Three types of drinks exist based on tonicity – hypotonic, hypertonic and isotonic – with hypotonic drinks offering the best solution for athletes or blue collar workers needing to rehydrate quickly and safely.
Tonicity refers to the concentration of carbohydrates (sugars) and electrolytes in a solution compared to the concentration of these components in human blood.
This, in turn, affects how quickly the body can absorb its fluids and nutrients, impacting hydration and energy levels differently depending on tonicity.
So while some sports drinks might provide the essential electrolytes and branch chain amino acids, particularly for outdoor blue collar workers who sweat an average of four to five litres in a 10-hour shift, not all drinks are equal.
Nor is drinking excessive amounts of water always the best way to rehydrate as this can lead to diluted blood sodium levels and deadly hyponatremia.
Instead, choosing the right drink by understanding tonicity and its impact on fluid uptake is essential for workers to rehydrate quickly and safely.
Isotonic, hypotonic and hypertonic rehydration drinks:
Isotonic drinks have a similar concentration of carbohydrates and electrolytes to human blood, legislated as an average osmolality of 250–340 milliOsmol/L, according to the Australian New Zealand Food Standards Code.
Hypotonic drinks (such as THORZT) have a lower concentration and hypertonic drinks have a higher concentration than blood.
This tonicity affects osmosis, the movement of water in and out of cells, impacting how quickly fluids and energy are absorbed by the body.
Hypotonic solutions cause blood cells to absorb fluids faster than they lose them, while the opposite occurs in hypertonic solutions and isotonic solutions are at equilibrium.
What this translates to in hydration drinks is that hypotonic solutions cause water to be absorbed quickly by the body due to low levels of carbohydrates and sodium, but provide low energy.
Isotonic drinks increase the absorption rate of water as well, though not as significantly, while also maximising the absorption rate of carbohydrates, providing an energy boost.
Conversely, hypertonic drinks, containing high levels of carbohydrates and minerals, are used to replace energy following prolonged strenuous exercise, however will not replace lost fluids as quickly.
Hypotonic vs isotonic for hydration
Both hypotonic and isotonic solutions have been found to be more appealing than water and to result in less body mass loss during exercise, with hypotonic drinks also likely to reduce some inflammatory responses due to physical exertion.
However, while isotonic drinks are often used to combat dehydration during exercise, hypotonic drinks could be a better solution and are recommended for those looking to replace fluids lost to sweat quickly.
According to Australian standards, isotonic drinks can only claim to treat or prevent mild dehydration as a result of sustained strenuous exercise, while no such restrictions exist for hypotonic drinks.
A 2011 study of 11 cyclists compared the effects of a commercial hypotonic drink with commercial isotonic, hypertonic and placebo alternatives.
Peak power was highest with the hypotonic drink and the study’s results were congruent with the hypotonic drink providing the fastest fluid uptake. The researchers determined that further research was warranted to determine exactly how much this impacts performance.
Regardless, for blue collar and industrial workers losing significant quantities of water due to sweating, choosing a hypotonic drink – such as THORZT – is likely to offer the quickest route back to hydration and good health.
Hypotonic drinks cause blood cells to swell as they absorb fluid faster than they lose it.