Vitamin D is a hormone that helps your body absorb calcium and is essential for the health of bones and muscles.
Most of the vitamin D you need is produced in the skin when it is exposed to sunlight. Small amounts are obtained from the diet.
Who’s at risk
You may have low vitamin D if you don't expose your skin to enough sunlight, or your body is unable to produce, absorb or obtain the vitamin D you need.
You may be at increased risk of low vitamin D if you:
- are confined indoors because of age, illness or disability
- have dark skin
- wear clothing that covers most of your body (for example, for religious or cultural reasons)
- avoid the sun because of concerns about skin cancer
- are obese
- have a condition that affects vitamin D absorption from your diet (for example, coeliac or Crohn's disease)
- take medicines (for example, for epilepsy) that interfere with vitamin D
- are a baby whose mother has low vitamin D.
Low vitamin D doesn't usually cause symptoms, although muscle aches, tiredness and weakness can occur. Some say it can leave sufferers feeling depressed or down.
Children with moderate-to-severe vitamin D deficiency are a risk of developing rickets (soft bones), but in Australia this is rare.
In older Australians, low vitamin D levels can lead to osteoporosis. Muscle weakness can increase the risk of falls that may cause bone fractures.
Studies have suggested possible links between vitamin D and a wide range of medical conditions, including diabetes and certain cancers. However, more research is needed before we know how much vitamin D deficiency may or may not influence these conditions.
Prevention and treatment
Most people can maintain healthy vitamin D levels through sensible sun exposure. This varies according to the time of day and across the seasons, your skin type and your location in Australia.
Natural food sources of vitamin D include oily fish, liver and eggs. In Australia, margarine and some milk products are fortified with vitamin D. However, if you are low in vitamin D, you won't correct it through diet alone.
Some people simply can’t get enough sun to maintain healthy vitamin D levels and will need a supplement.
Getting enough vitamin D is just one way to look after your bones and muscles - adequate calcium in your diet and regular exercise are also important.
If you're low in calcium, vitamin D has to work harder to maintain healthy bones. Dairy products, canned fish, tofu and some green vegetables are good calcium sources.
If you don't already have bone problems, weight-bearing exercises (such as jogging, tennis) and lifting weights can help prevent osteoporosis. Muscle-strengthening and balance exercises, such as tai chi, can help prevent falls and possible fractures.
When to contact a professional
If you're worried you might be at risk of low vitamin D, talk to your doctor or pharmacist. Blood tests aren’t usually recommended for low-risk individuals.
Tips for safe sun exposure and vitamin D
- During summer, most Sydney and Melbourne residents can get enough vitamin D by going for a short outdoor walk, mid-morning or mid-afternoon, with their arms exposed.
- During winter, two to three hours a week of sun is usually required.
- Dark-skinned people may need three to six times this exposure.
- Common sense is the key: to reduce the risk of skin cancer, avoid the sun, or use sun protection when the UV index is 3 or above.
- See the Osteoporosis Australia site for a map of recommended sun exposure for vitamin D, based on where you are in Australia, as well as the time of year.
This information provided by NPS MedicineWise, an independent, non-profit and evidence-based organisation funded by the federal government. For information about prescription, over-the-counter and complementary medicines, see nps.org.au.