While a randomized controlled trial of vitamin D3 supplementation in COVID-19 patients didn’t yield a significant reduction in monthly related health care use or disease severity, the authors say its role in reducing persistent symptoms warrants further study.
Mass General Brigham (MGB) researchers led the parallel two-group trial in adults in the United States and Mongolia, publishing the findings last week in The Journal of Nutrition. The US trial was conducted from December 2020 to September 2022, and the Mongolia trial ran from September 2021 to April 2022.
Inconsistent findings from previous studies
A total of 1,747 index patients with a new COVID-19 diagnosis were cluster-randomized with 277 household contacts to receive either oral vitamin D3 (loading dose of 9,600 international units per day [IU/d] for two days, followed by 3,200 IU/d for a month) or a placebo.
Participants completed weekly questionnaires on health care use (hospitalization, emergency department visits, and in-person or virtual clinic visits), symptom severity, long-COVID symptoms (index patients), and any new household-contact infections. The primary outcome was at least one health care visit (including hospitalization) or death within a month among index patients.
The median age of index patients was 38.0 years, 65.6% were women, 4.2% were Black, 4.8% were Hispanic, 43.2% were Asian, 44.3% were White, and 44.9% had vitamin D deficiency or insufficiency (less than 20 nanograms per milliliter). The characteristics of the household contacts were comparable.
“Though some small trials primarily done among highly-exposed healthcare workers or hospitalized patients have suggested prophylactic [preventive] or treatment benefits, concerns have been raised about randomization balance, and several larger trials have had null results,” the authors wrote. “Meta-analyses of randomized controlled trials (RCTs) have produced unclear findings, with some, but not all, suggesting clinical benefit from vitamin D.”
No reduction in household-contact infections
The median time between a positive COVID-19 test and the start of vitamin D3 supplementation or placebo was three days. The monthly cumulative incidence of health care use in index patients didn’t differ significantly between the 863 vitamin D3 and 884 placebo recipients (cumulative incidence, 0.28 vs 0.29, respectively; odds ratio [OR], 0.97). Likewise, supplementation didn’t lower the household-contact infection rate.
