Vitamin D is a hormone made in our bodies in the presence of sunlight. It is also found in small amounts in foods. Vitamin D is essential for bone and muscle health, and supports a healthy immune system. During winter, and ideally all year around, children from one year old and adults in the UK should take a daily supplement containing at least 400 international units (IU) of Vitamin D. This is equivalent to 10 micrograms (μg). This is because there is not enough sunlight in the UK during winter (October to March) for the body to make its own Vitamin D. Find out more about Vitamin D.