In brief
A vitamin your body makes when bare skin is exposed to the sun. It helps you absorb calcium for strong bones, and your muscles, nerves and immune system need it.
- People at higher risk of low vitamin D include those who stay indoors most of the time, people in care, people with naturally dark skin and those who cover most of their skin.
- A blood level of 50 nmol/L or more is sufficient for bone health, according to Pathology Tests Explained.
- Your doctor may recommend supplements if your level is low. In trials, vitamin D supplements did not prevent heart disease or ease depression.
How it works
You get vitamin D from sunlight on your skin and from foods such as oily fish, egg yolks, and fortified milks and margarines. The liver turns it into 25-hydroxyvitamin D, the form a blood test measures, and the kidneys convert that into calcitriol.
In Australia, you can usually get enough vitamin D from regular outdoor activities while following sun safety advice. When the UV Index is 3 or above, a few minutes outdoors on most days is usually enough. A long-term shortage causes rickets in children, bone pain and muscle weakness in adults, and fragile bones.
In Australia
Cancer Council Australia recommends sun protection when the UV index is 3 or above. When UV is 3 or above, a few minutes outdoors on most days is usually enough for vitamin D. In southern Australia in late autumn and winter, when UV is below 3, spend time outdoors in the middle of the day with some skin uncovered.
Myth check
The claim
Vitamin D supplements prevent heart disease and depression.
What the evidence says
In trials, vitamin D supplements did not prevent heart disease or ease depression, according to the US National Institutes of Health. Pathology Tests Explained lists 50 to 200 nmol/L as sufficient for bone health.
Food sources
- Oily fish such as salmon, tuna and mackerel
- Egg yolks
- Fortified milks and margarines
- Mushrooms
From the AskBioMap food guide:
Connections
8 connections on the map. Select a topic to read its page.
Vitamin D supports
- Immune system Supported
Your immune system needs vitamin D to fight off invading bacteria and viruses.
Source: NIH Office of Dietary Supplements, Vitamin D fact sheet for consumers
Vitamin D helps your body absorb calcium for strong bones, and your muscles need it to move.
Sources: NIH Office of Dietary Supplements, Vitamin D fact sheet for consumers; Pathology Tests Explained, Vitamin D
Vitamin D is linked with
Long-term vitamin D deficiency can cause loss of bone density and raise the risk of osteoporosis.
Sources: healthdirect Australia, Vitamin D deficiency; NIH Office of Dietary Supplements, Vitamin D fact sheet for consumers
- Muscle weakness and slow recovery Supported
Low vitamin D can cause bone pain and muscle weakness in adults.
Sources: NIH Office of Dietary Supplements, Vitamin D fact sheet for consumers; healthdirect Australia, Vitamin D deficiency
Vitamin D needs
The kidneys convert 25-hydroxyvitamin D into calcitriol.
Vitamin D is made by
Your body makes vitamin D when bare skin is exposed to the sun.
Sources: NIH Office of Dietary Supplements, Vitamin D fact sheet for consumers; Cancer Council Australia, Vitamin D
Vitamin D can be raised by
When the UV Index is 3 or above, most people keep enough vitamin D by spending a few minutes outdoors on most days.
Vitamin D is measured by
The test measures 25(OH)D, the form of vitamin D made in the liver.
Lab tests
Sources
Each connection above names its own source. See every source AskBioMap uses.
Summarised from healthdirect, the NIH Office of Dietary Supplements, Cancer Council and Pathology Tests Explained. Sources read on 13 and 19 October 2026. General education only, not medical advice. Spotted a mistake? Please tell us through the HuBu-Intel contact page.