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Dehydration may cause cancer treatment to be delayed until you can be rehydrated, so staying hydrated is an important consideration in treatment. Adequate hydration can also reduce some treatment side effects.

Dehydration and Hydration


All of us need to stay hydrated every day—it’s essential to life and good health. Dehydration can cause a whole collection of health impacts:1

  • Increased frequency of headaches
  • Dizziness
  • Fatigue
  • Dry or flaky skin
  • Constipation
  • Difficulty swallowing
  • Reduced muscle strength, power and endurance
  • Mental status changes (impaired mood, concentration, attention and focus, reaction speed, short-term memory) and even delirium
  • High blood pressure
  • Kidney stones

Preventing dehydration is important to everyone, but especially for people with cancer. Hydration is widely recommended within both conventional and complementary approaches to cancer care.

Signs of Dehydration

Mild or moderate dehydrationSevere dehydration
  • Thirst
  • A dry or sticky mouth or a swollen tongue
  • Fatigue or weakness
  • Irritability
  • Dizziness
  • Nausea and vomiting
  • Headaches
  • Constipation
  • Dry skin
  • Weight loss
  • Dark yellow urine or a decrease in urination
  • Extreme thirst
  • Low blood pressure
  • Fever
  • Rapid heartbeat
  • Lack of urination for more than eight hours
  • Sunken eyes
  • Inability to sweat
  • Inability to produce tears
  • Disorientation or confusion

Conditions That Can Cause Dehydration

  • Uncontrolled vomiting or diarrhea
  • Loss of appetite and changes to the way things taste, which may affect how much you eat and drink
  • Extended time in a hot environment
  • Vigorous exercise causing you to sweat

Hydration and Cancer

For people with cancer, dehydration may cause your treatment to be delayed until you can be rehydrated, so staying hydrated is an important consideration in  your treatment. Adequate hydration can also reduce some treatment side effects.

“Good hydration helps flush toxins out of the body and reduce treatment side effects, such as nausea, weakness, constipation and fatigue.”2

If you are having surgery, chemotherapy, radiation therapy and other treatments, you need to be extra attentive to your hydration:

  • Diuretics prescribed to treat high blood pressure and several chemotherapy drugs are designed to increase urination, so taking them may put you at increased risk of dehydration.
  • Some drugs can damage the kidneys and the bladder, and adequate hydration reduces the risk of that damage.
  • Toxic by-products of some drugs, as well as those released by dying cancer cells, need to be flushed from the body, and an adequate supply of liquids is crucial.
  • The surgical stress response as well as surgical complications can upset the balance of your fluids and electrolytes, so staying well hydrated both before and after surgery is important (being sure to follow your medical care team’s directions).
  • During treatments such as surgery and intravenous (IV) chemotherapy, IV fluids will hydrate you. But when the IVs are removed, you’re in charge of hydrating yourself.
  • If you have a fever or gastrointestinal problems such as nausea, vomiting, diarrhea, or difficulty swallowing, hydration is especially important.

Even if you are keeping up with your liquid intake goals, you may develop problems that cause you to lose more fluid than you’re able to take in, resulting in dehydration. Know what problems can cause dehydration, what to do if you have any of these problems, the signs of dehydration (above) and when to call your doctor.

Hydration and Surgery

While the recommendation formerly was to stop fluid intake several hours before surgery, updated guidance permits and even encourages clear liquids until two hours before surgery.

National anesthesia guidelines from the United Kingdom recommend drinking clear liquids until two hours before the start of anesthesia (but keeping a six-hour fast for solid food).3 Glucose-containing solutions before surgery show benefits:4

  • Decreased thirst, anxiety and hunger before surgery
  • Reduced loss of protein and muscle mass
  • Improved insulin resistance and nitrogen balance following surgery
  • Accelerated recovery and shorter hospital stay

Studies have found that hydration before surgery can decrease the perception of pain.5

More information on hydration and surgery:

How to Hydrate

An ounce of prevention, and about 64 ounces of fluids every day goes a long way to prevent dehydration. A simple reminder is “Drink before you’re thirsty.” 

Here are some tried and true tips from on staying hydrated:6

  • Drink lots of fluids: Drinking at least eight cups of water each day is a good rule of thumb. However, if you have any risk factors for dehydration, you should drink more. If you dislike plain water, try drinking a flavored water or adding a slice of citrus fruit, a drop of mint oil or a shake of cinnamon. Other fluids such as juice and non-caffeinated tea can contribute to your fluid count as well. If you're on a fluid restriction from your doctor, please follow those guidelines instead.
  • Eat foods with high water content: While drinking water is the best source of hydration, many foods contain water and can help replenish lost fluids. Choose foods like lettuce, watermelon, cucumbers and broccoli. Soups, ice pops, and yogurt also have high water content. Favor all-fruit, low sugar ice pops and unsweetened yogurt.
  • Get help managing side effects: If you are undergoing cancer treatment that is causing side effects such as nausea, vomiting, or diarrhea, then talk with your doctor about ways to prevent or reduce these side effects, including medication and other therapies (see Nausea and Vomiting).
  • Don't wait to drink: Make a conscious effort to drink enough on a regular basis. Drink more often if you begin feeling ill, before you exercise, and before you go out into hot weather.
  • Avoid foods and drinks that may contribute to dehydration: Beverages with sugar or caffeine may help to hydrate some, but are not as effective as low-sugar or beverages without caffeine, which may increase urination and loss of sodium. Beverages with electrolytes may be helpful to patients struggling with side effects such as vomiting, diarrhea, hot flashes or excessive sweating, and/or fever. Electrolytes are minerals including sodium, chloride, potassium, magnesium and calcium, that are critical in maintaining key body functions. While many sports drinks are supplemented with electrolytes, the sugar content of these flavored beverages may reduce their effectiveness.

Alcohol can also dehydrate you, causing your body to remove fluids from your blood through your kidneys at a much quicker rate than other liquids. If you don’t drink enough water with alcohol, you can become dehydrated quickly.7 If you are at risk for dehydration, avoiding alcohol is the wisest choice.

More Tips

Additional tips on calculating and tracking your fluid intake if you’re having trouble staying hydrated: 

  • A rule of thumb for women is to aim for at least 64 ounces a day, or eight cups. Men should aim for 96 ounces a day or 12 cups. For a more personalized goal, divide your weight by two to determine how many ounces of fluid to aim for in a day. To translate your daily goal into cups, divide the number of ounces by eight:H8 9

Example: body weight = 150 pounds / 2 = 75 ounces
75 ounces / 8 = 9.38 cups

  • If you are getting treatments or having symptoms that are likely to cause dehydration, get help from a registered dietitian or your oncology doctor or nurse to calculate your specific fluid needs.
  • Space out your fluid intake throughout the day, starting with drinking as soon as you wake up. Avoid overhydration and stomach upset that comes from taking in large amounts of liquids at one time (see below).
  • Measure your water for the day in a pitcher or bottle and aim to empty the pitcher by early evening. Or mark your water bottle or glass for 8 ounces and keep track of each time you empty it until you reach your daily goal.
  • Set a reminder alarm or use a phone app water drink reminder to nudge you to drink throughout the day. 
  • Keep a log of when you take in liquids and how much you take in. 


Overhydration: What Happens if I Take in Too Much Liquid?

It’s possible to take in more liquids than your body can handle, which can cause unpleasant and sometimes even serious problems. Normally, your kidneys can excrete up to one liter (about four cups) of total fluid per hour. Keep in mind you get fluid not just from what you drink but also from foods. It’s possible to exceed your kidneys’ capacity. If your kidneys are impaired at all, then you will become overhydrated even more quickly. 

Problems of overhydration:

  • Stomach discomfort from taking in more volume than it can handle
  • Swelling in your tissues (edema) and 
  • Fluid overload on your heart and lungs
  • Diluted electrolytes in blood, especially sodium (hyponatremia), can cause problems ranging from fatigue and weakness to confusion and—most seriously—convulsions.10


  1. Healthline. What does it mean when dehydration becomes long-term and serious? Viewed January 27, 2021; D’Aniello C. Hydration and delirium. Today’s Caregiver. Viewed January 27, 2021.
  2. How to stay hydrated during cancer treatment. Cancer Treatment Centers of America. June 10, 2020. Viewed January 27, 2021.
  3. National Health Service. Can I eat or drink before an operation? May 1, 2020. Viewed January 29, 2021; Desert West Surgery. Hydration: Tips on Water Before and After Surgery. Viewed January 29, 2021; The night and morning before surgery. Allina Health. June 15, 2015. Viewed January 29, 2021.
  4. Lassen K, Soop M et al; Enhanced Recovery After Surgery (ERAS) Group. Consensus review of optimal perioperative care in colorectal surgery: Enhanced Recovery After Surgery (ERAS) Group recommendations. Archives of Surgery. 2009 Oct;144(10):961-9.
  5. Ogino Y, Kakeda T, Nakamura K, Saito S. Dehydration enhances pain-evoked activation in the human brain in comparison with rehydration. Anesthesia Analgesia. 2014;118:1317–25.
  6. The Importance of Hydration. July 1, 2009. Viewed January 27, 2021.
  7. Does Alcohol Dehydrate You? Healthline. May 23, 2019. Viewed January 28, 2021.
  8. ow to stay hydrated during cancer treatment
  9. . Cancer Treatment Centers of America. June 10, 2020. Viewed January 27, 2021.
  10. Garone S. Chugging water all the time? How to avoid overhydration. Healthline. Viewed January 27, 2021.


This article has been taken from Beyond Conventional Cancer Therapies.