I guess I should link to this, given that a lot of these phosphate "preparations" are these God-awful homeopathic "remedies" or are trisodium phosphate drain scrubbers, etc. I could only find one sodium phosphate supplement (http://www.google.com/products?q=%22disodium+phosphate%22+standard+process&hl=en&aq=f), and it was difficult to find, for some reason. I've never used any phosphate supplement, but ATP disodium has a certain amount of phosphate. I don't intend to use sodium phosphate, but I don't want someone to read something of mine and end up getting some poisonous homeopathic product. But the safer approach would be to have one's doctor prescribe some small dosage form of a sodium phosphate supplement and take a very tiny fraction of it, and I'd strongly advise anyone to not take any phosphate supplement without discussing the possibility with one's doctor (and one would want to monitor one's serum phosphate and/or urinary phosphate, etc.). It's not really possible to monitor the effects of phosphate supplementation, though, and that's the reason it would be wise to keep the amounts extremely small and lower than the amounts found in food. There are case reports of people getting kidney failure or evidence of kidney damage a month or six months after taking a single dosage of 15 or 23 or 46 grams (15000 or 23000-46000 mg) of phosphate, and the people tended to not feel any real symptoms during those intervening months. So it's not just either "acute kidney failure or nothing," and one can't conclude that the absence of evidence or symptoms of kidney failure constitute evidence of the absence of kidney failure/damage.
It would also be worthwhile to make conservative assumptions about the amounts of phosphorus/phosphate that are actually in a supplement. If the supplement supplies, for example, 100 mg of "phosphorus," one can be fairly sure that that means 100 mg phosphate and does not mean 307 mg of phosphate. But given that I can't be 100 percent sure (only 90-some percent) what "100 mg phosphorus" really means (the articles literally do not make it possible to tell with certainty, even for food phosphorus, and I "defy" anyone to look at 20 or 30 articles and to get a consistent picture of what exactly the authors are referring to, when they say phosphorus or phosphate and make bizarre conversions), the conservative approach would be to assume that phosphorus means phosphorus and that 100 mg phosphorus means 307 mg of phosphate. In the case of the amounts of "phosphorus" in foods, the conservative approach would be to assume that 2400 mg phosphorus means 2400 mg phosphate. This is because there is an implicit assumption that the amounts of phosphate that are typically consumed, by the average person, in foods are not "deadly" or "poisonous." Assuming that they're not deadly, the assumption that 2400 mg of "food phosphorus" is actually referring to 7359 mg (2400/0.3261) (or 0.3229, in crazyville) of phosphate would give one a false impression that 7359 mg phosphate is safe and that a supplement of, say, 2000 mg of phosphate would be more likely to be safe than it is likely to be. Phosphate from a supplement is likely to be more potent than food-derived phosphate, even in comparison to phosphate derived from diphosphate or triphosphate additives in meats or from phosphate bound to casein in milk. It's likely to be more potent because its rate of dissolution is going to be faster, and that's going to enhance its rate of absorption and, hence, bioavailability. A high extent of bioavailability is not necessarily going to be desirable for phosphate, and this is because the research shows that calcification in the kidneys tends to occur when there's an abrupt and localized increase in the concentration of phosphate in the interstitial fluid in the kidneys or in the tubular fluid, etc. An abrupt increase can overwhelm the kidneys' capacity to filter the phosphate and can cause the Ca x P solubility product to exceed the Ksp, or solubility product constant, for the formation of amorphous calcium phosphate [2.3 x 10^(-7) M^2 (mol^2/L^2)]. But I tried to extrapolate the normal range of absolute serum phosphate values, based on data from trials providing data on the Ca x P product, in mg^2/dL^2, and on the typical Ca x P in mol/L (a typical value is supposedly 10^(-7), or about half of the Ksp). But there seems to be something strange with those numbers, too. I think they determined the Ksp value on "the other side of the mirror," back whenever they did it. The numbers are just bizarre, because you can't tell what they're actually referring to, even with a Ksp value. I thought that the Ksp value had been determined outside of the phosphate research community, etc. But all I can say is that there's something really strange with the numbers and conversions, and I've had a lot of calculus and am not rusty, as far as doing mathematics problems.
Another strategy to prevent abrupt increases in serum phosphate would be to take tiny amounts with carbohydrates, because there's an article showing that sodium phosphate produced a larger rise in serum phosphate when given with water, on an empty stomach, I think, than it did when given with juice. The authors attributed it to the known capacity of insulin to stimulate phosphate uptake into cells. If one has eaten within the last 2-3 hours, there'll probably be enough insulin to maximize that effect, but it's still worth knowing that there may actually be a measurable difference for something like that.
There's research suggesting that not much supplemental sodium phosphate is required to produce effects, under conditions of serum or intracellular phosphate depletion. For example, Jain et al. (1987) [Jain et al., 1987: (http://www.ncbi.nlm.nih.gov/pubmed/3666986)] found that 500 mg/day, for three days, of NaHPO4 (~ 400 mg phosphate, assuming the molar mass of NaHPO4 is 118.973, but there might be some strange stoichiometry--the salt might have been supplied as the dihydrate or monohydrate, in crystalline form, or as the "pentahydrate of Na3(HPO4)3" or something crazy like that, and that might account for the slight discrepancy of the authors' calculation and my calculation) improved the mood (they "felt better") and cognitive performance of people at high altitudes, evidently by increasing erythrocyte 2,3-diphosphoglycerate and thereby improving oxygen delivery to their brains. I guess I'd assume that that's actually phosphate, because to assume that they're referring to phosphorus would mean that the dose of phosphate is 1239 mg. That's unlikely to have been the dose, but the point is that assuming phosphorus means phosphate, when it comes to data from articles on supplemental phosphate/phosphorus, is the conservative approach. But the authors say that other researchers had gotten similar or comparable results, in past articles, from a dosage of 90 mmol/day of phosphate (about ten times the 400 mg dosage). I doubt even 400 mg would be necessary, but the point is that there's reason to be careful. There's other research showing that phosphate, at unknown or uncertain dosages (I can't get the full text), regulates and can increase energy expenditure/oxidative metabolism [Nazar et al., 1996: (http://www.ncbi.nlm.nih.gov/pubmed/8807564); Jaedig et al., 1994: (http://www.ncbi.nlm.nih.gov/pubmed/7816004); Kaciuba-Uściłko et al., 1993: (http://www.ncbi.nlm.nih.gov/pubmed/8123890); Jaedig and Henningsen, 1991: (http://www.ncbi.nlm.nih.gov/pubmed/1885267)]. That research is consistent with the research showing that intracellular phosphate depletion can produce a syndrome that resembles mitochondrial dysfunction, with lactic acidosis, etc. Chobanian et al. (1995) [Chobanian et al., 1995: (http://www.ncbi.nlm.nih.gov/pubmed/7900836)] found that the intracellular phosphate concentrations correlated positively with the intracellular ATP concentrations in the proximal tubules of dogs (meaning that the higher the phosphate levels, the higher the ATP levels, up to a point). The point of those articles is not that taking big dosages of phosphate is a good idea but that a lot of the popular nutritional approaches, as far as calcium supplementation and fear of phosphate-containing foods, are not necessarily going to be good. In many cases, people would probably not need to do anything except stop taking massive dosages of supplemental calcium to set some things straight, as far as their intracellular and intramitochondrial phosphate homeostatic mechanisms are concerned. A person can be severely depleted of intracellular phosphate and still experience toxic effects or kidney failure from large dosages of phosphate, though, and so it's necessary to discuss these things with one's doctor.
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