# Combined glycerol and sodium bicarbonate elicits improvements in fluid retention and blood buffering capacity

## TL;DR

This study found that combining glycerol and sodium bicarbonate improves fluid retention and blood buffering better than either alone.

## Contribution

The novel finding is that the combination of glycerol and sodium bicarbonate does not offer additional fluid retention benefits but improves blood buffering capacity.

## Key findings

- Fluid retention was significantly higher with glycerol + sodium bicarbonate compared to control.
- Blood pH and bicarbonate concentration were higher with sodium bicarbonate and its combination.
- No significant additive effects on fluid retention were observed with the combination treatment.

## Abstract

Background: It is unclear whether hyperhydration induced via glycerol, sodium bicarbonate or a combination of the two is most effective.

Aim: This study evaluated the effects of glycerol-, sodium bicarbonate-, and glycerol + sodium bicarbonate-induced hyperhydration on measures of fluid retention, blood buffering capacity, and gastrointestinal symptoms at rest, in comparison to a fluid-only control.

Eleven healthy participants (six male) completed four trials (randomised, crossover design). Treatments consisted of glycerol-(G) = 1.0 g·kg-1 body mass glycerol; sodium bicarbonate-(SB) = 0.3 g·kg-1 body mass sodium bicarbonate; and combined glycerol and sodium bicarbonate supplementation-(G + SB) = 1.0 g·kg-1 body mass glycerol + 0.3 g·kg-1 body mass sodium bicarbonate; and a fluid only control-(CON) = 25 mL·kg-1 body mass artificially sweetened water. At baseline and at 20 min intervals for 180 min, urine samples were collected and analysed for volume, colour, and specific gravity, and gastrointestinal symptoms and body mass were quantified. At 60 min intervals, capillary blood was analysed for pH, blood bicarbonate concentration and plasma volume change.

Compared to CON, fluid retention was significantly higher with G + SB from 120–180 min, SB from 120–140 min, and G from 160–180 min (p < 0.05), and accumulated urine volume was significantly lower with G + SB from 100–180 min, SB from 120–180 min, and G from 140–180 min (p < 0.05). There were no significant differences in fluid retention between G + SB, SB or G at any time point (p > 0.05). Compared to G and CON, blood pH and blood bicarbonate concentration was significantly higher with G + SB and SB from 60–180 min (p < 0.05).

Fluid retention improved in G, SB and G + SB compared to CON, although there were no additive effects with G + SB compared to SB or G. Buffering capacity was significantly higher with SB and G + SB compared to G and CON. Minimal GI symptoms were induced by G, SB, G + SB and CON.