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Bioavailability & elemental % of Magnesium Types


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#1 ozone

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Posted 20 July 2007 - 08:37 AM


I'm adding magnesium to my diet and have read about how there are a lot of different types. Well, it's recommended to get around 400mg/day however I assume this means the amount the body needs, not what's in the pill.

The effectiveness of a magnesium supplement is determined by its...
[1] amount of elemental magnesium in the compound (i.e., the general weight of magnesium to total chelate weight); AND
[2] bioavailability (i.e., amount that is absorbed in the intestines and ultimately available for biological activity in your cells and tissues)

So I'm trying to compile a list...

Magnesium Sulfate ---> Elemental Mag = 10%, Bioavailability = ?
Magnesium Chloride ---> Elemental Mag = 12%, Bioavailability = ?
Magnesium Oxide ---> Elemental Mag = 60%, Bioavailability = 4%
Magnesium Carbonate ---> Elemental Mag = 45%, Bioavailability = 30%
Magnesium Hydroxide ---> Elemental Mag = 42%, Bioavailability = ?

Magnesium Citrate ---> Elemental Mag = 16%, Bioavailability = 90%
Magnesium Lactate ---> Elemental Mag = 12%, Bioavailability = 99%
Magnesium Glycinate ---> Elemental Mag = 18%, Bioavailability = 80%
Magnesium Malate ---> Elemental Mag = 6.5%, Bioavailability = ?
Magnesium Taurate ---> Elemental Mag = 9%, Bioavailability = ?

Alot of those elemental numbers came from this government website so it's probably pretty accurate. But "bioavailability" is apparantly a new concept in the world of magnesium and actual numbers are harder to track down. Lots of websites said that Citrate had the highest levels, but I actually read that Lactate did, with Citrate following behind it. Then, because Malate and Taurate are also Chelates, they have high %'s too.

What threw me for a loop was on Relentless Improvement's website, for Ortho Bone, AOR's data sheet says the following: "But compared to other sources of the mineral, magnesium oxide has extremely low bioavailability (22.8%) .... Magnesium citrate is certainly somewhat better, at 29.64% absorption, but it’s still far from the best magnesium you can choose. Much better absorption is available from other forms – especially fully-reacted magnesium aspartate, with a remarkable 41.7% bioavailability."

That really threw me for a loop. Every single site that has listed the bioavailability for oxide has said it is either 4% or below... I have no clue where this 22.8% is that AOR is listing is coming from. If it were that high, it would make Mag-Oxide pretty worthwhile, but we all know it's a worthless supplement even with an elemental of 60%... Also, that 29% for citrate is screwey too... Citrate has the highest or second highest bioavailability... If it were just one weird number from AOR, okay fine. But two really odd numbers makes me believe that AOR's facts are wrong. Anyway, I'm not here to call AOR into question because I love them, I'm just trying to get legit numbers for the rest of the abovelisted magnesium compounds (or correct any mistakes I have) so I can order the proper supplement.

Btw, what is "Magnesium Amino Acid Chelate"? Is that another name for Mag Citrate? I can't quite figure it out.


EDIT: So just for those non-math inclined people out there, this is how you calculate how much mag a pill has:

(mg powder in pill) x (elemental %)/(100) x (bioavailability %)/100 = actual mag you are getting

Example: 500mg Mag Oxide
(500mg) x (60%)/100 x (4%)/100 = 12g of magnesium

Kind of a big difference eh? In my opinion, someone should sue the manufacturers for false advertising. Who the hell (Excuse my language) knows this crap?

Edited by ozone, 22 July 2007 - 03:00 AM.

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#2 s123

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Posted 20 July 2007 - 01:51 PM

Btw, what is "Magnesium Amino Acid Chelate"? Is that another name for Mag Citrate? I can't quite figure it out.


Magnesium citrate is the magnesium salt of citric acid.
I have never heard about magnesium amino acid chelate but a chelate is a kind of complex.
Thus I think magnesium amino acid chelate is a complex of magnisium which some kind of amino acid.

I looked it up:

The Magnesium Amino Acid Chelate is a complex mineral chelate consisting of Magnesium Ion (Magnesium Oxide) bonded to a mixture of ligands including glycine, aspartic acid and citric acid.


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#3 superpooper

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Posted 21 July 2007 - 02:14 AM

LOL, this is proof of what I've already known. I have a pretty severe magnesium deficiency. When I take magnesium oxide it's almost like I'm half my symptoms return within a 1-2 days. Magnesium citrate works great.
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#4 ajnast4r

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Posted 21 July 2007 - 03:32 AM

i dunno where you got citrate at 90% bio, ive always been told its very low...



stick with an albion labs glycinate..

solid research + its cheap
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#5 niner

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Posted 21 July 2007 - 06:28 AM

Magnesium Sulfate ---> Elemental Mag = 10%, Bioavailability = ?
Magnesium Chloride ---> Elemental Mag = 12%, Bioavailability = ?

I'm not sure the elemental percentages are really relevant, unless you are compounding your own pills. Supplements are usually labeled in terms of the weight of elemental magnesium present, not the weight of the hydrated salt. The magnesium sulfate supplement that I use is 250mg of Mg, and the tablet weighs 600 mg. That works out about right considering that it also has some binders and other agents in it.

Offhand, I would expect that the bioavailabilities for the simple salts would be a function of their solubility. The chloride and sulfate, for example are very soluble in water, so once they are in your stomach, the magnesium exists as a free Mg++ ion in solution, and will end up getting complexed with whatever endogenous ligands are floating around. In these cases, the counterion that it rode in with should just float off and do its own thing. So if the salt is very soluble, the bioavailability should be that of "naked magnesium", whatever that might be. (My guess is that sulfate, chloride, and hydroxide are not much different than carbonate.) Some of the ligands in the list (citrate - taurate) may well complex the magnesium in ways that enhance its bioavailability.

Rather than paying a fortune for an obscure magnesium salt, you could just take more of one of the cheap ones, like sulfate. Don't forget to consider dietary sources and multivitamins as well.
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#6 s123

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Posted 21 July 2007 - 08:52 PM

Magnesium Sulfate ---> Elemental Mag = 10%, Bioavailability = ?
Magnesium Chloride ---> Elemental Mag = 12%, Bioavailability = ?
Magnesium Oxide ---> Elemental Mag = 60%, Bioavailability = 4%
Magnesium Carbonate ---> Elemental Mag = 45%, Bioavailability = 30%
Magnesium Hydroxide ---> Elemental Mag = 42%, Bioavailability = ?

Magnesium Citrate ---> Elemental Mag = 16%, Bioavailability = 90%
Magnesium Lactate ---> Elemental Mag = 12%, Bioavailability = 99%
Magnesium Glycinate ---> Elemental Mag = 18%, Bioavailability = 80%
Magnesium Malate ---> Elemental Mag = 6.5%, Bioavailability = ?
Magnesium Taurate ---> Elemental Mag = 9%, Bioavailability = ?

Alot of those elemental numbers came from this government website so it's probably pretty accurate.


Strange, when I calculated the amount of elemental Mg I get different numbers.

MgSO4 --> 20.19%
MgCl2 --> 25.53%
MgO --> 60.30%
MgCO3 --> 28.83%
Mg(OH)2 --> 41.68%
Mg cit. --> 16.16%
Mg lac. --> 12.01%
Mg mal. --> 15.54%

Mg gly. and Mg tau. are chelated forms of Mg and because I don't now what the anion is, I cannot calculate these two.
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#7 ozone

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Posted 22 July 2007 - 03:02 AM


Alot of those elemental numbers came from this government website so it's probably pretty accurate.


Strange, when I calculated the amount of elemental Mg I get different numbers.


What do you mean by "you calculated"? Can you demonstrate or something? I'm very interested.

Edited by Michael, 04 February 2009 - 11:50 AM.
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#8 ozone

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Posted 22 July 2007 - 03:24 AM

I'm not sure the elemental percentages are really relevant, unless you are compounding your own pills.  Supplements are usually labeled in terms of the weight of elemental magnesium present, not the weight of the hydrated salt.  The magnesium sulfate supplement that I use is 250mg of Mg, and the tablet weighs 600 mg.  That works out about right considering that it also has some binders and other agents in it.


In a perfect world, that would indeed be true; but the reality is, it's not. A simple way to demonstrate this is with bioavailability. Obviously it plays a big difference in the amount of magnesium that you are actually getting, but do you really think that the manufacturers are including it in their calculations? I have 500mg mag oxide here and they weigh 1.3g. 60% of 1.3g is 780mg. The bioavailability is only 4% or so, and that means the pill is only 31mg of magnesium once digested. So basically, if the supplement manufacturers are not being up front about the bioavailability, then we cannot assume they are being upfront about the elemental % either.

Obviously, my oxide, and your sulfate, are properly listed taking elemental % into account. But that's not always the case unfortunately. You pointed out a great way to find out though. Just weigh your pill or look at it. If it's a citrate the size of a "1" capsule, and yet says it has 400mg of citrate in it, then obviously the elemental isn't being factored in. Unfortunately though, you don't know this until you buy it.
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#9 niner

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Posted 22 July 2007 - 03:42 AM

Strange, when I calculated the amount of elemental Mg I get different numbers.

MgSO4 --> 20.19%

The magnesium sulfate crystal has seven "waters of hydration" for each MgSO4 unit, so it's really MgSO4.7H2O

The dot in the formula indicates that the waters are loosely bound, but unless they are driven off by heating, there will always be seven of them there. Everything that is crystallized from water may have some number of waters in the crystal unit, although for many compounds the number is zero. Crystals can be formed with other solvents included in the formula unit, although that is much less common.
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#10 ozone

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Posted 22 July 2007 - 03:51 AM

i dunno where you got citrate at 90% bio, ive always been told its very low...

stick with an albion labs  glycinate..

solid research + its cheap


Hmm...

This lists Citrate as 55% in water...

If you check pub med, and anywhere else, you will read that both Citrate and Lactate have the highest. Obviously there are conflicting numbers, but any chelate is going to be high when compared to an inorganic salt; so glycinate is probably just as good.
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#11 niner

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Posted 22 July 2007 - 03:51 AM

In a perfect world, that would indeed be true; but the reality is, it's not. A simple way to demonstrate this is with bioavailability. Obviously it plays a big difference in the amount of magnesium that you are actually getting, but do you really think that the manufacturers are including it in their calculations? I have 500mg mag oxide here and they weigh 1.3g. 60% of 1.3g is 780mg. The bioavailability is only 4% or so, and that means the pill is only 31mg of magnesium once digested. So basically, if the supplement manufacturers are not being up front about the bioavailability, then we cannot assume they are being upfront about the elemental % either.

It's not that they aren't being upfront about bioavailability, they just aren't saying anything about it. That's not the same as lying. If they say their pill has 250mg of elemental magnesium and it doesn't contain that amount, that is lying, and could bring the FDA down on them. (For pharmaceuticals, and soon, I think, for supplements.) I trust the big name supplement makers not to get something as basic as that wrong. I don't like to deal with little rinky-dink outfits because I don't know if they have the resources to get anything right.
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#12 ozone

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Posted 22 July 2007 - 04:02 AM

In a perfect world, that would indeed be true; but the reality is, it's not. A simple way to demonstrate this is with bioavailability. Obviously it plays a big difference in the amount of magnesium that you are actually getting, but do you really think that the manufacturers are including it in their calculations? I have 500mg mag oxide here and they weigh 1.3g. 60% of 1.3g is 780mg. The bioavailability is only 4% or so, and that means the pill is only 31mg of magnesium once digested. So basically, if the supplement manufacturers are not being up front about the bioavailability, then we cannot assume they are being upfront about the elemental % either.

It's not that they aren't being upfront about bioavailability, they just aren't saying anything about it. That's not the same as lying. If they say their pill has 250mg of elemental magnesium and it doesn't contain that amount, that is lying, and could bring the FDA down on them. (For pharmaceuticals, and soon, I think, for supplements.) I trust the big name supplement makers not to get something as basic as that wrong. I don't like to deal with little rinky-dink outfits because I don't know if they have the resources to get anything right.


Most people don't visit this place, nor spend any time thinking about their vitamins. We are the exceptions, the 1%. Let's talk about the other 99%. If there was just 1 form of magnesium, fine; leave bioavailability off; no big deal. But in a pharmacy, they have tons of different types of magnesium. Not just oxide, but many others. Where am I going with this? Well...

Let's say I have a life-threatning illness that only magnesium can solve. The doctor tells me, you will live if you get around 500mg a day, but you will die if you don't. I go to the store, and pick out a bottle of 500mg magnesium oxide. Obviously I die, because I'm only getting ~20mg of magnesium if bioavailability is not factored in. Now here is the question: Who is my estate going to sue? I am a lawyer, and I can tell you right now, the answer is not clear. I want to hold the doctor liable, but I also feel that the manufacturer holds some blame too. I don't know, that's just what my gut says. So the common answer is to simply sue them both and then have them fight it out in court for liability.

Also, if you really want to get down and dirty with technicalities. The front of my bottle just says Magnesium 500mg. Nothing else, except for the logos and random marketing stuff. It's not until you flip it over and read the ingredients do you see "magnesium 500mg as magnesium oxide". If bioavailability didn't matter, then it shouldn't matter what kind it is and thus leaving it off the front of the label would be okay. However, because it plays such a big role, there should be an astric by the 500mg on the front of the bottle or something, and then below it, indicate that it's in oxide form or something to that effect.

Here is another example that would never happen, but it drives the point home. Say you buy a pack of gum. The front label says "Hubba-Bubba - Amazing Gum (7 sticks)", but when you open it up, you see how all the 7 sticks have been already chewed. You flip the package over on on the back it says "7 sticks - previously chewed". Are there 7 sticks in the package, yes, so they didn't technically lie. But don't you feel that in some way, the consumer was duped because he didn't get what he expected? Yes. While I cannot pinpoint with 99% accuracy where the consumer could sue the manufacturer for this, I'm virtually certain that given some time, I could find something.

Edited by ozone, 22 July 2007 - 04:18 AM.

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#13 niner

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Posted 22 July 2007 - 04:37 AM

OK, I can see your point. My first thought is that a competent health professional, i.e. your doctor or pharmacist, should be aware of the bioavailabilities and prescribe or recommend appropriately. Ha Ha. My own doctor recently prescribed 400mg Mag Oxide to me. And he's a "good" doctor. He's a brilliant diagnostician, knows his medicines, and knows when to call in a specialist. Yet he missed the boat on this one. If the oxide is really as bad as people here are saying, then it should probably be knocked out by a formulary committee, at least in a hospital, institutional, or insurance setting. Ideally, it should be off the market due to efficacy concerns. To make that happen would probably require changes to existing law. Remember, cigarettes used to be sold without warnings, from vending machines, and advertised on TV.
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#14 ozone

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Posted 22 July 2007 - 05:58 AM

OK, I can see your point.  My first thought is that a competent health professional, i.e. your doctor or pharmacist, should be aware of the bioavailabilities and prescribe or recommend appropriately.  Ha Ha.  My own doctor recently prescribed 400mg Mag Oxide to me.  And he's a "good" doctor.  He's a brilliant diagnostician,  knows his medicines, and knows when to call in a specialist.  Yet he missed the boat on this one.  If the oxide is really as bad as people here are saying, then it should probably be knocked out by a formulary committee, at least in a hospital, institutional, or insurance setting.  Ideally, it should be off the market due to efficacy concerns.  To make that happen would probably require changes to existing law.  Remember, cigarettes used to be sold without warnings, from vending machines, and advertised on TV.


Back in the day, I believe oxide was the only form available; and it wasn't until recently (in the last 15yrs I believe) that people have found magnesium oxide has little to no bioavailability. He's not going to be reading new studies off pub med on vitamins or minerals most likely; but I suppose a good doctor should. It's unfortunate that only patented meds get everyone's attention; and unpatented meds, vitamins, and minerals don't. I bet there are a LOT of doctors who probably miss this boat. Go back to him and see what he says; maybe bring a few pubmed studies along too heh.

Edited by ozone, 22 July 2007 - 04:29 PM.

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#15 graatch

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Posted 22 July 2007 - 06:23 AM

>stick with an albion labs glycinate..

Glycine has a psychoactive effect. It promotes insulin release, but I mean that besides being considered inhibitory, it can have some excitatory effects as well dosage-dependently... some people on another board experimented with using it at around 2g for focus.

Mag. glycinate actually worsened my sleep.
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#16 s123

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Posted 22 July 2007 - 03:05 PM


Strange, when I calculated the amount of elemental Mg I get different numbers.

MgSO4 --> 20.19%
MgCl2 --> 25.53%
MgO --> 60.30%
MgCO3 --> 28.83%
Mg(OH)2 --> 41.68%
Mg cit. --> 16.16%
Mg lac. --> 12.01%
Mg mal. --> 15.54%

Mg gly. and Mg tau. are chelated forms of Mg and because I don't now what the anion is, I cannot calculate these two.


What do you mean by "you calculated"? Can you demonstrate or something? I'm very interested.


Fist you look up the relative atomic mass of each element. That means how much gram of the element you need to have one mol. One mol of every component has the same amount of particles, 6.0221415 x 10^23 (the constant of Avogadro). Then you calculate the molecular weight of the component (that's the sum of the atomic mass of each of the elements that is in the molecule, don't forget the index of each element). Then you multiply the atomic mass of the element which it's index and divide it by the molecular weight and than you multiply it which 100 (to convert it to an percentage).

e.g. MgSO4

1 MgSO4 --> 1Mg + 1S + 4O
Mg: 24.31 g/mol
S: 32.07 g/mol
O: 16.00 g/mol --> 4O = 4 x 16.00 = 64.00 (g/4mol)

1 MgSO4 = 24.31 + 32.07 + 64.00 = 120.38 g/mol

%Mg = (24.31/120.38) x 100 = 20.19
%S = (32.07/120.38) x 100= 26.64
%O = (64.00/120.38) x 100 = ( ((16.00 x 4)/120.38) x 100 )= 53.16

Of course this is for water free MgSO4

MgSO4 which crystal water:

1 MgSO4.7H2O --> 1Mg + 1S + 11O + 14H
Then you do the same calculation.

Then you get for Mg: 9.86%

Indeed I calculated it without crystal water :)

MgSo4 also known as Epsom salt is a strong laxative.

The problem which MgO is that it’s solubility is very low. This is because very little MgO molecules divides into ions. But in your stomach the hydrochloric acid will convert the MgO to MgCl2 (completely soluble in water). But This is a very slow process and will not be completed because your food supplement doesn’t stay in your stomach but goes to your intestines. The same is true for Mg(OH)2 and MgCO3 but these will react match faster which hydrochloric acid.

MgCl2 and MgSO4 are fully soluble into water so it's bioavailability will be very high.

Edited by s123, 22 July 2007 - 03:44 PM.

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#17 ozone

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Posted 22 July 2007 - 04:35 PM

@s123

That's pretty sick chem 101 stuff hah! I was never any good at that. I was going to ask you to label the compounds but I figure I can brush up on my periodic table and look them up myself. Thanks a ton for this, I had no clue you could do this; I figured all those binders and other junk supposedly inside made this impossible.

By the way, it was mentioned on the LEF boards; this is the study we need if we want to discover the true bioavailability of the various types of magnesium.
http://www.ncbi.nlm....5293&dopt=Books
Before this, there were some studies testing oxide and citrate but I believe this tests a wider range. Plus, it states that prior tests, using plasma levels for detection, are inaccurate. Anyone have the results?
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#18 OneScrewLoose

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Posted 26 June 2009 - 11:11 PM

Haven't done those kinda calculations since AP chem...
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#19 catfanatic1979

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Posted 01 July 2009 - 02:55 AM

Lets not leave out Magnesium Orotate!
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#20 chrono

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Posted 02 February 2010 - 02:37 AM

Does anyone have any references for the bioavailability of magnesium taurate?

Based on the probably similarities mentioned in this thread, would it be fairly safe to assume it's in the 80-90% range?
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#21 MrSpud

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Posted 02 February 2010 - 04:05 AM

Just to throw another variable in, bioavailability of just about anything is very different if it is taken on an empty stomach vs. if taken with food or at the same time as other nutrients that either interfere or aid in absorption.

None of this is ever absolute and predictable and I don't think you can just assign a bioavailability number to different forms of a nutrient that precisely. I haven't looked up Magnesium (recently) but let's use CoQ10 as an example. All kinds of companies tout their higher price dosage forms of CoQ10 as being the most bioavailable, but if you dig into the data it typically ends up being that their dosage form of CoQ10 is only more bioavailable than dry CoQ10 powder taken on an empty stomach. If they put in emulsifiers and some digestable oil then their CoQ10 can make an emulsion in your stomach or intestines and get absorbed along with the oil much better than if you just take dry CoQ10 powder on an empty stomach because oil soluble CoQ10 is hard to digest and absorb. But if you compare all the forms of CoQ10 taken along with a fatty meal, the differences in bioavailability become much less significant.

I'm just using the CoQ10 as an example, but it applies to lots of nutrients where you are trying to achieve a steady level in the body over time rather than a one time single dose. If you are taking a drug that has to hit you fast and hard to work (like taking ibuprofen for a headache) then you want the most bioavailable form for sure. But if you are taking a nutrient where it doesn't matter how fast it hits you then bioavailability might not be as big of a deal. If you take it with food it might not just pass right through you without being absorbed even if it tested out low in a particular study.

But, like I said, I haven't looked up magnesium recently.

Edited by MrSpud, 02 February 2010 - 04:37 AM.

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#22 MrSpud

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Posted 02 February 2010 - 05:06 AM

Here is an interesting study on Magnesium bioavailability in rats http://www.john-libb...5/FE/article.md

It goes into depth about the trends of bioavailibility in many magnesium salts and says things like mag citrate was more bioavailible than mag oxide but concludes the following:

"In conclusion, the present study demonstrated that all ten organic and inorganic Mg salts were equally efficient in restoring blood Mg levels in plasma and red blood cells in rats. Because of the importance of the passive process, the quantity of Mg in the digestive tract is the major factor controlling the amount of Mg absorbed. However, the organic forms of Mg, in particular Mg gluconate, seem more absorbable than inorganic salts as assessed by intestinal absorption and urinary excretion."

Edited by MrSpud, 02 February 2010 - 05:45 AM.

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#23 chrono

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Posted 02 February 2010 - 06:58 PM

None of this is ever absolute and predictable and I don't think you can just assign a bioavailability number to different forms of a nutrient that precisely.


I was thinking in terms of drug pharmacology, where the % bioavailability refers to the amount remaining after first-pass metabolism in a particular ROA. I'm not all that familiar with mineral/nutrient absorption kinetics yet, but from the little digging I did it doesn't appear that magnesium goes through that same metabolic process (instead, a system of absorption in the intestine and kidneys, with homeostasis controlled by renal excretion?). So in this sense, those % bioavailability numbers up in the first post are probably misleading, though relatively indicative.

However, something like ibuprofen does indeed have such a number range ("absolute bioavailability"), which is further modulated by factors such as stomach contents, enzyme activity, and delivery system. When talking about drugs, this number is always important, whether you're looking for peak plasma or sustained levels over time, because it refers to the % of an ingested material that the body ends up having to work with, and almost always will have a direct impact on the amount in plasma over any period of time.

But it may not be as directly important when dealing with an endogenous substance of which the body tries to maintain a certain amount, modulated by variable excretion. I assume this is the mechanism which allows the conclusion of the interesting paper you linked to; that all forms were "equally efficient" at restoring (as opposed to simply raising) blood levels, even if input amounts varied (e.g. more % gluconate absorbed than oxide).


Anyway, all I was really looking for was any kind of specific information about the absorption characteristics of magnesium taurate. The general consensus seems to be that it should be in the upper range.
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#24 MrSpud

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Posted 03 February 2010 - 01:40 PM

Here's more thought's on the subject of bioavailability in general, just to add to the confusion.... err, I mean clarity. Sorry if I am confusing the issue of the specific topic of magnesium bioavailability, I just worry that people will buy into the hype of drawing a conclusion based on isolated results of studies that sometimes tend to magnify the significance of bioavailability.

From Nutritional Outlook magazine.

"Industry Should Reform Bioavailability Claims, Supplier Says
A review of a selection of published ingredient studies has concluded that many bioavailability ingredient claims are often weakened by a large variance between the amounts of active ingredients subjects absorbed. The review, published in the January issue of Natural Medicine Journal, looked at studies done on CoQ10 and carotenoids. It was led by ingredients supplier BioActives LLC (Worcester, MA).

"We noticed that in many studies, the intersubject variance--the difference between what individual subjects absorbed--was very large," told the study's lead author, Daniel Kagan, PhD, a managing partner at BioActives, to Nutritional Outlook. (He disclosed that a BioActives study was among the studies reviewed.)

Kagan says that many of the reviewed studies failed to adequately discuss such variances, if they occurred, and their implications. For instance, he says, in many cases when a study concluded that an ingredient was more bioavailable, the ingredient was actually only more bioavailable in a minority of subjects.

Wrote Kagan et al., "The results are reported based on statistically significant differences between the mean scores in different treatment groups...Some studies circumvent statistics altogether by singling out the one data point of the best absorber and [promoting] it as [being] 'up to X times more bioavailable.' While these claims are mostly based on statistically significant differences between treatment groups, they can be misleading, as the average of all the data may include subjects who were poor absorbers as well as those who were super-absorbers."

Or, as Kagan says, "The few super-absorbers are the ones that can drive the results."

As a result of what Kagan calls incomplete reporting, "it is difficult for physicians and consumers to compare the bioavailability claims of different formulations," wrote Kagan et al. Moreover, Kagan points out, if a consumer purchases a product labeled highly bioavailable when data actually showed it is highly bioavailable for some of the subjects and not highly bioavailable for others, then the consumer wouldn't know whether he or she is likely to be represented by the group that does or doesn't absorb the supplement well.


By contrast, Kagan et al. note that, "The pharmaceutical industry has a concrete definition of bioavailability and uses explicit methods for evaluating the bioavailability of drugs...In fact, bioavailability studies are an important part of the information necessary to support an FDA approval."

Kagan et al. suggest that the industry instead adopt new, standard terms when making bioavailability claims that indicate the likely percentage of consumers for whom an ingredient is bioavailable. If a bioavailability claim likely applies to 85% of consumers, an ingredient/product could then be deemed reliably bioavailable. If a claim applies to 99% of consumers, an ingredient/product could be deemed universally bioavailable. (The authors offer a method for calculating these criteria.)


The reviewers concluded, "The benefits derived from nutritional supplements are directly related to their bioavailability, yet the dietary supplement industry lacks well-defined standards to ensure adequate bioavailability."

Kagan adds that improving the accuracy of bioavailability claims may improve the chances that consumers will select supplements that are bioavailable for them. "Think of all the return customers companies are losing because the consumer did not realize the benefit of the supplement," he says.

For more information, e-mail Daniel Kagan at dankagan@earthlink.net.
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#25 chrono

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Posted 03 February 2010 - 03:37 PM

Here's more thought's on the subject of bioavailability in general, just to add to the confusion.... err, I mean clarity. Sorry if I am confusing the issue of the specific topic of magnesium bioavailability, I just worry that people will buy into the hype of drawing a conclusion based on isolated results of studies that sometimes tend to magnify the significance of bioavailability.


That's fine, I wasn't expecting anything, honestly. Just hoping that someone knew of an obscure footnote somewhere.

That's an interesting article, and definitely a good thing to be aware of (btw, it's better etiquette to link to an article, and maybe post the most relevant snippets). The loose controls of the supplement industry is a two-edged sword. Substances are available to us which someone hasn't paid millions to push through FDA trials, but companies are free to make loose claims.

Here's the full text of the article in Natural Medicine Journal that they refer to. A very interesting discussion of statistical factors, and how precise pharmacological terms are used loosely for marketing purposes.

But that's why there are science forums like this! :-D

Edited by chrono, 03 February 2010 - 03:40 PM.

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#26 MrSpud

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Posted 04 February 2010 - 04:42 AM

"(btw, it's better etiquette to link to an article, and maybe post the most relevant snippets). "


Sorry about the etiquette breach, sometimes I get carried away ('<..')
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#27 John2009

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Posted 18 November 2010 - 03:42 AM

Around 2008, I was told by Dr. Glen Aukerman http://www.fammed.oh...e.edu/10181.cfm that

Actually the magneisum oxide has been used for health for thousands of year versus the others that are 'marketed' as better. All the others are used for laxatives and as bowel preps which attests to their lack of absorption. We have found the oxide as the only reliable form for absorption but none raise the blood level since that is tightly controlled and the last place to show elevation or depletion of the body magnesium stores.


Also around 2008, I was told the following from the Life Extension Foundation Advisor hotline...

Magnesium citrate is better absorbed than magnesium oxide (about 70% vs. 30%). Therefore, for each milligram of elemental magnesium in magnesium citrate, you will get more benefit than from the same amount of magnesium in magnesium oxide. However, magnesium oxide is less expensive, so you will need to decide for yourself how to proceed. Another factor to consider is that because less of the magnesium oxide is assimilated, more remains in the bowel where it can sometimes cause loose stools. All in all, magnesium citrate (whether in Magna Calm or another formulation) is the better way to go unless the price differential means your choice is oxide or nothing.


In 2010, I received this respons from Paul Mason at www.mgwater.com...

Back in 1997, a researcher at Premier Services (the largest purveyor of agricultural Mg at that time) did research on MgO used for supplementing cattle to prevent The Staggers (grass tetany) which may be similar to delirium tremens in alcoholics, and can be fatal.

He found that the bioavailability of MgO depended on the surface area of the granules, and that he could greatly increase the bio-availability of MgO by finely sintering it during the manufacturing process. He noted that the MgO used in human supplement pills were coarsely sintered, and therefore not very bio-available.

I recommend instead Magnesium Citrate dissolved in water, for the highest bioavailability, taken 3 times per day (as magnesium passes through the body in about 8 hours. "Natural Calm" is one brand, available in health food stores or online.

Besides food, which provides men with an average of 327 mg of magnesium per day, I recommend 200 mg of magnesium DISSOLVED IN WATER, in divided doses. Magnesium in water is much more beneficial than magnesium in food, in preventing cardiovascular pathologies.

Here is my latest effort to improve magnesium intakes: www.MgWater.com/fda.html


Perhaps if the cheap oxide form were sintered during manufacturing, this would solve the problem and provide a very cost effective bio-available form of magnesium ? I guess it depends on how expensive the sintering process would be.

This study suggests the oxide form is more poorly absorbed...
http://www.ncbi.nlm....pubmed/11794633

I think an important question is, what form of magnesium occurs naturally in food and water ? Is that not the magnesium that is probably best since that is what we evolved using ?

Regarding the absorption issues, if the absorption rate of oxide versus citrate is 30% versus 70% respectively, then can't we just increase the oxide dose by 40% and obtain the same benefit as taking a 40% lower dose of citrate ? I don't know how it would work out cost wise.

The bottom line is that your body needs to use a certain amount of magnesium per day. Why can't an optimal dose be determined based on whatever form of magnesium is being used, so that the body gets what it needs regardless of which form is used ? I would like to see a list of different magnesium forms, and the required dose for each form that gives the body what it needs, along with a cost comparison. I think the bottom line is, how much of each different form of magnesium would you need to take to provide the body with what it needs, and what does it cost.

Here is some more info on magnesium...

http://ods.od.nih.go...thProfessional/

http://www.whfoods.c...utrient&dbid=75

http://lpi.oregonsta...rals/magnesium/
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#28 ritch

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Posted 18 November 2010 - 05:20 AM

Wow, some smart people on this site. It looks like the magnesium malate I just bought is not that good after all. I've always used the chelated version. But if you guys are really into the highest absorption rates, they do make transdermal magnesium. They sell it at puritan.com it's about $25 for a 2 month supply, not bad really. Aspartate should come down in price I'm guessing as the glycene version seems to be all the rage now.
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#29 aLurker

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Posted 18 November 2010 - 12:01 PM

Wow, some smart people on this site. It looks like the magnesium malate I just bought is not that good after all. I've always used the chelated version. But if you guys are really into the highest absorption rates, they do make transdermal magnesium. They sell it at puritan.com it's about $25 for a 2 month supply, not bad really. Aspartate should come down in price I'm guessing as the glycene version seems to be all the rage now.


I can't seem to find any peer reviewed studies on transdermal magnesium indicating it would be superior to oral intake in any way. If you can let me know. Kthnx.
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#30 ritch

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Posted 18 November 2010 - 03:55 PM


Wow, some smart people on this site. It looks like the magnesium malate I just bought is not that good after all. I've always used the chelated version. But if you guys are really into the highest absorption rates, they do make transdermal magnesium. They sell it at puritan.com it's about $25 for a 2 month supply, not bad really. Aspartate should come down in price I'm guessing as the glycene version seems to be all the rage now.


I can't seem to find any peer reviewed studies on transdermal magnesium indicating it would be superior to oral intake in any way. If you can let me know. Kthnx.


Isn't is common knowledge a transermal is more effective anyway? When experts such as Charles Poliquin say transdermal magnesium is the way to go, that's good enough for me.
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