The whole body impact of mild dehydration

There are two opposing theories about how much water you need to drink in a day. There’s the argument for 8 cups a day, regardless of how much you dislike the taste. Then there’s the tried-and-true advice to grab a glass whenever you’re thirsty. Which is it, and is it true that if you don’t hydrate, you die?

Answer: Drink water when you’re thirsty. And drink more water before you sweat. Drink even more water when you drink alcohol or an extra cup of coffee. After that, the rest depends on your individual needs. In other words, it depends, which is annoying, but I’ll show you a simple way to self-experiment.

As for the ‘hydrate or die’ saying, it’s a slight exaggeration of the fact that your body is 60% water, so without replenishing, you would die in 3 days.

To be clear, this article is not about preventing death from dehydration. I intend to help you find the right amount of water, beyond the bare minimum, that allows your body to function well. Adequate hydration will help regulate your mood and concentration, and increase your energy, reaction time, and memory, leading to improved physical performance. Drinking enough water can also prevent headaches, weight gain, constipation, and bad breath. This is why I consider hydration a fundamental of health.

How to hydrate

Someone who drinks enough water will pee about every two to three hours they’re awake. The pee should be pretty clear in color, too, like lemonade. So, all you need to do is sip on water throughout the day, whether you’re thirsty or not, until you get your urine to look a little lighter than a Coors. It’s a subjective way to measure hydration, yet a reasonable place to start.

The difference between dehydration and decreased hydration

Unless you’re reading this on day 3 of a hike in the Sonoran desert in July, you're probably not dehydrated. You would be too confused or too unconscious to care about future problems. Your pee would look like a pint of Guinness.

Which brings me to the main issue that confuses people about water: if you’re not dying from dehydration, and you drink water when you’re thirsty, then how much more water do you need to be healthy?

Unfortunately, there hasn’t been a study on a 175 lb. guy, who is moderately active (for a sleep-deprived new dad), that tests his memory, energy and mood after 8 cups of water. That tired dad (who still wakes up at 5:45 am to write) will have to do the experiment himself, which I did after seeing the negative health impact from mild dehydration in this study.

Blood markers to tell if you’re hydrated

Researchers used blood levels of sodium as a proxy for hydration in over 15k people, and found that serum sodium above 142 mmol/l is associated with a 39% increased risk of developing a chronic disease. That’s bad news because that level of sodium is a ways from what we consider dehydration. But this is what really made me fill my Nalgene: serum sodium above 144 mmol/l was associated with a 21% elevated risk of premature death.

My serum sodium level last month was 143 mmol/l suggesting I was mildly dehydrated at the time of the blood draw. It also suggests I have an increased risk of heart disease, despite being in the “normal” range.

“The analysis demonstrated that middle-age serum sodium in the upper part of normal range (135–146 mmol/l) is able to predict faster rate of the biological aging, and an increased burden of chronic diseases later in life, including heart failure, dementia, chronic lung disease, stroke, diabetes, peripheral vascular disease and atrial fibrillation. The analysis identified serum sodium threshold of 142 mmol/l that can be used in clinical practice to identify people at risk.”

My new hydration habit

I have a new goal now: drink enough water to prevent a heart attack, diabetes, and early death in the future, while also staying well-hydrated to improve my memory, mood, and performance. I want to maintain this semi-proficient ability to write, and still be able to surf with my grandkids when I’m 90. That means I need to lower my serum sodium levels by increasing the amount of water I drink in a day.

How much is enough?

I still haven’t answered exactly how much water, which is important to me figure out because there's obviously room for improvement. Plus, I don't love water. I'm also the type of guy who needs to know exactly how many Nalgenes to drink in a day in order to check it off the to-do list and move on to the next thing.

After reading a few studies, and summaries by important-sounding agencies like The Institute of Medicine of the National Academies, I realized that I’m not going to find a personalized answer. The recommended range of ounces per day varies from 16 oz, all the way up to half your bodyweight in ounces. For me, that's a whopping 90 oz a day, or 3 full Nalgenes.

This means you have to experiment to find your number, so start sipping.

Will you notice a difference?

As I said earlier, hydration is fundamental to your health. However, the tricky thing with fundamentals is that they need to be combined in order to maximize their effectiveness. Think of a basketball player, for example, who has the perfect jump shot after mastering the fundamentals of shooting. Even with his offense dialed, he still won’t be a great player if he doesn’t nail all the other fundamentals of the game, too–footwork, dribbling, passing, etc.

Will drinking more water each day make you feel noticeably better? Maybe, maybe not. But that’s not the point of the health game–the point is to nail all the fundamentals simultaneously to become a well-rounded, healthy guy so you can live better, longer.

Takeaway

Your body is 60% water, making hydration a fundamental to your health and longevity. To stay properly hydrated, you’ll want to drink water when you’re thirsty, eat fruit and veggies throughout the day, and drink about the same amount of coffee each day. Sweating and drinking alcohol increases your needs. Beyond that, it takes some self-experimenting to yield results that are catered to your daily demands.