Drink up: coffee won’t dehydrate you

We’re constantly hearing about how important it is to drink eight or more glasses of water a day. But, like many health recommendations parroted by mainstream medicine and popular science, this advice is too simplistic.

For instance, it has been suggested that caffeinated beverages don’t count toward our recommended fluid intake.

In the August issue of Insiders’ Cures, I told you how coffee could soon be touted as the next health drink. Research shows that a few cups of joe a day can help prevent diabetes, liver failure, prostate cancer, depression, and Parkinson’s disease.

And yet coffee still gets a bad rap from misguided medical “experts”—particularly when it comes to its supposed ability to dehydrate us. In fact, some of these “experts” recommend drinking an extra glass of water for every cup of coffee you consume to ensure adequate hydration.

I’ve been studying hydration for a dozen years now, including the importance of hydration at a cellular level. As I’ve often warned, both mainstream medicine and popular science have a fatally flawed, incomplete understanding of hydration—especially when it comes to evaluating its effects inside the body’s cells, muscles, and other tissues.

One of the most common misunderstandings has to do with coffee. I’ve been concerned about persistent efforts to give this healthful, natural beverage a bad rap, so I delved deeper into the oft-repeated claim that it causes dehydration.

It turns out that high doses of caffeine in coffee can act as a mild diuretic, causing cells to lose water. But as you know, I don’t recommend high doses of anything. If you drink coffee in moderation—one to four cups a day—there is plenty of research showing that it’s actually not dehydrating at all.

Back in 2002, a comprehensive review of 10 studies showed that caffeinated beverages (in moderation) are no more dehydrating than water itself.1

And a study published earlier this year showed that drinking four cups of coffee a day actually has the same hydrating effect on the body as four cups of water.

I’ll tell you more about that study in a moment. But first, let’s look more closely at how hydration works. And how various beverages—including green tea, and all the artificial, supposedly “super-hydrating” sports drinks —compare to coffee.

The science of hydration

Our blood and tissues have a delicate balance of electrolytes—minerals such as sodium and potassium that are important for many bodily functions. Virtually any fluid you consume—whether it’s coffee, beer, or even water—in excess can potentially throw off that electrolyte balance. So to help restore the balance, the body flushes fluids. And if you drink more fluids than your body happens to need at that point in time? More flushing. No matter how supposedly hydrating (or dehydrating) the fluid is supposed to be.

So clearly, maintaining proper fluid and electrolyte balance is a little more complicated than those mindless sports drinks promotions make it sound. And so is actually measuring hydration and dehydration. I have found that the researchers who are best at this measurement  are exercise physiologists. (I consulted with an exercise physiologist at Appalachian State University—Alan Utter, PhD—for some early work on South African rooibos.)

The latest research on the hydration effects of moderate daily coffee intake comes from the School of Sport and Exercise Sciences at the University of Birmingham, and the University of Bath, in the United Kingdom.

These researchers directly compared the effects of coffee versus water consumption, using a wide range of validated hydration measurement tests. Study participants included 50 men who habitually consumed three to six cups of coffee per day.2

During the study, the men’s physical activity, diet, and fluid intake were carefully controlled. Each participant consumed either four cups (about 27 ounces) of caffeinated coffee daily, or the same amount of water.

The researchers discovered that there were no changes in total body water, blood markers, urine volume, electrolyte concentration, or creatinine (measure of kidney function) in either the coffee or the water drinkers from the beginning to the end of the study. The only difference was that the coffee group excreted more sodium than the water group.

The researchers’ conclusion? Moderate coffee consumption (four cups per day) actually hydrates the body the same amount as water does.

What about green tea?

So if coffee and water both hydrate you equally, won’t green tea do the same thing?

Perhaps. But coffee has so many more proven potent health properties than green tea that it’s by far the wiser beverage choice.

Many people regularly drink green tea because of the myth that it provides health benefits, such as reducing the risk of cancer, or helping weight loss. But as I warned in the April issue of Insiders’ Cures, research shows that you would have to drink a whopping 16 cups a day to get the sort of health boosts promised from green tea. Plus, you’re also exposing yourself to unhealthy additives and contaminants in the tea bags and the tea leaves themselves.

Not to mention that  studies have not provided clear evidence that drinking green tea (or even taking green tea extract supplements) has any positive effects on preventing cancer.

In fact, a study of 60,000 men and women in Singapore actually found an increased risk of colon cancer in people who drank green tea, especially in men.3 Other studies looking at green tea and breast cancer have reported results ranging from a small protective effect to no effect at all. And the same sort of mixed results have been found for green tea’s effect on prostate and oral cancer.

Part of the problem is that nobody knows what the actual dose of active “antioxidants” or “anti-cancer” constituents are in a typical cup of brewed tea.

The bottom line is that current evidence shows it’s healthier to drink coffee than it is green or black tea. One to four cups of joe a day will not lead to dehydration, elevation in blood pressure, or other health problems, but it will help you stave off a variety of chronic mental and physical health issues.



Are you drinking enough?

The current Institutes of Medicine (IOM) fluid recommendations are 91 ounces a day for women and 125 ounces for men. However, the IOM notes that about 20 percent of that daily fluid requirement comes from food. So women only need to drink 73 ounces (for example, four cups of coffee and six glasses of water) and men need 100 ounces (for example, four cups of coffee and about nine glasses of water).

Of course, this goal is easier said than done. Actual fluid consumption in healthy adults has been observed to range from only 13 ounces a day up to a whopping 145 ounces. Turns out that the body is remarkably resilient at getting along with the resources it’s provided.

Keep  your caffeine in  your coffee cup

You probably saw the reports recently about a troubling trend regarding caffeine. Pure caffeine powder is being marketed irresponsibly as a dietary supplement claiming to increase alertness and athletic performance. In the aftermath of a fatal overdose in May, the FDA issued a warning about this dangerous supplement.4

Just one teaspoon of this potent powder contains the caffeine equivalent of about 25 cups of coffee. That’s practically a week’s caffeine consumption all at once! An acute overdose like this can result in heart problems, muscle spasms, kidney failure, brain seizures, and even death.

There are certainly much better ways to stay awake or jump-start your exercise regimen. If you want to boost your athletic performance, the first key is proper hydration of muscles and other tissues. As we’ve already learned, moderate coffee consumption hydrates you as well as water. And of course, it’s well known that the caffeine in coffee safely helps keep you alert.

Drink your caffeine in the form of coffee and stay far away from any type of caffeine powder. I’m generally in favor of high-quality dietary supplements, but when it comes to caffeine, it should be obtained from the diet and not from any sort of supplement.


1Armstrong LE. Caffeine, body fluid-electrolyte balance, and exercise performance. Int J Sport Nutr Exerc Metab. 2002 Jun;12(2):189-206.

2Killer SC, et al. No evidence of dehydration with moderate daily coffee intake: a counterbalanced cross-over study in a free-living population. PLoS One. 2014 Jan 9;9(1):e84154. doi: 10.1371/journal.pone.0084154. eCollection 2014.

3Sun CL, et al. Green tea and black tea consumption in relation to colorectal cancer risk: the Singapore Chinese Health Study. 2007 Oct;28(10):2143-8. Epub 2007 Aug 27.

4FDA Consumer Advice on Powdered Pure Caffeine. http://www.fda.gov/food/recallsoutbreaksemergencies/safetyalertsadvisories/ucm405787.htm. Accessed August 25, 2014.