Vitamin D: can you have too much of a good thing in chronic kidney disease?

Recommendation of vitamin D supplements is common although there is little information regarding the definition of the upper limit of safety. Kusunoki et al. now publish interesting data of a novel mechanism by which excess 25-hydroxyvitamin D exerts adverse effects on the kidney, using unilateral ureteral obstruction in the mouse as a model of kidney disease. Their report provides a new mechanism to be assessed as a surrogate measure of vitamin D toxicity that may be clinically relevant.