Most people with low vitamin D showed no biochemical sign of osteomalacia

Design

Cross-sectional analysis followed by randomised placebo-controlled trial

Population

423 Norwegian adults with low 25-hydroxyvitamin D (mean 34 nmol/L); 382 randomised

Primary outcome

Prevalence of biochemical patterns compatible with osteomalacia

Effect

0% with full pattern; 8.3% with most permissive pattern

Vitamin D deficiency thresholds are largely set to prevent osteomalacia. This Norwegian study, drawn from the population-based Tromsø cohort, looked at 423 people with low vitamin D (mean 25-hydroxyvitamin D 34 nmol/L) and asked how many had a biochemical pattern that could suggest osteomalacia: raised PTH, raised alkaline phosphatase and low calcium. It then randomised 382 of them to high-dose vitamin D or placebo for four months.

None had all three abnormalities together. Under the most permissive definition, 8.3% had a compatible pattern, and the figure depended heavily on the cut-offs chosen. Vitamin D supplementation did lower PTH and alkaline phosphatase and raise calcium compared with placebo, showing a biochemical effect.

For primary care, where vitamin D is tested and prescribed on a huge scale — including in India — this is a useful counterweight. A low level on its own rarely means bone disease. The study was not validated against bone biopsy, so it cannot set a new threshold, but it supports treating people rather than numbers.

• Do not assume a low vitamin D level alone means osteomalacia; check calcium, phosphate, alkaline phosphatase and PTH if bone disease is suspected.
• Look for clinical features — bone pain, proximal weakness, fractures, pseudofractures — before labelling osteomalacia.
• Avoid routine vitamin D testing in well people without risk factors.
• Supplement people at genuine risk: housebound, covered clothing, malabsorption, pregnancy, or low dietary intake.
• Remember supplementation lowers PTH and alkaline phosphatase, so recheck these if you are treating suspected osteomalacia.

Why it matters

It challenges the reflex that every low vitamin D result is a disease needing treatment.

Don't overread it

Biochemical patterns were not validated against bone biopsy, so this cannot define a new deficiency threshold.

The statistics, in plain English

The 8.3% figure comes from the loosest definition; stricter definitions gave zero. Because no one had a bone biopsy, these biochemical patterns are only proxies, so the true prevalence of osteomalacia is unknown. The randomised part shows vitamin D changed blood markers, not that it improved bones or symptoms.

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