Osteomalacia is defective mineralization of osteoid and can be caused by vitamin D deficiency. Because of the deficiency in vitamin D, there is decreased absorption of calcium in the gut leading to overall hypocalcemia. This hypocalcemia causes increased excretion of PTH, but since PTH uses vitamin D to mediate its effects the calcium deficit is not corrected. This results in overall decrease of Ca2+ with increase of PTH.
FA2020 p463 and p70