PRevention of COVID-19 with Oral Vitamin D supplemental Therapy in Essential healthCare Teams (PROTECT): Ancillary study of a randomised controlled trial

Abstract Background The study objectives were to ascertain the efficacy of vitamin D supplementation in rapidly increasing serum vitamin D and of implementation of a hybrid (virtual and in-person) trial. Methods In a randomised triple-blind controlled trial, healthcare workers were allocated to receive an oral bolus of 100,000 IU with 10,000 IU/week vitamin D3 or placebo. The co-primary outcomes of this ancillary study were the change from baseline in serum 25-hydroxyvitamin D [(Δ) 25(OH)D] and proportion with vitamin D sufficiency (25(OH)D ≥ 75nmol/L), at endpoint. Adherence to supplements and procedures as well as adverse event rates were documented. Results Thirty-four (19 intervention, 15 control) subjects were randomised, with 28 (41%) virtual visits. After 44.78 ± 11.00 days from baseline, a significant adjusted group difference of 44.2 (34.7, 53.8) nmol/L was observed in the Δ 25(OH)D (95%CI) in favor of supplementation; 77.8% of intervention, and 13.3% of control, patients were vitamin D sufficient (OR:6.11, 95%CI:1.6, 22.9). The adherence to intervention was 94.7% in the intervention and 100% in the control groups. Irrespective of visit type, high adherence was observed in sampling procedures and completion of fortnightly online questionnaire. No adverse events attributable to vitamin D were reported. Conclusion The vitamin D supplementation rapidly and safely raised 25(OH)D levels to sufficient levels for a biological effect. Similarly high adherence to study procedures was observed with virtual and in-person participation. Trial registration: This trial was registered at https://clinicaltrials.gov on July 23, 2020 (#NCT04483635)