Association of Serum Bicarbonate Levels With Gait Speed and Quadriceps Strength in Older Adults

Background: Metabolic acidosis is associated with skeletal muscle proteolysis, and alkali supplementation has shown improvements in lean body mass and urinary nitrogen wasting in several studies. However, the association of acidosis with functional outcomes has not been examined on a population-based level. Study Design: Cross-sectional study. Setting & Participants: 2,675 nationally representative adults 50 years or older in the National Health and Nutrition Examination Survey 1999-2002. Factor: Serum bicarbonate level. Outcomes: Low gait speed and low peak torque were defined as being in the lowest sex-specific quartile of gait speed and peak torque, respectively. Measurements: Serum bicarbonate was measured in all participants. Gait speed was determined from a 20-foot timed walk. Peak torque was calculated using peak isokinetic knee extensor force. Results: Serum bicarbonate level <23 mEq/L was present in 22.7% of the cohort. Compared with participants with bicarbonate levels >= 23 mEq/L, those with bicarbonate levels <23 mEq/L had higher body mass index and serum albumin levels; were more likely to have low socioeconomic status, a diagnosis of diabetes mellitus, or glomerular filtration rate <60 mL/min/1.73 m(2); and were less likely to use diuretics. Serum bicarbonate level <23 mEq/L compared with >= 23 mEq/L was associated with low gait speed (OR, 1.43; 95% CI, 1.04-1.95) and low peak torque (OR, 1.36; 95% CI, 1.07-1.74) after multivariable adjustment. The association with low peak torque was modified by race/ethnicity in women, but not men (ORs, 1.52 [95% CI, 1.08-2.13] for men, 2.33 [95% CI, 1.23-4.44] for nonwhite women, and 0.93 [95% CI, 0.47-1.82] for white women). Limitations: Cross-sectional study using a single bicarbonate measurement. Conclusions: Lower serum bicarbonate levels are associated with slower gait speed and decreased quadriceps strength in older adults. Further studies should examine the effect of alkali therapy on functional outcomes. Am J Kidney Dis. 58(1): 29-38. (C) 2011 by the National Kidney Foundation, Inc.