Whoa: Driving While Dehydrated Just As Dangerous As Driving Drunk

According to a new study, hydrating while driving is one of your most important moves for safety. (Photo: Getty Images)

It’s an unwritten law of road trips: You pee right before you leave and ration liquids during your journey to avoid making frequent pit stops.

But new research has shown that cutting back on liquids while driving could be a very dangerous habit. According to a study published in the journal Physiology and Behavior, driving while dehydrated is just as dangerous as driving drunk.

(Video: Loughborough University)

In the study, researchers from Britain’s Loughborough University carried out simulated tests on drivers when they were both hydrated and dehydrated. The tests included a two-hour monotonous drive with bends, a hard shoulder, rumble strips, and slow-moving vehicles that needed to be passed. On one day, participants were given nearly a cup of fluid to drink per hour and on the dehydration day, they were given just a few sips of liquid per hour.

When participants were hydrated, there were 47 driving incidents, but when they were dehydrated, that number was more than doubled at 101. The errors also increased during the two-hour period and were worse during the last leg of the drive. Those incidents included lane drifting, late braking, and touching or crossing the rumble strip or lane line.

Related: Does Drinking Alkaline Water Make You Extra Hydrated?

But how is dehydration linked to poor driving? Lead researcher Ron Maughan, PhD, tells Yahoo Health that our brain function becomes conserved when we’re dehydrated, which can then impact how well we drive.

That brain conservation can create a whole range of issues, says nutritionist Kim Larson, a spokesperson for the Academy of Nutrition and Dietetics. Dehydration impacts our mental clarity, reaction time, focus, concentration, thinking, and even our mood, she says, and the impact isn’t just felt when we’re driving. “Even if you’re sitting at a computer, you can experience the same symptoms,” she says.

Dehydration can also affect your blood volume, Larson says, which can lead to headaches, lethargy, and an overall fuzzy feeling — not exactly ideal symptoms to experience while driving…or any other time. 

Related: Why You Shouldn’t Drink Warm Bottled Water 

Your muscle function can be impacted by dehydration, too, says nutritionist Katie Ferraro, RD. While you’re probably not doing arm curls or anything else strenuous while you’re driving, you still need your muscles to be able to react quickly if something goes wrong on the road.

And you don’t need to be significantly dehydrated to experience the negative side effects. While dehydration is typically classified as losing two percent of your body weight in water, Larson says even losing one percent of our body’s water can affect us.

Unfortunately, there is no hard and fast number for how much liquid everyone should drink. The easiest way to tell if you’re hydrated is to look in the toilet, says Ferraro. Your pee should be light yellow; if it’s dark orange or yellow, you’re probably dehydrated. Ferraro also says you should be wary of smelly urine, which can be a sign that you need more water to help your kidneys work efficiently.

Related: How To Drink More Water 

If you prefer to strive for a particular amount, Larson recommends taking your weight and dividing it by two — that’s the number of ounces of liquids you should strive to drink in a day.

Planning for a road trip? Maughan says it’s best to play it safe and drink plenty of liquids before and during your drive. If you run out of something to drink during the trip, make a pit stop and get more—you can pee while you’re at it.

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