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What is vitamin D? | UV and vitamin D | Vitamin D deficiency
What is vitamin D?
The sun's UV radiation is both the main cause of skin cancer and the best natural source of vitamin D.
Vitamin D is a hormone that controls calcium levels in the blood. It is needed for strong bones, muscles and overall health.
You can get a small amount of vitamin D from food, around 5–10%. Your body can usually store vitamin D for between 30 and 60 days.
UV and vitamin D
Your vitamin D levels naturally fluctuate across the seasons. It's important to be physically active and spend some time outdoors.
- In summer, spring and autumn in Victoria, when UV levels are typically 3 and above, only a few minutes of sun exposure is required to help maintain healthy vitamin D levels. Most people won’t be at risk of low vitamin D using sun protection when the UV is 3 or higher.
- In winter, when UV levels are low (typically from May to mid-August in Victoria), it is more difficult to get the recommended UV exposure so vitamin D levels are typically lower at this time. We recommend getting active outdoors in the middle of the day with some skin exposed to help vitamin D production.
Spending longer in the sun will not increase your vitamin D levels. The body only needs a small amount of UV to make vitamin D. Any extra UV exposure will just add to skin damage, not vitamin D. You can’t naturally overdose on vitamin D.
Vitamin D deficiency
Low vitamin D levels and vitamin D deficiency are very different. Vitamin D deficiency occurs when vitamin D levels are extremely low. Vitamin D deficiency is not common. Some people are at greater risk of vitamin D deficiency including:
- People with naturally very dark skin. This is because the pigment (melanin) in dark skin doesn't allow the skin to absorb as much UV radiation.
- People who avoid the sun due to previous skin cancers, immune suppression or sensitive skin and those who have limited sun exposure, such as nightshift workers.
- People who usually wear covering clothing.
- People who spend a long time indoors, such as those who are housebound or in hospital.
- People who are obese or have disabilities, diseases or medications that affect vitamin D metabolism, including, end stage liver disease, renal disease and fat malabsorption syndromes such as cystic fibrosis, coeliac disease, inflammatory bowel disease.
- Breast-fed babies of vitamin D deficient mothers (formula milk is fortified with vitamin D).
People who may be at risk of vitamin D deficiency should talk to their doctor for advice, which may include supplementation. Deliberate over-exposure to UV radiation is never recommended, even for people who have a vitamin D deficiency.