Vitamin D

What it is

A fat-soluble vitamin made in skin from sunlight and obtained from oily fish, egg yolk, fortified foods and supplements. The blood marker is 25-hydroxyvitamin D. Supplements come as D3 or D2; 40 IU equals 1 microgram.

How it works

The strongest hair-specific evidence is genetic. In children with hereditary vitamin D-resistant rickets, a rare disease of the vitamin D receptor, those whose receptor is absent or cannot bind DNA lose their hair, while those whose receptor merely binds the hormone poorly keep it. Hair cycling appears to depend on the receptor working even without the active hormone. That supports a role for the receptor, not that extra vitamin D boosts growth. Malloy 2011

What the studies show

• A meta-analysis of 23 studies (3,374 patients, 7,296 controls) found lower vitamin D in non-scarring alopecia (about -7.3 ng/mL) and higher odds of deficiency (OR 3.11), with very high heterogeneity. Chen 2024
• A meta-analysis by alopecia type found deficiency in about 47-54% of patients with alopecia areata, female and male pattern loss and telogen effluvium. Levels were significantly lower than controls only in alopecia areata and female pattern loss; for male pattern loss the deficiency odds were not significant. Yongpisarn 2024
• A 2026 meta-analysis of 29 studies found lower vitamin D (standardized mean difference -0.87) and ferritin in telogen effluvium, with high heterogeneity. Ahmed 2026
• In 90 women with chronic telogen effluvium versus 90 controls, vitamin D, ferritin and B12 did not differ, but zinc was lower. Durusu Turkoglu 2024
• A systematic review of supplements in people without known deficiency graded vitamin D3 trials as low-quality evidence for benefit. Drake 2023

These are association studies. Low vitamin D could be a cause, a consequence of indoor life, illness or obesity, or a bystander. No placebo-controlled hair trial in non-deficient adults turned up.

How it's used in studies

Hair-specific supplementation trials are few and small, mostly in alopecia areata or in combination products, so no hair dose is established. For safety context, the European Food Safety Authority upper limit for adults is 100 micrograms (4,000 IU) a day.

Side effects and safety

Excess raises blood calcium (nausea, kidney stones, kidney injury) and is rarely a problem below the upper limit. Dose to a measured level, not to a hair goal. High-dose prescriptions exist for deficiency.

Bottom line

Worth a blood test if you have unexplained shedding or live with little sun, and worth correcting a confirmed deficiency. With a normal level, extra vitamin D is not a proven hair treatment and does not replace minoxidil or a DHT blocker for pattern loss. Discuss with a doctor.

Fun facts

• A rare receptor mutation can cause total hair loss in infants even when blood vitamin D is high, because the follicle needs the receptor itself. Malloy 2011