Are there any concerns or considerations?

Pre-exercise hyperhydration strategies involving glycerol supplementation need to be practiced in determining their effectiveness for individuals under real-life sorting scenarios. As such, the effectiveness of glycerol hyperhydration or rehydration strategies may depend upon the environmental conditions and exercise situations.

When used in accordance with the recommended ingestion protocols, glycerol is very safe with a very low prevalence of side-effects, making it relatively safe to use. However, the following concerns and considerations should be considered.

Concerns

• Gastrointestinal discomfort, which can, in turn, impair athletic performance
• The gain in body mass associated with more fluid being retained may create a performance impairment
• Nausea
• Headaches
• Laxative effect

Considerations

• Over and under drinking of fluids can be harmful so athletes should seek the advice of an Accredited Sports Dietitian for individual guidance around the use of glycerol.
• If an athlete is unable to tolerate such large volumes of fluid required to induce pre-exercise hyperhydration then a smaller volume of the same concentration of glycerol solution may be ingested closer to the commencement of exercise.⁹
• There is no physiological (i.e., cardiovascular and thermoregulatory) advantage in performing pre-exercise hyperhydration for athletes who can commence exercise in a euhydrated (i.e., normal state of body water content) state when the ability to drink prevents a fluid deficit within 2% of body mass.¹¹ As this is typically not the case during ultra-enduracne races, glycerol-induced hyperhydration is not recommended prior to such activities and may cause prolonged fluid overloading.
• Most laboratory-based hyperhydration studies have compared and quantified the fluid retention achieved through the ingestion large boluses of flavoured water, with and without the addition of glycerol (and sodium). While water services a scientific study as a good ‘control beverage’, a carbohydrate-electrolyte drink may provide a better hydration potential than water alone.¹²