Why You Get High Blood Sugar When You’re Sick and What to Do About It

Diabetes can make it harder to recover from even minor illnesses. A cold, the flu, and infections put additional stress on your body, and this stress triggers the release of hormones to fight the sickness. This increase in hormone production raises blood glucose levels, which can cause complications like diabetic ketoacidosis (DKA) and hyperosmolar hyperglycemic syndrome (HHS) if left untreated. 

So if you have diabetes, developing a sick day plan with your doctor is important. Taking proper action, which includes maintaining or reducing blood sugar levels, will help you get back to feeling better sooner.

Young adult man with cold, flu, running nose holding tea and looking at medication instructions
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Why Blood Sugar Spikes When You’re Sick

Any type of illness can raise blood sugar. There are two primary reasons why your blood sugar spikes when you get sick. Together, they are like a double-edged sword that makes managing sickness without a plan much more challenging for people with diabetes than those without. 

This is what happens to your blood sugar when you get sick:

  • Your body releases stress hormones like epinephrine (also known as adrenaline) to fight the illness. These hormones can raise your blood sugar levels and increase the amount of insulin your body needs. This makes it harder for your body to produce enough insulin to keep up with the increased demand.
  • When your body doesn’t have enough insulin to meet this increased demand, it starts burning fat as fuel and this produces ketones, which can make your blood toxic in high amounts. This can lead to diabetic ketoacidosis, which can be life-threatening if left untreated. 

When you’re sick, diabetic ketoacidosis can come on quite quickly (within a few hours). This is why following a preset diabetes sick day plan is a critical component of managing any type of illness. People with type 1 diabetes who cannot produce enough insulin on their own even during their healthiest days are at increased risk of this complication.

Sick Day Rules for Diabetes

Developing sick day rules is an important part of diabetes management and can help you recover from sickness. Talk to your doctor and share any concerns you may have about properly caring for yourself during times of illness. This includes sicknesses like the common cold and flu and infections, as well as physical stress related to any surgeries and times of heightened emotional stress.

Take Your Medicine As Usual

Insulin is a life-saving medication. Take your insulin as usual, even if you have been feeling very sick and vomiting. Ask your doctor, if necessary, how to adjust your insulin dose based on blood glucose test results.

If you are taking other diabetes-related medications to help manage your blood sugar levels, take these medications as you usually would, even in cases where you have been vomiting. Do not stop taking your medication even if you cannot eat.

If at any time you become doubtful about taking your medication or grow unsure about what the proper dose and time to take your medication should be, contact your healthcare team immediately. 

Eat As You Normally Would

Your diabetes diet is designed to help you manage your blood glucose and keep you feeling well. You should do your best to continue eating as you normally would, even when you don’t feel well. Consuming carbohydrate-rich drinks and snacks can help you prevent having low blood sugar (hypoglycemia).

Eating normally means:

  • Consuming the same types and combinations of foods you generally eat
  • Balancing your meals as you typically do, whether that’s by the plate method, carb counting, or another plan
  • Eating the same quantity of food during meals and snack times

Check Your Blood Sugar Regularly

Checking your blood sugar regularly is the only way to better understand how your body is responding to your illness. It is generally advised that you check your blood sugar with an at-home glucometer at least four times per day. Be sure to record your numbers and keep this information readily available so you can share it with your healthcare team.

For people with type 1 diabetes who may be more concerned about DKA, you can check your blood sugar levels every two hours. Again, record these measurements and keep them close so you can share them with your healthcare team when the time comes.

Follow Your Doctor’s Instructions

Every case of diabetes is unique. This is why constant communication with your doctor is so important. For example, your doctor may advise you to take more insulin to help reduce your blood sugar. Whatever they advise, follow their lead. If you have questions or concerns, be as open and honest as you can to ensure both of you have all the correct information and that you are confident about your course of action when sick. 

Drink Sugar-Free Fluids

Staying properly hydrated has many benefits during times of illness, including helping your body flush out toxins and excess sugar that drives up your blood glucose. 

Aim for one cup (8 ounces) of sugar-free and caffeine-free fluids every hour during the day. Try to consume the beverage in small sips over the course of an hour. The American Diabetes Association suggests taking sips every 15 minutes or so throughout the day to prevent dehydration when someone with diabetes is sick.

Appropriate beverages to drink include:

  • Water
  • Sugar-free carbonated beverages 
  • Unsweetened herbal tea
  • Unsweetened and decaffeinated coffee
  • Sugar-free sports drinks
  • Tomato juice

Use Diabetes-Friendly OTC Medications

One of the first things many people do when they feel sick is reach for over-the-counter (OTC) cold and flu medications or pain relievers. Not every medication is diabetes-friendly, however. Some medications may contain sugar or alcohol in their inactive ingredients. These ingredients can cause your blood sugar to rise and are therefore not recommended for people with diabetes.

You should talk to your doctor or local pharmacists about their recommendations, and call your healthcare team if you’re unsure what you can and cannot safely take.

Testing When You’re Sick

While monitoring your blood glucose levels is always advised, it’s especially important when you are sick because your blood sugar can change quickly.

When you are sick, you should:

  • Check your blood sugar every four hours to make sure it’s within the normal range and not dipping or spiking into dangerous levels.
  • Take your temperature at least every morning and evening to check for signs of fever, which could mean an infection. Get immediate medical care if your temperature is over 101 degrees for 24 hours.
  • Losing weight without trying while sick can be a sign of high blood sugar. Weigh yourself or have someone else weigh you once a day.
  • People with type 1 diabetes need to check their ketones while they are sick to monitor their risk of diabetic ketoacidosis. If you have ketones in your urine or blood, it is considered a medical emergency.

What to Eat

Maintaining your regular diabetes-friendly diet is advised even when you’re sick. However, it’s not always easy to eat or drink the exact same way when you’re not feeling well.

To prevent your blood sugar from getting too low (hypoglycemia), you should aim to consume about 50 g of carbohydrates every four hours, even if that means you need to make some different food choices that are easier while feeling sick. For example, eat 1½ cups of unsweetened applesauce or drink 1½ cups of fruit juice.

Even though you may not have much of an appetite when you’re ill, it’s important to consider your overall caloric intake to maintain a healthy weight.  

Foods that are good for people with diabetes include:

  • Broth or bouillon 
  • Dry toast 
  • Ice pops or sherbet 
  • Instant cooked cereals
  • Juice
  • Pudding
  • Milk
  • Regular gelatin (not sugar-free)
  • Regular soft drinks
  • Saltine crackers
  • Soup
  • Sports drinks
  • Unsweetened applesauce
  • Yogurt

When to See a Doctor

Despite your best efforts, sometimes your blood sugar can still spike when you’re ill. It’s important to keep a record of your blood sugar levels and other metrics your doctor has advised you to keep track of (such as testing for ketones in urine). Keep this information somewhere portable, so you can share with your doctor should the need arise. 

When you have diabetes and get sick, there are certain situations that require immediate medical attention. If you have any of the following symptoms, contact your doctor right away:

  • Blood glucose levels above 240 mg/dL even though you’ve taken your diabetes medicine
  • Blood glucose levels below 60 mg/dL 
  • Diarrhea for more than six hours
  • Brain fog and severe fatigue
  • High fever (above 101 degrees)
  • Signs of DKA or HHS
  • Trouble breathing
  • Urine or blood ketone levels above normal
  • Vomiting more than once
  • Weight loss of 5 pounds or more

Do not delay treatment. If you cannot see your healthcare provider, go to the emergency room. 

Let your medical professional know the following:

  • How long you have been sick  
  • Current symptoms
  • Blood sugar levels  
  • Urine ketone levels  
  • What you have been able to eat and drink  
  • Your temperature (whether or not you have a fever)  
  • Amount of insulin taken (if relevant)

A Word From Verywell

Having a sick day plan that you and your doctor come up with can help you get better and prevent serious health complications like DKA and HHS. Keep this plan somewhere you can easily access when you begin to feel unwell. Take medications as prescribed, try to eat as you typically would and stay adequately hydrated, record your blood sugar at regular intervals, and follow the advice of your doctor. 

If you start to experience any symptoms of DKA and HHS, seek immediate medical help from your doctor or an emergency room. There are many ways you can get through your illness while staying on top of your diabetes management so you can get back to feeling well again.

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Article Sources
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  1. Centers for Disease Control and Prevention. Managing sick days. Updated March 31, 2020.

  2. UW Health. Sick day guidelines when you have type 1 diabetes. Published October 2016. 

  3. National Institute of Diabetes and Digestive and Kidney Diseases. Take care of your diabetes during sick days & special times. Published February 2014. 

  4. HHS.gov. What should a person with diabetes do if they get sick with flu or cold? Updated September 12, 2014. 

  5. American Diabetes Association. Planning for sick days.