The latest on hydration

Dear Reader, 

If you were stranded in the desert with nothing but beer, coffee, and soda in your thirst-aid kit, your best course of action may just be to drink what’s in it. Caffeinated and alcoholic beverages indeed have a diuretic effect, meaning that they increase the amount of water you lose through urine. Even so, it’s unlikely that drinking these beverages alone will lead to dehydration. But before you pour yourself another cup of coffee, it might be useful to note that whether a drink contains caffeine or alcohol isn’t the only thing that determines how hydrating—or dehydrating—a drink is. Macronutrients (such as carbohydrates, fats, and proteins), electrolytes, and even the temperature of your beverage can affect how hydrating a beverage is—or seems to be. 

Your body needs water to survive. Around 50 to 70 percent of the body is water and it uses and loses it every time you breathe, sweat, or urinate. Dehydration occurs when you lose more water than you take in. This happens when water moves out of your cells into the bloodstream or when your total blood volume decreases, causing symptoms like thirstiness, dry mouth, dark-colored urine, fatigue, and dizziness. When you’re dehydrated, the brain sends signals to activate the sensation of thirst, prompting you to drink and restore the water content in your body. 

You may be familiar with the advice: “drink eight glasses of water a day.” While this can be a useful way to build healthy hydration habits, it’s also good to keep in mind that an individual’s recommended water intake depends on their health condition and needs. Folks who live in hot climates, are physically active, sweat a lot, are pregnant or breastfeeding, or are ill may need more water to stay healthy. For most healthy people, however, drinking fluids whenever they feel thirsty is sufficient to stay hydrated. It may be useful to note that “fluids” doesn’t just mean water. Around 80 percent of your daily water intake comes from water and other beverages, while the remaining 20 percent comes from food. In fact, many fruits and vegetables (like watermelon and spinach) are almost entirely composed of water! 

The drinks that you mention—beer, coffee, and cola—have diuretic effects. Alcohol flushes water out of your body by preventing the release of vasopressin, a hormone that regulates urine output. Caffeine, which is present in coffee and many types of soda, also has a similar effect. The strength of this diuretic effect depends on how regularly you consume caffeine. Studies have shown that regular coffee drinkers—who have built up some tolerance to the effects of caffeine—are less likely to experience diuretic effects compared to those who only drink the occasional cup of joe. Coffee with a higher caffeine content, such as coffee made with dark-roast coffee beans, may also have stronger effects than decaf coffee or coffee made with light-roast beans. Even though coffee may be less “hydrating” than water, the good news is that drinking coffee is unlikely to cause dehydration so long as you cap your caffeine intake at 400 milligrams (about 4 cups) or less a day. Since water makes up almost 98 percent of a six-ounce brew, you’re also taking in more fluid than you lose! 

So, what makes a drink hydrating? Drinks rich in macronutrients such as carbohydrates, fat, and protein break down slower in your stomach and take longer to enter the bloodstream. This allows the fluids to be retained in your body for a longer time. Drinks with higher concentrations of electrolytes also help to increase fluid retention in the body. According to the Beverage Hydration Index (BHI), which measures how hydrating a drink is compared to plain water, skimmed milk and full-fat milk are among the most effective at helping your body stay hydrated. Some other factors can also indirectly affect how much hydration you might be getting from a drink. Studies have found that cold, carbonated beverages quench thirst so effectively that people tend to underestimate how much they’ve had to drink. As a result, people may drink less liquid when it's cold or carbonated, reducing their overall fluid intake.  

The roadmap to staying hydrated may have a few more twists and turns than you initially thought, but that just means there are different ways to get to the same destination. There are a lot of factors that determine how your body is hydrated including what those sources are and how they’re processed.  

Here’s to hoping you never have to be deserted in the desert!