Vitamin D is one of the most important vitamins for our health, with benefits including calcium regulation and maintaining strong bones.
But, known as the sunshine vitamin, many of us aren't getting enough of it in darker months, and some even need more of it throughout the whole year.
Here's what you need to know about vitamin D supplements, whether you should take them, and why.
Sources of vitamin D
We can get vitamin D from natural sources, including sunlight in the right months. It's also found in a small number of foods including:
oily fish (like salmon, sardines, herring and mackerel)
fortified foods – (like some fat spreads and breakfast cereals)
It's also important to note that cows' milk in the UK is generally not a great source of vitamin D because it's not fortified (containing extra vitamins), unlike how it is in some other countries.
Another source is supplements, for those who need it.
Why should I take vitamin D supplements?
If you're not getting enough vitamin D, this can lead to bone deformities like rickets (can cause bone pain, poor growth and weak bones) in children, and bone pain caused by the condition osteomalacia in adults, according to the NHS.
"Vitamin D is one of the most important vitamins for our health as it helps to regulate the amount of calcium and phosphate in the body. Vitamin D supports the brain and immune system and promotes healthy bones, teeth and muscles," explains dietitian Christina Jax, of leading healthy eating app Lifesum.
"Having sufficient levels of vitamin D may also protect against a range of chronic diseases, infections and conditions, including type 1 diabetes and heart disease. Vitamin D can also support weight management, reduce the risk of depression and improve lung function and cardiovascular health."
When should I take vitamin D supplements?
The government advises that everyone should consider taking a daily vitamin D supplement during the autumn and winter.
"When outdoors, the body creates vitamin D from direct sunlight on the skin. The majority of people make all the vitamin D they need from sunlight, typically between early April until late September," says Jax.
But, she adds, "People should consider taking a vitamin D supplement in autumn and winter, typically between October and March, as we don’t make enough vitamin D from sunlight alone, but always consult your doctor first."
So, while you should get enough sunlight in the warmer months, you need to lean more on diet in colder months, because the sun is not strong enough or the body to make vitamin D like it usually does, after soaking it up on your skin.
But, as it's hard to get the needed amount from food alone, the NHS advises that adults and children over four (including pregnant and breastfeeding women) should consider taking a supplement every day of 10 micrograms of vitamin D during autumn and winter.
And people at high risk of not getting enough vitamin D, which is all children aged one to four, and all babies (unless they're having more than 500ml of infant formula a day) should take a daily supplement throughout the year. Speak to your doctor about how much.
Who should take vitamin D supplements?
Not everyone's bodies will be able to make enough vitamin D naturally.
"Studies have also shown that certain groups have lower vitamin D levels than average and may not make enough vitamin D from sunlight, such as older people, the housebound, people from an African, African-Caribbean or south Asian background, those not often outdoors and those that cover up a lot of their skin when outdoors," explains Jax.
The Department of Health and Social Care also advises adults and children over four take a daily 10 microgram supplement throughout the year if they:
aren't outdoors much (they're frail, or housebound)
are in an institution like a care home
usually wear clothes that cover up most of their skin when outdoor
You can take vitamin D in the form of supplements or drops (for under fives), available at most pharmacies and supermarkets, but women and children who qualify for the Healthy Start scheme get free vitamin D supplements.
However, you want to be careful you don't take too much vitamin D, which can cause too much calcium to build up in the body (called hypercalcaemia). This can have the opposite effect of what you want to achieve and weaken bones and damage the kidneys and heart.
Always speak to your doctor before taking supplements to find out whether you need them, the right amount for you, and whether it's safe for you to take them.
The NHS website also states: "There have been some reports about vitamin D reducing the risk of coronavirus (COVID-19). But there is currently not enough evidence to support taking vitamin D solely to prevent or treat COVID-19."
Watch: Low vitamin D levels linked to inflammation