Glycerol and IV fluids for rehydration in nine male cyclists
What it found
Adding glycerol to drinks helped restore blood volume after heavy sweating, but did not clearly reduce urine output compared with drinks alone.
This was tested in nine trained male cyclists.
What they found
Studies in people
Blood volume recovery
Adding glycerol to drinks restored blood volume more than plain drinks. Combining a fluid drip with glycerol drinks gave the highest blood volume of all four methods.
Urine output
Men who received a fluid drip produced about 40% less urine than those who only drank fluids. Adding glycerol to the drinks did not consistently lower urine output compared with the same method without glycerol.
Stress and salt hormones
Fluid drips led to lower levels of the stress hormone cortisol during rehydration. Aldosterone, a hormone that controls salt balance, was also lower when men received drips compared with drinking alone.
Thirst sensation
Men felt thirstier after receiving both a fluid drip and glycerol drinks compared with glycerol drinks alone. Thirst levels were similar across all methods during the cycling test that followed.
Cycling performance
A separate report from this same trial found that men cycled a 40 km test faster after taking glycerol, after a drip, or after both, compared with plain drinks. Times improved by 3.5% to 4.1%.
What the authors conclude
- They conclude that combining a fluid drip with oral glycerol helped athletes hold onto more fluid than other methods.
- The authors advise that this approach may benefit athletes who train multiple times a day in hot conditions with short breaks.
- They note that future research should look at whether glycerol works better mixed with sports drinks than with plain water.
How it was done
Athletes sometimes use fluid drips into a vein to rehydrate quickly, but the body often flushes that extra fluid out as urine. The authors wanted to see if drinking glycerol alongside fluids could help the body hold onto more water.
Nine endurance-trained men exercised in heat until they lost 4% of their body weight. They were then given back 150% of the lost fluid over two hours using four different methods: drinks only, drinks with glycerol (1.5 g/kg), half drip and half drink, or half drip and half drink with glycerol. Each man tried all four methods in random order, at least two weeks apart.
What it can’t tell you
- Only nine highly trained young men took part, so the results may not apply to women, older adults or everyday shoppers.
- The study measured effects over a few hours of exercise and recovery, not long-term daily use of glycerol.
Who paid
- Authors work at
- The University of Queensland, Australia
The paper
- Title
- Hydration and endocrine responses to intravenous fluid and oral glycerol
- Type
- Randomised controlled trial
- Evidence
- Studies in people
- Summarised from
- Full text
- Cite
- van Rosendal SP, Strobel NA, Osborne MA, Fassett RG, Coombes JS (2015). Hydration and endocrine responses to intravenous fluid and oral glycerol. Scandinavian journal of medicine & science in sports. doi:10.1111/sms.12367Free full textPubMed 25943662DOI
Summary written 30 Sep 2026. Check it against the paper before it changes what you eat. How we summarise papers · Report an error