Vitamin D (calciferol) is the collective name for a group of fat-soluble compounds essential for human health, including vitamin D2 (ergocalciferol) and vitamin D3 (cholecalciferol, the active form synthesised in humans).

Vitamin D regulates mineral (calcium and phosphate) levels in the blood, and in doing so plays a crucial role in building and maintaining healthy bones. Having enough vitamin D in the body is also important for the body’s immune system, muscles and nerves to all function at their best.  

How does the body get vitamin D?

The major natural source of vitamin D is from the sun. When the skin is exposed to UV radiation from the sun, vitamin D is formed through a series of processes that start in the skin. In Australia it is important to balance the risk of skin cancer from too much sun exposure with maintaining vitamin D levels. According to the Cancer Council, most people need just a few minutes of sun exposure daily to get enough vitamin D when UV levels are above 3. When UV levels are below 3, sun protection is generally not required and going outside in the middle of the day for a walk, gardening etc is advised to support vitamin D production.  

Can we get vitamin D through food?

Very few foods contain vitamin D. Some of the best dietary sources of vitamin D are the following:

• Fatty fish such as salmon, herring, sardines and mackerel

• Cod liver oil  

• Eggs

• Mushrooms – can be a great source if sliced up and left in the sun for an hour, as through this process they will increase their vitamin D production and content.  

• Margarines fortified with vitamin D – this is mandatory in Australia.  

• Cow or plant-based milk and yoghurt fortified with vitamin D – not mandatory/optional in Australia, so check labels.

Who is at risk of vitamin D deficiency?

Because sunlight is the principal source of vitamin D for humans, those with lower sun exposure are at higher risk of vitamin D deficiency, for example people who are housebound or in residential care, people who wear concealing clothing for religious or cultural purposes, and people with naturally very dark skin (the melanin in dark skin affects UV penetration).  

Other groups at risk of low vitamin D for reasons other that minimal sun exposure include:

• People with conditions or surgeries associated with impaired gut absorption (e.g. bariatric surgery, coeliac disease, cystic fibrosis, Crohn’s disease and ulcerative colitis) or people with diseases affecting the liver and kidneys (affects vitamin D metabolism)

• People with reduced ability to synthesise enough D3 in the skin (adults aged 65 years or older and those living with obesity)

• People taking medications affecting vitamin D metabolism e.g. some anticonvulsants and glucocorticoids  

Vitamin D levels can be checked with a blood test, so consult your GP if you feel you may be at risk of deficiency. Eating more foods containing vitamin D is not enough to correct deficiency. If you are deficient, it is important to get advice from your GP or a dietitian about how to supplement with the appropriate dosage and form of vitamin D.