articleLow urine pH and acid excretion do not predict bone fractures or the loss of bone mineral density : a prospective cohort study

Background: The acid-ash hypothesis, the alkaline diet, and related products are marketed to the general public. Websites, lay literature, and direct mail marketing encourage people to measure their urine pH to assess their health status and their risk of osteoporosis. The objectives of this study were to determine whether 1) low urine pH, or 2) acid excretion in urine [sulfate + chloride + 1.8x phosphate + organic acids] minus [sodium + potassium + 2x calcium + 2x magnesium mEq] in fasting morning urine predict: a) fragility fractures; and b) five-year change of bone mineral density (BMD) in adults. Methods: Design: Cohort study: the prospective population-based Canadian Multicentre Osteoporosis Study. Multiple logistic regression was used to examine associations between acid excretion (urine pH and urine acid excretion) in fasting morning with the incidence of fractures (6804 person years). Multiple linear regression was used to examine associations between acid excretion with changes in BMD over 5-years at three sites: lumbar spine, femoral neck, and total hip (n = 651). Potential confounders controlled included: age, gender, family history of osteoporosis, physical activity, smoking, calcium intake, vitamin D status, estrogen status, medications, renal function, urine creatinine, body mass index, and change of body mass index. Results: 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. Conclusion: Urine pH and urine acid excretion do not predict osteoporosis risk. Background Osteoporosis is a disease that causes pain, disability, reduced quality of life [1], mortality [2], and places substantial demands on health care budgets [3,4]. According to the acid-ash hypothesis, the modern diet produces residual acid after metabolism [5-7]. This diet-derived acid is thought to be buffered by bicarbonate from bone, followed by bone calcium excretion in the urine [5-7]. Numerous papers in the medical literature (experimental trials [6-14], cross sectional studies [5,15], prospective studies [16-19], and animal models [20]) identify the potential acid load of the diet as a risk factor for osteoporosis. Well-respected textbooks [21] and reference works [22,23] uphold this concept. Of public health importance, the acid-ash hypothesis is marketed to the general public as the "alkaline diet", to decrease acidity, to help the body regulate its pH, and to prevent numerous disease processes. Websites[24,25], lay literature [26-28], magazine advertisements, and direct mail marketing encourage people to measure their urine pH to assess their risk of osteoporosis as well as their general health status [24,29]. Urine pH of people consuming modern diets tends to be slightly acidic, with pH of approximately 6 [14,30]. When urine pH is found to be acidic, the "alkaline diet" and the purchase of products to achieve acid-base balance are advocated. In the medical literature, the diet acid load has been quantified in food ([sulfate + chloride + 1.8x phosphate + organic acids] minus [sodium + potassium + 2x calcium + 2x magnesium] in mEq/day [10]), as well as in urine * Correspondence: tanisfenton@shaw.ca 1 Department of Community Health Sciences, Faculty of Medicine, University of Calgary TRW Building, 3rd Floor, 3280 Hospital Drive NW, Calgary, Alberta,