Magnesium is important for maximizing vitamin D function on different levels, including several steps in vitamin D metabolism which are dependent on magnesium as a co-factor, magnesium deficiency can decrease parathyroid hormone synthesis and secretion and also the number of available VDRs in target tissue, as well as magnesium deficiency is known to cause vitamin-D-resistant hypocalcemia, which can be corrected after magnesium replacement [68]. Here, PTH is linked to magnesium deficiency.