Is Coffee Actually Dehydrating? Here’s What Dietitians Say

Coffee is ubiquitous in the lives of many Americans, with nearly 3 in 4 drinking a cup or more daily. However, it’s often said that coffee can dehydrate you, and you should limit how much you drink, especially if it’s first thing in the morning. Some even say you should drink a glass of water before your morning coffee. For regular coffee drinkers, the thought of putting off their morning cup of joe may sound impossible, or it may even be unpleasant. So, is it worth it? Is coffee dehydrating? We asked multiple dietitians for their take, and their answers may surprise you.  

Caffeine and Its Diuretic Effect

Coffee is known for its caffeine, the active ingredient that acts as a central nervous system stimulant. This compound is one of the primary reasons many people drink coffee, especially as a morning beverage. Caffeine is a known diuretic with its effects amplified in large doses. “A diuretic is any substance that promotes the excretion of water and excess salt through the production of urine,” says Amy Goblirsch, RDN. “Diuretics are commonly used to treat heart failure, hypertension and certain kidney diseases.”

Although often said to be an energy booster, the caffeine in coffee doesn’t exactly work as you’d expect. “It’s important to keep in mind that caffeine does not give our body energy,” says Chloe Giraldi, M.S., RD, an eating disorder and sports dietitian. “In its role as a stimulant, it only helps us feel more alert or focused by binding to adenosine receptors in our brain (which are typically responsible for making us feel sleepy throughout the day)—by blocking these receptors, we are left with temporary feelings like alertness.”

So, Does Coffee Dehydrate You?

There’s a lot of confusion about coffee’s effect on hydration. Because caffeine acts as a diuretic, it’s thought that drinking coffee contributes to dehydration. However, the diuretic effect of caffeine is mild, especially in those who have a tolerance to caffeine. Research has shown that caffeine intake at recommended doses does not result in dehydration.

“The thought that coffee consumption causes dehydration is due to outdated research that stated 300 milligrams or more of caffeine can cause diuresis—an increased production and elimination of urine by the kidneys,” says Umo Callins, M.S., RD, CSSD, LD CPT, a board-certified sports dietitian. As a reference, 1 cup of regular coffee contains almost 100 mg of caffeine. 

However, Callins says the increase in diuresis is short-term and often not to the point of causing dehydration. “Current research shows that people who regularly consume the average amount of caffeine from coffee (2 to 3 cups) don’t experience a significant diuresis effect,” she says.

Factors to Consider

The Amount of Coffee You Drink

Going overboard on caffeine can have adverse effects on hydration. “Excessive amounts of caffeine, such as 500 mg or more, may cause a short-term increase in urine output,” says Callins. It’s also important to note that this applies to people who regularly consume not only coffee but also other caffeinated beverages, such as tea and energy drinks. A tolerance to caffeine builds up over time, which reduces the diuretic effects of caffeine.

Other Dietary Habits

The amount of caffeine you consume throughout the day is critical when determining how coffee influences hydration. Sara Cully, RD, ACSM-CPT, CIEC, recommends focusing on daily intake versus the morning beverage alone. “Since it’s not uncommon to serve or offer coffee at social gatherings or in public settings, it’s important for the individual to know their limits, especially if they have heart problems like irregular heart rhythms, acid reflux, sleep issues, headaches or anxiety,” she says. Regularly turning to water or other decaffeinated beverages is essential for optimal hydration. Additionally, the foods you eat can contribute to total water intake. These include fruits, vegetables, soups and broths, smoothies and milk.

Does Coffee Count Toward Your Water Intake?

In short, yes! “Coffee can provide hydration since most of the beverage is water, but it shouldn’t be the only fluid you consume all day,” says Cully. Remember that coffee only contributes to hydration if caffeine doesn’t exceed 500 mg daily. And since you can build a tolerance to caffeine, this recommendation only applies to those who regularly consume caffeinated coffee or other caffeinated beverages.

Still, it’s not advised to drink coffee as your primary source of hydration, mainly if your preferred coffee beverage contains added sugar or a significant source of saturated fat, such as cream. Water is essential for optimal hydration and should be the primary beverage for healthy adults.

How Much Coffee Is Too Much?

Because coffee contains caffeine, you should not consume it excessively. The Dietary Guidelines for Americans recommends healthy adults consume no more than 400 mg of caffeine daily. That’s equivalent to approximately 4 cups of brewed coffee; however caffeine content can vary between roasters. Other beverages like tea and energy drinks can also contribute to this 400 mg limit. The recommendation changes for those who are pregnant or breastfeeding as well as those who have chronic health conditions, making them more sensitive to caffeine.

Additionally, athletes may need to pay special attention to their total caffeine intake. “Certain organizations like the National Collegiate Athletic Association (NCAA) and the International Olympic Committee (IOC) have limits around caffeine intake,” says Giraldi. Finally, children and teens should limit or avoid caffeine completely. “Children under the age of 12 should avoid all caffeine,” says Jenny Lo, M.S., RD. “Teens between the ages of 12 and 18 should limit caffeine to 100 mg per day (approximately one 8-ounce cup of coffee).”

How to Know If You’re Dehydrated

Everyone’s fluid needs vary depending on a variety of factors, from age and body size to medications, chronic health conditions and activity level. Because of this, it’s essential to listen to your body’s cues. And if you have questions about your total fluid requirements, discuss your hydration needs with your primary health care provider. Signs of dehydration can vary from person to person but generally may include:

• Headache
• Lethargy
• Dark urine
• Low urine output
• Fast heart rate
• Thirst
• Dry skin or cracked, dry lips 

Tips to Stay Hydrated While Enjoying Coffee

Even though coffee does not cause dehydration, as was once believed, it’s still important to hydrate with other beverages, especially water. “If coffee is prioritized over other fluids and an individual only drinks four coffees (32 ounces) daily, and nothing else, the reason they are not hydrated enough is because they have not consumed enough fluid in the day, and this is not the coffee’s fault,” Cully says. Consider drinking water or other decaffeinated beverages in between your cups of coffee. If you crave additional flavor in your water, try adding herbs or fresh fruit. Or if a hot beverage is what you crave, switch to a decaffeinated hot tea or hot water with a squeeze of lemon. All of these can contribute to your daily hydration needs.

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The Bottom Line

There’s no need to eliminate your daily coffee over concerns of it causing dehydration. Instead, enjoy your coffee while sticking to the recommended daily limits. Add decaffeinated beverages to your day, especially water, to ensure you meet your hydration requirements without exceeding total caffeine recommendations.