Many people are a deficiency of cholecalciferol , and understanding its function is essential for general health. This manual will cover everything you need to know about this very essential nutrient, https://www.amazon.com/Pure-Plant-Company-PurePlantD3-Organic/dp/B0H2K421Z9?maas=maas_adg_B9050C58E16D97E1F4C2B637FC967105_afap_abs&ref_=aa_maas&tag=maas&th=1