Association between the markers of metabolic acid load and higher all-cause and cardiovascular mortality in a general population with preserved renal function

Although metabolic acid load has been associated with many well-known risk factors for mortality, its clinical implications are not yet clear. To evaluate the association between biomarkers of metabolic acid load, such as serum bicarbonate, serum anion gap and urine pH and mortality, we analyzed the health records of 31 590 adults who underwent a health screening between January 2001 and December 2010 and had an estimated glomerular filtration rate >= 60 ml min(-1) per 1.73 m(2). Urine pH was measured by a dipstick test performed on fast morning urine sample and categorized as acidic (urine pH <= 5.5), neutral and alkaline (urine pH >= 8.0). Using the Cox proportional hazard model, the adjusted hazard ratio (aHR) of all-cause mortality of the lowest quartile of serum bicarbonate was 1.460 (95% confidence interval (CI) 1.068-1.995) compared with the highest quartile, after a median follow-up of 93 months. The aHRs of cardiovascular and cancer mortality of the lowest quartile of serum bicarbonate were 2.647 (95% CI 1.148-6.103) and 1.604 (95% CI 1.024-2.513), respectively, compared with the highest quartile. Acidic and neutral urine pH were significantly associated with a higher all-cause mortality (aHR 2.550, 95% CI 1.316-4.935; aHR 2.376 95% CI 1.254-4.501, respectively), compared with an alkaline urine pH. In conclusion, higher metabolic acid load was associated with an increased all-cause and cardiovascular mortality in a healthy population. The association between metabolic acid load and mortality and the causality of the relationship need to be confirmed.