Magnesium Hydroxide: This form is often used as an antacid and/or in laxatives. It can be found in over-the-counter products, such as milk of magnesia. Because It has poor bioavailability, it is considered one of the least optimal forms to use as a supplement. Magnesium Oxide: This form of magnesium is one of the most commonly used in supplements. It is desirable because it is inexpensive and the compound is very small, so large amounts of elemental magnesium can be delivered without taking up much space in a tablet or capsule. Magnesium oxide has long been considered a poor source of magnesium,
After being absorbed from foods and supplements, magnesium passes through the gastrointestinal tract (GI) via the mouth, esophagus, stomach, and the small and large intestines. When the magnesium compound reaches the stomach, the acidic environment starts to dissociate magnesium ions which bind with water molecules. Magnesium is absorbed primarily in the lower part of the small intestines and passes from the villi, tiny finger-like surfaces inside the small intestine, and into capillaries, blood vessels surrounding the small intestine.
Magnesium Absorption Categories:
Magnesium that is not absorbed in the small intestine travels to the large intestine, where a small amount is also absorbed. Typical magnesium absorption is broken down into three categories:
- 40% of magnesium is absorbed in the small intestine
- 5% is absorbed in the large intestine
- 55% leaves the body as waste
Note: These figures may vary. For instance, certain forms of magnesium supplements, such as magnesium oxide, (have a low absorbable magnesium potency).
The latest studies have also shown that there are two different transport systems for magnesium:
- Active transcellular transport at low concentrations.
Active transcellular uptake occurs by a recently identified magnesium channel called TRPM6 (transient receptor potential channel 6), which is expressed along the brush border membrane of the small intestine.1 This is where magnesium-amino acid complexes can be absorbed intact.
- Passive paracellular pathway at high intestinal concentrations.
The passive paracellular pathway is responsible for 80-90% of magnesium uptake in the intestinal tract. Passive pathways work more effectively in an acidic (lower pH) environment, which is why magnesium absorption is optimal on an empty stomach and away from other minerals, drugs, fibers, and alkalizing agents
The following factors contribute to higher magnesium levels:
1. Higher intakes of magnesium-rich foods, using magnesium bath salts and magnesium oil, or taking oral magnesium supplements.
2. Higher absorption of magnesium in the small intestines, in the case of oral and dietary magnesium.
3. Lower elimination as waste through the gastrointestinal “GI” tract.
4. Lower excretion by the kidneys.
Advantages of Amino Acid Forms of Magnesium
(Such as 100% fully reacted Magnesium Glycinate)
1. The glycine molecules occupy the reactive sites of magnesium, reducing its ability to bind with other substances that reduce absorption (such as medications or plant compounds like phytates).
2. When magnesium is bonded to glycine it reduces the binding of water which could reduce the frequently encountered problem of loose stools.
3. Amino acids like glycine increase solubility of the whole compound, improving bioavailability.
4. A portion of the magnesium – amino acid compound may be absorbed via the amino acid active transport pathway.
6. The presence of an amino acid, such as glycine, may help lower intestinal acidity towards a pH that would improve passive paracellular transport
Blaine et al. Renal Control of Calcium, Phosphate, and Magnesium Homeostasis Clin J Am Soc Nephrol. 2015 Jul 7; 10(7): 1257–1272