Vitamin D may help prevent benign paroxysmal positional vertigo (BPPV), which occurs when tiny crystals in the inner ear get dislodged. In a 2020 trial, researchers randomly assigned 1,050 people who had been treated for BPPV—with a simple maneuver that moves the crystals back into place—to either an intervention or an observation group. Of the 500 people in the intervention group, 348 had insufficient vitamin D levels (under 20 ng/mL) when they entered the study. Only they were given vitamin D (400 IU) and calcium carbonate (500 mg) twice a day.