This article explains why Vitamin D matters, who is most at risk of deficiency, how Vitamin D status is assessed, and how supplementation should be approached safely.
Although Australia has abundant sunlight, deficiency remains common in people with limited sun exposure, darker skin pigmentation, malabsorption, certain medical conditions, or medication-related risk factors.
What Vitamin D Does:
Vitamin D is often described as a vitamin, but its active form – calcitriol – acts more like a hormone.
Vitamin D produced in the skin or obtained from food and supplements is converted first in the liver to 25-hydroxyvitamin D – the form measured in blood tests – and then mainly in the kidneys to calcitriol – the biologically active form.
Its best-established roles are supporting calcium and phosphorus absorption, helping maintain bone mineralisation, and contributing to normal muscle function.
Vitamin D also interacts with immune and inflammatory pathways, although the strength of evidence varies across different conditions.
Health Conditions Associated with Low Vitamin D:
Low Vitamin D is clearly linked with bone and muscle problems such as rickets, osteomalacia, osteoporosis risk, impaired mineralisation and muscle weakness.
Observational studies have also reported associations with immune dysfunction, diabetes, cardiovascular disease, mood disorders, liver disease, gum disease and some cancers; however, association does not always prove that low Vitamin D is the direct cause.
Some research has explored links between Vitamin D status and cognition, including dementia and Alzheimer’s disease.
These findings are best presented as an area of ongoing research rather than as proof that Vitamin D optimisation prevents or reverses neurodegenerative disease.
Autoimmune and inflammatory conditions, including alopecia areata, vitiligo, psoriasis, inflammatory bowel disease and autoimmune thyroiditis, have also been studied in relation to Vitamin D.
Vitamin D may influence immune regulation, but supplementation should be framed as a supportive strategy rather than a stand-alone treatment.
In children, low Vitamin D has been associated with increased risk of asthma exacerbations in some studies. This does not mean Vitamin D is a substitute for standard asthma care, but it supports identifying and correcting deficiency in at-risk children.
Multiple sclerosis, cancer outcomes, pregnancy, respiratory infections, statin-related muscle symptoms and thyroid function have all been discussed in the Vitamin D literature.
These topics should be described carefully: some findings are promising; others are observational, and some remain contested.
The most reliable message is that deficiency should be identified and corrected, while disease-specific treatment decisions should remain under appropriate medical care.
Sun Exposure and Deficiency Risk:
Sunlight remains the main natural source of Vitamin D, but advice needs to balance Vitamin D production with skin cancer risk.
In Australia, sun protection is generally recommended when the UV Index is 3 or above. People at high risk of skin cancer should not deliberately seek extended sun exposure for Vitamin D; supplementation may be safer.
People with deeply pigmented skin, covering clothing, indoor lifestyles, chronic illness or limited UV exposure may need personalised advice and – where appropriate – testing and supplementation.
Common Reasons for Vitamin D Deficiency:
- Limited skin exposure: People who spend little time outdoors, wear covering clothing, work indoors, are housebound, or avoid sunlight for medical or personal reasons are at increased risk.
- Older age: Ageing skin may produce Vitamin D less efficiently, and older adults may also spend less time outdoors.
- Individual variation: Genetics, body composition, baseline Vitamin D status and metabolism can influence how readily levels rise with sunlight or supplementation.
- Malabsorption or biliary disease: Conditions that impair fat absorption, including some gut, liver or bile-related disorders, can reduce absorption of fat-soluble nutrients such as Vitamin D.
- Dietary pattern and low intake: Diet alone usually provides only modest Vitamin D. People with very limited intake of Vitamin D-containing foods may require sunlight, fortified foods or supplementation depending on their risk profile.
- Deeply pigmented skin: People with darker skin generally require more UVB exposure to produce the same amount of Vitamin D as people with lighter skin.
- Disorders of the liver may impair Cholecalciferol conversion (termed hydroxylation). Patients with non-alcoholic fatty liver disease often have marked D deficiencies (Targher, G. et al: 2007).
- Medication-induced deficiency: taking Phenytoin Sodium (Dilantin) in long-term anti-convulsant therapy.
- Air pollution in large urban cities reduces solar UVB wavelengths of light from which Vitamin D is synthesised.
- Bathing/showering too soon after sunlight exposure can (in theory) wash away the D being produced ON the skin’s surface (Holick, MF et al: 1980). In their rat skin studies, Gaylor et al (1964) found sebum – natural skin oil produced by sebaceous glands – retained > 70% of 25(OH) D’s precursor: 7-dehydrocholesterol.
Whether these studies can be extrapolated to human subjects is yet unpublished or unproven.
- Topically applied sunscreens or blockers inhibit UVA/UVB and prevent Vitamin D synthesis in the skin. Sensible sunlight exposure on skin uncovered by sunscreens or clothing is necessary to obtain Vitamin D from sunlight.
- Inadequate or inappropriate dosing: Some people do not respond adequately to low-dose supplementation, while others may be harmed by excessive dosing. Dose decisions should be based on baseline levels, risk factors, adherence, medical history and follow-up testing.
Food, Cofactors and Testing:
Dietary sources include oily fish, egg yolk, UV-exposed mushrooms and fortified foods. Cod liver oil is not usually preferred solely for correcting deficiency because it may contain high amounts of Vitamin A.
For many Australians, especially during winter or when sun exposure is limited, diet alone may not maintain adequate Vitamin D status.
Nutrients such as magnesium, zinc and overall protein and mineral intake support broader bone and metabolic health. However, they should not be presented as guaranteed activators of Vitamin D in isolation; nutritional status should be considered as part of the whole clinical picture.
Vitamin D status is assessed with a blood test for 25-hydroxyvitamin D.
Current Australian guidance generally regards levels of 50 nmol/L or higher at the end of winter as adequate for bone and muscle health, while results below 50 nmol/L indicate deficiency
The current accepted range for Vitamin D is 50-375 nmol/L; most integrative practitioners recommend a minimum of 100 nmol/L for optimal metabolic functioning (and scalp follicle hair growth)
Routine testing of the general population is not recommended; rather testing is more appropriate for people with symptoms or risk factors: osteoporosis or osteomalacia risk, malabsorption, chronic kidney disease, deeply pigmented skin, chronic lack of sun exposure, low thyroid function, scalp hair thinning, or other recognised risk factors.
Supplementation and Safety:
Supplementation should be individualised; moderate daily or weekly dosing is generally preferred over unsupervised mega-dosing.
Follow-up testing is usually delayed until at least three months after starting or changing treatment. Higher doses may be appropriate in selected cases, such as malabsorption or severe deficiency, but should always be medically supervised.
People with kidney disease, hypercalcaemia, hyperparathyroidism, sarcoidosis or other granulomatous disease, metastatic bone disease, pregnancy, complex endocrine conditions, or potential medication interactions should seek medical advice before supplementing.
Symptoms, blood calcium, kidney function and the full clinical context matter as much as the Vitamin D number itself.
Cholecalciferol, or Vitamin D3, is commonly used and is effective for raising 25-hydroxyvitamin D. Ergocalciferol, or Vitamin D2, may be used in some products but may produce less sustained levels in some settings.
Product strength, formulation, dosing frequency and patient comprehension should be checked carefully, as dosing errors are a preventable cause of toxicity or treatment failure.
Practitioner Action Points:
• Use selective case-finding rather than population screening for Vitamin D deficiency.
• Measure serum 25-hydroxyvitamin D when the result will change clinical management.
• Interpret results alongside calcium-phosphate-PTH physiology, renal function, fracture risk, symptoms and ongoing risk factors.
• Correct deficiency but avoid presenting Vitamin D as a stand-alone therapy for complex inflammatory, endocrine, neurological or malignant disease.
• Prefer clear daily or weekly dosing plans, verify product strength, and retest no earlier than three months after treatment changes when monitoring is indicated.
• Balance sun exposure advice with skin cancer risk, especially in Australia, and individualise recommendations by skin type, UV Index, season, occupational exposure and cancer history.
Copyright Anthony Pearce 2009 (revised May 2026) and editorially updated for practitioner-facing clinical clarity, evidence framing and safety.
This article is intended for professional education and should be applied with clinical judgement, current local guidance and individual patient assessment.