8 Hours of Sleep, 8 Glasses of Water—Do These Rules Apply to Everyone?

By Ching Dee for Belo Medical Group on November 10, 2020

Since we were kids we’ve been told to drink at least eight glasses of water a day and make sure to sleep at least eight hours every night, but is it the same advice for all of us? 

If you’re curious, keep reading because we’re breaking down these two health “rules” to see if it’s still applicable to everyone.

Should I drink 8 glasses of water every day?

The importance of water in our diet is unquestionable, but experts say the amount of water you should drink depends on several factors.

According to the Mayo Clinic, one of the best hospitals in the United States, “water is your body’s principal chemical component and makes up about 50% to 70% of your body weight. Your body depends on water to survive. Every cell, tissue and organ in your body needs water to work properly.” 

The Mayo Clinic mentioned that the U.S. National Academies of Sciences, Engineering, and Medicine has determined that an “average, healthy adult living in a temperate climate” will need about 2.7 liters (for women) to 3.7 liters (for men) of fluids a day.

For athletes, according to Exercise Science professor Tamara Hew-Butler at Oakland University, drinking water could just be a matter of when your body tells you to do so. “Our bodies already possess an extremely sensitive measure of dehydration. It’s called thirst. As long as we drink whenever we feel thirsty, we really won’t dehydrate. That’s how humans have done it for millions of years and it’s worked out fine,” she tells TruTV host Adam Conover in the hydration episode of “Adam Ruins Everything”

In a 2015 article for The New York Times, Indiana University School of Medicine professor of pediatrics Aaron E. Carroll called this age-old advice as a myth and that the recommended amount of water one needs will depend on several factors like your age, location, overall health, diet, and level of physical activity.

“There is no formal recommendation for a daily amount of water people need. That amount obviously differs by what people eat, where they live, how big they are and what they are doing,” he wrote. “But as people in this country live longer than ever before, and have arguably freer access to beverages than at almost any time in human history, it’s just not true that we’re all dehydrated.”

Our very own Dr. Vicki Belo points out that water is still “the cheapest and best way to keep your body healthy”.

“Drink ten glasses of water a day, because if you think about how big our body is and how little we drink, right? … It’s like a river. Our body becomes stagnant with the dirt and the toxins if we don’t flush it out with water,” Dr. Belo shared in an interview with PEP.ph in 2018.

Should I sleep at least 8 hours every night?

The short answer is yes, most adults need around 7 to 9 hours of sleep at night. But experts also point out that the quality of sleep – not just the length of sleep – is important.

In the same PEP.ph article, Dr. Belo said sleeping late is one of the main culprits in weight gain and unhealthy skin.

“Sleeping late is really bad… You’ll notice that if you don’t sleep, you will gain weight, you will have dark circles, you will not feel as healthy. You will always feel tired,” she explained. “You have to remember when we are up right now, we are very active. We are spending our energy. It’s only when you sleep that you repair.” 

She goes on to explain that during sleep, the body secretes necessary hormones to repair the body and it starts two hours after you fall asleep. Any delays in your bedtime means delay in the release of the repair hormones, which could signal problems within the body.

“Usually 8 to 9 p.m. you should be ready to sleep. It’s more important the time you sleep than how many hours of sleep, although of course 7 to 8 hours is really a good number,” she concludes.

Dr. Belo’s statement is supported by a 2015 study by the Sleep Health Journal of the National Sleep Foundation, where it states that young adults (ages 18 to 25) and adults (ages 26 to 64) need around 7 to 9 hours of good quality sleep, while older adults (ages 65 and above) need a little less at 7 to 8 hours of sleep every night.

According to neuroscientist and sleep specialist Chelsie Rohrscheib in a Quartz article in 2018, “While humans need, on average, eight hours of sleep each night, the exact length of time it takes to accomplish these sleep functions is highly dictated by an individual’s genes… It’s extremely rare for a person to require less than six hours of sleep per night… The exception to this rule are individuals with a genetic variant that allows the brain to function more efficiently on less than six hours of sleep, but this is extremely rare and very few people actually have this gene.”

Lastly, it’s also important to take note of the role of sleep in keeping our bodies healthy. In a study published by Nature Reviews Immunology in 2004, adequate sleep helps build up our immune response, which is especially important now that we are in the middle of a global pandemic. 

“There is increasing evidence that sleep deprivation has detrimental effects on the immune response, indicating that sleep should be considered a vital part of the immune system and that there is a reciprocal relationship between sleep and immunity… The concept that lack of sleep might be compromising immunity in the population has far-reaching public-health implications for both individuals and society.”

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