Food and Behaviour Research

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Vitamin D Supplementation May Reduce ADHD Symptoms - Systematic Review

Brian Park, PharmD

Vitamin D

Study suggests that vitamin D supplementation may alleviate ADHD symptoms.


Many studies have reported abnormally low levels of Vitamin D in children (and adults) with ADHD - and Vitamin D is now known to play important roles in brain development and function, not just physical health.

However, to determine whether Vitamin D actually plays any causal role in ADHD symptoms requires randomised controlled clinical trials, comparing the effects of Vitamin D supplementation with placebo treatment.

Only a few such trials were identified in this systematic review, involving 256 children clinically diagnosed with ADHD. All children were already receiving stimulant medications, to which the supplementation was added.

Pooled findings showed that Vitamin D supplementation (at varying doses) significanly reduced total ADHD symptoms compared with placebo, with no adverse side effects.  

Improvements were also seen from Vitamin D in each of the main ADHD symptom domains of inattention, hyperactivity and behaviour - but not for oppositional behaviour.

Vitamin D deficiencies are now so common in most developed countries that supplementation is recommended - especially during the winter months. Public health recommendations in the UK, EU and US range from 10-20 mcg/day (i.e. 400-800 IU)

However, up to 4000 IU / day is generally regarded as safe - and the studies of ADHD reviewed here used fairly high doses - ranging from 1000 IU/day to 50,000 IU / week.

For details of this research, see:

And for more information on this topic, please see the following lists, which are regularly updated

A recent systematic review and meta-analysis assessed the benefits and harms of vitamin D supplementation in patients with attention-deficit/hyperactivity disorder (ADHD).

To investigate these outcomes, study authors searched various clinical databases for randomized controlled trials (RCTs) where vitamin D supplementation was used alone or as an adjunctive therapy in ADHD patients. 

Based on their inclusion criteria, the authors identified 4 RCTs involving 256 children with ADHD being treated with methylphenidate and concomitant vitamin D. These studies, which ranged from 6 to 12 weeks in duration, utilized doses of vitamin D between 1000 IU/day and 50,000 IU/week. 

“We found that vitamin D supplementation may alleviate ADHD symptoms, which were supported by improvements in ADHD total scores, inattention scores, hyperactivity scores, and behavior scores,” the authors stated. However, they added, statistically significant improvements in oppositional measures were not observed. 

With regard to safety, findings from the analysis showed no significant differences in adverse events between vitamin D and placebo; supplementation with vitamin D also resulted in increased vitamin D levels in these patients.

Based on their findings, the authors concluded that vitamin D supplementation, as an adjunct to methylphenidate, may benefit patients with ADHD, however evidence for this effect was found to be of low quality.

“Future studies should consider baseline vitamin D levels and address different dosing (low or high dose) and the frequency of vitamin D supplementation,” they added.