moderate-to-severe ADHD.
Practical guide
- Test 25(OH)D at ADHD diagnosis, particularly for children with restrictive diets or limited sun exposure.
- Correct deficiency: 1,000–2,000 IU/day cholecalciferol (age-appropriate).
- Continue guideline-based ADHD management — stimulants, behavioural therapy, school accommodations, sleep hygiene.
- Do not use vitamin D as a rationale for delaying or refusing evidence-based ADHD treatment.