Table 1

Characteristic of included randomised controlled trials

Study	Country	Severity of COVID-19	Intervention group	Control group	Definition of vitamin D deficiency	Follow-up
Bugarin 202325	Croatia	Severe COVID-19	10 000 IU of cholecalciferol daily during ICU stay	Standard care	<20 ng/mL	3 months
Bychinin 202221	Russia	Severe COVID-19	60 000 IU of cholecalciferol once every 7 days followed by daily maintenance doses of 5000 IU. The high dose is repeated on days 8, 16, 24 and 32.	Placebo	<20 ng/mL	During hospitalisation
Cervero 202222	Spain	NA	10 000 IU of cholecalciferol daily for 14 days	Standard care	<30 ng/mL	28 days
Dilokpattanamongkol 202424	Thailand	NA	2 mcg of alfacalcidol daily during the hospitalisation	Standard care	<20 ng/mL	During hospitalisation
Maghbooli 202115	Iran	NA	3000–6000 IU per day of vitamin D3 for 30 days	Placebo	<30 ng/mL	2 months
Murai 202116	Brazil	Moderate to severe COVID-19	Single dose of 200 000 IU of vitamin D3	Placebo	<20 ng/mL	4 months
Niet 202223	Belgium	NA	25 000 IU of vitamin D3 per day over four consecutive days, followed by 25 000 IU per week up to 6 weeks	Placebo	<20 ng/mL	9 weeks
Rastogi 202226	India	NA	Daily 60 000 IU of cholecalciferol for 7 days, and a weekly supplementation of 60 000 IU provided to those with 25(OH)D>50 ng/mL or else continued on daily vitamin D 60 000 IU supplementation for another 7 days up until day 14	Placebo	<20 ng/mL	3 weeks
Singh 202417	India	Severe	A single dose of 60 000 IU of cholecalciferol	Placebo	<10 ng/mL	During hospitalisation
Soliman 202227	Egypt	Moderate to severe COVID-19	200,000 units intramuscularly once as a single dose	placebo	<20 ng/mL	6 weeks

ICU, intensive care unit; IU, international unit; NA, not applicable.