Current opinion on the regulation of small intestinal magnesium absorption.

Magnesium (Mg2+) has an important role in numerous biological functions, and Mg2+ deficiency is associated with several diseases. Therefore, adequate intestinal absorption of Mg2+ is vital for health. The small intestine was previously thought to absorb digested Mg2+ exclusively through an unregulated paracellular mechanism, which is responsible for approximately 90% of total Mg2+ absorption. Recent studies, however, have revealed that the duodenum, jejunum, and ileum absorb Mg2+ through both transcellular and paracellular routes. Several regulatory factors of small intestinal Mg2+ uptake also have been explored, e.g., parathyroid hormone, fibroblast growth factor-23, apical acidity, proton pump inhibitor, and pH-sensing channel and receptors. The mechanistic factors underlying proton pump inhibitor suppression of small intestinal Mg2+, such as magnesiotropic protein dysfunction, higher mucosal bicarbonate secretion, Paneth cell dysfunction, and intestinal inflammation, are currently being explored. The potential role of small intestinal microbiomes in Mg2+ absorption has also been proposed. In this article, we reviewed the current knowledge on the mechanisms and regulatory factors of small intestinal Mg2+ absorption.