Benign paroxysmal positional vertigo recurs in roughly half of patients, and the usual response is to repeat the repositioning manoeuvre. This prospective, randomised, double-blind, placebo-controlled trial at two tertiary otolaryngology centres in Baghdad tested prevention instead, randomising 160 adults with confirmed idiopathic BPPV and serum 25-hydroxyvitamin D below 20 ng/mL to cholecalciferol 10,000 IU weekly or matched placebo for 24 months.
Supplementation raised vitamin D concentrations at every timepoint and reduced recurrence throughout: 15.0% against 35.0% at six months, 22.5% against 48.8% at twelve, 25.0% against 52.5% at eighteen, and 27.5% against 55.0% at 24 months — a 50% relative reduction with a number needed to treat of 3.6. No hypercalcaemic episodes occurred and adherence exceeded 94% in both groups.
A number needed to treat of 3.6 for a cheap, safe, oral supplement is unusual in any field. The population is the constraint and also the point: everyone enrolled was vitamin D deficient, so this says nothing about supplementing replete patients and should not be extrapolated to them. In settings where vitamin D deficiency is common — much of South Asia and the Middle East included — the practical implication is to measure 25-hydroxyvitamin D in patients with recurrent BPPV and to treat deficiency when found.
- Recurrence at 24 months 27.5% vs 55.0%; number needed to treat 3.6
- Benefit consistent at 6, 12, 18 and 24 months
- Only in patients with 25-hydroxyvitamin D below 20 ng/mL
- No hypercalcaemia; adherence above 94% in both arms
The statistics, in plain English
A number needed to treat of 3.6 means fewer than four patients must be supplemented to prevent one recurrence over two years — an unusually strong result that reflects both a large effect and a high baseline recurrence rate of 55%. Two cautions: this is a single trial at two centres in one country, and the separation appears early and widens, which is consistent with a real effect but would also be produced by any imbalance in baseline recurrence risk that randomisation happened not to correct in 160 patients.
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