Anemia is a disorder caused by a reduction of the oxygen-carrying capacity of the blood. It causes pallor, weakness, breathlessness and fatigue. It has been shown that in patients with kidney disuse, each 10 ng/mL increase in serum levels of 25 (OH) D is associated with a 29% reduced risk of anemia, whereas each increase of 10 mg/dl of c-reactive protein (CRP) were associated with dramatically increased risk. There is every reason to believe that those without kidney disease would have the same benefit from higher levels of vitamin D. In my book, I discussed the profound association of higher vitamin D levels with lowered levels of CRP, an inflammatory chemical that is a strong promoter of heart disease. Vitamin D's ability to control CRP may also be the reason for the impressive, positive influence of vitamin D on anemia.
Let's get back in the sunlight (without burning, of course).
 Kendrick, J. et al. Report to the conference of the National Kidney Foundation, Spring Clinical Meetings. May 16, 2008