In short
- London blood-test data: median winter vitamin D is 45 nmol/L; hair follicles function best above 75.
- Vitamin D deficiency is linked to telogen effluvium, alopecia areata and androgenetic alopecia severity.
- 1,000–4,000 IU daily is safe for most adults; blood-monitor annually.
- Correction alone rarely regrows hair — but deficiency prevents other treatments from working.
London's latitude (51.5°N) means the sun is too low to produce vitamin D in skin from October to March. Combined with indoor lifestyles and higher rates of darker skin tones, London has one of Europe's higher rates of vitamin D insufficiency.
The hair follicle needs vitamin D
Hair follicle keratinocytes express vitamin D receptors. Deficiency is associated with telogen effluvium (diffuse shedding), worse alopecia areata outcomes, and blunted response to androgenetic alopecia treatment.
Testing and target
A private vitamin D test in London costs £30–£45; often included in a hair panel. Target above 75 nmol/L; ideally 100–125. Below 50 is deficient by NICE thresholds.
Dosing that works
For most Londoners: 1,000 IU daily maintenance, 4,000 IU daily correction for 8 weeks then retest. Take with the fattiest meal of the day for absorption. Vitamin D3 (cholecalciferol) is preferred over D2.
Correcting vitamin D won't regrow hair on its own — but without it, everything else works worse.
Frequently asked
Common questions
Should I take vitamin D year-round?+
In London, yes — even summer sun is insufficient for most adults with typical indoor lifestyles.
Can I overdose?+
Only at very high doses over long periods. Doses under 4,000 IU/day are considered safe without monitoring.
Does vitamin D interact with hair medications?+
No known interactions with finasteride, minoxidil, spironolactone or dutasteride.
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