Woman drinking water in bed

Does drinking water before bed can improve sleep? The link between hydration and energy levels

Posted by for Wellbeing

Keeping hydrated throughout the day is important for maintaining energy levels — but can water before bed also improve sleep? 

I’ve always believed that drinking a glass of water can increase alertness, turning on the tap in lieu of another coffee when the afternoon slump hits. In truth, it’s definitely not as energising as caffeine, but there’s still something refreshing about a big glass of water.

But then I saw some advice from the Sleep Foundation that suggested a glass of water before bed can induce sleepiness by supporting the body’s natural drop in core body temperature. 

So what’s water really best for – wakefulness or sleepiness?

Does water help energy levels?

A 2019 paper found that dehydration as a result of water deprivation had negative effects on vigour, short-term memory and attention. After participants rehydrated, they felt less fatigued and saw improvements in their short-term memory, attention and reaction times.

In another study from 2005, tiredness was increased and alertness was reduced after 24 hours of water deprivation. In women, reaction times were prolonged. 

“Being just 1% dehydrated can affect alertness, focus and concentration,” says dietitian Sophie Medlin. “This is because of how crucial water is to every function in our body and particularly to our brain function.”

Dr Greg Potter, chief science officer at Resilient Nutrition, explains that this comes down to “how dehydration changes the signalling of key chemicals called neurotransmitters in the brain”. Given that around 75% of our brain is made up of water, it makes sense that a reduction in hydration will have a knock-on impact on how your brain is functioning and firing. A glass of water really can help switch the brain on. 

Does water help you sleep?

Strong Women’s editor Miranda Larbi swears by a glass of water before bed to lull her into a deep sleep. And it’s not just anecdotal evidence – a 2019 paper found that those who slept for around six hours a night, rather than the recommended eight, were more likely to be inadequately hydrated. Not drinking enough seems to have a big impact on our snoozing.

“Whenever our body is missing something crucial, it can cause us to sleep less well,” explains Medlin. “This is thought to be a survival mechanism – our bodies keep us awake so that we go and get water. It’s the same when we go to bed hungry or if we have a deficiency like anaemia or low salt levels, we often find our sleep is disrupted.”

A 2007 paper expands on the claims made by the Sleep Foundation. In the study, researchers found that a warm drink in the evening helps your body’s thermoregulation, meaning that hot water or non-caffeinated teas might be best to signal to your body that it’s time to sleep.  

Glass of water next to a laptop
Water energises you at your desk, but could it also make you sleepy before bed?

However, Dr Potter points out that drinking water immediately before bed can disrupt your night. “It can increase the urge to urinate during the sleep period, a phenomenon known as ‘nocturia’. Certain people are especially prone to this, for example, those with smaller bladders than others.

“Another cause of nocturia is dysregulation of one’s body clock. This clock usually drives changes in hormones such as arginine vasopressin that result in slowed urine production at night, but clock dysfunction can lead to continued high rates of urine production at this time.”

He recommends that if you find you have to get up to pee multiple times at night, you might want to restrict your fluid intake, and particularly your intake of diuretics such as alcohol and caffeine, in the hours before you go to bed. But more importantly, you want to have healthy sleep and morning routines to regulate your rhythm so that a glass of water before bed doesn’t keep you up at night. 

Should you drink water before bed?

It seems that immediate water intake can improve your brain’s alertness, but without adequate daily hydration you won’t be getting to sleep. “In general, it’s best to aim for a state of hydration during wakefulness and to modify your fluid intake before sleep according to whether you struggle with nocturia,” says Dr Potter.

Medlin adds that “because water is so essential, even being just slightly dehydrated can lead to sleep disturbance, problems with feeling drowsy and all other bodily functions.

“Often we don’t realise when we’re a little dehydrated but our body will be experiencing ill effects. That’s why it’s so important to keep a close eye on how much you’re drinking everyday and know the signs of dehydration, including teeth marks on your tongue, darker urine and a dry mouth.” 

Images: Pexels/Getty

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Chloe Gray

Chloe Gray is the senior writer for stylist.co.uk's fitness brand Strong Women. When she's not writing or lifting weights, she's most likely found practicing handstands, sipping a gin and tonic or eating peanut butter straight out of the jar (not all at the same time).