Vitamin D is essential for healthy bones. In the UK we get most of our vitamin D from sunlight exposure from around late March/early April to the end of September. Find out how to get enough without risking sun damage.
We need vitamin D to help the body absorb calcium and phosphate from our diet. These minerals are important for healthy bones, teeth and muscles.
A lack of vitamin D, known as vitamin D deficiency, can cause bones to become soft and weak, which can lead to bone deformities.
In children, for example, a lack of vitamin D can lead to rickets. In adults, it can lead to osteomalacia, which causes bone pain and tenderness.
Our body creates vitamin D from direct sunlight on our skin when we're outdoors. From about late March/early April to the end of September, most people should be able to get all the vitamin D we need from sunlight.
We also get some vitamin D from a small number of foods, including oily fish such as salmon, mackerel, herring and sardines, as well as red meat and eggs.
Vitamin D is also added to all infant formula milk, as well as some breakfast cereals, fat spreads and non-dairy milk alternatives.
The amounts added to these products can vary and may only be added in small amounts. Manufacturers must add vitamin D to infant formula milk by law.
Another source of vitamin D is dietary supplements.
Most people can make enough vitamin D from being out in the sun daily for short periods with their forearms, hands or lower legs uncovered and without sunscreen from late March or early April to the end of September, especially from 11am to 3pm.
It's not known exactly how much time is needed in the sun to make enough vitamin D to meet the body's requirements.
This is because there are a number of factors that can affect how vitamin D is made, such as your skin colour or how much skin you have exposed.
But you should be careful not to burn in the sun, so take care to cover up or protect your skin with sunscreen before your skin starts to turn red or burn.
People with dark skin, such as those of African, African-Caribbean or south Asian origin, will need to spend longer in the sun to produce the same amount of vitamin D as someone with lighter skin.
How long it takes for your skin to go red or burn varies from person to person. Cancer Research UK has tips to help you protect your skin in the sun.
Your body can't make vitamin D if you're sitting indoors by a sunny window because ultraviolet B (UVB) rays (the ones your body needs to make vitamin D) can't get through the glass.
The longer you stay in the sun, especially for prolonged periods without sun protection, the greater your risk of skin cancer.
If you plan to be out in the sun for long, cover up with suitable clothing, wrap-around sunglasses, seeking shade and applying at least SPF15 sunscreen.
In the UK, sunlight doesn't contain enough UVB radiation in winter (October to early March) for our skin to be able to make vitamin D.
During these months, we rely on getting our vitamin D from food sources (including fortified foods) and supplements.
Using sunbeds isn't a recommended way of making vitamin D.
Children aged under 6 months should be kept out of direct strong sunlight.
From March to October in the UK, children should:
Cover up with suitable clothing, including wearing a hat and wraparound sunglasses
Spend time in the shade (particularly from 11am to 3pm)
Wear at least SPF15 sunscreen
To ensure they get enough vitamin D, babies and children aged under 5 years should be given vitamin D supplements even if they do get out in the sun.
Some groups of the population are at greater risk of not getting enough vitamin D.
The Department of Health recommends that these people should take daily vitamin D supplements to make sure they get enough.
These groups are:
All babies from birth to 1 year old (including breastfed babies and formula-fed babies who have less than 500ml a day of infant formula)
All children aged 1 to 4 years old
People who aren't often exposed to the sun (for example, people who are frail or housebound, or are in an institution such as a care home, or if they usually wear clothes that cover up most of their skin when outdoors)
For the rest of the population, everyone over the age of 5 years (including pregnant and breastfeeding women) is advised to consider taking a daily supplement containing 10 micrograms (μg) of vitamin D.
But the majority of people aged 5 years and above will probably get enough vitamin D from sunlight in the summer (late March/early April to the end of September), so you might choose not to take a vitamin D supplement during these months.
You can get vitamin supplements containing vitamin D free of charge if you're pregnant or breastfeeding, or have a child under 4 years of age and qualify for the Healthy Start scheme.
You can also buy single vitamin supplements or vitamin drops containing vitamin D for babies and young children at most pharmacies and larger supermarkets.
Speak to your pharmacist, GP or health visitor if you're unsure whether you need to take a vitamin D supplement or don't know what supplements to take.
If you choose to take vitamin D supplements, 10μg a day will be enough for most people.
People who take supplements are advised not to take more than 100μg of vitamin D a day, as it could be harmful (100 micrograms is equal to 0.1 milligrams).
This applies to adults, including pregnant and breastfeeding women and the elderly, and children aged 11 to 17.
Children aged 1 to 10 shouldn't have more than 50μg a day. Babies under 12 months shouldn't have more than 25μg a day.
Some people have medical conditions that mean they may not be able to take as much vitamin D safely.
If in doubt, you should talk to your doctor. If your doctor has recommended you take a different amount of vitamin D, you should follow their advice.
The amount of vitamin D contained in supplements is sometimes expressed in international units (IU), where 40 IU is equal to 1 microgram (1µg) of vitamin D.
There's no risk of your body making too much vitamin D from sun exposure, but always remember to cover up or protect your skin before the time it takes you to start turning red or burn.