Vitamin D and plasma magnesium in pregnancy

Abstract

Although there is a close relationship between many aspects of magnesium and calcium metabolism, the mechanisms involved in the control of plasma magnesium concentration are much less clearly understood than are those for calcium. Absorption from the gut and excretion by the kidney appear to be the major points at which magnesium homeostasis is controlled [l] and there is evidence that vitamin D and its metabolites are involved in these processes to some extent. Thus, in a recent balance study on patients with a variety of disorders of calcium and bone metabolism, administration of vitamin D or its hydroxylated metabolites significantly increased the net absorption of magnesium, though to a smaller extent than that of calcium [2]. Conversely, malabsorption of magnesium has been reported in osteomalacia and rickets [3]. In pregnancy, alterations in vitamin D metabolism have been observed [4]. In addition, some reports suggest that there is a small fall in plasma magnesium, although it may rise again in the last few weeks of gestation [5]. The opportunity to gain further information on the relationship, if any, between vitamin D and plasma magnesium during pregnancy arose during the course of a study on the effects of vitamin D supplementation in Asian women.