cohort_flow_chart a Searched for all records in: Web of Science For any record that contains in title, abstract or keywords the term: vitamin D AND contains in title or abstract, or keywords one or more of the terms: covid, coronavirus, COVID-19, SARS-CoV-2, 2019-nCoV, HCoV-19, hCoV-19. Total records retrieved N =1095 b Removed records that met one or more the following conditions: same corresponding author, no email. Total records removed N = 210 a->b c Included records: N = 888 a->c d Identified the corresponding author, and retrieved their emails when available: N = 888 c->d e Currently invited authors: N = 888 d->e f Undelivered emails: N = 23 e->f g Net number invited authors: N = 865 e->g