Vitamin D Calculator

Vitamin D is synthesised in skin on exposure to UVB radiation (sunlight wavelength 280–315 nm). In the UK, sufficient UVB is only available from April to September (10am–3pm). During winter months (October–March), the sun is too low in the sky to provide adequate UVB at UK latitudes, so supplementation is recommended for most people.

1. 1Melanin in skin absorbs UVB — darker skin requires more sun exposure
2. 2Fair skin: 10–15 min/day (summer) provides adequate vitamin D
3. 3Dark skin: 40–60 min/day (summer) required
4. 4NHS recommends 10 mcg (400 IU)/day supplement for everyone October–March
5. 5Vitamin D3 (cholecalciferol) is more effective than D2 (ergocalciferol)