Vitamin D helps the body to regulate the amount of calcium and phosphate in the body, according to the NHS.
The nutrients help to keep bones and muscles healthy.
Sunlight is a great source of vitamin D, but during the winter months – when daylight hours are much shorter – some people could be at risk of a vitamin D deficiency.
You may be at risk of a deficiency if you suffer from back pain.
“Vitamin D deficiency affects bone health, and can result in a throbbing or achy feeling in your bones,” said Holland & Barrett.
“This is often most noticeable in the knees and back.
“People who don’t have enough of this important vitamin can develop rickets.
“Vitamin D also plays a role in osteoporosis, bone pain, and an increased risk of fractures.”
For many people, signs of a vitamin D deficiency are subtle, and are difficult to spot.
Other signs of a deficiency include extreme tiredness, frequent infections, hair loss and muscle pain.
If you think you may have a deficiency, you should see a GP and get your blood levels checked.
You can remedy your deficiency by being exposed to more sunlight, or by making simple dietary changes.
Oily fish and red meat are the best sources of vitamin D, according to the NHS.
Other great sources of the sunshine vitamin include liver, egg yolks and some breakfast cereals.
You could also boost your vitamin D intake by taking daily supplements.
The Department of Health recommends that adults take 10mcg supplements during the winter months.
You can buy the supplements at pharmacies or supermarkets.