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Both Coca-Cola and Pepsi add phosphoric acid $H_3PO_4$ to their colas to give them a signature "bite".

The kidneys use a phosphoric acid/dihydrogen phosphate/hydrogen phosphate homeostasis as one mechanism to eliminate/excrete excess acid from the body.

The issue of whether sodas containing phosphoric acid can exacerbate osteoporosis and related conditions has been explored here and in some detail on Wikipedia, but I'm more interested in direct effects on the kidney.

I'm interested to know if the overall renal physiology is adversely affected by extra phosphoric acid that long-term moderate consumption (say a single 2L bottle per week for a year) of soda would introduce (including interrupting or saturating the Na-Pi transporter)?

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Could you define "long-term"? Say, one 200ml can of soda/day for 10 years? –  nico Dec 2 '12 at 8:46
@nico That's a good idea. I was trying to make it more abstract and less "medical advice"y. –  jonsca Dec 2 '12 at 8:47
It's just that I have the feeling that the result would vary a lot depending on the frequency of assumption (not that I have any data whatsoever regarding this issue. Very interesting nevertheless!) –  nico Dec 2 '12 at 10:00
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1 Answer

up vote 2 down vote accepted

The phosphoric acid in cola will contribute to dietary intake of phosphate. I may be missing something, but, since the transporter functions to reabsorb phosphate that has been filtered out at the glomerulus, excess phosphate will spill over into the urine.

According to Wikipedia the RDA for phosphorus is 700 mg and the tolerable upper intake level is 4000 mg. Coca cola contains 17 mg phosphorus (as phosphate) 100 ml-1 (which is 340 mg in 2 L)

According to this source,

in the United States, an average person drinks 412 8-ounce drinks — or 3296 ounces — of Coke per year.

This works out at 9 oz per day = 266 ml = 45 mg phosphorus

For comparison (from here):

  • white flour contains 595 mg 100 g-1
  • one boiled egg contains 220 mg
  • canned salmon contains 240 mg 100 g-1
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No, you didn't miss anything, great answer! I was thinking about the precision of the acid-base balance of that particular system being disturbed (realizing, of course, that it potentially only handles "spillovers" from the bicarb system, I think). It's interesting to see the comparison of the content with other foods, though I'd be curious about how much of that in the egg, etc., is AMP/ATP and others. –  jonsca Dec 3 '12 at 3:31
Brain fart on selecting this as the answer, sorry for the delay. –  jonsca Jul 11 '13 at 22:36
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