D3 is an unsung beneficial necessity so far as I am concerned. Finally the medical community is recognizing and measuring concentrations with labs. Sometimes you still have to ask for it and monitor it yourself. In poultry science the benefits are long recognized and well researched.
I went to an exclusive medical facility once for an executive physical.
The supervising doctor said I was the only person he ever tested, whose D3 was at the correct level.
I was taking 5,000 iu/day at the time. I take 7;000 iu daily now.