Vitamin D Fact Sheet https://www.healthline.com/nutrition/how-much-vitamin-d-to-take#How-Much-Vitamin-D-Should-You-Take?https://www.healthline.com/health-news/what-to-know-about-vitamin-d-and-covid-19https://ods.od.nih.gov/factsheets/VitaminD-Consumer/https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3356951/