Osteomalacia – a softening of the bones. In the absence of Vitamin D, the bones soften and swell. Osteomalacia is the softening of the bones caused by impaired bone metabolism primarily due to inadequate levels of available phosphate, calcium, and vitamin D, or because of resorption of calcium.

The impairment of bone metabolism causes inadequate bone mineralization.
The most common cause of osteomalacia is a deficiency of vitamin D, which is normally derived from sunlight exposure and, to a lesser extent, from the diet. The most specific screening test for vitamin D deficiency in otherwise healthy individuals is a serum 25(OH)D level.

Less common causes of osteomalacia can include hereditary deficiencies of vitamin D or phosphate (which would typically be identified in childhood) or malignancy.