These [Brixen et al., 1992: (http://www.ncbi.nlm.nih.gov/pubmed/1422972); Calvo and Heath, 1988: (http://www.ajcn.org/cgi/reprint/47/6/1025.pdf)(http://www.ncbi.nlm.nih.gov/pubmed/2837078); Narva et al., 2003: (http://www.jacn.org/cgi/reprint/22/1/88.pdf)(http://www.ncbi.nlm.nih.gov/pubmed/12569119?dopt=Abstract); Kärkkäinen et al., 1997: (http://www.ajcn.org/cgi/reprint/65/6/1726.pdf)(http://www.ncbi.nlm.nih.gov/pubmed/9174467)] are some articles showing serum phosphate (or phosphorus) responses to phosphate ingestion from milk or sodium phosphate. The molarity conversion issues are just very difficult to see, and I'm only now becoming able to interpret the meaning of statements about "serum P" or "P ingestion." Usually or almost always, a dosage of "P" means phosphate. One can tell because people who obtain the highest amounts of phosphate from their diets get between 2,200 and 2,400, or so, mg of phosphate per day from foods. But, supposedly, only about 50 percent of the phosphate from vegetable protein (from grains or non-animal-derived foods that are not specifically processed in a way that increases their phosphate contents) is utilizable. That doesn't mean it displays 50 percent bioavailability, by any means, and I think less than 50 percent is utilizable. Even phytates that enter the systemic circulation are excreted in the urine, to a large extent, and apparently don't enter cells very easily (I discussed an article on that topic in a past posting). I honestly don't understand what the meaning of serum phosphate and serum phosphorus actually are, because the conversion factors that every article gives is based on the molar mass of phosphorus (even for converting "serum phosphate" from mg/dL to mM). I think many researchers don't understand the conversions either, because I've seen some serious issues with the calculations being made by some researchers. I don't see how anyone could understand it. One can sometimes get a sense of a conversion by comparing one's calculations to established norms, but that doesn't mean one really knows what "serum P (mM)" or "serum phosphate (mM)" actually means (except in comparison to "serum P (mg/dL)" or "serum phosphate (mg/dL)" in those specific instances. If you don't know what they're referring to to start with, you can't tell what the meaning of the converted number is. Here are the conversion factors used frequently in the literature, from what I can tell (though I can't guarantee these will be valid, with 100 percent certainty, all the time, given that it's essentially not possible to be sure what anyone is referring to--I wish I were exaggerating this):
To convert serum "phosphate" or "phosphorus" from mg/dL to mM, multiply by 0.3229
To convert from mM to mg/dL, divide by 0.3229 or multiply by 3.097 (3.097 is one tenth of the molar mass of phosphorus, not phosphate, though this conversion factor is used to interconvert serum "phosphate" values)
At least some of the newer animal studies on phosphate metabolism express the dietary contents in terms of "phosphate" intake. I keep thinking I'm missing something, but I'm not. I challenge anyone to make sense of it and explain what the absolute serum phosphate values are. If one starts with serum phosphate, in mM, and tries to do a run-of-the-mill calculation of mg/dL of phosphate, one gets a very large number that's outside of the normal range of "serum P" values. The only thing one can know is the range of phosphate intakes in the diet.
Incidentally, there's obviously no such thing as "elemental phosphorus," in a chemical form, the blood, and the serum phosphate consists of inorganic phosphate [PO4(3-)] and pyrophosphate and some other minor, organic phosphate compounds, such as ATP and those dinucleoside polyphosphates, etc. Most of it is inorganic phosphate, but one can't start with a "serum phosphorus" value and do a calculation, starting with moles of phosphorus present in the circulating phosphate, based on the percent of the circulating phosphate that's phosphorus (it's 32.6 percent, I think). One gets some bizarre number in that case, too.
But the point of this posting is that milk and other dairy products elevate serum phosphate significantly (Kärkkäinen et al., 1997; Narva et al., 2003). Narva et al. (2003) only looked for statistically-significant differences between the effects of two types of milk, not between milk and no milk. But one can see that there's a noticeable elevation. There are many other articles that show this, and I downloaded a couple that actually show it more effectively. But my point is that the same people who say that phosphate is so bad tend to recommend that people drink milk for calcium. Milk acutely elevates both serum calcium and phosphate, and the potential for calcification is a function of the product of [Ca] (it's the serum Ca per se, in mg/dL, and not just ionized calcium that's used to calculate it) and [P]. Researchers refer to it as the molar product, but the units are mg^2/dL^2. The product is supposed to be maintained lower than 55 or 60 mg^2/dL^2 (http://scholar.google.com/scholar?hl=en&q=product+mg2%2FdL2+calcium+phosphorus). It's true that milk elevates serum phosphate but does not elevate parathyroid hormone (PTH) levels, usually, and tends to either decrease or produce no change in PTH levels. But that's not necessarily better than the effect of phosphate intake without calcium, because that doesn't usually elevate serum PTH much, if at all, either, providing the dietary phosphate intake isn't too high. But Brixen et al. (1992) found that phosphate supplementation produced acute increases in serum phosphate that were much larger than the increases that occurred after a few days. That's evident in Figure 1. Nonetheless, the idea that a steady state serum phosphate response to supplementation or even to an increase in dietary intake, in extreme cases, will occur is not necessarily consistent with the data shown in some articles. In that article showing Fanconi's syndrome in the context of mitochondrial disorders [Earle et al., 2004: (http://cat.inist.fr/?aModele=afficheN&cpsidt=15701034)], discussed here (http://hardcorephysiologyfun.blogspot.com/2009/08/hypoparathyroidism-resulting-from.html), one interpretation of the graph of the serum phosphate response of patient 1 (the response to supplementation/repletion of phosphate, for the correction of laboratory-confirmed hypophosphatemia) is that somewhere between 50 and 100 days were required for the serum phosphate to reach a "non-steady-state steady state" and to increase to an undesirably-high level. The homeostatic mechanisms regulating phosphate metabolism were severly disturbed in some of those patients, and the researchers were probably using large amounts of phosphate (the dosages weren't reported). But the point is that there's still reason to be cautious about any source of exogenous phosphate. The upper limits for daily phosphate intake, as reported by researchers, tend to be in the vicinity of 4,000-5,000 mg/day.
If I were going to make any change in the dietary phosphate-to-calcium ratio and wanted to evaluate the effects of that change, I would be inclined to make as precise a change as I reasonably could, such as by estimating the phosphate intake, and try to find a safe, long-term ratio that would make sense in the context of my individual state and level of activity, etc. Obviously, one would want to discuss this type of thing with one's doctor, but one point of the research I cited, in this posting, is that foods, such as milk, can produce significant increases in serum phosphate and that looking at and considering only PTH levels, as a way of evaluating "bone health," is not necessarily going to allow one to draw conclusions that make sense. Those milk-induced increases in serum phosphate are not likely to be present the next day, at the blood test for fasting serum phosphate, but are likely to have biological effects, for better or worse. Milk is even listed, in some old articles, alongside some of those poorly-designed phosphate supplements that contain and contained massive dosages, and the phosphate content is 247 mg phosphate (I'm almost positive that this refers to phosphate and not phosphorus) per 245 grams (~ 1 mg/g) see #01085: (http://www.nal.usda.gov/fnic/foodcomp/Data/SR15/wtrank/sr15w305.pdf)]. I've seen that figure in many different articles. 1 cup is 240 mL, but what's the density? Presumably it's 1 g/mL or thereabouts, but it's astonishing that figuring out this type of information is as much like pulling teeth as it is. So that means one cup of milk has about 247 mg of phosphate, and it's much more potent a source of phosphate than something like soy protein or whatever other phytate-containing, vegetable-derived food is likely to be. That pdf I linked to is the fairly-horrendous USDA table of the "phosphorus" content of foods. If one wants to know the phosphate content of a given food, such as Corn Flakes or another breakfast cereal or whatever, one could also do a search on google scholar and substitute the food in question for Corn Flakes (http://scholar.google.com/scholar?q=%22corn+flakes%22+content+phosphate+OR+phosphorus&hl=en). There tends to be some article in which researchers report the phosphate or mineral content, or whatever, of a given food. For example, I was looking, the other day, and seeing how much copper is in some breakfast cereals, even. I was wondering why supplementing with copper or zinc, at all, would ever seem like an appealing thing to do (such as in the absence of a doctor's instructions or outside of specific deficiency states or disease states) [Johnson et al., 1998: (http://www.ajcn.org/cgi/reprint/67/5/1035S.pdf)(http://www.ncbi.nlm.nih.gov/pubmed/9587148)]. I can't say what the right approach would be for any individual.
No comments:
Post a Comment