[Vitamin D deficiency/insufficiency in patients with chronic kidney disease stage 3 and 4 -- current concept and its therapeutic strategy].

Vitamin D deficiency/insufficiency, which is clinically represented by low 25(OH)D concentration, is frequently seen in patients with CKD stage 3 and 4. Although its cause is unknown, hypovitaminosis D is partly associated with low 1,25(OH)2D in these patients, possibly leading to advancement of renal osteodystrophy. Recently, in United States, K/DOQI (Kidney disease outcomes quality initiative) guideline indicated that vitamin D deficiency/insufficiency of 25(OH)D concentration less than 30 ng/mL should be treated by supplementation of ergocalciferol. A Japanese guideline to treat vitamin D deficiency/insufficiency should be urgently established.