Bottom line: Hypomagnesemia may cause hypocalcemia through suppression of parathyroid hormone (PTH) release and inducing end-organ resistance to PTH.
Presence of magnesium acts as an inhibitor of PTH production, but the effect of magnesium is usually superseded by the level of calcium. If decrease in magnesium is greater than the change in calcium, increased hormone secretion would be expected. However, severe hypomagnesemia is associated with reduced secretion of PTH. This is because chronic hypomagnesemia can results in a deficiency in intracellular magnesium, which interferes with secretion and peripheral responses to PTH. The mechanism of the cellular abnormalities caused by hypomagnesemia is unknown, although effects on adenylate cyclase (for which magnesium is a cofactor) have been proposed.
For more information, see Hypocalcemia. In: Harrison’s Online [AccessMedicine]