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Increasing alkali supplementation decreases urinary nitrogen excretion when adjusted for same day nitrogen intake

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Abstract

Summary

We examined whether escalating doses of potassium bicarbonate (KHCO3) supplements alter urinary nitrogen excretion expressed as a ratio to same day nitrogen intake (measure of muscle-protein breakdown). The ratio declined significantly from placebo to low to high dose of KHCO3 supplementation in older adults over 3 months, suggesting muscle-sparing.

Introduction

Neutralization of dietary acid load with alkali supplementation (i.e., KHCO3) has been hypothesized to have muscle protein-sparing effects. In controlled feeding studies with fixed nitrogen (N) intake/day, 24-h urinary N excretion is a good marker of muscle breakdown. However, in studies with self-selected diets, changes in 24-h urinary N excretion can be influenced by shifts in N intake.

Methods

We evaluated changes in 24-h total urinary N excretion as a ratio of N excretion to concurrent N intake in 233 older men and women who participated in an 84-day KHCO3 supplementation randomized placebo-controlled trial.

Results

After adjustment for relevant cofactors, escalating doses of KHCO3 (1 mmol/kg/day [low] or 1.5 mmol/kg/day [high]) resulted in a progressive decline in urinary N excretion/N intake compared to placebo (overall P for trend = 0.042). The 84-day change in urinary N excretion/N intake in the high-dose KHCO3 group was statistically significantly lower compared to placebo (P = 0.012) but not compared to the low-dose KHCO3 group (P = 0.276). The 84-day change in urinary N excretion/N intake in the low-dose KHCO3 group did not differ significantly from placebo (P = 0.145).

Conclusions

Urinary N excretion expressed as ratio to same day N intake declined steadily with increasing doses of KHCO3 supplementation from low 1 mmol/kg/day to high 1.5 mmol/kg/day, suggesting a nitrogen-sparing effect. Compared to urinary N excretion alone, this ratio could be a more reasonable measure of muscle protein metabolism in large-scale long-term human studies.

Trial registration: Clinicaltrials.gov NCT1475214

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Acknowledgements

This study was funded by NIH/NIAMS grant number 1RO1AR060261. This material is based upon work supported by the US Department of Agriculture, under agreement No. 58-1950-0-014. Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the authors and do not necessarily reflect the view of the US Department of Agriculture.

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Authors and Affiliations

  1. Nutrition, Exercise Physiology and Sarcopenia Laboratory, Jean Mayer USDA Human Nutrition Research Center on Aging at Tufts University, 711 Washington Street, Boston, MA, 02111, USA

    L. Ceglia & B. Dawson-Hughes

  2. Division of Endocrinology, Diabetes and Metabolism, Tufts Medical Center, Boston, MA, USA

    L. Ceglia & B. Dawson-Hughes

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  1. L. Ceglia
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  2. B. Dawson-Hughes
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Correspondence to L. Ceglia.

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Ceglia, L., Dawson-Hughes, B. Increasing alkali supplementation decreases urinary nitrogen excretion when adjusted for same day nitrogen intake. Osteoporos Int 28, 3355–3359 (2017). https://doi.org/10.1007/s00198-017-4196-8

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  • DOI: https://doi.org/10.1007/s00198-017-4196-8

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