How is magnesium absorbed?

Updated: Aug 23, 2018
  • Author: Tibor Fulop, MD, PhD, FACP, FASN; Chief Editor: Vecihi Batuman, MD, FASN  more...
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Answer

Magnesium is absorbed principally in the small intestine, through a saturable transport system and via passive diffusion through bulk flow of water. Absorption of magnesium depends on the amount ingested. When the dietary content of magnesium is typical, approximately 30-40% is absorbed. Under conditions of low magnesium intake (ie, 1 mmol/d), approximately 80% is absorbed, while only 25% is absorbed when the intake is high (25 mmol/d).

The exact mechanism by which alterations in fractional magnesium absorption occur has yet to be determined. Presumably, only ionized magnesium is absorbed. Increased luminal phosphate or fat may precipitate magnesium and decrease its absorption.

In the gut, calcium and magnesium intakes influence each other's absorption; a high calcium intake may decrease magnesium absorption, and a low magnesium intake may increase calcium absorption. PTH appears to increase magnesium absorption. Glucocorticoids, which decrease the absorption of calcium, appear to increase the transport of magnesium. Vitamin D may increase magnesium absorption, but its role is controversial.


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