Anyone can get vitamin D deficient, particularly in winter. However, the following groups have a higher risk of deficiency:

• People with darker skin types, such as those from African, Afro-Caribbean and South Asian backgrounds
• Those who get little, or no, sun exposure. For example, people who cover their skin at all times when outside or those who are not able to go outside easily.

The ultraviolet (UV) component of sunlight is the main source of vitamin D for most people in the UK. However, as well as being the primary source of vitamin D, UV radiation is a major cause of a skin cancer. As skin cancer is the most common type of cancer in the UK this complicates the question of how best to achieve healthy levels of vitamin D, often known as vitamin D sufficiency.

There are both environmental and individual factors that impact how long you should spend in the sun to achieve vitamin D sufficiency. These are the UV index on the day in question, and your skin colour, as well as any protective measures being taken, such as the use of sunscreen, shade, or protective clothing.

Usually the time it takes to achieve vitamin D sufficiency, particularly in people with light skin, is less than the time it takes to burn. Long exposures can have a negative impact on vitamin D production, and even cause vitamin D in the skin to break down, so should be avoided.

It is impossible to give precise guidance on how long it might take to produce sufficient vitamin D in your skin as this depends not only on the UV index and your skin colour but also on many other factors such as your posture (e.g. walking around or lying horizontal), how much of your skin is not covered by clothing, the degree of cloud cover and the influence of nearby shade such as buildings and trees.

What we can say is that for most people going about their day-to-day activities, their sun exposure is such that they can maintain reasonable levels of vitamin D, especially during the spring, summer and autumn, without the need to deliberately sunbathe.

In addition to sun exposure, small amounts of vitamin D can be obtained through your diet although the contribution of diet is insufficient to achieve healthy levels of vitamin D. Another option is vitamin D supplements, which is particularly useful for groups who might be at a higher risk of deficiency. The UK Government recommends 10 micrograms of vitamin D daily, and slightly less for babies younger than one. Most people will only need to take supplements in winter, whereas those in groups with a higher risk of deficiency should take these supplements all year round. In 2016, SACN reviewed the evidence on vitamin D and health to ensure UK dietary recommendations were up to date. Read the full report here.