As the days shorten and sunlight fades, many Britons experience a familiar winter slump. The cause, say experts, is low vitamin D, often called the sunshine vitamin. During autumn and winter, the UK sun is too weak for the skin to produce sufficient vitamin D, even on bright days, prompting health officials to recommend daily supplements.
Vitamin D is essential for calcium absorption and bone health. It helps regulate calcium and phosphate levels, preventing conditions such as osteomalacia in adults and rickets in children. Beyond bones, vitamin D influences muscle strength and may support the immune system, with some studies suggesting it reduces severity of respiratory infections like flu or COVID. However, evidence linking it to cardiovascular disease or mood regulation remains inconclusive.
Most vitamin D (80–90%) comes from sunlight, while diet provides only 10–20%. Good food sources include oily fish, red meat, egg yolks and fortified cereals. From late March to September, most people produce enough naturally, but from October to early March, supplementation is advised for everyone aged four and over.
The recommended dose is 10 micrograms (400 IU) daily for adults and children over four. Babies under one year who are breastfed or partly breastfed should receive 8.5–10 micrograms year-round, while formula-fed babies need supplements only if consuming less than 500ml of formula per day. Supplements up to 25 micrograms (1,000 IU) are considered safe.
Vitamin D comes in two forms: D₂ (ergocalciferol) and D₃ (cholecalciferol). Research indicates D₃ is more effective at raising and sustaining blood levels. People with darker skin tones—such as those of African, African-Caribbean or south Asian heritage—may need year-round supplementation due to reduced vitamin D synthesis from sunlight.
