Flu & People with Diabetes

Diabetes mellitus is a chronic disease that is becoming more prevalent worldwide. Diabetes causes high blood sugar, which is harmful to health in many ways.

As of 2015, 30.3 million people in the United States, or about 9.4% of the population, had diabetes. Unfortunately, more than 1 in 4 people with diabetes don’t know they have it.

Having undiagnosed diabetes increases the risk of diabetes-related complications such as kidney disease, heart disease, amputations, and more.

Diabetes affects blood sugar levels, but there’s more to it than that. High blood sugar impacts the immune system, making people with diabetes more susceptible to illness and infections. Illness also can raise blood sugar, further complicating the cycle.

Symptoms of the flu

Influenza, or the flu, is caused by a virus that attacks the respiratory system. It can affect people of all ages and can become a serious health issue in certain high-risk people.

Symptoms of the flu are similar to the common cold at first. Unlike the common cold, symptoms of the flu develop suddenly versus gradually over time. Common flu symptoms include:

Common symptoms of the flu include:

  • Fever

  • Aching muscles

  • Chills and sweats

  • Headache

  • Dry, persistent cough

  • Shortness of breath

  • Tiredness and weakness

  • Runny or stuffy nose

  • Sore throat

  • Eye pain

  • Vomiting and diarrhea (more common in adults than children)

Flu season occurs in the fall and winter in the Northern Hemisphere, where cases of the flu usually begin around October, peak in February, and start to fall in March as spring approaches. In the Southern Hemisphere, flu cases usually appear during April through September. However, during the COVID-19 pandemic, cases of the flu have dropped significantly.

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While most people recover from the flu, there are complications that can arise. People who are considered high-risk may have more serious complications from contracting the flu. Per the Centers for Disease Control & Prevention (CDC), these types of high-risk criteria include:

  • Adults 65 years and older

  • Children younger than 2 years old

  • Asthma

  • Neurological and neurodevelopmental conditions

  • Blood disorders (such as sickle cell disease)

  • Chronic lung disease (such as chronic obstructive pulmonary disease [COPD] and cystic fibrosis)

  • Endocrine disorders, such as diabetes – In previous flu seasons, 30% of people hospitalized for the flu had diabetes.

  • Heart disease (such as congenital heart disease, congestive heart failure, and coronary artery disease)

  • Kidney diseases

  • Liver disorders

  • Metabolic disorders (such as inherited metabolic disorders and mitochondrial disorders)

  • People who are obese with a body mass index [BMI] of 40 or higher

  • People younger than 19 years old on long-term aspirin- or salicylate-containing medications.

  • People with a weakened immune system due to disease (such as people with HIV or AIDS, or some cancers such as leukemia) or medications (such as those receiving chemotherapy or radiation treatment for cancer, or persons with chronic conditions requiring chronic corticosteroids or other drugs that suppress the immune system)

  • People who have had a stroke

  • Pregnant women and women up to 2 weeks after the end of pregnancy

  • People who live in nursing homes and other long-term care facilities

  • People from certain racial and ethnic minority groups are at increased risk for hospitalization with flu, including non-Hispanic Black persons, Hispanic or Latino persons, and Native American or Alaska Native persons

Emergency warning signs related to the flu requiring immediate medical attention include:

  • Difficulty breathing or shortness of breath

  • Persistent pain or pressure in the chest or abdomen

  • Persistent dizziness, confusion, inability to arouse

  • Seizures

  • Not urinating

  • Severe muscle pain

  • Severe weakness or unsteadiness

  • Fever or cough that improves but then return or worsen

  • Worsening of chronic medical conditions

Some of the complications that can arise from the flu include:

  • Sinus and ear infections

  • Pneumonia

  • Inflammation of the heart (myocarditis)

  • Inflammation of the brain (encephalitis)

  • Inflammation of the muscle (myositis, rhabdomyolysis)

  • Multi-organ failure

  • Sepsis 

  • Worsening asthma attacks in those with a previous history of asthma

  • Worsening of chronic heart problems

How will the flu affect blood sugar levels?

Illness and infection tend to raise blood sugar levels due to the stress illness puts on the body. Stress hormones are released, which can lead to insulin resistance and raised blood sugar levels. For this reason, many people struggle with higher-than-normal blood glucose levels when they have the flu.

If someone is unable to eat normally, or if they are vomiting excessively, they may develop low blood sugar. Low blood sugar can become life-threatening if it’s severe. Having fruit juice or glucose tablets on hand to treat low blood sugar is a good idea for people with diabetes.

Family, friends, and caregivers of people with diabetes should be aware of the signs of low blood sugar as well:

  • Blood sugar below 70 mg/dL

  • Shakiness

  • Dizziness

  • Sweating

  • Hunger

  • Fast heartbeat

  • Inability to concentrate

  • Confusion

  • Irritability or moodiness

  • Anxiety or nervousness

  • Headache

Flu and diabetes

Having the flu can worsen blood sugar levels as the body works to fight off the infection. People may lose their appetite and eat less, which can lead to hypoglycemia (low blood sugar), especially if they are taking medications to lower their blood sugar.

People with diabetes are encouraged to follow sick day management tips to help promote healthy blood sugar levels. Some of the suggestions for sick days include:

  • Continue taking insulin and diabetes pills as usual.

  • Test blood sugar every 4 hours and keep track of the results.

  • Drink extra calorie-free liquids, and try to eat as normal.

  • Weigh in daily; losing weight without trying is a sign of high blood glucose.

  • Check temperature every morning and evening to check for infection.

Some handy foods and beverages to keep on hand for sick days:

  • Sports drinks

  • Juice boxes

  • Canned soup

  • Regular gelatin

  • Regular soft drinks

  • Instant cooked cereals

  • Crackers

  • Instant pudding

  • Unsweetened applesauce

If someone is unable to eat meals, they should eat or drink about 50 grams of carbohydrates every 4 hours, such as 1½ cup of unsweetened applesauce or 1½ cup of fruit juice. 

If blood sugar levels rise very high, another complication that can occur is diabetic ketoacidosis (DKA), which is especially common in people with type 1 diabetes. DKA results from insulin levels being so low that the body starts to burn fat for fuel instead of glucose. DKA can become life-threatening, so should be treated as a medical emergency. Signs of DKA include:

  • Excessive thirst

  • Frequent urination

  • Nausea and vomiting

  • Stomach pain

  • Weakness or fatigue

  • Shortness of breath

  • Fruity-scented breath

  • Confusion

Hyperglycemic hyperosmolar syndrome (HHS) is a condition that impacts people with type 2 diabetes. An infection (such as the flu) is one of the risk factors for HHS, which has symptoms including:

  • Blood sugar level of 600 mg/dL or higher

  • Excessive thirst

  • Dry mouth

  • Increased urination

  • Warm, dry skin

  • Fever

  • Drowsiness, confusion

  • Hallucinations

  • Vision loss

  • Convulsions

  • Coma

With these possibilities of extreme high and low blood sugar levels, it’s important for people with diabetes to be in touch with their healthcare providers if they are infected with the flu.

Diabetes and flu vaccine

The flu vaccine is one of the best ways to prevent the flu. Even if someone gets the flu after being vaccinated, the chances of severe complications are lower among those vaccinated against the flu. People may also be less likely to die from flu-related issues when receiving the flu vaccine.

It’s recommended for all people 6 months of age and older to receive a flu vaccine appropriate for their age and medical background. The vaccine is administered intramuscularly and is also available in a nasal mist.

It takes about two weeks for the antibodies to develop after receiving the flu shot, so it’s ideal to be vaccinated before flu cases start to spread. Pregnant women are also encouraged to receive their flu shot since they are considered high-risk for developing complications from the flu.

The formulations of the flu shot changes with each flu season to provide the most accurate protection against the current strain of the virus. Immunity from the flu also becomes less strong overtime after getting the flu shot. For these reasons, it’s recommended to get a flu vaccine each year.

Steps to prevent the flu

One of the best ways to prevent the flu is to get the flu shot each year. Besides that, the CDC recommends:

  1. Avoid close contact: Avoid close contact with people who are sick. When you are sick, keep your distance from others to protect them from getting sick too.

  2. Stay home when you are sick: If possible, stay home from work, school, and errands when you are sick. This will help prevent spreading your illness to others.

  3. Cover your mouth and nose: Cover your mouth and nose with a tissue when coughing or sneezing. It may prevent those around you from getting sick. Flu and other serious respiratory illnesses, like respiratory syncytial virus (RSV), whooping cough, and COVID-19, are spread by cough, sneezing, or unclean hands.

  4. Clean your hands: Washing your hands often will help protect you from germs. If soap and water are not available, use an alcohol-based hand rub.

  5. Avoid touching your eyes, nose, or mouth: Germs are often spread when a person touches something that is contaminated with germs and then touches his or her eyes, nose, or mouth.

  6. Practice other good health habits: Clean and disinfect frequently touched surfaces at home, work, or school, especially when someone is ill. Get plenty of sleep, be physically active, manage your stress, drink plenty of fluids, and eat nutritious food.


The flu is a virus that usually peaks in infection rates in the fall and winter (October through February in the Northern Hemisphere). Its common symptoms include fever, muscle aches, chills, headache, dry cough, fatigue, shortness of breath, runny or stuffy nose, sore throat, eye pain, vomiting, and diarrhea.

While most people recover from the flu, it can cause complications in high-risk individuals, such as the elderly or immunocompromised. 

People with diabetes are more prone to becoming very ill from certain illnesses and infections such as the flu. The stress of an illness can also raise blood sugar levels, leading to further possible complications. If blood sugar levels rise very high, it can cause further issues such as diabetic ketoacidosis (DKA) or hyperglycemic hyperosmolar syndrome (HHS).

If people with diabetes contract the flu, they should follow sick day management guidelines such as checking their blood sugar often, taking their medications as prescribed, and eating as normally as they can. They should also be in close contact with their primary care providers to adapt their care plan as needed, given the severity of the illness.

The best way to prevent the flu is to receive the flu vaccine every year. Other good prevention tips include proper hand washing, staying home when sick, and avoiding close contact with people who are sick. 

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  1. https://www.niddk.nih.gov/health-information/diabetes/overview/what-is-diabetes
  2. https://www.cdc.gov/mmwr/volumes/69/wr/mm6937a6.htm
  3. https://www.cdc.gov/flu/highrisk/index.htm

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