Vitamin D and Eczema (Atopic Dermatitis)
Atopic dermatitis often flares in winter. Vitamin D deficiency correlates with severity in cross-sectional studies, and small RCTs of supplementation report significant improvement in SCORAD (Scoring Atopic Dermatitis) index — meaningful, though the effect size is modest and best-established in deficient patients.
Why winter matters
Two things happen in winter that hurt atopic skin: 25(OH)D falls (less UVB), and low indoor humidity strips barrier lipids. Vitamin D upregulates cathelicidin (LL-37), an antimicrobial peptide that keeps the skin barrier resistant to Staphylococcus aureus — a bacterium implicated in eczema flares. Low vitamin D → less cathelicidin → more staph colonisation → more flares.
RCT evidence
- Amestejani 2012 — 60 adults; cholecalciferol 1,600 IU/day for 60 days significantly improved SCORAD vs placebo (44% reduction vs 15%).
- Camargo 2014 (Mongolia) — 107 children with winter-related eczema; 1,000 IU/day for 1 month improved eczema area and severity index.
- Sidbury 2008 — small crossover in children; benefit signal in the deficient subgroup.
- 2016 meta-analysis (4 RCTs) — pooled significant SCORAD reduction favouring vitamin D.
Practical dosing
- Test 25(OH)D — most eczema patients with winter flares are deficient.
- Adults: 2,000 IU cholecalciferol/day for 2–3 months, then re-test and titrate.
- Children: 400–1,000 IU/day depending on age and baseline.
- Vitamin D does not replace daily emollients, low-potency topical steroids for flares, or dupilumab/JAK inhibitors for severe disease — it's an adjunct.
Phototherapy — the other side of the vitamin D story
Narrowband UVB (311 nm) is an established dermatology treatment for moderate-to-severe atopic dermatitis. It doesn't work primarily by raising vitamin D (though it does that too), but by directly modulating skin T-cells and reducing epidermal Langerhans cell counts. Home UVB units are second-line to office-based phototherapy.