Magnesium absorption
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Understanding Magnesium Absorption: Mechanisms and Influencing Factors
Mechanisms of Magnesium Absorption
Magnesium (Mg) absorption primarily occurs in the distal intestine, with significant absorption also taking place in the small intestine and descending colon. The absorption process involves both intercellular diffusional and solvent drag mechanisms, especially at usual dietary intakes1. At lower dietary intakes, a saturable component becomes more prominent, indicating a more complex absorption mechanism that can reach an absorptive maximum1 3.
Influence of Vitamin D on Magnesium Absorption
Vitamin D plays a dual role in magnesium absorption. Pharmacological doses of vitamin D can enhance Mg absorption in both vitamin D-deficient and vitamin D-replete animals. However, a substantial portion of Mg absorption occurs independently of vitamin D. Additionally, vitamin D may increase urinary Mg excretion, potentially reducing overall Mg retention1 3.
Interaction with Calcium and Phosphate
Magnesium absorption can be influenced by the presence of other minerals such as calcium and phosphate. While calcium has little to no effect on Mg absorption, Mg can modestly depress calcium absorption. This interaction suggests that Mg and calcium absorption processes are mediated by different transport mechanisms1 3.
Dose-Dependent Absorption
Magnesium absorption is dose-dependent, with fractional absorption decreasing as intake increases. For instance, absorption rates can drop from 65% at the lowest intake to 11% at the highest intake, indicating a curvilinear relationship between Mg intake and absorption2. This relationship is represented by a combination of a hyperbolic function and a linear function, suggesting the presence of both saturable and non-saturable absorption mechanisms2.
Bioavailability from Different Sources
The bioavailability of magnesium varies depending on its source. Organic magnesium compounds, such as magnesium citrate and magnesium malate, are generally better absorbed than inorganic compounds like magnesium oxide. Additionally, magnesium from food sources, such as almonds, is as bioavailable as from soluble magnesium acetate, whereas enteric-coated magnesium chloride shows significantly lower bioavailability2 5.
Absorption in Different Intestinal Regions
Magnesium absorption occurs throughout the small intestine, including the jejunum and ileum. The rate of absorption increases with higher luminal Mg concentrations but tends to saturate at higher levels. Interestingly, the ileal absorptive process becomes fully saturated at higher concentrations, unlike the jejunum3. In ruminants, the primary site of Mg absorption is the rumen, with potential-dependent and potential-independent uptake mechanisms playing crucial roles10.
Role of Fructooligosaccharides
Fructooligosaccharides (FOS) have been shown to enhance Mg absorption in the colon and rectum. Rats fed a diet containing FOS exhibited increased Mg absorption compared to those on a control diet. This suggests that indigestible and fermentable carbohydrates can facilitate colorectal absorption of Mg6.
Regulatory Factors and Small Intestinal Absorption
Recent studies have identified several regulatory factors influencing small intestinal Mg absorption, including parathyroid hormone, fibroblast growth factor-23, and pH-sensing channels. Proton pump inhibitors can suppress Mg absorption by affecting magnesiotropic proteins and increasing mucosal bicarbonate secretion7.
Conclusion
Magnesium absorption is a complex process influenced by various factors, including dietary intake, vitamin D levels, and the presence of other minerals. Understanding these mechanisms and interactions is crucial for optimizing Mg absorption and addressing deficiencies. Further research is needed to explore the long-term effects of different Mg compounds and the regulatory mechanisms involved in Mg homeostasis.
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Most relevant research papers on this topic
Magnesium absorption: mechanisms and the influence of vitamin D, calcium and phosphate.
Magnesium absorption primarily occurs in the distal intestine, with vitamin D increasing it, but some absorption occurs independently, and interactions with calcium and phosphate remain unclear.
Literature Review
Highly CitedIntestinal absorption of magnesium from food and supplements.
Magnesium absorption from food and supplements is curvilinear, with less magnesium absorbed than calcium at higher intakes, and enteric coating can impair magnesium bioavailability.
Non-RCTHighly CitedMagnesium absorption in the human small intestine. Results in normal subjects, patients with chronic renal disease, and patients with absorptive hypercalciuria.
Magnesium absorption in the human small intestine is mediated by a different transport process than calcium absorption, and may be dependent on vitamin D.
In Vitro StudyHighly CitedMagnesium absorption from mineral water
Magnesium absorption from mineral water is mainly dose dependent, making comparisons between studies difficult.
Dose-Dependent Absorption Profile of Different Magnesium Compounds
Magnesium citrate increases muscle and brain magnesium levels dose-independently, while magnesium acetyl taurate increases brain magnesium levels when administered as a split dose.
Non-RCT
Animal Study
Rigorous JournalCalcium and magnesium absorption from the colon and rectum are increased in rats fed fructooligosaccharides.
Fructooligosaccharides significantly increase calcium and magnesium absorption from the colon and rectum in rats, facilitating colorectal absorption of these minerals without affecting net water absorption.
RCTAnimal StudyHighly CitedCurrent opinion on the regulation of small intestinal magnesium absorption
Small intestinal magnesium absorption is regulated through both transcellular and paracellular routes, with potential roles for parathyroid hormone, fibroblast growth factor-23, apical acidity, proton pump inhibitor, and pH-sensing channel and receptors.
Effect of supplemented magnesium from magnesium oxide or dolomitic limestone upon digestion and absorption of minerals in sheep.
Magnesium supplementation in sheep increases preintestinal absorption, with magnesium oxide having the highest value, but both sources enhance mineral levels.
RCT