Unlike other vitamins, your body can actually make vitamin D on its own – all it needs is sunlight, which is why it's often called the "sunshine vitamin". But from October to March in the UK, there often isn't enough sun to go around, so a daily supplement helps keep your levels healthy through the darker months. Vitamin D contributes to the maintenance of normal bones and muscle function, and to the normal function of the immune system.
Vitamin D is a bit of an unusual one: it's more of a hormone than a vitamin, and your body makes it from sunlight rather than relying on food. Its main job is helping the body absorb calcium, which is why it matters so much for bones, teeth and muscles, and it also contributes to the normal function of the immune system. Because UK sunlight isn't strong enough over winter, the NHS suggests most people consider a daily supplement during the darker months – and some groups benefit from taking one year-round.
