Vitamin D (25-OH): what your result means.

Vitamin D (measured as 25-hydroxyvitamin D) functions as a hormone involved in bone health, muscle function and immune regulation. Despite Australia's sunshine, deficiency is common, driven by indoor work, sun avoidance and darker skin tones at southern latitudes.

Why Vitamin D (25-OH) matters

Low vitamin D is associated with reduced bone density, falls and fracture risk, and impaired muscle function. It is among the cheapest deficiencies to correct, and Endocrine Society thresholds give clear, evidence-based targets for repletion.

Associated risks when out of range: Immune dysfunction (low). Bone loss risk (low). Higher all-cause risk (low).

What the clinical evidence shows

The evidence base behind how the HodieLabs Evidence-Based Clinical Library interprets Vitamin D (25-OH), from randomised trials, prospective cohorts and genetic (Mendelian randomisation) studies. Full citations in the reference list below.

• VITAL trial (Manson et al. NEJM 2019): in ~25,000 unselected adults, vitamin D supplementation did not reduce cardiovascular events or cancer incidence, supplementing the already-replete adds little.
• D-Health trial (Neale et al. Lancet Diabetes & Endocrinology 2022): Australia's largest vitamin D trial (~21,000 adults) found no reduction in all-cause mortality from routine high-dose supplementation of a mostly vitamin D-sufficient population.
• VITAL fracture analysis (LeBoff et al. NEJM 2022): supplementation did not reduce fractures in generally healthy, largely replete midlife and older adults, reinforcing that the evidence supports correcting measured deficiency, not blanket dosing.
• Australian Health Survey (ABS 2011–13): roughly one in four Australian adults had vitamin D deficiency (<50 nmol/L), rising in winter and southern states. Deficiency is genuinely common, which is why measuring beats guessing.

Evidence-based reference ranges

The HodieLabs Evidence-Based Clinical Library interprets Vitamin D (25-OH) against published clinical authority standards, never arbitrary "optimal" ranges. Measured in nmol/L:

Clinical interpretation

• 25-OH vitamin D reflects total body stores. It is the correct form to test (not 1,25-OH).
• In Australia, deficiency is common in winter months, dark-skinned individuals, and those who avoid sun.
• Supplement with D3 (not D2) taken with a fat-containing meal for absorption; retest at 3 months.
• EVIDENCE CAVEAT: The Endocrine Society 2024 prevention guideline notes that in healthy adults, outcome-specific 25(OH)D thresholds have not been established in clinical trials. The Society suggests against routine testing and routine supplementation in generally healthy adults under 75 without specific indications. The 50–125 nmol/L range is the accepted sufficiency range, but should not be presented as a settled evidence-based "optimal" target for all healthy adults.

What improves it: the evidence-based levers

• Sunlight exposure optimisation
• Supplementation if low
• Recheck if correcting deficiency

Recommended testing frequency: Annual, as part of a comprehensive panel. Single markers are always interpreted in context.

How Vitamin D (25-OH) testing works at HodieLabs

Vitamin D (25-OH) is measured in every Health Blueprint at our Melbourne Preventative Health & Longevity Clinic, interpreted by a doctor against the guideline-cited ranges above and tracked over time through your HodieLabs membership.

References

1. Manson JE, et al. Vitamin D supplements and prevention of cancer and cardiovascular disease (VITAL). N Engl J Med. 2019;380:33–44.
2. Neale RE, et al. The D-Health Trial: a randomised controlled trial of the effect of vitamin D on mortality. Lancet Diabetes Endocrinol. 2022;10:120–128.
3. LeBoff MS, et al. Supplemental vitamin D and incident fractures in midlife and older adults. N Engl J Med. 2022;387:299–309.
4. Holick MF, et al. Evaluation, treatment, and prevention of vitamin D deficiency: an Endocrine Society clinical practice guideline. J Clin Endocrinol Metab. 2011;96:1911–1930.

This page is general information from the HodieLabs Evidence-Based Clinical Library, not medical advice. Speak with your GP about what testing and care is appropriate for you.