The Effect of Alkaline Potassium Salts on Calcium and Bone Metabolism

Abstract

Diets in industrialized nations are no longer based predominately on potassium rich fruit and vegetables, resulting in substantially lower potassium intakes as well as the alkaline anions such as bicarbonate and citrate that accompany potassium in fruit and vegetables. The reduction in potassium and alkali intake while maintaining adequate dietary protein intake leads to an imbalance between the acid producing and the base producing components of the diet. This dietary net acid load is theorized to require mobilization of skeletal base to aid in acid neutralization, leading to ongoing skeletal resorption to maintain systemic acid base homeostasis. Short-term calcium balance studies suggest that supplementing the diet with alkaline potassium salts lowers urine calcium losses with no increase in stool calcium, resulting in a net improvement in calcium balance. The majority of studies examining potassium supplements also suggest bone resorption is reduced by potassium citrate or bicarbonate. However, not all studies show a reduction in bone turnover and the two existing bone density trials provide conflicting results. In particular, controversy remains over whether the benefits to calcium metabolism demonstrated in the short-term calcium balance studies persist. To address this controversy, we conducted a randomized, placebo controlled trial in 52 men and women (mean age 65.2 + 6.2 years) who were randomly assigned to potassium ­citrate 60, 90 mmol, or placebo daily with measurements of bone turnover markers, net acid excretion, and calcium metabolism including intestinal fractional calcium absorption and calcium balance at baseline and 6 months. At 6 months, 24-h urine calcium was significantly reduced in both potassium treatment groups and fractional calcium absorption was not changed by potassium citrate supplementation. In subjects randomized to potassium citrate 90 mmol/day, net calcium balance was significantly improved compared to placebo. Serum C-telopeptide, a marker of bone resorption, decreased significantly in both potassium citrate groups compared to placebo, while bone specific alkaline phosphatase did not change. Our study supports the hypothesis that supplementation with alkaline potassium salts such as potassium citrate has the potential to improve skeletal health. Studies with definitive outcomes such as bone density and fracture are needed.