Vitamin D Deficiency in Australia: Why One in Three Australians Are Low

Australia is renowned for its abundant sunshine, so it may come as a surprise that vitamin D deficiency is remarkably common across the country. Research published in the Medical Journal of Australia estimates that approximately one in three Australian adults have vitamin D levels below the recommended threshold during winter and spring. Understanding why this occurs — and what your blood test results mean — is essential for protecting your bones, immune system and long-term health.

What Is Vitamin D and Why Is It Important?

Vitamin D is a fat-soluble vitamin that functions more like a hormone in the body. It is essential for calcium absorption, bone mineralisation and immune regulation. Low vitamin D levels have been associated with an increased risk of osteoporosis, fractures, muscle weakness, autoimmune conditions and even cardiovascular disease. Emerging research also links vitamin D status to mood regulation and mental health.

Unlike most vitamins, dietary sources of vitamin D are limited. The primary source for most Australians is synthesis in the skin upon exposure to ultraviolet B (UVB) radiation from sunlight. Small amounts can be obtained from oily fish (such as salmon, sardines and mackerel), egg yolks, fortified margarine and some mushrooms exposed to UV light.

How Vitamin D Is Measured

Vitamin D status is assessed by measuring serum 25-hydroxyvitamin D [25(OH)D] in a blood test. This is the main circulating form of vitamin D and reflects both dietary intake and sun exposure. Australian guidelines classify vitamin D levels as follows:

Deficient: Less than 50 nmol/L — increased risk of bone disease and other health complications.

Sufficient: 50–75 nmol/L — adequate for most healthy individuals.

Optimal: 75–150 nmol/L — the range many experts consider ideal for broader health benefits.

Potentially harmful: Greater than 250 nmol/L — risk of toxicity, although this is extremely rare and almost exclusively caused by excessive supplementation rather than sun exposure.

Why Are So Many Australians Deficient?

Several factors converge to make vitamin D deficiency surprisingly prevalent in Australia:

Geography and season: While northern Australia receives strong UVB radiation year-round, southern cities such as Melbourne, Hobart and Adelaide experience significantly reduced UVB intensity during winter. From May to August, it can be difficult to produce adequate vitamin D from sun exposure alone in these regions, even with regular outdoor activity.

Sun-safe behaviours: Australians are rightly cautious about sun exposure due to the country’s high rates of skin cancer. The "Slip, Slop, Slap" public health campaign has been enormously successful in reducing melanoma rates, but it has also contributed to reduced vitamin D synthesis. Sunscreen with an SPF of 30 or higher blocks approximately 95–99% of UVB radiation.

Indoor lifestyles: Modern Australians spend the majority of their day indoors — commuting in cars, working in offices and relaxing at home. Even in sun-drenched cities like Brisbane and Perth, many people simply do not get enough incidental sun exposure to maintain adequate vitamin D levels.

Skin pigmentation: Australians with naturally darker skin require significantly more sun exposure to produce the same amount of vitamin D as those with lighter skin. Melanin acts as a natural sunscreen, reducing UVB penetration. This places Indigenous Australians and those of African, South Asian and Middle Eastern descent at higher risk of deficiency.

Age and body composition: Older Australians produce vitamin D less efficiently in their skin and may also spend less time outdoors. Additionally, vitamin D is sequestered in adipose tissue, meaning individuals with higher body fat percentages may have lower circulating levels despite adequate sun exposure.

Symptoms of Vitamin D Deficiency

Mild vitamin D deficiency may produce no obvious symptoms, which is why blood testing is so important. As levels drop further, common symptoms include:

• Fatigue and general tiredness

• Muscle weakness or aches

• Bone pain, particularly in the lower back, hips and legs

• Frequent infections or slow wound healing

• Low mood or depressive symptoms, especially during winter months

Severe, prolonged deficiency can lead to osteomalacia (softening of the bones) in adults and rickets in children, though these conditions are now uncommon in Australia thanks to awareness and supplementation.

How to Optimise Your Vitamin D Levels

Sensible sun exposure: The Cancer Council Australia recommends a balance between sun protection and vitamin D synthesis. In summer, a few minutes of mid-morning or mid-afternoon sun exposure on the arms and face most days of the week is generally sufficient. In winter, particularly in southern states, longer exposure of 15–30 minutes around midday may be needed. It is important not to burn — sunburn does not produce more vitamin D but does significantly increase skin cancer risk.

Supplementation: For those unable to achieve adequate levels through sun exposure alone — including shift workers, the elderly, those with dark skin and people living in southern Australia during winter — supplementation is safe and effective. The recommended dose for most adults with mild deficiency is 1,000–2,000 IU (25–50 µg) of vitamin D3 (cholecalciferol) daily. Higher doses may be prescribed by your doctor for more severe deficiency. Vitamin D3 is preferred over D2 (ergocalciferol) as it is more effective at raising and maintaining serum levels.

Dietary sources: While diet alone rarely provides sufficient vitamin D, including oily fish two to three times per week, eggs and fortified foods can contribute to your overall intake. Some Australian milk and plant-based milk alternatives are now fortified with vitamin D.

When to Get Tested

Current Australian guidelines do not recommend universal vitamin D screening for the general population. However, testing is recommended for individuals at high risk of deficiency, including those with osteoporosis or low bone density, dark skin, limited sun exposure, malabsorption conditions (such as coeliac disease or inflammatory bowel disease), chronic kidney or liver disease, and those taking medications that affect vitamin D metabolism.

If you have had a previous low result, retesting after three months of supplementation is advisable to ensure your levels have responded. At Yearly, our blood test tracking platform makes it easy to monitor your vitamin D levels over time, helping you and your healthcare provider adjust your supplementation strategy with confidence.

Key Takeaways

Vitamin D deficiency is common in Australia despite the country’s sunny climate. Geography, sun-safe behaviours, indoor lifestyles and skin pigmentation all play a role. Regular blood testing, sensible sun exposure and appropriate supplementation can help you maintain optimal levels and support your overall health.

References

1. Daly RM, Gagnon C, Lu ZX, et al. Prevalence of vitamin D deficiency and its determinants in Australian adults aged 25 years and older: a national, population-based study. Clin Endocrinol (Oxf). 2012;77(1):26–35.
2. Nowson CA, McGrath JJ, Ebeling PR, et al. Vitamin D and health in adults in Australia and New Zealand: a position statement. Med J Aust. 2012;196(11):686–687.
3. Cancer Council Australia. Position statement – sun exposure and vitamin D. Sydney: Cancer Council Australia; 2023.
4. Australian Bureau of Statistics. Australian Health Survey: Biomedical Results for Nutrients, 2011–12. Canberra: ABS; 2014.
5. Holick MF. Vitamin D deficiency. N Engl J Med. 2007;357(3):266–281.