Drink When You’re Thirsty

 

How much water should you drink? Eight glasses a day? Ten? The Mayo Clinic says that men should drink thirteen cups "of total beverages" every day, and women nine. But, really, you should just drink when you’re thirsty. It turns out your body is pretty good at judging when it's low on water. In fact, drinking when you’re not thirsty might even confuse your brain.

However popular these X-cups-per-day rules of thumb are, researchers say they're actually not based on empirical evidence. A recent study in the Proceedings of the National Academy of Sciences looked at how the brain regulates the sensation of thirst and the reflex that allows you to swallow and found that the brain actually tamps down on that swallowing reflex once you’ve had enough to drink. Drinking when you’re not thirsty forces you to override that instinct. "It's a biological mechanism in quite ancient parts of the brain, and it seems intent on stopping you from drinking too much," Michael Farrell, the study’s co-author, told Australia Public Broadcasting.  

To watch people’s thirst in action, Farrell and his team put nineteen people in a room and had them exercise. By the end, the participants had lost about one percent of the their body weight in water from sweating, and they were thirsty. So the researchers placed them into an MRI scanner and gave them water, watching their brains as they hydrated. They were then asked to keep drinking, even after they were no longer thirsty. As it got less and less enjoyable to drink, their brains revealed a few interesting things about regulating thirst.

First, it became harder and harder for the subjects to swallow, and the motor cortex that controls swallowing had to work harder to make it happen. Then areas of the brain that are known to inhibit swallowing began to come alive, like the amygdala and the periaqueductal gray—a region of gray matter in the middle of the brain. "Our interpretation is that the PAG and amygdala were sending messages to the swallowing switch to prevent it turning on," Farrell told ABC. "Consequently, the motor cortex had to send stronger than usual signals to turn the switch on."

So, forget the strict thirteen glass water regimen, and stop forcing yourself to drink when you’re not thirsty. Your brain has many years of evolutionary training to help you figure out when to drink, and how much, and you should just listen to it.

 

Popular notion holds that eight glasses of water is the optimal amount to drink each day, but many people find this hard to achieve. Now, a new study may shed light on why, after identifying a swallowing mechanism that stops us from consuming too much liquid when we are not thirsty.

Researchers have discovered a swallowing mechanism that makes drinking too much water challenging.

Given that around 60 percent of human body weight is made up of water, it is no surprise that water is essential for human health, aiding every bodily function.
But how much water do we need to drink on a daily basis?
While you may have heard that eight 8-ounce glasses of water each day - known as the "8x8 rule" - is the aim, there is no scientific evidence that pinpoints precisely how much fluid is the optimal amount.
Based on studies to date, the Institute of Medicine (IOM) recommend that women should aim to drink around 2.2 liters of total beverages daily (around 9 cups), while men should aim to consume around 3 liters of total beverages daily (around 13 cups).
However, contrary to these recommendations and the so-called 8x8 rule, the new study suggests we should only drink when we are thirsty, after discovering a mechanism that makes drinking excess water challenging.
Study co-author Michael Farrell, of the Biomedicine Discovery Institute at Monash University in Australia, and colleagues publish their finding in the Proceedings of the National Academy of Sciences.

Right prefrontal cortex 'overrides' swallowing inhibition for excess water

For their study, the team enrolled a number of participants and asked them to drink large amounts of water immediately after exercise, when they were thirsty, and later on in the day, when they were not thirsty.
In each condition, the researchers asked the participants to rate how difficult it was to swallow water.
Compared with water consumption just after exercise, the participants found it three times more difficult to drink water later on when they were not thirsty.
"Here, for the first time, we found effort-full swallowing after drinking excess water which meant they were having to overcome some sort of resistance," says Farrell. "This was compatible with our notion that the swallowing reflex becomes inhibited once enough water has been drunk."
The team used functional magnetic resonance imaging (fMRI) on each of the participants, which allowed them to measure brain activity just before they swallowed water in each experimental condition.
They discovered that certain areas of the right prefrontal cortex of the brain showed significantly higher activity when participants had to make an effort to swallow the water, suggesting that this brain region "overrides" the swallowing inhibition to allow excess water consumption.

'Drink according to thirst'

Farrell and team stress that drinking too much water can cause significant harm, it can lead to hyponatremia, for example, where blood sodium levels are abnormally low.
"There have been cases when athletes in marathons were told to load up with water and died, in certain circumstances, because they slavishly followed these recommendations and drank far in excess of need," notes Farrell.
The researchers say their findings suggest that when it comes to water intake, we may fare better by listening to the body's needs.

"If we just do what our body demands us to we'll probably get it right - just drink according to thirst rather than an elaborate schedule."

Michael Farrell

Still, the team points out that water intake remains essential to human health, and there are certain groups - such as elderly individuals - who do not consume enough water.
Learn more about why drinking water is important.

Written by Honor Whiteman

 Drinking too much water, especially during exercise, could kill you!

A group of 17 international experts worked together to design a new set of guidelines that provide details on how to drink water in the safest way and avoid getting into overboard. The Clinical Journal of Sports Medicine published the new guidelines which came with warnings and was official launched at the International Exercise-Associated Hyponatremia Consensus Development Conference.
Reportedly 14 athletes already died because of exercise-linked hyponatremia, which is caused by overdose of water or sports drinks.
The guidelines, however, underscored that individuals could avoid hyponatremia: drink water only when thirsty.
"Using the innate thirst mechanism to guide fluid consumption is a strategy that should limit drinking in excess and developing hyponatremia while providing sufficient fluid to prevent excessive dehydration," the guidelines specified.
Exercise-linked hyponatremia (EAH) occurs when a person consumes excessive water, which could overwhelm the kidneys from eliminating too much water. When it this happens, sodium in the body becomes diluted causing the cells to swell, which could place a person's life in threat.
An individual with mild EAH usually manifests one or all of the following symptoms: lightheadedness, dizziness, nausea, puffiness and weight gain during an athletic event. However, when the condition worsens, vomiting, headache, confusion or worst delirium, seizure and comatose are manifested.
An individual is at risk of EAH during activities that require excessive stamina, like marathons, swimming, military exercises and even yoga.
Athletes and individuals engaged in excessive physical activities are advised to take 1.5 to 2. extra cups of water to replenish fluid loss. At this time, the body's sodium level drops because of excessive perspiration, thus, instead of taking too much water, drinking sports drink with sodium will help replace lost sodium and restore balance in the body. This eventually reduces a person's risk of suffering from hyponatremia.