Could you have it?
Nutrition keeps coming up in ADHD research, and there’s a good reason why. Dopamine is one of the key brain chemicals involved in ADHD, and your brain can't make it out of thin air. It relies on specific vitamins and minerals, particularly iron and vitamin D, to help produce it. So running low on these nutrients could leave your brain short of what it needs, putting more strain on an already dysfunctional system.
A Sample Size That’s Hard to Ignore
In 2025, a massive meta-analysis investigated the role of vitamin D in ADHD (1). It pooled 37 studies which covered more than 24,000 participants across 13 countries.
The Vitamin D Gap in ADHD: Twice as Likely to be Low
Children with ADHD were twice as likely to be vitamin D deficient, compared to children without ADHD. On average, their blood levels were around 6.5 ng/mL (roughly 16 nmol/L) lower (1).
Interestingly, five studies looked at mothers: low vitamin D during pregnancy or at birth was associated with around 50% higher odds of ADHD in their children (1).
Putting Vitamin D Supplements to the Test
The researchers also pooled seven trials testing vitamin D supplementation, mostly alongside standard ADHD medication (1). Vitamin D supplementation resulted in small but significant improvements in overall ADHD symptoms, inattention, behaviour and parent-rated symptoms, compared to placebo. Hyperactivity remained unchanged.
The authors also noted that while this is promising, the trials were small, and the studies varied in children’s ages, how ADHD was diagnosed and measured, and study design.
Do Adults With ADHD Run Low Too?
Vitamin D's role in dopamine signalling doesn't switch off in adulthood. While most of the research so far has focused on children, a 2026 study compared adults with ADHD to those without (2). None were taking ADHD medication or vitamin supplements.
Adults with ADHD had significantly lower vitamin D levels, on average around 6 ng/mL (15 nmol/L) lower, almost exactly the gap seen in children. Those with lower levels also tended to have more severe symptoms across the board, including inattention and hyperactivity. It's a small study, and it shows a link rather than cause and effect. As the authors point out, low vitamin D could worsen symptoms, or alternatively, ADHD-related habits like diet or less time in the sun, could lower vitamin D. Even so, it suggests the pattern seen in children may carry on into adulthood.
Vitamin D in the Brain, and Why it Matters for ADHD?
Researchers think vitamin D may help control how much dopamine the brain can make. There are three clues behind this.
Clue 1: It's in the right place.
Vitamin D receptors are found throughout the human brain. So is the enzyme that switches vitamin D into its active form. In post-mortem brain tissue, the receptors were most concentrated in the hypothalamus and in the substantia nigra, a home to many of the brain's dopamine-producing cells (3). That matters because dopamine is the brain chemical most closely linked to ADHD, so much that it’s one of the main targets of ADHD stimulant medication.
Clue 2: It's a cog in dopamine production.
In lab studies, active vitamin D increased levels of tyrosine hydroxylase, the enzyme that starts dopamine production (4). In other words, vitamin D may help regulate how much dopamine the brain can make.
Clue 3: It affects serotonin too.
The same research found that vitamin D boosted tryptophan hydroxylase 2, the enzyme that makes serotonin in the brain (4). Researchers have proposed that vitamin D directly switches on the gene for this enzyme. Low levels could then affect serotonin-linked functions like impulse control and planning, both central to ADHD (5).
Correlation Does Not Equal Causation
One big question remains: which comes first? The studies show the two go together more often than by chance, not which one causes the other. Low vitamin D may add to symptoms, while ADHD-related habits, such as a less varied diet or less time outdoors, might lower vitamin D - it could be a bit of both. Either way, low vitamin D is worth correcting, regardless of what's driving it.
The takeaway
Vitamin D is no substitute for ADHD medication. But low levels appear to be more common in people with ADHD, and vitamin D plays a role in the key brain system involved. Making sure your levels are where they should be is a simple and easy win to add to your wider ADHD toolkit. If you're worried you might be low, your GP can arrange a simple blood test.
References
1. Ismail, Y.A., El-Bayaa, N.M., Fouad, M.M. et al. The association between serum vitamin D concentration and Attention Deficit/Hyperactivity Disorder: a systematic review and meta-analysis of observational and interventional studies. Middle East Curr Psychiatry 32, 97 (2025). https://doi.org/10.1186/s43045-025-00586-y
2. Esra, D., Havva, K. Evaluation of the relationship between vitamin levels and symptom severity in adults with attention-deficit/hyperactivity disorder. Sci Rep 16, 9329 (2026). https://doi.org/10.1038/s41598-026-41493-4
3.Eyles DW, Smith S, Kinobe R, et al. Distribution of the Vitamin D receptor and 1α-hydroxylase in human brain. Journal of Chemical Neuroanatomy. 2005;29:21–30. doi: 10.1016/j.jchemneu.2004.08.006
4. Pertile RAN, Brigden R, Raman V, Cui X, Du Z, Eyles D. Vitamin D: A potent regulator of dopaminergic neuron differentiation and function. J Neurochem. 2023 Sep;166(5):779-789. doi: 10.1111/jnc.15829. Epub 2023 May 14. PMID: 37084159.
5. Patrick RP, Ames BN. Vitamin D and the omega-3 fatty acids control serotonin synthesis and action, part 2: relevance for ADHD, bipolar disorder, schizophrenia, and impulsive behavior. FASEB J. 2015 Jun;29(6):2207-22. doi: 10.1096/fj.14-268342. Epub 2015 Feb 24. PMID: 25713056.
