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

Area of Science:

• Gerontology
• Nutritional Biochemistry
• Metabolic Health

Background:

• Alkali supplementation, specifically potassium bicarbonate (KHCO3), is hypothesized to preserve muscle protein.
• Urinary nitrogen (N) excretion is a marker for muscle breakdown, but intake variations complicate interpretation in self-selected diets.
• This study addresses the effectiveness of KHCO3 in mitigating muscle protein breakdown under real-world dietary conditions.

Purpose of the Study:

• To investigate if escalating doses of potassium bicarbonate (KHCO3) supplements influence urinary nitrogen excretion relative to nitrogen intake in older adults.
• To determine the muscle-sparing effects of KHCO3 supplementation over an 84-day period.
• To evaluate the utility of the urinary N excretion to N intake ratio as a marker for muscle protein metabolism.

Main Methods:

• A randomized, placebo-controlled trial involving 233 older men and women over 84 days.
• Participants received escalating doses of KHCO3 (1 mmol/kg/day or 1.5 mmol/kg/day) or a placebo.
• Changes in 24-hour total urinary N excretion, normalized to concurrent N intake, were analyzed.

Main Results:

• Escalating doses of KHCO3 progressively reduced the urinary N excretion/N intake ratio compared to placebo (P for trend = 0.042).
• The high-dose KHCO3 group showed a statistically significant decrease in the ratio compared to placebo (P = 0.012).
• No significant difference was observed between the low-dose KHCO3 group and placebo (P = 0.145).

Conclusions:

• Increasing doses of KHCO3 supplementation (1 to 1.5 mmol/kg/day) demonstrated a nitrogen-sparing effect in older adults.
• The ratio of urinary N excretion to N intake is a more reliable indicator of muscle protein metabolism in long-term human studies than urinary N excretion alone.
• KHCO3 supplementation may offer a viable strategy for preserving muscle mass in aging populations.