- Some people say that drinking caffeinated drinks, such as tea and coffee, will dehydrate you.
- This might not be accurate.
- Business Insider spoke to Ali Webster, PhD, RD to find out what happens to your body if you drink only tea and coffee all day with no water.
- Webster said the hydrating aspects of tea and coffee outweigh the small diuretic effect they can have.
- Some associate caffeinated drinks with dehydration because of the dry feeling they can leave in the mouth, but this, she said, doesn’t translate to dehydration.
- Heavy caffeine intake, however, can cause other unwanted side effects.
- Monitoring your urine is the simplest way to assess hydration.
The smugness of people who drink copious amounts of water every day might be somewhat unfounded – or their scorn for people who only drink tea and coffee might be, at least.
Many health fanatics and fitness influencers advocate drinking several litres of water every day. Some also argue that caffeinated drinks like tea and coffee won’t hydrate you in the same way that the pure stuff will, and will even dehydrate you.
But is this just a myth?
Business Insider spoke to Ali Webster, PhD, RD, and associate director of nutrition communications at the International Food Information Council Foundation(IFIC), to find out what happens to your body if you drink only tea and coffee all day – and no water.
The hydrating aspects outweigh the small diuretic effect
Speaking about a day of drinking just tea and coffee, Webster said: “You’ll probably be extremely over-caffeinated!”
She continued: “When consumed in large doses – about the amount in five cups of coffee – caffeine can induce a small diuretic effect, meaning that our bodies increase urine production to remove more fluid.”
However, she said this doesn’t necessarily mean they’re less hydrating.
“The hydrating aspects of tea and coffee outweigh the minor increase in fluid offloading, so these drinks have a net positive effect on hydration,” she said.
“In addition, building up a caffeine tolerance – like what happens when your morning cup of coffee becomes your morning three cups of coffee – will lower the diuretic effect.”
The dry mouth sensation
One other reason that caffeinated drinks are commonly associated with dehydration, according to Webster, is because some people experience a dry mouth feeling after drinking them.
“This is due to tannins, which are compounds found in tea, coffee, some fruits, and even dark chocolate,” she said. “When we eat or drink these foods, tannins bind to our saliva, causing that drying, astringent feeling.”
However, she said this doesn’t translate into dehydration, since these drinks are mostly water.
Coffee could have similar hydrating qualities to water
Researchers at the School of Sport and Exercise Sciences at the University of Birmingham directly compared the effects of coffee consumption against that of water ingested across a range of hydration assessment techniques.
In the study 50 male coffee drinkers, who usually drank three to six cups per day, participated in two three-day trials.
In separate instances each participant consumed either four 200ml cups of coffee in a day or the same amount of water.
“Our data show that there were no significant differences across a wide range of haematological and urinary markers of hydration status between trials,” they said.
They deduced that this suggests that coffee, when consumed in moderation by regular male coffee drinkers, provides similar hydrating qualities to water.
It should be noted, however, that this was a small study. The UK’s National Health Service (NHS) previously published commentary on the limitations of the study, highlighting that its short period meant that no longer term effects could not be analysed.
It also said that as the participants were all healthy males, it may not apply to people suffering from diarrhoea, vomiting, or living with conditions like kidney disease, who are at risk of dehydration, among others.
Heavy caffeine can cause other side effects
“Drinking coffee or tea as a beverage of choice is fine – up to a point,” Webster went on.
“For most healthy adults, it’s safe to consume up to 400mg of caffeine a day – that’s about four cups of regular coffee or eight cups of black tea. Green tea has slightly less caffeine than black tea (about 25mg per cup), and herbal teas usually aren’t caffeinated.”
However, Webster warned that heavy caffeine intake can cause other unwanted side effects, such as stomach upset, heartburn, restlessness, increased anxiety or nervousness, insomnia, muscle tremors – the “coffee jitters”-, and increased heart rate.
In that respect, Webster said: “It’s best to also include other fluids that don’t contain caffeine, especially water.”
“On average, about 80% of our water intake comes from drinking fluids and the other 20% comes from food – especially those with a high water content, like many fruit and vegetables.
She added that the recommended daily fluid intake for women is around 11 glasses of water, or 2.2 litres, and for men it’s about 13 glasses, or three litres. However, she said some people might need more than these guidelines, if say they are very active or live in walmer climates.
“Drinking enough water is important for removing waste products that result from normal body metabolism,” she continued. “In a person with properly functioning kidneys, excess water is absorbed in the gastrointestinal tract, filtered through the kidneys, and removed from the body through urination.
“People with certain kinds of kidney disease or those who drink large volumes of water in a short time frame may not be able to efficiently filter out the extra water, which can lead to water retention.”
Water retention refers to excess fluid buildup in the circulatory system, body tissues, or cavities. It can cause swelling and puffiness in the hands, feet, and other areas of the body.
There’s a simple way to monitor your hydration
“The best way to maintain water balance in the body [is] to monitor your urine colour – it should be pale yellow, like the colour of lemonade – and pay attention to your thirst sensation,” Webster said.
“If you feel thirsty, it’s likely that you’re already a little dehydrated. If you’re not thirsty and your urine is pale yellow, you’re likely getting enough water.”
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