Body mass index (BMI) versus age hexile, BMI-adjusted (Adj) urine pH, creatinine clearance (CCr) versus age hexile, and BMI + CCr-adjusted urine pH. Triangles, men; circles, women. Dashed lines are for visual clarity only and imply no interposed information. Values are means ± SE. Linear contrast F = 146, both sexes combined, P < 0.001.