Bioavailability of Magnesium Salts – A Review
Background: Magnesium supplementation is of value in several different medical disorders. Several kinds of Mg-salts are commercially available.
Purpose: This review evaluates their bioavailability criteria such as solubility, urinary excretion, and plasma levels of magnesium from studies of different Mg-salts.
Conclusion: Although methodology differences were large, the results consistently demonstrate a better bioavailability for Mg-citrate.
I’m posting this mainly because I’ve stated in a number of places that magnesium citrate is what you want to take for magnesium supplementation, since it’s better absorbed. This review article reinforces previous research.
Magnesium is of course of great benefit to health and probably most people should be supplementing with it. I do so myself with a daily tablet of magnesium citrate, containing 200 mg magnesium. If you recall from chemistry class, mineral salts may be more or less prone to dissolving and to absorption from the gut. Milk of magnesia, for example, is magnesium hydroxide, and is used to treat constipation. Magnesium hydroxide just isn’t absorbed well at all, which from one aspect is good, since that makes it non-toxic, as almost all of it remains in the gut. But for supplementation of magnesium, it doesn’t work at all.
Magnesium oxide is another form of magnesium that’s commonly found in drug stores and similar places, but unfortunately magnesium oxide is also hardly absorbed at all from the intestinal tract. Some studies have shown virtually zero absorption of magnesium oxide. Of course, most people, including most doctors and other health practitioners, don’t know this.
Yet other forms of magnesium supplements exist, such as epsom salts (magnesium sulfate), which has a bit better absorption. Epsom salts can also be used to soak in, and some magnesium does get absorbed through the skin. However, you never know what dose you’re getting and so don’t know whether the supplementation is effective or not.
In these types of studies, magnesium citrate always comes out as the most bioavailable form of magnesium. There’s really no reason to take any other kind, other than the fact that you may have to order from Amazon or similar place, as local stores may not have it. The citrate itself also has some health benefits.
You can find magnesium citrate on my supplements buying guide. The recommended dose is one 200 mg tablet daily, but if you are just starting magnesium supplementation and know or suspect that you are deficient, then two doses of 200 mg daily may be appropriate. Those with kidney disease should consult a doctor before beginning; for everyone else, magnesium has low toxicity and virtually no side effects.
2 Comments
The study does not test chelated forms of magnesium. It is generally believed that some of these have better bioavailability than magnesium citrate or magnesium oxide. Magnesium glycinate, for example, is very well absorbed and is often better tolerated in the digestive tract–no laxative effect.