Water & Sleep: What You Need to Know

We all know that staying hydrated is key to keeping our bodies and minds healthy. From helping our kidney and liver functions to improving skin and joint health^[1], hydration plays a crucial role in our overall wellbeing. No wonder so many of us are making an effort to drink more water.

But did you know that staying hydrated can also have a big impact on how well you sleep? We explore the connection between hydration and sleep quality, and answer the all-important question - should you drink water before bed?

The relationship between hydration and sleep

The adult human body is 55-60%^[2] water and it plays a significant role in many bodily functions, such as:

• Regulating your body temperature
• Transporting nutrients and oxygen to your cells
• Protecting your organs^[1]

But the need for hydration doesn’t stop when we go to sleep. Even when we sleep, our body is hard at work regulating our hormones. 

One of these hormones is vasopressin, an antidiuretic hormone that plays a crucial role in helping our bodies retain water. Vasopressin levels increase at night, signalling to your kidneys to retain more water, which helps prevent dehydration while you sleep^[3]. This is an essential part of our circadian rhythm, which governs our sleep-wake cycle.

How are dehydration and poor sleep related?

Dehydration and poor sleep often go hand in hand, with each one potentially increasing the effects of the other.

The effects of dehydration on sleep:

Research shows that when people are less hydrated, they’re more likely to get less sleep and experience lower sleep quality^[4]. However, more studies are needed to fully understand the specific impact of dehydration on sleep and how widespread it may be.

• The physical symptoms of dehydration, such as a dry mouth, thirst, headaches, and muscle cramps, can make it more difficult to fall asleep and stay asleep.

Dehydration can dry out your mouth and nasal passages, which may lead to snoring. This can disrupt your sleep as well as the sleep of those around you^[5].

The effects of poor sleep on dehydration:

Poor sleep and dehydration can cause a vicious cycle with studies showing that people who regularly sleep 6 hours or less a night have higher rates of dehydration^[4].

• An expert report suggests that disrupted sleep can disrupt the production of vasopressin^[6], which can cause feelings of dehydration.
• Chronic lack of sleep can negatively affect kidney function^[7], which plays an important role in regulating water levels in the body.

Understanding how hydration and sleep quality affect each other highlights the importance of staying hydrated and getting a good night’s rest.

If you have any concerns or questions about your sleep quality or dehydration, please speak with a medical professional.

How to stay hydrated for better quality sleep

Most adults are advised to drink about two litres of water every day. However, if you’re very active, feeling unwell, or breastfeeding, you might need to drink more to stay properly hydrated.

Delphine Sayre, a medical herbalist at Cavendish Cancer Care, prefers not to be too prescriptive about how much water we should drink. She explains that “we are all individuals and increasingly what data is showing is that what is right for one person is not necessarily the same for another and listening to your body is important”.

Paying attention to your body and being aware of the symptoms of dehydration can be a great first step to figuring out your hydration needs.

This doesn’t simply mean drinking more water when we feel thirsty - often when we feel thirsty, we’re already slightly dehydrated.

Signs of dehydration to look out for

Signs of dehydration can include:

• Headaches
• Darker urine
• Tiredness
• Going to the toilet less
• Dry and less supple skin
• Dizziness
• A dry mouth
• Hunger

You might be surprised to learn that craving sweet treats can be a sign of dehydration. When we’re properly hydrated, we release stored glucose effectively, which fuels our body throughout the day. 

But when we're dehydrated, this process is disrupted, making us crave sugary foods for a boost of energy. Additionally, not drinking enough water can increase the risk of hyperglycemia (high blood sugar) and the onset of diabetes^[8].

Tips on how to stay hydrated

Here are some tips to help you stay hydrated throughout the day from Cavendish Cancer Care’s medical herbalist, Delphine Sayre and dietitian, Helen Ruckledge:

• Start your day with a glass of water as this immediately hydrates your body for the day.
• Treat yourself to a nice water bottle that you can drink from throughout the day.
• Set reminders or use a tracking app to prompt you to have a drink if you might forget.
• Include more hydrating foods into your diet such as watermelon, tomatoes, oranges, cucumbers and spinach as they also contribute to your fluid intake.
• Limit your caffeine and alcohol intake as they are both diuretics, meaning that they make you need to use the toilet more and cause your fluid levels to drop.

Improve your sleep hygiene to avoid excess sweating

It’s perfectly normal to sweat while we sleep, in fact, we usually lose around 200 ml of sweat each night^[9]. But, if you tend to overheat in the night and wake up feeling noticeably sweaty, this could contribute to your dehydration.

Here are some tips on how to improve your sleep hygiene to stay cool while you sleep:

• Ensure your bedroom is between 18 - 20°C^[10]
• Wear light nightwear^[11]
• Use natural, breathable bedding^{[11], [12]}
• Sleep on a mattress with a high heat capacity, to allow for consistent heat management^[13]
• Keep a consistent, relaxing sleep routine to help reduce your body temperature before you sleep

As we have mentioned above, poor sleep quality can increase the risk of dehydration. Take the time to review the quality and duration of your sleep and if you have any concerns, please reach out to your local GP.

What if I don’t like the taste of plain water?

Many people don’t enjoy the taste of water, and that’s okay, you don’t have to only drink water to stay hydrated.

Cavendish Cancer Care’s resident dietitian, Helen Ruckledge explains that you can drink other beverages to stay hydrated. 

Helen says, “Drinking three or four caffeinated drinks like tea or coffee can count towards hydration, although above this amount try to swap to a herbal decaffeinated option, water, or soft drinks such as cordial.” 

However, studies show that drinking large amounts of caffeinated coffee (five cups or more per day) could have a dehydrating effect^{[14] [15] [16]}. If you consume around this amount of caffeinated coffee per day, make sure you also increase your water intake throughout the day.

Delphine Sayre suggests trying out some herbal decaffeinated teas or simply adding some berries, mint or lemons to your water to improve the flavour. She explains that “lemon juice wakes up your liver and digestive enzymes^[17] and helps us get ready for the day.”.

How to tell if you’re well hydrated

You can tell if you’re well hydrated mostly from a lack of dehydration symptoms, for example, if you:

• Have good energy levels
• Don’t feel thirsty
• Are going to the toilet regularly
• Feel clear headed
• Don’t experience dizziness
• Don’t experience headaches

… then you’re most likely to be well hydrated.

Top tip - Try not to cause yourself stress by overthinking skin elasticity and obsessing over toilet visits and urine colour. Simply aim to check in with your body at regular intervals during the day and make hydration part of your daily routine.

How to reduce getting up at night to pee

Most healthy adults produce less urine at night, but some do often need to go to the toilet in the middle of the night. This is called ‘nocturia’, when you need to wee multiple times in the middle of the night.

Nocturia is more common during pregnancy and perimenopause and with some medical conditions. It is also simply a part of ageing. It can be quite disruptive to sleep, especially as it can be quite difficult to get back to sleep once you’ve woken up.

Here are some tips to try and help with this:

• Always try to empty your bladder before bed, even if you think you don’t need to.
• Avoid caffeine and alcohol, particularly in the hours before bedtime. Alcohol and caffeine are diuretics, meaning you’re much more likely to need to pee after a couple of drinks.
• Reduce your fluid intake around two hours before bed. This means staying hydrated throughout the day, rather than rushing to hydrate yourself at night.
• Be mindful of eating salt and protein-rich foods late in the day. Digesting high salt and protein food can cause increased urine production^[18], so avoiding these late at night can reduce your need to visit the toilet.

Frequently going to the toilet in the night could be related to your habits but it can also be a medical issue, be aware of your habits and please talk to your doctor if you have any concerns.

Should I drink water before bed?

Try being your own sleep researcher by experimenting with different strategies to find what works best for you. We all have individual sleep and hydration needs, so why not test having a drink before bed or going without to see the effect it has on your sleep.

If you do feel the most thirsty before bed, however, the best approach is to focus on hydration throughout the day and taking a multi-pronged approach to sleep, of which hydration is just one element. 

As we have explained above, if you go to bed thirsty, it’s likely that the physical effects of dehydration will impact on your ability to sleep.

Ultimately, there is nothing wrong with having a glass of water before bed or on your nightstand if you wake up feeling thirsty. Try to find what works best for you.

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Written by Chloe Angus of Cavendish Wellbeing. Cavendish Wellbeing provides health and wellbeing services to local organisations on a range of subjects including sleep, nutrition and mental health.

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References:

[1] Wergin, A. (2022) Water: Essential for your body, Mayo Clinic Health System. Available at: https://www.mayoclinichealthsystem.org/hometown-health/speaking-of-health/water-essential-to-your-body-video. 

[2] Water Science School (2019) The Water in You: Water and the Human Body, USGS Science For a Changing World. Available at: https://www.usgs.gov/special-topics/water-science-school/science/water-you-water-and-human-body. 

[3] Cuzzo, B., Padala, S.A. and Lappin, S.L. (2023) Physiology, vasopressin, National Library of Medicine. Available at: https://www.ncbi.nlm.nih.gov/books/NBK526069/. 

[4] Rosinger , A.Y. et al. (2019) Short sleep duration is associated with inadequate hydration: Cross-cultural evidence from US and Chinese adults, National Library of Medicine. Available at: https://pubmed.ncbi.nlm.nih.gov/30395316/.

[5] Melone, L. (2023) 7 Easy Fixes for Snoring, WebMD. Edited by B. Nazario. Available at: https://www.webmd.com/sleep-disorders/features/easy-snoring-remedies.  

[6] Gizowski, C., Trudel, E. and Bourque, C.W. (2017) Central and peripheral roles of vasopressin in the circadian defense of body hydration, U.S. National Library of Medicine. Available at: https://pubmed.ncbi.nlm.nih.gov/29224666/.

[7] Studying sleep’s impact on Kidney Health (no date) National Kidney Foundation. Available at: https://www.kidney.org/studying-sleep-s-impact-kidney-health.

[8] Roussel, R. et al. (2011) Low Water Intake and Risk for New-Onset Hyperglycemia, American Diabetes Association. Available at: https://diabetesjournals.org/care/article/34/12/2551/39030/Low-Water-Intake-and-Risk-for-New-Onset.

[9] HealthMatch Staff (2022) How much weight do you lose overnight?, HealthMatch. Edited by B. Vallance, BNutrSc. Available at: https://healthmatch.io/weight-management/how-much-weight-do-you-lose-overnight. 

[10] Harding, E.C., Franks, N.P. and Wisden, W. (2019) The Temperature Dependence of Sleep, PubMed National Library of Medicine. Available at: https://pubmed.ncbi.nlm.nih.gov/31105512/.

[11] Shin, M. et al. (2016) The effects of fabric for sleepwear and bedding on sleep at ambient temperatures of 17°C and 22°C, PubMed National Library of Medicine. Available at: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4853167/.

[12] Li, X., Halaki, M. and Chow, C.M. (2024) How do sleepwear and bedding fibre types affect sleep quality: A systematic review, Wiley Online Library. Available at: https://onlinelibrary.wiley.com/doi/10.1111/jsr.14217#jsr14217-bib-0034. 

[13] Kräuchi, K. et al. (2017) Sleep on a high heat capacity mattress increases conductive body heat loss and slow wave sleep, ScienceDirect. Available at: https://www.sciencedirect.com/science/article/abs/pii/S0031938417304365?via%3Dihub.

[14] Raman, R. (2019) Does Coffee Dehydrate You?, Healthline. Edited by K. Marengo LDN, RD. Available at: https://www.healthline.com/nutrition/does-coffee-dehydrate-you. 

[15] Bird, E.T. et al. (no date) Caffeine ingestion and lower urinary tract symptoms in healthy volunteers, National Library of Medicine. Available at: https://pubmed.ncbi.nlm.nih.gov/16167356/. 

[16] Neuhäuser-Berthold et al. (no date) Coffee consumption and total body water homeostasis as measured by fluid balance and bioelectrical impedance analysis, National Library of Medicine. Available at: https://pubmed.ncbi.nlm.nih.gov/9194998/. 

[17] WebMD Editorial Contributor (2024) Health Benefits of Lemon, WebMD. Edited by J. Begum. Available at: https://www.webmd.com/diet/health-benefits-lemon. 

[18] Alwis, U.S. et al. (2020) Could Evening Dietary Protein Intake Play a Role in Nocturnal Polyuria?, National Library of Medicine. Available at: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7464190/.