Vitamin D halved the return of positional vertigo over two years in 160 deficient patients

Positional vertigo is one of the few conditions in medicine with a cure that works in minutes. A clinician tips the head through a sequence of positions, the loose crystals in the inner ear are guided back where they belong, and the spinning stops. Patients describe it as miraculous, which is fair.

The problem is that it comes back. Roughly half of people have another episode within a couple of years, and the manoeuvre has to be repeated. A trial in Baghdad, published in the Annals of Otology Rhinology and Laryngology, tested whether treating one common deficiency changes that. Over two years the recurrence rate halved.

What positional vertigo is and why it returns

Inside the inner ear are tiny crystals of calcium carbonate that sit on a membrane and help the brain sense gravity. When some break loose and drift into one of the fluid-filled canals that sense rotation, ordinary head movements start producing violent, short-lived spinning.

MedlinePlus describes vertigo as the feeling that you or your surroundings are moving when they are not, and notes that dizziness is one of the more common reasons adults see a doctor.

The repositioning treatment moves the crystals back. It does not address whatever let them come loose, which is why recurrence is the rule rather than the exception, and why a preventive treatment would be valuable.

Why vitamin D was the thing to test

The crystals are made of calcium carbonate, and calcium handling in the body runs through vitamin D. If deficiency makes the crystals more fragile or their reabsorption less efficient, then correcting it might reduce how often they come loose.

That is a plausible chain rather than a demonstrated one, and observational work had already found more deficiency among people with recurrent episodes. What was missing was a trial.

How the vertigo trial was run

This was a prospective, randomized, double-blind, placebo-controlled trial at two tertiary otolaryngology centers in Baghdad, and its most useful feature is the entry criterion.

Participants were 160 adults with confirmed idiopathic benign paroxysmal positional vertigo and serum 25-hydroxyvitamin D below 20 ng/mL, which is the conventional threshold for deficiency. They were randomized to receive 10,000 units of cholecalciferol weekly or matched placebo for 24 months.

Testing a nutrient only in people short of it is the design most vitamin trials should use and often do not. A supplement cannot correct a deficiency that is not there, which is why so many vitamin D trials in well-nourished populations return nothing.

What happened to recurrence over two years

The gap opened early and stayed open. Recurrence was significantly reduced with cholecalciferol versus placebo at every check, and by 24 months the figures were 27.5% on the supplement against 55.0% on placebo.

That is a halving, and the trial reports a number needed to treat of 3.6. For roughly every four deficient patients treated for two years, one avoided an episode they would otherwise have had, which is an unusually good number for a preventive measure.

Safety was straightforward: no hypercalcemic episodes occurred, and adherence exceeded 94% in both groups, which is high for a two-year trial and suggests the weekly dosing schedule suited people.

What a 160-person trial in one city cannot settle

The sample is modest for a trial with this much riding on it, and it comes from two hospitals in a single city. Vitamin D deficiency is common in Baghdad, and populations differ in both baseline levels and sun exposure, so the size of the benefit elsewhere is unknown.

The result also applies only to deficient patients. Anyone with a normal vitamin D level was excluded by design, and nothing here suggests that topping up an adequate level does anything at all.

And a single trial, however clean, is a single trial. The effect reported here is large, and large effects from small trials have a well-documented habit of shrinking when bigger ones are run.

What to take from the vitamin D and vertigo result

The actionable question is about testing rather than supplementing. If you have had positional vertigo more than once, whether your vitamin D level has ever been measured is a reasonable thing to ask, and this trial is a reasonable thing to mention.

What it does not license is self-prescribing a high-dose supplement for dizziness. Vertigo has several causes with quite different treatments, the trial enrolled only people with a confirmed diagnosis and a measured deficiency, and 10,000 units a week is a treatment dose rather than a nutritional one. The lesson worth keeping is the study design: this is what a vitamin trial looks like when it tests the people who might actually benefit.