Vitamin D is essential for maintaining healthy bones, muscles, and a properly functioning immune system. In the UK, however, sunlight during the autumn and winter months is not strong enough to support adequate vitamin D production in the skin. This makes supplementation important to prevent deficiency and its associated health issues.
Dr Henrik Premasundaram, a GP and health screener, explains that while a balanced diet supplies most vitamins, vitamin D is largely obtained through sunlight exposure. “You simply can’t get enough vitamin D from diet alone because it relies primarily on sunlight to be produced by the body,” he says. He adds that vitamin D deficiency can cause tiredness and, in severe cases, affect mood.
Bridget Benelam, a nutrition scientist at the British Nutrition Foundation, confirms that sunlight triggers a chemical reaction in the skin necessary for vitamin D production. “From October to March in the UK, the sunlight isn’t strong enough, so the body relies on stores accumulated in summer and dietary sources,” she says.
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Low vitamin D levels often develop without obvious symptoms but, over time, can lead to bone pain, muscle weakness and a higher risk of falls, especially in older adults. In children, severe deficiency can cause rickets, while in adults it may lead to osteomalacia, characterised by soft, weak bones.
Research also suggests vitamin D supplements may have wider benefits. A 2023 study involving over 12,000 participants found that those taking supplements had 40% fewer dementia diagnoses compared to those who did not.
The amount of sunlight needed for sufficient vitamin D varies by skin type, age, clothing and weather conditions. Dr Premasundaram stresses that even on sunny days in inclement UK weather, skin exposure to UVB rays is often too low in autumn and winter. Exposure of just the face is insufficient, as a larger skin surface area is required to produce adequate vitamin D.
Dietary sources of vitamin D are limited but include oily fish such as salmon, mackerel and sardines, eggs, fortified cereals, fat spreads, and vitamin D-enriched mushrooms. For example, a 140g portion of baked salmon offers around 10 micrograms, the recommended daily intake.
Given these challenges, health experts advocate vitamin D supplementation, especially from October to March. The UK Government recommends everyone over five years take a daily 10 microgram vitamin D supplement during this period. Supplements are also advised for babies and young children, with doses varying by age and feeding method.
People with darker skin, those who cover up for cultural or religious reasons, and those who spend little time outdoors should consider taking vitamin D supplements throughout the year as they are at higher risk of deficiency.
Data from the National Diet and Nutrition Survey shows nearly 18% of adults in the UK are vitamin D deficient. Yet surveys by the British Nutrition Foundation reveal only around half of the population know about the recommendation for winter supplementation.
Dr Premasundaram notes that taking vitamin D supplements can also improve mood and energy levels. “I take vitamin D regularly, and I feel less tired,” he says, acknowledging that some benefits might be placebo but emphasising the positive impact on wellbeing.
Daily vitamin D supplements offer a simple, cost-effective way for people in the UK to maintain their health during months when sunlight is insufficient to meet their needs.