I keep hearing that magnesium oxide is not a good supplement to try for magnesium because it's said your body only absorbs 4% of it. But how could that be possible when the National Institute of Health says that magnesium oxide has the most magnesium content than all the other popular magnesium's ( magnesium citrate and chloride) combined. Where exactly is the source where they claim it only absorbs 4% in your body does anyone know where that information came from?
Magnesium oxide cannot absorb as magnesium oxide. Instead, as with most minerals, the magnesium has to react with an acid turning it in to an absorbable salt. Problem is that many people lack sufficient levels of stomach acid as levels drop with age and there is a major over use of antacids, acid blockers (proton pump inhibitors), carbonates and oxides in supplements and alkaline waters all of which further reduce stomach acid reducing mineral absorption.
In the case of magnesium oxide, when this is combined with water it forms the highly alkaline and caustic magnesium hydroxide. This not only neutralizes stomach acid inhibiting magnesium absorption, but it also burns the intestinal wall due to its caustic nature. This is why magnesium hydroxide is used as a laxative such as Milk of Magnesia.
Acidified forms of magnesium, such as magnesium citrate or malate, do contain less actual magnesium. But these are better absorbed than magnesium oxide and the amounts in supplements are increased to still meet the body's demands.
Another simple way to look at this is that more is not always better. Pure magnesium metal has more magnesium than magnesium oxide, but I would not advocate ingesting magnesium metal. Elemental germanium contains more germanium than the safe organic germanium (Bis betacarboxyethyl germanium sesquioxide), but elemental or even germanium dioxide will shut the kidneys down quickly, as where organic germanium is beneficial to the body.