Vitamin D is crucial for the body, as it helps to keep your bones, teeth and muscles healthy, according to the NHS.
Without enough vitamin D, it’s difficult to regulate the amount of calcium or phosphate in the body.
A severe lack of the vitamin may even lead to bone deformities, rickets, or osteomalacia.
You could lower your risk of a vitamin D deficiency by spending time in direct sunlight.
Everyone should spend between 20 and 30 minutes in the sun to avoid a deficiency, warned physician Dr Daniel Quemby.
But, during the winter months, people won’t be able to absorb enough ultraviolet light to produce vitamin D, he said.
So, people should consider taking a vitamin D supplement to prevent a deficiency from September to March.
“Vitamin D has been the big buzz word over the past 10 years, and I think 70 per cent of the world’s population doesn’t have enough vitamin D,” said Quemby.
“You tend to get it from green leafy vegetables, egg yolks, and sunlight.
“It makes it in your skin from direct sunlight, and people used to say ‘don’t go out in the midday sun’, but they’re now saying you should get at least half an hour, 20 minutes to half an hour of good sun.
“And you can’t do it this time of year, even though it’s the middle of the day, because the angle of the sun is not at the correct position to allow you to make the vitamin D.
“It has to be when the sun is at its zenith in the summer months. So you’re going to have to do it between April and August, but in October it’s negligible.”
Vitamin D isn’t just important for your bones, added Quemby. It’s also one of the most important vitamins for the immune system.
You could be at risk of a vitamin D deficiency if you have bone or back pain, if you feel constantly tired, or if you are frequently getting ill.
Other warning signs include hair loss, muscle pain, and having cuts or wounds that take longer to heal than normal.
But taking vitamin D supplements could help you to top up on the ‘sunshine’ vitamin, he added.
All adults are recommended to take a 10mcg vitamin D supplement during the winter months, said the NHS.
But, taking too much vitamin D can have an opposite effect, and may be harmful.
Don’t take more than 100mcg of vitamin D in a single day. 10mcg should be enough for most people, it said.
If supplements aren’t for you, try adding more oily fish, red meat, or egg yolks to your diet.