This study examined the association of the dietary
acid load, estimated by net endogenous
acid production, with serum
bicarbonate levels in adult participants in the National Health and Nutrition Examination Survey 1999-2004.
RESULTS: The mean serum
bicarbonate was 24.9 mEq/L (SEM=0.1), and the mean estimated net endogenous
acid production was 57.4 mEq/d (SEM=0.4). Serum
bicarbonate was linearly associated with age, such that the oldest participants had the highest serum
bicarbonate levels. After multivariable adjustment, participants in the highest quartile of net endogenous
acid production had 0.40 mEq/L (95% confidence interval, -0.55 to -0.26) lower serum
bicarbonate and a 33% (95% confidence interval, 3 to 72) higher likelihood of
acidosis compared with those participants in the lowest quartile. There was a significant interaction by age of the association of net endogenous
acid production with serum
bicarbonate (P=0.005). Among participants 20-39, 40-59, and ≥60 years old, those participants in the highest net endogenous
acid production quartile had 0.26 (95% confidence interval, -0.49 to -0.03), 0.60 (95% confidence interval, -0.92 to -0.29), and 0.49 (95% confidence interval, -0.84 to -0.14) mEq/L lower serum
bicarbonate, respectively, compared with participants in the lowest quartile.
CONCLUSION: Greater dietary
acid is associated with lower serum
bicarbonate in the general US population, and the magnitude of this association is greater among middle-aged and elderly persons than younger adults.