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Does Coffee Actually Dehydrate You? Addressing Myths

Coffee is the go-to drink for millions of people in the United States. That jolt of caffeine gives you a boost of energy, helping you wake up in the morning or get through the mid-afternoon slump. But caffeine is a diuretic, leading many people to ask: does coffee dehydrate you?

Learn more about dehydration, the coffee dehydration link, and the daily limit for coffee.

Understanding dehydration

Dehydration means your fluid balance is off. Fluid losses exceed fluid intake, affecting the body’s normal functions. Dehydration is potentially life-threatening in infants, children, and older adults.

More than 50% of the human body is made up of water, and every cell needs water to function. Without enough water, cells, tissues, and organs won’t work properly.

Illnesses, heavy sweating, and poor fluid intake may lead to dehydration. Your body is very good at letting you know when you’re not getting enough fluids. If you’re thirsty, you’re dehydrated and need to drink.

Other signs and symptoms of dehydration include:

  • Dry mouth
  • Dark-yellow urine
  • Fatigue
  • Headaches
  • Dizziness
  • Dry skin

How much water you need every day depends on age, weight, activity level, weather, and general health. The Dietary Reference Intake (DRI) of water for women is 2.7 liters (11 cups) a day and for men 3.7 liters (16 cups) a day.

You can meet your daily intake needs for water through food and drinks. It’s estimated that about 20–30% of daily fluid intake comes from food.

Does coffee dehydrate you?

Caffeine is the substance behind the coffee dehydration myth. One cup of coffee contains about 90–200 milligrams of caffeine, which is a mild diuretic, increasing urination.

Your body quickly absorbs the caffeine in your coffee, and within 30 minutes, you feel alert and energized. It may also briefly increase blood pressure and heart rate. Your body is unable to store caffeine, and the liver removes it from the bloodstream and sends the substance to the kidneys for excretion.

Caffeine affects the water-salt balance in the kidneys, triggering an increase in urine production (diuresis) and an increase in sodium excretion in the urine (natriuresis). These effects cause a short increase in urination and are the reason so many people associate coffee with dehydration. However, the amount of fluid loss from the increase in urination isn’t enough to cause dehydration.

Additionally, your body builds up a tolerance to the diuretic effects of caffeine. If you’re a regular coffee drinker, the amount of fluids you lose from the increase in urination is negligible. Further, your daily intake of coffee may benefit hydration and fluid balance.

The diuretic effects of coffee and other beverages

A 2014 study published in PLoS One compared the hydrating effects of coffee versus water by measuring total body water in a group of male coffee drinkers. The researchers found no significant difference in total body water content whether the men drank coffee or water. They concluded that drinking moderate amounts of coffee — 3–6 cups a day — is as hydrating as water for regular coffee drinkers.

In fact, coffee has nearly the same hydration index as plain water, according to a 2016 study published in The American Journal of Clinical Nutrition (AJCN).

Beverage hydration index

However, consuming six or more cups of coffee — increasing caffeine consumption to 500 milligrams or more — a day may cause a short-term increase in urine output in regular coffee drinkers. Still, the increase in urine output won’t cause dehydration.

It is said that health risks are minimal in most people who limit their daily intake of coffee to 3–5 cups a day. Though caffeine is the reason for the daily limit, moderate coffee consumption has been shown to benefit health.

Coffee is filled with many health-promoting compounds like antioxidants that are linked to longevity and reduction of certain disease risks.

Should I avoid coffee if I am dehydrated?

The National Institutes of Health (NIH) suggests avoiding caffeine to prevent dehydration. If you’re mildly dehydrated, drink water. If you’re moderately dehydrated, drink an electrolyte replacement beverage like a sports drink.

Research shows that an oral rehydration solution and skim milk are the best hydrating beverages.

Does coffee count towards my daily fluid intake?

If coffee is a regular habit, then you can count it towards your daily fluid intake. According to the previously mentioned AJCN study, coffee has the same hydrating effects as water.

However, water should make up most of your daily fluid intake. Coffee counts, but it may also contribute to your daily calorie intake if you like your cup of joe light and sweet. And fancy coffee drinks like frappuccinos and macchiatos have added sugar and fat you don’t need.

Black coffee, plain tea, sparkling water, and unsweetened flavored waters are good beverage options for meeting your daily fluid needs.

Coffee consumption guidelines

The Food and Drug Administration (FDA) says healthy adults can safely consume up to 400 milligrams of caffeine a day, or about 3–5 cups of coffee a day.

However, if you have a health condition such as an arrhythmia (irregular heartbeat) or you’re pregnant, your doctor may recommend limiting caffeine consumption to reduce health risks.

Drinking too much coffee, and, in turn, too much caffeine, may cause side effects like difficulty sleeping, headaches, or acid reflux.

Decaf coffee is an option for those who like to drink coffee but want to limit caffeine. However, decaf coffee isn’t 100% caffeine-free.

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