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Why Does Coffee Dehydrate You?

For sure, you have heard so many things, both positive and negative, about coffee. One of the common arguments against coffee is that it can cause dehydration. If you do not drink coffee, you can be easily persuaded not to drink or start to develop a love affair with this bittersweet beverage. If you are coffee lover, you can find one thousand and ways to debunk this myth and still enjoy every sip of a freshly brewed coffee.

The so-called negative effects of coffee are often attributed to its caffeine content. Also found in tea, soda and chocolate, caffeine is a widely consumed substance in every country around the world. It is a known natural stimulant used to perk people up. It is a legal and unregulated substance; however, this famous chemical is often attributed to bad health effects, one of which is dehydration.

The idea that drinking coffee can dehydrate you had surfaced as early as 1928. The study published in The Journal of Pharmacology and Experimental Therapeutics noted an increase in urination among people who drank caffeinated beverages, coffee included. This study led to the belief that coffee was diuretic.

More recent studies

In 2005, Lawrence Armstrong, a professor in the Department of Kinesiology at the University of Connecticut and director of the Human Performance Laboratory, and his team of researchers analyzed whether drinking coffee can cause dehydration.

They controlled the diets of 59 healthy males for 11 days, supplementing their daily consumption with body-mass-appropriate doses of caffeine, administered twice a day via capsule. Throughout the study, the researchers employed 20 different hydration biomarkers, such as urine volume and fluid-electrolyte balance, to assess dehydration.

“The truth of the matter is, a small increase in urine output has little to do with dehydrating the body,” Armstrong told Live Science. “If you drink a liter of water, [urination] will increase. Doesn’t mean you shouldn’t drink water.”

Armstrong’s study showed significant results because it covered beyond the 24-hour period. The study lasted for 11 days and significant data was gathered from the participants to indicate that drinking coffee is not the sole reason for dehydration.

In fact, the groups who took caffeine and the group that took placebo demonstrated hydration indicators like urine volume. The researchers were able to conclude that a higher dose of caffeine would not dehydrate a person, nor would smaller doses.

In another report, BBC Health noted a study conducted by Sophie Killer at Birmingham University in the UK. She not only measured the volume of urine, but tested their blood for signs of kidney function, as well as calculating the total amount of water in the body. The men in the study drank four cups of coffee a day, far more than the average coffee-drinker. Yet, there was no evidence that they were any more dehydrated than those who drank water, alone.

Another study, published in PubMed, observed two groups of people who took increasing doses of caffeine for 11 days. The researchers did not notice a significant increase in urine volume of the caffeine group versus the non-caffeine group.

What is dehydration?

According to WebMD, dehydration occurs when more water and fluids are exiting the bod than are entering the body. With about 75 percent of the body made up of water found inside cells, within blood vessels, and between cells, survival requires a rather sophisticated water management system.

Good thing our bodies have a natural alarm system and our thirst mechanism tells us when we need to increase fluid intake. We lose water constantly throughout the day, as we breathe, sweat, urinate, and defecate. The body can also shift water around to areas where it is more needed if dehydration begins to occur. We can replenish the water in our body by drinking fluids, though some fluids, like sea water, actually dehydrate you because they have too much salt or other dissolved minerals that take extra water to remove.

In most cases, dehydration can be easily managed by increasing your fluid intake. However, some cases of dehydration need immediate medical attention.

What causes dehydration?

Primarily, dehydration happens when we lack water in the body, lost too much water or both. Here are some medical conditions that may cause dehydration:

  • Diarrhea – the most common cause of dehydration and related deaths. The large intestine absorbs water from food matter, and diarrhea prevents this function, leading to dehydration.
  • Vomiting – leads to a loss of fluids and makes it difficult to replace water by drinking it.
  • Sweating – the body’s cooling mechanism releases a significant amount of water. Hot and humid weather, as well as vigorous physical activity, can further increase fluid loss from sweating.
  • Diabetes – high blood sugar levels cause increased urination and fluid loss.
  • Frequent urination – usually caused by uncontrolled diabetes, but also can be due to alcohol and medications such as diuretics, antihistamines, blood pressure medications, and anti-psychotics.
  • Burns – water seeps into the damaged skin and the body loses fluids.

So, why do some people feel that drinking coffee dehydrate them?

There is no specific reason why people feel that way. Based on the several researchers mentioned earlier, caffeine in itself does not cause dehydration. According to Armstrong, for a person to reach a coffee overdose, this person had to consume 10,000 milligrams of caffeine per day. An 8-ounce cup of brewed coffee has 95 milligrams of caffeine, on the average. To reach overdose and dehydration, one must have had 100 cups of coffee in a day.

In addition, a person can exhibit excessive urination after drinking coffee only if this person had been drinking coffee in succession and had no other liquid. By principle, our body will take in all kinds of fluids and process it, leaving the waste product to be carried out by the body through urine. Essentially, if you had been drinking coffee and had no other liquid intake, most likely, you would still be urinating as if you were drinking water.

Finally, the hot nature of coffee can trigger our body to perspire. This is especially true if you are drinking hot coffee during the summer days. Hot coffee adds to the increased temperature that your body is already feeling. As a result, your body releases sweat to cool you down. If you drink coffee often during the summer, you will feel really dehydrated. What you can do to avoid this is enjoy a cold brew, instead of the usual hot brewed coffee.


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