“Get plenty of fluids and rest.” 

Most of us have received this advice when we’re sick, whether from our mother, our doctor, or the good ol’ Internet. Our bodies naturally push us to rest more when we’re ill. We head for our beds and seldom have the energy to carry out our usual activities. Staying hydrated, however, often requires a more conscious effort. And unlike other key facets of our wellbeing like exercise and socializing, our water intake doesn’t get time off when we don’t feel up to par. In fact, it becomes even more important when we’re under the weather.  

Why is hydration important when sick? Does the body use more water when the immune system is trying to fight off an illness? 

Hydration is particularly important while sick for many reasons. For one, it helps facilitate the immune system’s response to infection. It also assists the body in maintaining homeostasis by keeping fevers under control. And finally, it replenishes fluids lost to vomiting or diarrhea, common symptoms of many illnesses. Here’s a deeper look into how water plays a role in all of these processes.  

Immune Response

Whenever our bodies are infected by a virus, bacteria, or parasite, the immune system kicks into action. The immune system’s complex network— which includes organs such as the spleen and tonsils, as well as larger entities like the lymphatic system— works in conjunction to rid the body of the foregin invader. When this occurs, water becomes important. It transports lymphocytes and other infection-fighting cells through the blood. 

Also, when we have the common cold or many kinds of respiratory illnesses, it’s typical for the body to secrete mucus. Mucus, which is made of 98% water, helps trap infectious agents and carries away inflammatory cells that are produced by the body. Staying hydrated helps to thin mucosal secretions so that they can be cleared from our airways. Dehydration can result in thicker secretions, which not only manifests in a stuffy nose and harsher cough, but can slow recovery. 

Fever Control

When we feel we’re coming down with a fever, one of our first instincts is to reach for the thermometer. The number on the screen does much more than tell us whether or not to head to the doctor, though. It can shed important insight into how much water the body is losing. An adult with a 102°F fever loses 30 ounces of fluid in a 24-hour period. Three ounces of water are lost when breathing and coughing.

Guidelines suggest that most adults drink between 2 or 3 liters of water per day, depending on gender, activity level, and overall health. So a woman who normally drinks 70 ounces (about 2 L) of water per day would need to drink at least 100 ounces on a day during which she is spiking a 102°F fever. Based on these numbers, chances are the majority of us don’t keep up with the recommended fluid intake while sick. 

Let’s backtrack a little bit. What exactly is happening during a fever? Well, when we have a fever, our body temperatures rise high enough to where water is lost through the skin’s surface to try and keep us cool. If we don’t actively replace the lost water, though, the body can become dehydrated rapidly. And we sweat more than we realize during fevers. On average, between 17 to 35 ounces (500-1000 grams) of water is lost in a 24-hour period during a fever. That’s why it’s important to stay on top of our fluid intake during fevers, so that water lost to sweat can be replenished.  

Replacing Lost Fluids and Electrolytes

We’ve all been there before. Stomach bugs that make our intestines feel as if they’re in knots, leaving us in the bathroom for hours at a time. Illnesses frequently lead to vomiting and diarrhea, excessively in many cases. When we vomit or have diarrhea on a recurring basis, our bodies become dehydrated. We also lose key electrolytes—minerals like calcium and potassium—which control blood pH, muscle function, and various organ processes. 

Dehydration in these cases can impair other bodily functions as our bodies also try to fight off illness. It’s important to watch for signs of dehydration such as lightheadedness, dizziness, and dry mouth. In children or toddlers, dehydration may show up as decreased tear production, fewer diaper changes, and sunken eyes. Always see your physician or seek medical attention if you feel you are unable to hydrate adequately in cases of ongoing vomiting or diarrhea. 

Parting Thoughts 

Water, while important when we aren’t sick, is even more vital for our health when we’re ill. It helps to maintain homeostasis when our fevers spike by cooling the body down. When we have episodes of vomiting or diarrhea, it replaces lost fluids and addresses resulting electrolyte imbalances. It also helps assist the immune system in transporting crucial cells that target and fight illness-causing invaders. 

It is important to remain hydrated when ill to speed up our recovery and alleviate the stress the body is already going through. Be sure to stay on top of your water intake, and monitor yourself for any signs of dehydration. 

FAQ

Q: How much water should I be drinking when sick? 

A: It is recommended that adults consume 2-4 ounces every 15 minutes while sick. To stay proactive about dehydration, ensure that every 3-4 hours, you are passing light yellow urine. 

 

Q: How can I encourage my child to drink more fluids while sick? 

A: The CDC has excellent tips on how to keep children hydrated when dealing with illnesses such as the flu. Tips include giving them ice chips or cubes, as well as offering squeeze bottles or straws if they are too weak to hold a cup. 

 

Q: Can keeping up with my water intake protect me against infectious illnesses?

A: Certain sources do indicate that staying properly hydrated can put the body in a better state for fighting off viruses and other illness-causing germs. Keeping up with your water intake is best for your overall health. 

References

1. Overview of the Immune System. Retrieved from niaid.nih.gov (December 30, 2013)
2. Lymphatic System. Retrieved from my.clevelandclinic.org (February 23, 2020)
3. Mucus, Our Body’s Silent Defender. Retrieved from my.clevelandclinic.org (February 6, 2019)
4. Why Do You Need to Drink Plenty of Water When Sick? Retrieved from livestrong.com (June 25, 2019)
5. Nutrition and Hydration: Key Weapons in the Fight Against COVID-19. Retrieved from nutritioncare.org (2020)
6. How Much Water Should I Drink Daily? Retrieved from webmd.com. 
7. What to Know About Dehydration. Retrieved from healthline.com (September 18, 2019)
8. L. Reithner. Insensible water loss from the respiratory tract in patients with fever. Acta Chir Scand. 1981; 147(3): 163-167. 
9. What to Know About Dehydration. Retrieved from healthline.com (September 18, 2019)
10. Electrolytes. Retrieved from medlineplus.gov (November 2, 2021)
11. What is Dehydration? What Causes It? Retrieved from webmd.com (May 20, 2021)
12. Dehydration and Your Child. Retrieved from my.clevelandclinic.org (September 10, 2020)
13. Nutrition and Hydration: Key Weapons in the Fight Against COVID-19. Retrieved from nutritioncare.org (2020)
14. Tips to Prevent Fluid Loss (Dehydration). Retrieved from cdc.gov (December 15, 2009)
15. Protect Yourself to Prevent Cold and Flu. Retrieved from everydayhealth.com (December 14, 2012)