💊 What it does
Vitamin D is essential for calcium absorption, bone mineralisation, immune function, and muscle strength. It also plays a role in mood regulation and has been linked to reduced risk of respiratory infections. Unlike most nutrients, the body manufactures vitamin D from sunlight — but only when UVB rays are strong enough, which in the UK means April to September at best.
👤 Who needs it
Anyone living in the UK or northern latitudes. People who work indoors, wear covering clothing, have darker skin, are over 65, or are housebound. The UK government recommends everyone consider a supplement from October to March. Vegans are at particular risk as few plant foods contain meaningful vitamin D.
🥦 Food sources first
Very few foods contain significant vitamin D. UV-exposed mushrooms (especially maitake and portobello left gill-side up in sunlight for 15–30 minutes) can provide useful amounts. Fortified plant milks and cereals contribute small amounts. For most people, food sources alone are insufficient — this is one nutrient where supplementation is genuinely evidence-based.
🗓 When to supplement
October to March is the minimum for UK residents. Year-round supplementation is sensible for anyone with limited sun exposure, darker skin, or who works indoors. A blood test (25-OH vitamin D) is the gold standard for knowing your status — levels below 50 nmol/L indicate insufficiency.
🏷 Best form to look for
D3 (cholecalciferol) is significantly more effective at raising blood levels than D2 (ergocalciferol). Most D3 is derived from lanolin (sheep's wool) — for a fully plant-based option, look for lichen-derived D3, now widely available.
⏰ When to take it
Take with a meal containing fat — vitamin D is fat-soluble and absorption drops significantly on an empty stomach. Morning or lunchtime works well for most people.