FGF23 and vitamin D deficiency: There are various causes of osteomalacia, such as hypophosphatemia due to excess production of fibroblast growth factor 23 (FGF 23), vitamin D deficiency and resistance, renal tubular acidosis, tumors, hypophosphatasia, or mineralization inhibitors.[1–8] Osteomalacia, especially vitamin D-deficient osteomalacia, is rarely observed in midlife, at least in Japan, although it is common in certain countries, particularly in southern Asia and Europe.