I had had severe fatigue for a long time, and the endocrinologist (my 3rd one) checked me for everything she could think of, and tests came back showing very low Vitamin D
. I guess it made sense -- I seldom spend time outside, and
we live in a cold and
rainy climate, so where would I get the sunshine needed to make Vitamin D myself? The dr. said my 'reservoir' of D was empty, and taking just a regular daily dose would never let me catch up to where I should be, so she prescribed the big dose.