70% of Americans drink coffee every week; 62% drink it daily. As with all things we enjoy, we have to ask: is coffee good for you, and does coffee dehydrate you?

These questions are important because dehydration can exacerbate certain conditions, such as diabetes, or even contribute to the risk of developing such serious health conditions as kidney damage and brain damage. Therefore, keeping an eye on your daily hydration status and paying attention to habits that may affect it, such as coffee consumption, are important. Fortunately, the news on coffee is predominantly good: whether caffeinated or not, coffee consumed in moderation does not significantly impact your hydration status, and this popular drink does not negatively impact your overall health status, either — whether you have diabetes or are generally healthy. 

Why is it important to stay hydrated?

Before we get into the science around "does coffee dehydrate you," let's look at hydration in general. Consuming water, which comprises 55-78% of our bodies, benefits all aspects of physiological functioning. Water helps the body excrete toxins and waste, produces the saliva in your mouth, provides lubrication and cushioning for your bones and joints, helps transport and cycle nutrients and oxygen throughout the body and can help normalize blood pressure. Water is so fundamental to human functioning that a mere loss of 1-2% body water content can result in a noticeable impairment of cognitive function, as well as a significant damper on one’s mood. Staying hydrated is thus an important aspect of achieving optimal health. 

As with most diet and health guidelines, recommendations will vary from individual to individual based on factors such as age, sex, physical activity level, and pregnancy and breastfeeding status. At the end of the day, the goal is to balance your water intake with your daily water losses to maintain internal homeostasis and regular body functioning. 

We consume water in more ways than one. Plain drinking water is the most obvious and simple way to stay hydrated; it is also by far one of the healthiest as it contains zero calories. Yet, water also exists in everyday food and beverages, like coffee. To the gastrointestinal tract, the form that the fluid presents itself typically makes little difference in how the food becomes metabolized and fluid is consumed. Therefore, the more comprehensive measure of hydration status is the daily fluid intake, defined as “the amount of water consumed from foods, plain drinking water, and other beverages.” 

What are the symptoms of dehydration, and who tends to experience it?

Symptoms of dehydration — an imbalance of proper water levels in the body — include a dry mouth, dry tongue, extreme thirst, dark-colored urine, and even fatigue and dizziness (if your dehydration is extreme). 

You could experience dehydration after some sort of physical activity; after a prolonged period of not drinking fluids; or if you are vomiting, experiencing diarrhea, urinating more frequently or you have a fever. And as we get older, our total body water content (BWC) decreases, putting us at a higher risk of dehydration. If you have certain preexisitng medical conditions — including uncontrolled or untreated diabetes and kidney disease, or taking diuretic medications (commonly prescribed for high blood pressure) — you may be at increased risk of becoming dehydrated. 

Possible early sign of diabetes

Symptoms of dehydration could be an early warning sign that you are developing prediabetes, the precursor disorder to type 2 diabetes (T2D). These symptoms — including excessive thirst, frequent urination and dry mouth — culminate from the kidney’s overexerted efforts to flush out high concentrations of blood sugar in the body through urine. Normally, insulin (a hormone produced by the body) carries out the process of removing sugar from the blood and introducing the sugar into the body’s cells. However, people with diabetes have difficulty producing or using insulin for this purpose, so the kidneys continue to flush the body of extra glucose through urine — resulting in more frequent bathroom trips and leading to dehydration. Frequent bathroom trips do not automatically point to prediabetes or diabetes, however. (Learn more: What Are the Warning Signs Of Prediabetes?) 

Why is dehydration potentially dangerous?

Dehydration can lead to serious complications, including:

• Heat injury. If you don't drink enough fluids when you're exercising vigorously and perspiring heavily, you may end up with a heat injury, ranging in severity from mild heat cramps to heat exhaustion or potentially life-threatening heatstroke.
• Urinary and kidney problems. Prolonged or repeated bouts of dehydration can cause urinary tract infections, kidney stones and even kidney failure.
• Seizures. Electrolytes — such as potassium and sodium — help carry electrical signals from cell to cell. If your electrolytes are out of balance, the normal electrical messages can become mixed up, which can lead to involuntary muscle contractions and sometimes to a loss of consciousness.
• Low blood volume shock (hypovolemic shock). This is one of the most serious, and sometimes life-threatening, complications of dehydration. It occurs when low blood volume causes a drop in blood pressure and a drop in the amount of oxygen in your body.

         Source: Mayo Clinic

If you have certain preexisting conditions, such as diabetes, dehydration can significantly exacerbate your disorder, or contribute to complications (see below). 

Does coffee dehydrate you?

Now, to our main question: Does coffee dehydrate you? Coffee contains a natural diuretic, caffeine. A diuretic is a substance that tends to increase the excretion of urine. (You can also find natural diuretics in some fruits, vegetables and herbs; and synthetic pharmaceutical diuretics are medications, also known as water pills, that increase urination, too.) 

However, despite caffeine being a diuretic, most health experts do not believe that coffee  significantly impacts your hydration status. Here’s why: 

Water is coffee’s main ingredient

Think about how you make your cup of joe in the morning — whether with a french press or a Keurig; it requires water, which actually counts toward your daily fluid intake. If you drink regular (caffeinated) coffee, the water content will likely offset the diuretic effects of the caffeine, as we discuss next. 

Caffeine is a diuretic, but coffee’s water content is an offset

Not only does the high water content of coffee offset the diuretic effects of caffeine, but it also seems clear that regular coffee users have built at least a slight tolerance to the effects of caffeine. A 2014 study presented data showing “no significant differences in the hydrating properties of coffee or water across a wide range of hydration assessment indices,” in 50 male coffee drinkers who consumed either coffee or water for the study. Study authors concluded that drinking coffee does not result in dehydration, so long as the coffee is consumed “in a moderate dose of 4mg/kg BW caffeine in four cups per day.” 

Does decaf coffee dehydrate you?

Another question people ask: Does decaf coffee dehydrate you? Decaf coffee — which is not entirely devoid of caffeine, but rather contains minimal amounts of it — poses even less of a dehydration risk. 

What else is in coffee?

Aside from caffeine, coffee contains many other bioactive compounds including polyphenols, chlorogenic acids (CGAs), trigonelle, magnesium and diterpenes. Much scientific research has pointed to the numerous benefits of the bioactive compounds found in coffee, such as antioxidant, anti-inflammatory, anti-cancer, anti-diabetes, and antihypertensive properties. A 2019 meta-analysis went further and linked these bioactive compounds with anti-obesity effects. In short, regular consumption of coffee may be beneficial for overall health, as long as you don’t overload your coffee drink with added sugars and fats.

Should you drink coffee if you have diabetes?

Individuals with prediabetes or diabetes are often instructed to control what they eat, how much they eat, and when to eat to better manage their blood sugar levels and prevent various complications related to the disorder. 

As we explained in depth in our report, Coffee and Diabetes, coffee is a beverage that causes blood sugar levels to rise in the first few hours of consumption. However, a 2019 meta-analysis, which reviewed all of the more worthy clinical studies published up through 2017, helped reverse most earlier fears that coffee-drinking is dangerous for those with diabetes. This review concluded that while coffee impairs your glucose response acutely, i.e., over the short term (hours), coffee actually improves glucose metabolism when consistently consumed over long periods (2 to 16 weeks): the glucose curve is reduced, glucose transport and disposal improve, and the insulin response increases. Neither did long-term coffee consumption result in any significant changes in insulin sensitivity.

If you are currently healthy, coffee consumption is actually associated with a decreased risk of type 2 diabetes, Preliminary research also indicates that coffee drinkers have a lower risk of developing certain cancers (breast, colorectal, endometrial, and prostate cancer), certain cardiovascular conditions, strokes and Parkinson’s disease.

A word of caution to select groups

While the Food and Drug Administration (FDA) has deemed it safe to consume up to 4-5 cups (400 milligrams) of caffeinated coffee per day, more excessive consumption can lead to some diseases in sensitive populations such as lactating and pregnant women, children, and aged people. Excessive caffeine consumption has been associated with certain diseases and conditions, including hypertension, cardiovascular diseases, bone density, various cancers, mental and behavioral disorders, and reproduction and developmental abnormalities.

Key Takeaways

Dehydration, especially for individuals with diabetes, can be a common (and troubling) occurrence. It can happen just by forgetting to drink water throughout the day. But, does coffee dehydrate you? Coffee is a beverage that contains a natural diuretic, caffeine, which may increase urination frequency. However, dehydration does not result just from urinating more frequently, but rather from a combination of the latter plus not replenishing the body with additional fluids to balance out water loss. Even if caffeine may urge you to make more trips to the bathroom, coffee also has a high water content that likely offsets the diuretic effects of the caffeine. So as long as coffee is consumed in moderation and the caffeine per cup of coffee is controlled, coffee is not likely to cause dehydration. Furthermore, coffee consumption is not associated with any major health risks, and in fact regular consumption has been shown to help reduce the risk of developing type 2 diabetes.