Everyone gets sick from time to time. Whether it's a cold, the flu, COVID-19, food poisoning, or another illness, being sick places extra stress on your body. For people with diabetes, that stress often makes blood sugar more difficult to manage.
Even if you're eating very little—or not eating at all—your blood sugar may become much higher than usual. Having a plan before you become sick can help you stay safe, prevent complications, and know when it's time to seek medical care.
Why Does Illness Raise Blood Sugar?
When you're sick, your immune system releases hormones that help your body fight infection, including cortisol, glucagon, and adrenaline. These hormones signal your liver to release more glucose into your bloodstream so your body has enough energy to respond to illness. At the same time, they also make your body less responsive to insulin.
As a result, many people with diabetes develop higher blood sugar during illness—even if they aren't eating normally.
Can Blood Sugar Ever Go Low During Illness?
Yes. Although illness often raises blood sugar, some people develop low blood sugar because they eat less than usual, vomit after eating, have diarrhea, continue taking medications that lower glucose, or become dehydrated. This is why frequent monitoring is so important whenever you're sick.
Continue Monitoring Your Blood Sugar
Illness can cause blood sugar to change quickly. Check your glucose as often as your healthcare provider recommends. If you use a continuous glucose monitor (CGM), continue watching your glucose trends and pay attention to alerts.
Remember that symptoms are just as important as device readings. If your symptoms don't match your CGM, follow your healthcare provider's recommendations about confirming your glucose with a blood glucose meter.
Stay Hydrated
One of the biggest risks during illness is dehydration. High blood sugar causes the kidneys to remove extra glucose through the urine, leading to increased fluid loss. Vomiting, diarrhea, fever, and poor appetite can make dehydration even worse.
Drink fluids regularly throughout the day — water is usually the best choice. If you have difficulty eating, your healthcare provider may recommend fluids that contain carbohydrates in certain situations to help prevent low blood sugar. If you're unable to keep fluids down, seek medical advice promptly.
Keep Taking Your Diabetes Medications
Many people assume they should stop taking their diabetes medications when they aren't eating. In many cases, this is not correct. Your body often needs insulin and other diabetes medications during illness, even if you're eating less.
However, some medications may need to be adjusted during certain illnesses or if you become dehydrated. Never stop insulin on your own unless your healthcare provider specifically instructs you to do so. If you're unsure how to manage your medications while you're sick, contact your healthcare provider as soon as possible.
Try to Eat If You Can
Your appetite may decrease during illness. Even if you don't feel like eating full meals, try to consume fluids and foods that you can tolerate — soup, applesauce, yogurt, crackers, toast, rice, bananas. If you cannot eat solid foods, focus on staying hydrated and contact your healthcare provider for guidance.
Know When to Check Ketones
People with type 1 diabetes and some people with insulin-treated diabetes may need to check ketones during illness. Your healthcare provider may recommend checking ketones if your blood sugar remains significantly elevated, you have vomiting, you have symptoms of diabetic ketoacidosis (DKA), or you're unable to keep food or fluids down.
Ketones can be checked using urine test strips or a blood ketone meter, depending on your diabetes care plan. Follow the instructions provided by your healthcare team.
Watch for Signs of Diabetic Ketoacidosis (DKA)
Diabetic ketoacidosis is a serious medical emergency that occurs most often in people with type 1 diabetes but can also occur in some people with type 2 diabetes. Symptoms may include:
- Very high blood sugar
- Moderate or large ketones
- Nausea or vomiting
- Abdominal pain
- Rapid or deep breathing
- Fruity-smelling breath
- Increasing fatigue
- Confusion
DKA requires immediate medical treatment.
Rest and Recover
Your body needs energy to heal. Allow yourself time to rest while continuing to monitor your diabetes carefully. Avoid strenuous exercise if you're significantly ill, dehydrated, or have moderate or large ketones unless your healthcare provider instructs otherwise.
Have a Sick-Day Plan Before You Need It
One of the best ways to prepare for illness is to create a sick-day plan with your healthcare provider. Your plan may include when to check your blood sugar, when to check ketones, which medications to continue, when medication adjustments may be needed, when to call your healthcare provider, and when to seek emergency care. Having written instructions available can reduce stress when you're not feeling well.
Keep a Sick-Day Supply Kit
Consider keeping supplies together in one location:
- Blood glucose meter and test strips
- CGM supplies, if applicable
- Ketone test strips or a blood ketone meter, if recommended
- Thermometer
- Fast-acting glucose for hypoglycemia
- Easy-to-tolerate foods
- Water and electrolyte-containing fluids
- A list of your medications
- Contact information for your healthcare provider
Replacing expired supplies regularly can help ensure they're available when you need them.
Frequently Asked Questions
Should I stop taking insulin if I'm not eating?
No. Most people who use insulin should continue taking it during illness, although doses sometimes need adjustment. Never stop insulin without guidance from your healthcare provider.
Why is my blood sugar high if I haven't eaten?
Illness causes your body to release stress hormones that increase glucose production by the liver and reduce insulin effectiveness. This is a normal response to illness.
Should I exercise when I'm sick?
It depends. If you have a mild illness and feel well enough, light activity may be appropriate. However, if you have fever, dehydration, vomiting, moderate or large ketones, or significant fatigue, it's generally best to rest until you've recovered. Follow your healthcare provider's recommendations.
Do I need to check ketones every time I'm sick?
Not everyone does. Ketone testing is especially important for many people with type 1 diabetes and others at risk for diabetic ketoacidosis. Ask your healthcare provider whether ketone testing should be part of your sick-day plan.
When Should You Contact Your Healthcare Provider?
Contact your healthcare provider promptly if your blood sugar remains consistently above your target range, you're unsure how to adjust your medications, you have repeated vomiting or diarrhea, you're unable to eat or drink normally, you have moderate or large ketones, or your illness is getting worse instead of improving. Early guidance can often prevent more serious complications.
Seek Emergency Medical Care Immediately If
Go to the nearest emergency department or call emergency medical services if you have difficulty breathing, severe dehydration, persistent vomiting that prevents you from keeping fluids down, confusion or difficulty staying awake, symptoms of diabetic ketoacidosis, loss of consciousness, a seizure, or severe hypoglycemia that does not improve with treatment or requires another person to assist. These symptoms require immediate medical attention.
The Bottom Line
Illness can make diabetes much more difficult to manage, even if you're eating very little. Checking your blood sugar more frequently, staying hydrated, continuing medications as directed, and knowing when to check ketones can help reduce the risk of serious complications.
The most important step is to have a sick-day plan before you need one. Work with your healthcare provider to create a plan that's tailored to your medications, type of diabetes, and overall health. Being prepared can help you recover more safely and with greater confidence.