- Vitamin D deficiency affects approximately 1 in 4 Australian adults, including people who spend time outdoors
- Sunscreen, indoor work, early-morning exercise, and darker skin tones all reduce vitamin D synthesis
- Blood levels are the only reliable way to assess your vitamin D status; symptoms alone are insufficient
- The laboratory "normal range" is set for bone health, not overall wellbeing; many researchers consider 75–100 nmol/L optimal
- Vitamin D supplementation should be guided by your actual blood level, not taken speculatively
Why do Australians have low vitamin D?
It seems counterintuitive. Australia has some of the highest UV radiation levels in the world. Yet data consistently shows that vitamin D insufficiency is widespread across the country, affecting people in every state, in every season, and across all age groups.[1]
The explanation lies in the gap between the UV we receive and the UV our skin actually converts to vitamin D.
Several factors work against adequate synthesis, even in sunny climates:
Indoor work and lifestyle. Most Australians spend the majority of their daylight hours indoors. Office workers, healthcare staff, and students may receive very little direct UV exposure during peak synthesis hours (approximately 10am–2pm).
Sunscreen and sun-protective clothing. Australia's public health messaging around skin cancer appropriately encourages high SPF sunscreen and sun-protective clothing. Both significantly reduce vitamin D synthesis. SPF 30 sunscreen reduces vitamin D production by approximately 95% when applied correctly.
Early-morning exercise. Many Australians who exercise outdoors do so before 8am, when UV radiation is insufficient for vitamin D synthesis. This is particularly common among runners, cyclists, and outdoor gym participants.
Skin tone. Melanin is a natural UV filter. People with darker skin tones require significantly more sun exposure to synthesise the same amount of vitamin D as those with lighter skin, a physiological reality that means some populations face a considerably higher deficiency risk in Australia's UV conditions.
Age. The skin's capacity to synthesise vitamin D decreases with age. People over 50 produce approximately 75% less vitamin D from the same UV exposure compared to younger adults.
What does vitamin D actually do?
Vitamin D functions more like a hormone than a vitamin; it regulates gene expression across dozens of body systems. Key roles include:
- Calcium absorption and bone mineralisation: the role most associated with vitamin D in clinical medicine
- Immune regulation: vitamin D receptors are present on virtually every immune cell; deficiency is associated with increased susceptibility to respiratory infections
- Muscle function: low vitamin D is associated with muscle weakness and reduced physical performance
- Mood regulation: low vitamin D is associated with low mood, though the relationship is complex and not fully understood
- Cardiovascular health: vitamin D receptors are present in heart muscle and blood vessel walls; observational research links deficiency with cardiovascular risk markers
It is important to note that while associations exist between vitamin D levels and these health areas, research is ongoing and having sufficient vitamin D does not guarantee protection from any particular condition.
What's the difference between "normal" and "optimal"?
This is one of the most important distinctions in interpreting vitamin D results.
Laboratory reference ranges for vitamin D (25-hydroxyvitamin D, or 25-OH vitamin D) are typically set at:
- Deficient: below 25–30 nmol/L
- Insufficient: 30–50 nmol/L
- Sufficient: above 50 nmol/L
These thresholds are primarily set to prevent rickets and osteomalacia, the severe bone diseases caused by profound deficiency. Many researchers and clinicians consider 75–100 nmol/L to be the range more broadly associated with wellbeing and immune function, though this remains an area of ongoing research.
What this means in practice: A result of 52 nmol/L is technically "sufficient" under laboratory reference ranges, but sits at the low end. Some research and clinical discussion suggests levels above 75 nmol/L may be associated with broader wellbeing benefits, though this remains an area of ongoing investigation and individual responses vary. The best guide for your situation is a conversation with your healthcare professional.
How is vitamin D measured?
Vitamin D status is measured via a simple blood test, specifically the 25-hydroxyvitamin D (25-OH vitamin D) marker. This form represents the body's total vitamin D stores and is the accepted clinical measure.
The test requires a standard venous blood draw. Results are reported in nmol/L (the standard in Australia).
Vitamin D is not measured in a standard full blood count (FBC) and must be specifically included in a blood panel.
If my level is low, what should I do?
If a blood test shows low vitamin D, the appropriate response depends on how low the level is and any underlying factors contributing to deficiency. Management options may include:
- Increased safe sun exposure during appropriate hours
- Dietary adjustments (fatty fish, egg yolks, and fortified foods contain vitamin D, though diet alone rarely corrects significant deficiency)
- Vitamin D supplementation at a dose guided by your blood level and healthcare professional
It is important to note that vitamin D is a fat-soluble vitamin, which means excess amounts accumulate in the body rather than being excreted. Taking high-dose supplements without knowing your level can lead to toxicity. Always consult a healthcare professional before starting vitamin D supplementation.
FAQ
Can I get enough vitamin D from diet alone?
Very few foods contain meaningful amounts of vitamin D. Fatty fish (salmon, sardines), egg yolks, and some fortified foods provide some, but dietary sources alone are generally insufficient to maintain adequate blood levels without sun exposure.
Does a vitamin D supplement need to be prescribed?
Low-dose vitamin D supplements are available over the counter in Australia. However, the appropriate dose depends on your current blood level, and higher-dose supplementation should be guided by a healthcare professional.
How often should vitamin D be tested?
If you have a known deficiency and are supplementing, retesting after 3 months is generally recommended to assess response. Otherwise, annual testing is sufficient for most people.
Is vitamin D testing included in a standard GP blood test?
Not automatically in Australia; it must be specifically requested. Vitamin D testing is included as standard in the Honed Health Essential Health Panel.
Can vitamin D deficiency cause fatigue?
Low vitamin D is associated with fatigue in observational research, though fatigue has many potential causes. A blood test can help identify whether low vitamin D is a contributing factor, but interpretation should involve a healthcare professional.
