Precision Hydration founder and Sports Scientist Andy Blow explains what effect the temperature of a drink can have on your performance in hot conditions...
Can hot drinks cool you down in hot weather?
As a youngster I recall my Dad telling me to have a cup of hot tea if I ever complained about the temperature in the summer, because this would allegedly cool me down.
At the time, I thought this was one of the dumbest things I’d ever heard but, as it turns out, there may be some solid scientific evidence to support this old wives’ tale (so I owe you a big apology for rolling my eyes on this one Dad!).
In conditions where humidity is low and the evaporation of sweat is very efficient, it’s been demonstrated that drinking a hot beverage can cause a disproportionately large sweating response to the actual rise in core body temperature. So, there’s a net heat loss from the body as this extra sweat evaporates.
But, for athletes exercising in the heat and already sweating profusely, drinking hot drinks is neither an appealing, practical or sensible approach.
So, a more relevant question should be, is there a measurable performance difference when drinking very cold drinks vs ambient temperature ones?
The effects of drinking cold water / ice on performance
The effect of cold water (and more specifically ice) ingestion on performance in the heat has been studied quite extensively and generally tends to suggest that the consumption of ice slurries or very cold drinks can be beneficial in certain situations.
There are practical issues to consider though, as the delivery of ice or very cold liquids to athletes during competition isn’t easy, so figuring out if doing so is worth the hassle is important before you consider asking a friend to mobile follow you around with a cooler full of ice on your next bike ride or run!
The management of your core body temperature is perhaps the biggest challenge faced by your body when exercising in the heat. This is because muscular contraction leads to the production of a lot of excess heat that needs to be offloaded to the external environment, usually via the evaporation of sweat.
But, the ingestion of cold water or ice can, theoretically at least, provide an alternative avenue of ‘internal’ heat transfer (rather than having to sweat it all away).
Much of the research in this area has focused on the use of ‘ice slurries’ consumed immediately before exercise to reduce core temperature at the start of an activity, thus giving more ‘headroom’ for core temperature to rise once a race starts. The theory is that this temperature 'buffer' delays the fatigue that inevitably comes when a critical temperature limit is finally reached.
In most studies where pre-cooling with drinks has been tested (such as this example comparing pre-cooling to heat acclimation), researchers have used ice rather than very cold liquids. This is important because the phase change of ice into water in the stomach consumes a lot more heat energy than simply warming up a cold liquid.
So, you get way more ‘bang for your buck’ by necking half a litre of ice slurry than the same volume of cold water, even if that water is extremely close to freezing point.
When should you drink cold drinks / ice?
The studies in this area usually demonstrate measurable performance gains in shorter, higher intensity events, such as cycling time trials or running races where metabolic heat production is very high.
But it’s unclear if they’ll be as effective in longer races where intensities are lower and thermoregulation is less of a limiting factor.
This has led to the adoption of the practice of pre-race ice ingestion becoming relatively popular with pro-cyclists before time-trials.
When we spoke to Team Sunweb’s nutrition expert Lisa Nijbroek, she said:
We use the slush puppy machine before hot time-trials to keep the body core temperature low during the warm-up which often includes bursts of high intensity. This ultimately improves performance.
Apart from the practical challenges posed by trying to get ice drinks to athletes during competition or training, another big reason why research has focused on using them before exercise is the effect that internal cooling can have on sweat rate.
While hot drinks can increase sweat rates, the consumption of ice or very cold liquid can measurably reduce sweat output. This can potentially lead to them ‘cancelling out’ the benefits of the internal heat transfer - a corresponding reduction in external heat loss means that you don’t get measurably cooler overall from drinking the cold drink.
Despite this, in circumstances where access to ice or very cold drinks is possible during exercise, there doesn’t seem to be a strong reason to restrict access to them.
If overall heat loss remains about the same, then the psychological benefits of tasting a lovely ice cold drink could potentially still lead to a small boost in overall performance or at least reduce the perception of effort.
One exception to the rule that cold drinks or ice don’t contribute to overall heat loss might be in environments or situations where evaporation of sweat is already very difficult (i.e. in high humidity or in circumstances where clothing doesn't allow sweat to be wicked away efficiently).
In these scenarios, any reduction in sweating caused by cold drinks won’t have a negative effect on evaporative cooling anyway, so there would theoretically be an overall improvement in heat loss.
This might make them most appropriate in sports like American Football where protective clothing impedes sweat evaporation or in indoor or extremely humid environments where sweating is minimally effective on its own.
One other possible reason why colder beverages might be deemed to be better than ambient temperature ones is the simple fact that an icy cold drink tends to taste vastly more appealing when you’re working hard on a hot day.
In turn, this may act as an encouragement to drink a little bit more fluid overall than you otherwise would.
As dehydration progressively leads to a reduction in blood plasma volume, increasing cardiovascular strain in the heat, it’s not inconceivable that having chilled drinks bottles might work to keep your overall hydration levels topped up more effectively.
So, there could be an argument for making them available where it’s practical to do so.
Fluid absorption rates at different temperatures
It’s been frequently suggested that the temperature of drinks can affect gastric emptying and fluid absorption rates (with colder fluids allegedly getting into the bloodstream faster than warmer ones), but there doesn’t seem to be much in the way of solid evidence to support this.
So, it’s unlikely that there’s a significant difference in the way that cold vs ambient temperature fluids ‘behave’ once ingested into the body.
Does drinking cold drinks in hot weather improve performance?
Ultimately, there’s plausible evidence that using very cold or preferably ice-based drinks immediately prior to shorter, faster races in the heat could lead to a drop in pre-race core body temperature and a measurable improvement in subsequent performance.
Ice slurries are likely to be more effective than cold drinks because of the extra heat energy consumed in the conversion of the ice back into liquid.
In terms of what this looks like from a practical point of view, Team Sunweb’s riders consume about 500ml of ice slushie (made from a carbohydrate-based drink mix) while undergoing their warm-up on rollers immediately before the start of a time-trial in hot weather.
When it comes to drinks consumed during exercise, it’s unlikely that the temperature of the liquid will have a meaningful effect on the rate of absorption into the bloodstream.
But, as colder drinks lead to higher rates of voluntary consumption, there might be an argument in their favour because they could result in better overall replenishment of sweat losses and preservation of blood volume.
It might also be that, where practically possible, drinking ice slurries or very cold drinks during conditions of high humidity or when clothing prevents the easy evaporation of sweat, an overall net cooling effect can be achieved because any negative effect on sweat rate is unimportant.
It’s worth noting that this is less likely to be the case in drier conditions where sweating remains effective due to the potential for the cold liquids to blunt overall sweat output.
Finally, it’s well worth remembering that your Dad is usually right; if you’re sitting around in a hot, dry environment and wanting to cool down, a nice hot cup of tea might actually be what you need - it will stimulate some sweating and result in an overall heat loss.
So, listen to your old man!