Vitamin D helps regulate the amount of calcium and phosphate in the body.
These nutrients are needed to keep bones, teeth and muscles healthy.
A lack of vitamin D can lead to bone deformities such as rickets in children, and bone pain caused by a condition called osteomalacia in adults.
It's important to take vitamin D as you may have been indoors more than usual this year.
You should take 10 micrograms (400 IU) of vitamin D a day between October and early March to keep your bones and muscles healthy.
Good sources of vitamin D
From about late March/early April to the end of September, most people should be able to get all the vitamin D they need from sunlight.
The body creates vitamin D from direct sunlight on the skin when outdoors.
But between October and early March we do not get enough vitamin D from sunlight. Read more about vitamin D and sunlight.
Vitamin D is also found in a small number of foods.
- oily fish – such as salmon, sardines, herring and mackerel
- red meat
- egg yolks
- fortified foods – such as some fat spreads and breakfast cereals
Another source of vitamin D is dietary supplements.
In the UK, cows' milk is generally not a good source of vitamin D because it is not fortified, as it is in some other countries.