Men's Osteoporosis Support GroupUrine pH and bone mineral density: three studies There are three recent articles on the topic of acid-promoting diets, low urine pH and bone mineral density (BMD). Two say there is no problem from a high-protein, high acid diet and one says there is a problem. The discussion will try to find reasons for their differing opinions. Proc Nutr Soc. 2010 Feb;69(1):166-73. Epub 2009 Dec 3. Postgraduate Symposium: Positive influence of nutritional alkalinity on bone health. Wynn E and others. PMID: 19954569. These authors state the problem as, "Western diets consumed by adults generate approximately 50-100 mEq acid/d[ay]; therefore, healthy adults consuming such a diet are at risk of chronic low-grade metabolic acidosis, which worsens with age as a result of declining kidney function." The problem stems from the body's built-in buffering system being the bones. That is, they are dissolved to create positive ions to negate the effect of the acids in the blood stream. Fruits, vegetables, potassium and magnesium are associated with metabolic alkalosis, and are beneficial to bone health. Whereas, "In healthy male volunteers an acid-forming diet increases urinary Ca excretion by 74% and urinary C-terminal telopeptide of type I collagen (C-telopeptide) excretion by 19% when compared with an alkali (base-forming) diet." [Note: C-telopeptide is a biochemical marker of bone resorption]. The authors also point out, "Cross-sectional studies have shown that there is a correlation between the nutritional acid load and bone health measured by bone ultrasound or dual-energy X-ray absorptiometry." They cite a study of 256 women aged 75 or older that showed such a correlation. They mention other studies ". . . of thirty young women that in Ca sufficiency an acid Ca-rich water has no effect on bone resorption, while an alkaline bicarbonate-rich water leads to a decrease in both serum parathyroid hormone and serum C-telopeptide". BMC Musculoskelet Disord. 2010 May 10;11:88. Low urine pH and acid excretion do not predict bone fractures or the loss of bone mineral density: a prospective cohort study. Fenton TR and others. PMID: 20459740. There is free full text of this article online, too. This was a Canadian cohort study that involved 6804 person years to examine the association between urine pH and the incidence of fractures and BMD change in the lumbar spine, femoral neck, and total hip in 651 individuals over five years. The results showed: "There were no associations between either urine pH or acid excretion and either the incidence of fractures or change of BMD after adjustment for confounders." The authors concluded, "Urine pH and urine acid excretion do not predict osteoporosis risk." Curr Opin Clin Nutr Metab Care. 2010 Aug 16. [Epub ahead of print]. Acid diet (high-meat protein) effects on calcium metabolism and bone health. Cao JJ, Nielsen FH. PMID: 20717017. This is a review article for which I have no copy, so I can't adequately evaluate the reasons for the authors' conclusions. But they do conclude, "On the basis of recent findings, consuming protein (including that from meat) higher than current Recommended Dietary Allowance for protein is beneficial to calcium utilization and bone health, especially in the elderly. A high-protein diet with adequate calcium and fruits and vegetables is important for bone health and osteoporosis prevention." Editor's comments. First, note the completely conflicting comments from the Cao and Nielsen study when compared to the Wynn and others study. Cao and Nielsen state, "However, recent findings do not support the assumption that bone is lost to provide the extra calcium found in urine. Neither whole body calcium balance is, nor are bone status indicators, negatively affected by the increased acid load." Wynn and others state, "In healthy male volunteers an acid-forming diet increases urinary Ca excretion by 74% and urinary C-terminal telopeptide of type I collagen (C-telopeptide) excretion by 19% when compared with an alkali (base-forming) diet." Someone is wrong here and Wynn and others provide data in their abstract which we can evaluate, Cao and Nielsen don't. Time and further good, high quality, controlled clinical trials will have to determine exactly what is going on regarding the acid-forming diet and bone health. In the Fenton and others study, there is a free full copy online so it is much easier to evaluate the quality of the study. I have a couple of concerns about this study. My first is that the results are based upon the urine pH of the study participants--a five-year study. During this entire five years there were only two urine pH measurements taken: one at the start of the study and one at the end. The conclusion being that urine pH doesn't change over a five year period, and that means we can conclude that two urine pH measurements taken five years apart exactly measure the urine pH over the entire study period. Here is a study by Parks JH, Barsky R and Coe, FL in the Journal of Urology, that found, "Urine pH was reduced in the 2 sexes during summer but the decrease was far more marked in men, who had a uric acid supersaturation spike." Here is a study in Cancer, Measurement of urine pH for epidemiological studies on bladder cancer, by Alguacil J and others, that found "When using a spot urine sample from a single morning to classify participants with respect to their urine pH, 80% of individuals fell into the acidic urine pH (pH equal to or lower than 6.0) group. When we required subjects to have urine pH equal to or lower than 6.0 in six consecutive AM spot urine samples and seven spot PM urine samples, only 20% of participants fulfilled this criterion." I thus interpret the use of only two urine pH tests over a five-year period as in no way showing what the urine pH actually was of the participants in the Fenton and others study. My second concern would be that if the urine pH test is not predictable because it was only done twice over the five-year study, then the fracture and BMD results are also not valid. That is, you have to have a valid urine pH test result to correlate it with fractures and BMD. Thus I conclude this study in completely invalid and should not be given consideration regarding the effect of urine pH on fracture risk or BMD. For more on this topic see the recent Osteoporosis Issues that discusses the effect of diet on urine pH, potential renal acid load (PRAL), and BMD. Note there are several studies cited there that indeed show an effect of an alkaline-forming diet on bone health. More research is needed and I'll post it here when I see it.
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