What is vitamin D?

Vitamin D is a fat-soluble vitamin that is very important for bone health. It helps your body to absorb calcium from food. It also regulates the amount of calcium in your blood and strengthens your skeleton.

Vitamin D comes in 2 forms: vitamin D2 (ergocalciferol) and vitamin D3 (cholecalciferol). Vitamin D2 is from plant sources. It is found in fortified food and some supplements. Vitamin D3 is produced by sunlight on the skin. It is also found in some animal foods and supplements.

Vitamin D needs to be activated and turned into a hormone to work effectively. This is done by the liver and kidneys.

Why is vitamin D important for my health?

The most important role of vitamin D is regulating the absorption of calcium from the foods we eat. It also helps with hormone function and nervous system regulation. Vitamin D is vital for bone development and strength, cell growth and maintaining a healthy immune system.

What are the natural sources of vitamin D?

The main source of vitamin D comes from the skin being exposed to ultraviolet (UV) radiation from the sun. While vitamin D is found in some food, it is in small amounts. Australians tend to meet their vitamin D needs from the sun, mostly in the form of UVB rays.

The Australian government publishes recommended dietary intakes (RDIs) for all vitamins. Babies, children, teenagers and adults aged 19–50 years should have 5μg (micrograms) of vitamin D per day. Adults aged 51-70 years should have 10μg of vitamin D per day. Adults aged over 70 years should have 15μg of vitamin D per day.

During the summer months, you only need to spend a few minutes mid-morning or mid-afternoon outdoors (when the UV index is 3 or more) to get enough vitamin D. But make sure to wear sunscreen and a hat since UV radiation causes skin cancer.

In the autumn and winter when the UV index is lower than 3, you should aim to do outdoor activities in the middle of the day. Some skin needs to be uncovered (for example, your arms and face) to get your dose of vitamin D.

See the sunshine map to see how much sun exposure you need where you are in Australia.

You may also need to eat food that is relatively high in vitamin D to boost your intake, especially in the winter. Vitamin D2 can be found in mushrooms. Vitamin D3 is mainly from animal sources such as liver, tuna and salmon. Egg yolks are also an excellent source of D3. You will get around 10 per cent of your daily needs in each egg.

You can also find food that is fortified with added vitamin D, including some milk, soy drinks, margarines, breads or cereals.

Read more here on sources of vitamin D.

Should I take vitamin supplements?

It is very difficult to get enough vitamin D from your diet alone. The easiest way to increase your intake of vitamin D is through careful sun exposure. To get enough vitamin D from the sun without risking sun cancer, you need to consider your skin type, where you live, the time of year and the time of day.

People who spend lots of time indoors, those who cover their skin, and those who live in Australia’s southern regions, may find it more difficult to get enough sun exposure. If you are concerned that you may be vitamin D deficient, you can ask your doctor for a simple blood test to check.

If your blood test shows you are low in vitamin D, your doctor may recommend a supplement.

Can taking vitamin D supplements cause side effects?

Taking too much of any medicine or supplement has risks. For this reason, only people with a vitamin D deficiency should have vitamin D supplements. If you are at a high risk of deficiency, for example, because of your lifestyle, your doctor will organise a blood test for you.

Before taking any vitamin supplement, speak with your doctor or an accredited dietician. While vitamins can supplement your diet, they should not be used as a replacement for a healthy lifestyle.

Can I take too much vitamin D?

While there is no negative effect of excess vitamin D from the sun, extended exposure to harmful UV radiation does dramatically increase your risk of skin cancer. Wearing a hat and sunscreen will not put you at risk of vitamin D deficiency.

High doses of vitamin D supplements over time can cause vitamin D toxicity. A condition called hypercalcaemia (where there is too much calcium in your blood) is the most common result of taking too much vitamin D. Signs of this condition include nausea, dehydration and constipation.

If you are concerned that you have taken too much of a vitamin D supplement, call the Poisons Information Centre (13 11 26) immediately.