Context: Bicarbonate has been implicated in bone health in older subjects on acid-producing diets in short-term studies.

Objective: The objective of this study was to determine the effects of potassium bicarbonate and its components on changes in bone resorption and calcium excretion over 3 mo in older men and women.

Design, Participants, and Intervention: In this double-blind, controlled trial, 171 men and women age 50 and older were randomized to receive placebo or 67.5 mmol/d of: potassium bicarbonate, sodium bicarbonate, or potassium chloride for 3 mo. All subjects received calcium (600 mg of calcium as triphosphate) and 525 IU of vitamin D₃ daily.

Main Outcome Measures: 24-Hr urinary N-telopeptide and calcium were measured at entry and after 3 mo. Changes in these measures were compared across treatment groups in the 162 participants included in the analyses.

Results: Bicarbonate affected the study outcomes whereas potassium did not; the two bicarbonate groups and the two no bicarbonate groups were therefore combined. Subjects taking bicarbonate had significant reductions in urinary N-telopeptide and calcium excretion, when compared with subjects taking no bicarbonate (both before and after adjustment for baseline laboratory value, sex, and changes in urinary sodium and potassium; P = 0.001 for both, adjusted). Potassium supplementation did not significantly affect N-telopeptide or calcium excretion.

Conclusions: Bicarbonate, but not potassium, had a favorable effect on bone resorption and calcium excretion. This suggests that increasing the alkali content of the diet may attenuate bone loss in healthy older adults.