Do we really need 8 glasses of water a day?

Do we really need 8 glasses of water a day?

Do we really need 8 glasses of water a day?

Water is necessary for life, experts say, and dehydration has definitely negative consequences. But there are also many misconceptions around it, such as the idea that we need to drink water all day - an idea that is reinforced by dozens of smartphone applications that send several related reminders about hydration.

How much water do we have to drink every day? It's a simple question with no easy answers. To date, numerous studies have given different versions, but in reality, our needs depend on many factors, including the state of health, gender and age, how active we are and where we live.

The guideline for 8 glasses of water a day, according to one theory, started from a misinterpretation of the Board of Directors' advice of the National Food and Nutrition Research Board in 1945. There is still no scientific evidence for magical number eight but the idea it remains, perhaps because nobody has come to something more specific. There's probably no magical number anyway. The body's needs vary according to body size, environmental conditions and activity levels. Also, besides water, people get plenty of fluids from food and drinks.

The truth is that our cells need water to function and research has linked dehydration with headaches, dizziness and lethargy, reductions in short-term memory, effectiveness in solving mathematical problems and other cognitive functions, especially after a loss of over 2% body weight due to fluid loss. In a 2015 study that put 11 young men into a driving simulator, errors were twice as likely to occur when they had reduced the consumption of liquids overnight. Mild dehydration can often occur in our body and, in most cases, does not pose problems, says Stephen Mears, a sports nutrition researcher at Loughborough University in the UK, one of the authors of the above study. In another research work in 2015, he and his colleagues examined the concentrations in the urine of 156 people who did various professions. 56% of the participants showed signs of dehydration at the beginning of their work shift. About half of them were still dehydrated after at least 7 hours of work and 35% of the total had been dehydrated at the end of their shift. The researchers did not measure how much or how dehydration affected performance and according to Mears, the results are not necessarily disturbing. "I would not say it was a problem," he says, "I would say it is something that could be improved."

Weight control is another area where water can help, especially when consumed instead of different calorie drinks. In a 2012 study of 318 overweight or obese adults, those randomly selected to consume water or non-calorie beverages instead of their usual calorie drinks were twice as likely to lose 5% weight over a six-month period than those who could drink what they wanted. However, other studies have failed to provide the same evidence, and often those who use water as a weight loss tool are left with vague instructions on when, why or how much to drink, says dietary epidemiologist Jodi Stookey in a recent article . Its evaluation in 134 randomized trials has identified possible situations that can make water more useful as a weight loss tool. In particular, it suspects that water is more effective when combined with a low-calorie diet or reduced carbohydrate.

As for exercise, the American College of Sports Medicine has for years recommended that athletes drink plenty of fluid while exercising to avoid loss of over 2% of their body weight. Greater sweating could damage aerobic performance, speed, strength and endurance. But this number has also been the subject of discussion. Some people tolerate dehydration better than others. And sometimes, dehydration can provide an edge. Distinguished marathon runners regularly lose 5% or more of their body weight through sweat during races, says Mears. And some run faster as they are lighter. According to some studies, the fastest runners and triathletes lose more than 3% or 4% of their weight during races. Also, contrary to what is generally believed, dehydration does not seem to increase the risk of cramping. Former Ethiopian marathon runner Haile Gebrselassie lost 10% of his body weight during some races, and yet he broke world records. But the percentage of his sweat is not for everyone. In a recent study, Spanish researchers analyzed sweat samples from 157 experienced runners and found different concentrations of salt in athletes' sweat that were irrelevant to age, body size, exercise, or even sweat rate. How much salt we lose affects how much salt and water we need to replace to stay hydrated, says Dirk de Heer, a physiology researcher at the University of North Arizona.

Concludes that more and more experts recommend drinking water only when we are thirsty during exercise or our daily activities as overconsumption of water can lead to thinning of sodium levels in the blood, something equally dangerous for our body.

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