Dietary acid, age, and serum bicarbonate levels among adults in the United States

Background and objectives Greater dietary acid has been associated with lower serum bicarbonate levels in patients with CKD. Whether this association extends to the general population and if it is modified by age are unknown. Design, setting, participants, & measurements This study examined the association of the dietary acid load, estimated by net endogenous acid production, with serumbicarbonate levels in adult participants in theNational 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. Aftermultivariable adjustment, participants in the highest quartile of net endogenous acid production had 0.40 mEq/L (95% confidence interval, 20.55 to 20.26) 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, 20.49 to 20.03), 0.60 (95% confidence interval, 20.92 to 20.29), and 0.49 (95% confidence interval, 20.84 to 20.14) mEq/L lower serum bicarbonate, respectively, compared with participants in the lowest quartile. Conclusion Greater dietary acid is associatedwith lower serumbicarbonate in the generalUS population, and the magnitude of this association is greater among middle-aged and elderly persons than younger adults.