Vitamin D and Hair Growth
Vitamin D deficiency is strongly associated with hair loss, particularly in alopecia areata, and supplementation may be beneficial for patients with documented deficiency, though the evidence for routine supplementation in preventing hair loss remains limited.
The Biological Role of Vitamin D in Hair Follicles
Vitamin D plays a critical role in hair follicle cycling through the vitamin D receptor (VDR), which is essential for normal hair growth 1. The VDR is expressed in hair follicle keratinocytes with greatest activity during the anagen (growth) phase 1. Animal studies demonstrate that mice with VDR knockout mutations develop progressive hair loss, with nearly total alopecia by 8 months, establishing the receptor's fundamental importance independent of vitamin D levels themselves 1. In humans, mutations in the VDR gene cause vitamin D-dependent rickets type II, which characteristically presents with sparse body hair and often total scalp alopecia 1.
Evidence Linking Vitamin D Deficiency to Hair Loss
Alopecia Areata
Multiple case-control studies consistently demonstrate lower vitamin D levels in patients with alopecia areata compared to healthy controls 1:
- Egyptian study (2016): 83.3% of alopecia areata patients had vitamin D deficiency (<50 nmol/L) versus 23.3% of controls, with vitamin D levels inversely correlating with disease severity 1
- Turkish study (2014): 91% of alopecia areata patients were vitamin D deficient versus 33% of controls, with a significant inverse correlation between vitamin D levels and severity (SALT score: P < 0.001, r = −0.41) 1
- Israeli study (2014): 70% of alopecia areata patients had vitamin D deficiency (<20 ng/mL) versus 25% of controls, with multivariate analysis showing an odds ratio of 2.3 for vitamin D insufficiency (<30 ng/mL) 1, 2
- Italian study (2013): 42.4% of alopecia areata patients had vitamin D deficiency versus 29.5% of controls 1
A 2016 Indian study found that 96.7% of alopecia areata patients were vitamin D deficient compared to 73.3% of controls, with the lowest levels associated with alopecia totalis/universalis 3. VDR expression was reduced in all alopecia areata patients and inversely correlated with histological inflammation 4.
Androgenetic Alopecia
Evidence for androgenetic alopecia is emerging but less robust. A 2024 systematic review identified vitamin D deficiency as a potential modifiable risk factor for androgenetic alopecia, though the evidence is not entirely consistent 5. A 2021 review concluded that serum vitamin D might be a useful parameter for diagnosing onset and severity of androgenetic alopecia 6.
Critical Limitation: Causality Remains Unclear
The only prospective study to date found no association between vitamin D status and risk of developing alopecia areata 1. The Nurses' Health Study (55,929 women) found no difference in incident alopecia areata between highest versus lowest quartiles of vitamin D score, and no association with dietary, supplemental, or total vitamin D intake 1. This suggests that vitamin D deficiency may be a consequence rather than a cause of alopecia areata—potentially due to sun avoidance from psychosocial stress related to hair loss 1.
Treatment Evidence: Topical Vitamin D Analogs
Topical calcipotriol (0.005%) shows promise but lacks placebo-controlled trials 1:
- Narang et al. (2017): 59.1% of 22 patchy alopecia areata patients had hair regrowth with twice-daily application, with onset at 4.21 ± 2.13 weeks 1. Patients with lowest baseline vitamin D levels had greatest improvement 1.
- Turkish study (2015): 75% of 48 patients achieved ≥50% hair regrowth after 12 weeks 1
- Side effects: Skin irritation, pruritus, pigmentation, scaling, and folliculitis 1, 7
Important caveat: 34-80% of alopecia areata patients undergo spontaneous recovery without treatment, making interpretation of uncontrolled trials challenging 1.
Clinical Recommendations
When to Check Vitamin D Levels
Check serum 25(OH)D levels in patients with 8:
- Alopecia areata (particularly moderate to severe disease)
- Androgenetic alopecia with other signs of nutritional deficiency
- Chronic diffuse telogen effluvium
Supplementation Strategy
For documented vitamin D deficiency (<20 ng/mL or <50 nmol/L): Supplement to achieve normal levels, as deficiency inversely correlates with disease severity 1, 8. However, no double-blind trials have examined oral supplementation as a treatment strategy for alopecia areata 1.
For normal vitamin D levels: Routine supplementation is not supported by current evidence, as the prospective Nurses' Health Study found no preventive benefit 1.
Topical Calcipotriol
Consider topical 0.005% calcipotriol twice daily for patchy alopecia areata in patients with documented vitamin D deficiency, but warn about potential side effects including folliculitis 1, 7. Monitor for local irritation and discontinue if folliculitis develops 7.
Common Pitfalls to Avoid
- Do not assume causality: Lower vitamin D levels in hair loss patients may be consequence rather than cause 1
- Do not over-supplement: No evidence supports high-dose vitamin D for hair growth in patients with normal levels 1
- Do not rely solely on vitamin D: Address other potential deficiencies (iron, zinc) and consider standard treatments like intralesional corticosteroids for alopecia areata 8
- Do not ignore spontaneous remission: 34-50% of alopecia areata patients recover within one year without treatment 8