Here is a human study that finds that oxide is crappy, and the organics (and chloride) are better but about equivalent to each other. This is looking at urinary excretion, so it's telling you something about absorption from the gut, but not about utilization.
Magnes Res. 2001 Dec;14(4):257-62.
Bioavailability of US commercial magnesium preparations.Firoz M, Graber M.
Department of Veterans Affairs Medical Center, Northport, NY 11768, USA.
Magnesium deficiency is seen with some frequency in the outpatient setting and requires oral repletion or maintenance therapy. The purpose of this study was to measure the bioavailability of four commercially-available preparations of magnesium, and to test the claim that organic salts are more easily absorbed. Bioavailability was measured as the increment of urinary maginesium excretion in normal volunteers given approximately 21 mEq/day of the test preparations. Results indicated relatively poor bioavailability of magnesium oxide (fractional absorption 4 per cent) but significantly higher and equivalent bioavailability of magnesium chloride, magnesium lactate and magnesium aspartate. We conclude that there is relatively poor bioavailability of magnesium oxide, but greater and equivalent bioavailability of magnesium chloride, lactate, and aspartate. Inorganic magnesium salts, depending on the preparation, may have bioavailability equivalent to organic magnesium salts.
This study looks at ten different salts in rats, determining bioavailability by taking advantage of the existance of a stable isotope, Mg. They obtain a quite different result, in that there wasn't that much difference between any of them. The organic salts were better than the inorganic salts, but not that much
Magnes Res. 2005 Dec;18(4):215-23. Links
Study of magnesium bioavailability from ten organic and inorganic Mg salts in Mg-depleted rats using a stable isotope approach.Coudray C, Rambeau M, Feillet-Coudray C, Gueux E, Tressol JC, Mazur A, Rayssiguier Y.
Centre de Recherche en Nutrition Humaine d'Auvergne, Laboratoire des Maladies Métaboliques et Micronutriments, INRA de Theix/Clermont-Ferrand, Saint-Genès-Champanelle, France. email@example.com
Literature data on the bioavailability of various Mg forms provide scarce information on the best Mg salt to be used in animal and human supplementation. This study aimed to investigate the bioavailability of different forms of Mg in rats using Mg stable isotopes. Eighty male Wistar rats aged 6 weeks were fed a semi-purified Mg-depleted diet for three weeks. The rats were then randomised into ten groups and received, for two more weeks, the same diet repleted with Mg (550 mg Mg/kg [of food, not body wt]) as: oxide, chloride, sulphate, carbonate, acetate, pidolate, citrate, gluconate, lactate or aspartate. After 10 days of Mg-repleted diet, the rats received orally 1.8 mg of an enriched 26Mg. Faeces and urine were then collected for 4 consecutive days. Isotope ratios in faeces and urine were determined. The Mg absorption values obtained varied from 50% to 67%. Organic Mg salts were slightly more available than inorganic Mg salts. Mg gluconate exhibited the highest Mg bioavailability of the ten Mg salts studied. Urinary 26Mg excretion varied from 0.20 mg to 0.33 mg, and feeding with the organic pidolate, citrate, gluconate and aspartate salts resulted in higher urinary 26Mg excretion than with inorganic salts. Ultimately, 26Mg retention was higher in the rats receiving the organic salts such as gluconate, lactate and aspartate than in those receiving the inorganic salts. Taken together, these results indicate that 26Mg is sufficiently bioavailable from the ten different Mg salts studied in the present experiment, although Mg gluconate exhibited the highest bioavailability under these experimental conditions.
This is an interesting study where they look at both "compensation of Mg deficiency" and "anti-inflammatory activity". You can't tell from the abstract how they measured compensation of deficiency, but at least the anti-inflammatory endpoint represents the true cellular absorption that you really care about. It's where the rubber meets the road, as it were. Here, the orderings are mostly reversed, with orotate the best, but chloride close. Curiously, orotate and chloride are the worst at the "compensation of Mg deficiency" metric, but this may not be very meaningful, given that magnesium levels are hard to determine correctly and this may have been a condition of severe deficiency; it might not be entirely relevant to typical humans with decent diet.
Vopr Pitan. 2007;76(5):67-73.
[Study of anti-inflammatory activity of some organic and inorganic magnesium salts in rats fed with magnesium-deficient diet][Article in Russian]
Spasov AA, Iezhitsa IN, Kravchenko MS, Kharitonova MV.
The purpose of the present research was comparative study of anti-inflammatory action of some Mg salts in rats fed with Mg-deficient diet. It was shown in our study that administration of Mg L-aspartate with pyridoxine leads to higher compensation of Mg deficiency in rats with diet-induced Mg depletion as compared with other Mg supplementations. According to the Mg deficiency correction rate Mg salts may be ranged in the following order: Mg L-aspartate with pyridoxine > or = Mg chloride with pyridoxine > or = Mg lactate with pyridoxine > or = Mg L-aspartate > Mg chloride > Mg orotate. In our study administration of Mg salts resulted in decreased number of blood leukocytes, reduced peripheral vasodilation visible in the external ear, decreased spleen weight, and as consequences in reduced inflammatory and immunological response. According to correction rate of the inflammatory response Mg salts may be ranged in the following order: Mg orotate > or = Mg chloride > or = Mg chloride with pyridoxine > or = Mg L-aspartate > or = MgL-aspartate with pyridoxine > or = Mg lactate with pyridoxine.
There is a wealth of evidence that Magnesium Orotate is beneficial in situations ranging from athletic performance to survival of heart disease patients. This is good clinical data from humans, looking at the endpoints we really care about as opposed to levels in bodily fluids. The question is, is it due to better magnesium utilization or to the orotate counterion itself? This paper would suggest that it's the orotate itself, although they describe it as a "cellular fixative of magnesium" (whatever that means).
Vestn Ross Akad Med Nauk. 2002;(2):39-41.
[Orotic acid as a metabolic agent][Article in Russian]
Stepura OB, Tomaeva FE, Zvereva TV.
The paper reviews clinical and experimental studies into the mechanisms of action of orotic acid (OA). OA has been shown to take an active participation in metabolic processes in the body. As a pyrimidine precursor, it plays a key role in the biosynthesis of nucleic acids and protein, regulates water-salt exchange, by increasing diuresis and reducing the volume of extracellular fluid. OA is also a cellular fixative of magnesium by producing pronounced antiarrhythmic, vasodulator, and cardioprotective effects. OA has ascertained to stimulate erythro- and leukopoiesis. The involvement of OA in metabolic processes explains its cardio- and neuroprotective effects. By enhancing the resistance of myocytes to ischemia, OA favourably affects the clinical course of myocardial infarction and on manifestations of heart failure. OA has been noted to have an angioprotective action and to play an important role in the energy provision of the hypertrophic myocardium, by increasing its contractility. The ability to enhance the functional reserves of the heart adapted to higher exercises accounts for its use in sportive medicine. When there are emergency emotional and vestibular stimuli, OA drugs show an antistressor actions and are effective in treating patients with borderline nervous and mental disorders. Whether OA can be used to treat gastrointestinal diseases is to be clarified.
My approach to the magnesium question is to use orotate, but due to its high cost, I only take 200 mg a day. I get the rest of my Mg from my diet and multi. This runs me about 27 cents a day. I use the orotate from Kal. I started using it for the promise of better athletic performance, but I think I'm sleeping better and am calmer since using it.
Edited by niner, 29 May 2008 - 01:40 AM.