A randomised trial gave cholecalciferol or placebo to vitamin D-deficient patients with recurrent benign paroxysmal positional vertigo, mean age 36.8 years, and followed them for two years.
Recurrence fell at every timepoint: 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 twenty-four. That is a halving of recurrence sustained across two years, with a number needed to treat of 3.6. Serum 25-hydroxyvitamin D rose as expected and no hypercalcaemic episodes occurred.
A number needed to treat under four, for a cheap and safe intervention, in a condition that recurs in half of untreated patients, is about as favourable an arithmetic as outpatient ENT offers.
The important boundary is who it applies to. This was a trial in patients who were vitamin D deficient and had recurrent disease. It is not evidence for supplementing everyone with positional vertigo, and it is not evidence for treating a first episode. The practical version is to measure vitamin D in the patient who keeps coming back, and to treat the deficiency if it is there — which in much of India it will be.
- Measure 25-hydroxyvitamin D in patients with recurrent BPPV, not in first presentations.
- Treat if deficient: recurrence roughly halved and stayed halved to two years.
- Number needed to treat was 3.6 — quote that, it is unusually favourable.
- This does not replace repositioning manoeuvres; it reduces how often you repeat them.
- No hypercalcaemia occurred, but this was a trial population with monitoring.
The statistics, in plain English
Number needed to treat is the number of patients you must treat for one to benefit, and 3.6 is very low — for comparison, most preventive treatments in medicine sit in the tens or hundreds. It is calculated from the absolute difference, here 55.0% against 27.5%, which is why absolute figures matter more than relative ones. Two caveats. This is a single trial, and single trials of cheap interventions with dramatic results are exactly the ones that shrink on replication. And the population was specifically vitamin D-deficient patients with recurrent disease, so the NNT applies to them: in a population with normal vitamin D, the expected benefit is not this and may be nothing.
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