Vitamin D studies can be divided into three categories. (1) Treating Vitamin D deficiency – vitamin D deficiency is associated with huge number of problems, mo

Vitamin D studies can be divided into three categories. (1) Treating Vitamin D deficiency – vitamin D deficiency is associated with huge number of problems, more is discovered all the time. Deficiency can and can and should be corrected with supplements. Evidence is overwhelming. In many Nordic regions you can't get enough D from food+sun alone. Absorption efficiency decreases with age, elderly should take more. Deficiency is easy to check with a blood test. (2) Defining good level of vitamin D in blood serum – it seems that good level is slightly higher than previously thought, but evidence is still coming in. Taking little more (~2x recommended) is not harmful. (3) Taking extra amounts of vitamin D – numerous studies, little evidence or contradictory evidence.