High‐Dose Monthly Vitamin D for Prevention of Acute Respiratory Infection in Older Long‐Term Care Residents: A Randomized Clinical Trial

Randomized clinical trial in older adults living in long-term care facilities in Colorado, United States. The active high-dose arm included 55 participants and the standard-dose comparison arm included 52 participants; mean age in the high-dose arm was about 80 years, and most participants were women and non-Hispanic White.

The active supplement was oral vitamin D3 100,000 IU once monthly for 12 months. The comparison arm received standard-dose supplementation monthly (reported as either placebo monthly or vitamin D3 12,000 IU monthly), with usual-care vitamin D intake also accounted for in the trial design.

Monthly high-dose vitamin D3 reduced acute respiratory infections but increased falls. In the high-dose versus standard-dose comparison, ARI events occurred in 17 (31%) versus 24 (46%) participants, with an incidence rate ratio of 0.60 (0.38-0.94; P=.02), and upper respiratory infections were also reduced, incidence rate ratio 0.52 (0.31-0.90; P=.02). Falls were more frequent with high-dose vitamin D3, incidence rate ratio 2.33 (1.49-3.63; P<.001), while fractures were not increased and no hypercalcemia or kidney stones were observed. Time to first ARI, lower respiratory infections, hospitalizations, and death were not significantly different.

The trial was small and conducted in a specific population of older long-term care residents in Colorado, which limits generalizability. Several secondary outcomes were null, and the increased falls signal raises safety concerns despite the respiratory infection benefit.