Dehydration Effects

13 Detrimental Effects of Dehydration

Drinking the recommended two liters of water a day can seem impossible. How bad can being a little dehydrated really be? We’ve looked at the latest research to show you just how detrimental even mild dehydration can be to your health. You won’t be forgetting your water bottle any time soon!



What does it mean to be dehydrated?

Dehydration occurs any time we lose more water than we take on board. You’d be surprised how many ways we can lose water from our bodies: urinating, sweating, defecating, vomiting and just breathing all cause water loss. Certain circumstances cause us to lose even more fluid. This includes exercising, especially in hot conditions, illness with diarrhea and vomiting, and even a night out drinking alcohol. 

Since about three-quarters of the human body is made up of water, it’s essential to make up for those losses by taking in enough fluids. If you need any more convincing, we’ve reviewed the research showing just how bad being even a little dehydrated is for you. Here are 13 detrimental effects of dehydration.



1. Headaches

You may be familiar with the throbbing headaches that can develop after exercising in the heat or sitting too long in the sun. These might be the first painful reminders that you haven’t had enough to drink (1). If you’re slightly dehydrated over a long period (ie, chronic mild dehydration), these frustrating headaches can follow you around daily. Drinking more water, rather popping an aspirin, is likely to be the best remedy. 



2. Muscle cramps


Another distressing side effect of dehydration, also intensified by exercising in hot conditions, is muscle cramps. Loss of both water and electrolytes in sweat contribute to these muscle pains, which often occur in the calves. Such cramps can keep you up at night and interfere with your ability to exercise.

A recent study has found it may actually be the loss of electrolytes, rather than dehydration per se, that causes these cramps. This is evidence that electrolyte-rich rehydration is better at preventing cramps than water alone (2).  



3. Impaired ability to exercise

Dehydration is known to reduce our ability to do strenuous exercise, making us tire quicker (3). This is more the case with aerobic exercise like running than with anaerobic, strength-based exercise like weightlifting. Furthermore, headaches and muscle cramps can make exercising more difficult and less enjoyable. Don’t let lack of water ruin your endorphin-kick — hydrate!



4. Weight gain

weight and dehydration

Not only is dehydration reducing your ability to exercise, but it could also be hampering your efforts to lose weight. Studies have suggested that being adequately hydrated is likely to aid weight loss by suppressing food cravings and actively burning fat (4). Furthermore, chronic mild dehydration has been linked to metabolic diseases like obesity and diabetes – so being just a little dehydrated could be doing you a lot of harm. 



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5. Blurry vision 

blurred vision from dehydration 

Your eyes are a little like the windshield of a car. You need to keep your windshield washer fluid topped up or your wipers will just smear dirt over the glass, and you won’t be able to see very much! Similarly, your tear ducts are constantly pushing tears out onto your eyes, where they are pushed around by your eyelids. This keeps your eyes lubricated and removes any dirt. Dehydration makes this process less effective and can lead to blurry vision. 


6. Impaired mood and concentration 

Dehydration can affect aspects other than your physical health, such as mood and concentration. One study found that inducing mild dehydration in people led to reduced cognitive functions such as memory and judgment (5). Another study in young women found that when they were dehydrated they had impaired mood and concentration and felt tasks were more difficult (6). It’s likely that dehydration affects us all differently; however, it is clear that to stay healthy and happy, it is vital to stay hydrated.



7. Poor skin health

Our skin is the largest organ in our body and faces a range of challenges from being exposed to the outside world. Healthy, hydrated skin has a property called “turgor,” or elasticity. When you’re well-hydrated, your pinched skin quickly returns to its normal shape. When you’re dehydrated, the skin can lose this ability and can remain in the pinched position when let go. Another effect of dehydration on skin is the appearance of sunken eyes due to this reduced elasticity. Dehydrated skin can also appear dry, but this is different from simple dry skin and moisturizing won’t do much good. But drinking water will have you looking great and get your skin functioning properly in no time.



8. Kidney problems 

The kidneys filter metabolic waste from our blood, dilute it in water, and pass it from the body as urine. When you’re dehydrated your body holds onto available water and you produce less urine, which appears darker because the metabolic waste is more concentrated. This is thought to have consequences for the kidneys. 

Some doctors suggest that drinking enough water can help prevent and speed up clearance of urinary tract infections (UTIs) (7) and that, conversely, dehydration could increase our risk of infections. Furthermore, dehydration may increase the risk of developing painful kidney stones and even cause the kidneys to function less effectively long-term (ie, chronic kidney disease).



9. Tiredness 

It’s a great idea to start the day with a glass of water to wash away those morning cobwebs, because dehydration contributes to feelings of fatigue and tiredness. Busy lives, stress and inadequate sleep are often difficult to avoid, but staying well-hydrated is something you can easily do to fight off the sleepiness!



10. Pain 

Do you have days when your back or joint pain is worse than usual? Dehydration may be to blame. Studies have found that people who are dehydrated, rate pain higher when exposed to a painful stimulus than those who are well-hydrated (8). If true, dehydration could be not only giving you headaches, but making other pains in your body feel even worse – another good reason to hydrate!



11. Bad breath 

When you’re dehydrated your mouth and tongue can become dry. Not only is this uncomfortable, it may contribute to developing bad breath (9). Drinking fluids and swallowing saliva washes bits of food and bacteria out of your mouth. If you don’t drink enough, they’ll hang around and cause a bad smell, something none of us wants! 



12. Sore throat 

When you breathe through your nose, the air that comes in gets warmed up and humidified before moving down into your airway. Dehydration makes the humidification process less effective, and breathing in dry air can contribute to throat irritation and a dry cough (10). Again, hydrating is a simple way to avoid these annoying, uncomfortable symptoms.



13. Blackouts 

blackout in a station

In the most severe cases (usually due to illness with vomiting and diarrhea), dehydration can cause seizures and loss of consciousness, or blackouts. This is due in part to hypovolemia, or low blood volume, which reduces blood flow to the brain (11). Seizures can also result when significant loss of body fluids causes a severe electrolyte imbalance. Although this is unlikely in healthy individuals, it just shows how essential proper hydration is to our health.

Writer: Charlotte Harrison



[1] Popkin, B. M., D'Anci, K. E., & Rosenberg, I. H. (2010). Water, hydration, and health. Nutrition reviews, 68(8), 439–458. doi:10.1111/j.1753-4887.2010.00304.x - An interesting review including studies and observational evidence linking dehydration and headaches.

[2] Lau, W. Y., Kato, H., & Nosaka, K. (2019). Water intake after dehydration makes muscles more susceptible to cramp but electrolytes reverse that effect. BMJ Open Sport & Exercise Medicine, 5(1). doi:10.1136/bmjsem-2018-000478 - This study used electric shocks to cause muscle cramps in volunteers. They found electrolyte-rich rehydration reduced the “crampiness” of muscles, while plain water rehydration increased how easy it was to make muscles cramp - ouch!

[3] Walsh, R., Noakes, T., Hawley, J., & Dennis, S. (1994). Impaired High-Intensity Cycling Performance Time at Low Levels of Dehydration. International Journal of Sports Medicine, 15(07), 392-398. doi:10.1055/s-2007-1021076 - In this study a group of men cycled intensely until they became exhausted. They found that those who were dehydrated became exhausted faster.

[4] Thornton, S. N. (2016). Increased Hydration Can Be Associated with Weight Loss. Frontiers in Nutrition, 3. doi:10.3389/fnut.2016.00018 - This is a review of studies on humans and animals suggesting that a substance called angiotensin II, released when we drink, plays a role in weight loss by reducing intake and actively burning fat (known as lipolysis). 

[5] Cian, C., Barraud, P., Melin, B., & Raphel, C. (2001). Effects of fluid ingestion on cognitive function after heat stress or exercise-induced dehydration. International Journal of Psychophysiology, 42(3), 243-251. doi:10.1016/s0167-8760(01)00142-8 - Studies like this one dehydrate participants by having them exercise, sometimes in heat, until they lose a certain amount of water weight. They are then compared to hydrated participants on a range of tasks – in this case, psychological tests of cognitive function.

[6] Armstrong, L. E., Ganio, M. S., Casa, D. J., Lee, E. C., Mcdermott, B. P., Klau, J. F., . . . Lieberman, H. R. (2011). Mild Dehydration Affects Mood in Healthy Young Women. The Journal of Nutrition, 142(2), 382-388. doi:10.3945/jn.111.142000 - Similar to the above, this study used a mood questionnaire to find that dehydration increased feelings of fatigue and caused a “total mood disturbance.”  

[7] Beetz, R. (2003). Mild dehydration: A risk factor of urinary tract infection? European Journal of Clinical Nutrition, 57(S2). doi:10.1038/sj.ejcn.1601902 - This paper reviews evidence of several studies linking hydration and UTIs. The evidence is conflicting; however, many conclude that staying adequately hydrated is a simple measure that could aid treatment of UTIs. 

[8] Perry, B. G., Bear, T. L., Lucas, S. J., & Mündel, T. (2015). Mild dehydration modifies the cerebrovascular response to the cold pressor test. Experimental Physiology, 101(1), 135-142. doi:10.1113/ep085449 - This paper investigated blood flow in the brain, but also found that when a limb is submerged in very cold water, people rated the pain higher if they were dehydrated.

[9] Bollen, C. M., & Beikler, T. (2012). Halitosis: The multidisciplinary approach. International Journal of Oral Science, 4(2), 55-63. doi:10.1038/ijos.2012.39 - This review explains the link between dry mouth (xerostomia) and bad breath (halitosis) due to reduced saliva and its antimicrobial properties.

[10] Sore Throats - ENT Health. ENT Health(2019). - This websites lists the reasons for developing a sore throat. The most common is a cold (usually viral infection), but dehydration can cause a sore throat by irritation

[11] Fainting - Causes. (2019). - This NHS website describes how dehydration can cause fainting due to reduced amount of fluid in the body and therefore reduced blood pressure.



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