From improving cognitive function to lowering the risk of chronic diseases like Type 2 diabetes, coffee has many beneficial qualities. However, there are those who say that coffee dehydrates you. Is this true?
FOR generations, well-meaning friends, fitness instructors and even the occasional doctor have warned coffee lovers that their beloved beverage is secretly sabotaging their hydration efforts.
The advice is often delivered with grave seriousness: every cup of coffee you drink requires two glasses of water to compensate, or you'll end up as dried out as yesterday's toast.
Coffee shops practically need "drink responsibly" warnings, if you believe some of the scaremongering. But can your morning cuppa really leave you dehydrated?
Verdict:
FALSE
Despite what your gym instructor might have told you, coffee does not dehydrate you, at least not in the way most people think.
Yes, while it is true coffee is a diuretic, meaning it can make you urinate more frequently, the effect is far too mild to cause actual dehydration, especially if you're a regular coffee drinker.
A comprehensive review published in the Journal of Human Nutrition and Dietetics examined studies on caffeine and fluid balance and found that doses of caffeine equivalent to the amount normally found in standard servings of tea, coffee and carbonated soft drinks appear to have no diuretic action.
The most credible published research offers no support for the suggestion that drinking caffeinated beverages as part of a normal lifestyle leads to fluid loss in excess of the volume consumed.
Here's the science: yes, caffeine acts as a mild diuretic by reducing sodium reabsorption in the kidneys, which can temporarily increase urine production.
However, your body develops a profound tolerance to these effects if you regularly drink tea or coffee.
A 2014 study published in PLOS ONE directly compared the effects of moderate coffee consumption against water intake across a range of validated hydration assessment techniques.
Fifty male coffee drinkers who habitually consumed three to six cups per day participated in two trials, drinking either four 200ml servings of coffee or water over three consecutive days.
The results? There were no significant differences in total body water between the coffee and water groups.
Coffee, when consumed in moderation by caffeine-habituated males, contributes to daily fluid requirements and does not pose a detrimental effect to fluid balance.
Research published in Frontiers in Nutrition found that habitual coffee consumers drinking amounts not exceeding 3mg of caffeine per kilogramme of body weight should not worry about detrimental diuretic effects.
For context, that's roughly three to four cups of coffee for an average-sized adult.
A meta-analysis of 28 investigations examining caffeine-induced diuresis found the overall effect size was small.
Interestingly, when studies including exercise were omitted, physical activity appeared to actually reduce the diuretic effect of caffeine.
The Mayo Clinic confirms that caffeinated drinks usually won't dehydrate you, though water remains the best option for hydration.
The American Academy of Family Physicians states that normal caffeine intake does not increase the risk of dehydration in athletes or non-athletes.
The US National Institutes of Health says that for most people, it is not harmful to consume up to 400mg of caffeine a day, roughly four cups of coffee. The UK's National Health Service agrees, stating it's fine to drink tea and coffee as part of a balanced diet.
So where did this myth come from? Early research showing the acute effects of caffeine as a mild diuretic in people who hadn't consumed it for days or weeks led to widespread assumptions.
However, these studies don't reflect real-world consumption patterns amongst regular coffee drinkers.
The truth is, coffee contains a lot of water. A standard cup is about 95% water, which more than compensates for any mild diuretic effect. Unless you're drinking absurdly large amounts of very strong coffee, you're getting more fluid in than you're losing out.
Of course, this doesn't mean you should replace all your water with coffee.
Excessive caffeine consumption can cause other issues like jitters, sleep disruption and increased heart rate. Moderation, as with most things, is key.
But if you're a regular coffee drinker enjoying your usual three or four cups a day, you can rest assured that your beloved brew is contributing to your daily fluid intake, not working against it.
Your body is perfectly capable of handling your caffeine habit without turning you into a human raisin.
So the next time someone sanctimoniously tells you to "drink extra water to make up for that coffee", you can smile politely and inform them that science has thoroughly debunked that particular myth.
Then enjoy your coffee, guilt-free and fully hydrated.
References:
1. https://pubmed.ncbi.nlm.nih.
2. https://pmc.ncbi.nlm.nih.gov/
3. https://journals.plos.org/
4. https://pmc.ncbi.nlm.nih.gov/
5. https://www.frontiersin.org/
6. https://pmc.ncbi.nlm.nih.gov/
