While the official RDA RDI for Vitamin D as of 2013 still stands at 600 IU - 800 IU per day for adults, 2,000 IU day are considered much more realistic with average sun exposure, and 4,000 IU day with limited sun exposure, or when pregnant. For bone loss prevention, serum levels of Vitamin D should be 75 nmol L or higher, while 100-125 nmol L are believed to be optimal for cancer prevention. Magnesium is required for Vitamin D to function properly and to normalize serum Vitamin D levels following adequate Vitamin D intake... Full Text