Vitamin D
Vitamin D (Cholecalciferol)
Correlated with AGA in observational studies. No RCT yet shows that supplementation reverses or slows hair loss.
How Vitamin D works — and how well we know it
Vitamin D receptors are present on hair follicle keratinocytes, and vitamin D signaling appears to play a role in the hair growth cycle. Multiple correlational studies show lower serum 25-hydroxyvitamin D levels in patients with AGA and alopecia areata vs. controls — but causation has not been established by RCT.
oral
600–2,000 IU/day to maintain serum 25(OH)D > 30 ng/mL. Higher doses (5,000–10,000 IU/day) sometimes used to correct deficiency.
Available as a dietary supplement and prescription. RDA 600–800 IU/day; supplement marketing often uses 2,000–5,000 IU/day.
Patients with documented deficiency — common, given widespread sub-optimal levels. General health benefit even if hair benefit is uncertain.
Evidence distribution across 2 claims
Why the grade is D. Correlation between low vitamin D and AGA is consistent across multiple observational studies, but no RCT has demonstrated that supplementation improves AGA outcomes in deficient or non-deficient patients.
Every claim, traced back to its source
We took every major claim made about Vitamin D and matched it to the specific experimental model behind it. Click a claim to see the model, the finding, and our assessment of how much weight it deserves.
2 claims · evidence-by-evidence breakdown
1In VitroWeight: ModerateVitamin D receptors are required for normal hair cyclingVDR signaling matters for hair cycling — but that doesn't mean supplementing helps non-deficient adults.
VDR-knockout mouse models and in vitro studies of human follicle keratinocytes.
VDR-null mice develop alopecia. In vitro, VDR signaling affects keratinocyte proliferation and hair shaft formation.
The mechanism is real — VDR signaling matters for hair follicles. Whether vitamin D *supplementation* affects this signaling in adults with normal-range serum levels is a different question, and one the in vitro data cannot answer.
- Demay MB (2012). Endocrinol Metab Clin North Am PMID 22877429
2Open-LabelWeight: ModerateMultiple observational studies show lower serum vitamin D in AGA vs. controlsConsistent correlation across studies. Direction of causation is unclear.
Case-control studies comparing serum 25(OH)D in AGA patients vs. age-matched controls.
Banihashemi 2016 (n=80 women), Rasheed 2013 (n=80), and others consistently show lower mean 25(OH)D in AGA patients. Effect sizes are clinically meaningful (typically 5–15 ng/mL lower).
The correlation is consistent, but interpretation is hard. Lower vitamin D may cause AGA, AGA-related stress may lower vitamin D, or both may reflect a third factor (poor overall health, sedentary lifestyle). Without an RCT of supplementation, we can't distinguish.
- Banihashemi M et al. (2016). Indian J Dermatol PMID 27688438
- Rasheed H et al. (2013). Skin Pharmacol Physiol PMID 23428658
What's still missing from the science
- An RCT of vitamin D supplementation for AGA, ideally stratified by baseline 25(OH)D.
- Mendelian randomization studies to disentangle the causation question.
- Topical vitamin D analog (calcipotriol) trials for AGA — currently limited.
Our verdict on Vitamin D
Not in our formulary yet
We don't carry this ingredient. We only formulate around actives where the evidence — and the safety profile — is strong enough to recommend with confidence. As the data matures, we may revisit.
Related treatments
How does Vitamin D stack up against its closest peers?
A genuine cause of reversible hair shedding in iron-deficient patients — but useless and potentially harmful if your iron stores are normal.
Read the breakdown →A botanical 5-alpha reductase inhibitor whose only high-quality trials (in BPH) showed no benefit over placebo; the positive AGA data are small and low-quality.
Read the breakdown →One small Malaysian RCT showed a hair-count increase. Never replicated. Used by Nutrafol to justify its tocotrienol content.
Read the breakdown →