The bioavailability of magnesium, like many other drugs, has been
studied widely by scientists. A common way to conduct experiments on
the bioavailability of supplements is to study the supplements' rate
of solubility in a weak acid solution, similar to that of the human
body.
Bioavailability is most often affected by what form of anion or salt
-- such as oxide, gluconate, chloride or lactate dihydrate-- that is
used in the supplement. It is digested not in the stomach, but in the
small intestine. Overall, magnesium supplements are a highly
effective way of gaining magnesium for the body. A study conducted in
1992 concluded that rates of absorption by supplement and
intravenously were comparable and the supplements did provide
sufficient magnesium absorption. Healthy people absorb 30 to 40
percent of magnesium administered orally.
A factor that can also decrease bioavailabiity of magnesium is what
kind of coating the supplement has-- a study found that if the
magnesium supplement has an enteric coating-- a coating such as that
that aspirin would have to prevent being broken down in the stomach--
the supplement is less effective (1). When four different forms of
magnesium supplements are studied, "results suggested lower
bioavailability of magnesium oxide, with significantly higher and
equal absorption and bioavailability of magnesium chloride and
magnesium lactate" (A) (Study 2 below). There is a graph with the
results of the study here:
http://dietary-supplements.info.nih.gov/factsheets/images/magnesium.figure1.jpg
The effectiveness of magnesium supplements is therefore dependent upon
their inherent bioavailability, but also on how much elemental
magnesium (the magnesium itself) is included in a supplement.
Studies have found that magnesium L-lactate dihydrate is perhaps the
most effective form of supplemental magnesium. It is available in a
sustained-release formation that ensures maximum absorption by the
small intestine. The measured solubility and bioavailability of
magnesium L-lactate dihydrate is higher than that of other studied
formats of the drug, and patients taking it appear to have a low
incidence of side effects.
Sources:
A. http://dietary-supplements.info.nih.gov/factsheets/magnesium.asp
B. http://en.wikipedia.org/wiki/Enteric_coating
C. http://www.premierchemicals.com/corner/articles/update.htm
D. http://www.geriatrictimes.com/g020208.html
Citations:
1. Fine KD, Santa Ana CA, Porter JL, Fordtran JS. Intestinal
absorption of magnesium from food and supplements. J Clin Invest
1991;88:296-402.
2. Firoz M and Graber M. Bioavailaility of US commercial magnesium
preparation. Magnes Res 2001;14:257-62.
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