Glucose Intolerance: Causes, Symptoms, and Treatment

The human body is truly amazing in its ability to keep everything balanced and in tune to help keep you healthy and feeling good. However, when there is a disruption in one of the body’s processes, it can cause problems quickly. 

Healthy blood sugar levels are essential to your health. Blood sugar problems such as prediabetes, type 1 diabetes and type 2 diabetes are becoming more prevalent, impacting millions of people of all ages. Having high blood sugar levels can cause serious health complications over time, such as kidney disease, eye damage, nerve damage, and poor wound healing and amputations.

Knowing the signs that you might be suffering from a blood sugar imbalance can help you get an early diagnosis and even reverse the problem if it’s caught early enough.

What is glucose intolerance?

Glucose intolerance is the term for conditions that result in higher than normal blood glucose (sugar) levels. Glucose intolerance can lead to diabetes, a chronic health condition where the body can no longer keep blood glucose rising too high.

Many different conditions can result in glucose intolerance, such as impaired fasting glucose, impaired glucose tolerance, prediabetes, and type 2 diabetes. Glucose intolerance is usually a risk factor for developing type 2 diabetes later on if it’s not corrected.

What causes Glucose Intolerance

  • Age : While possible at any age, glucose intolerance is more common in people over 45 years old.
  • Obesity : Extra body fat changes hormones and other substances in a way that contributes to problems with insulin use.
  • Diet : A low-fat diet is believed to help reduce the risk and incidence of diabetes-related conditions.
  • Genetics : If a parent or sibling has diabetes, your risk is higher. Genetics may also predispose you to weight gain.
  • Sedentary lifestyle : Physical activity lowers blood glucose levels. Being active at least three times per week, for 30 minutes, lowers your risk of insulin-related conditions.

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Types of Glucose Intolerance 

DiagnosisBlood Glucose Range mg/dL

Normal levels
Under 100

Impaired fasting glucose

Impaired glucose tolerance

Intermediate hyperglycemia

Type 2 diabetes

Impaired fasting glucose 

Impaired fasting glucose means that your blood sugar level is high after fasting for 8-12 hours. You can find out if you have impaired fasting glucose by having a blood test after fasting, typically in the morning after waking and before eating anything. A normal fasting blood sugar is below 100 milligrams per deciliter (mg/dL). Impaired fasting glucose occurs with a fasting blood sugar of 100 mg/dL or higher. If fasting blood sugar is 126 mg/dL or higher, it is indicative of having diabetes mellitus.

Impaired glucose tolerance

Impaired glucose tolerance means that your body can’t lower your blood sugar after you eat or drink something that raises blood sugar. A glucose tolerance test involves drinking a drink with 75 grams of sugar in it and having your blood sugar measured two hours later. A normal result is 139 mg/dL or lower. Anything between 140 and 199 is considered impaired glucose tolerance, whereas diabetes is diagnosed when the result is 200 mg/dL or higher.

Women are screened for gestational diabetes during pregnancy using glucose tolerance tests. Gestational diabetes is when you get diabetes during pregnancy without having a history of diabetes. It usually resolves after pregnancy, but it does increase your risk of getting type 2 diabetes later in your life. 

The first screening test for gestational diabetes is the one-hour glucose test, where the patient is given a drink containing 50 grams of sugar. According to The American College of Obstetricians and Gynecologists (ACOG), blood sugar levels are checked one hour later and should be less than 130 or 140 mg/dL, according to The American College of Obstetricians and Gynecologists (ACOG). 

If the pregnant woman fails the one-hour glucose test, the next screening test is the three-hour glucose test, where she is given a drink containing 100 grams of sugar. Blood sugars are checked one, two, and three hours later.

Gestational diabetes is diagnosed if blood sugar is >180 mg/dL after one hour, >155 mg/dL after two hours, and/or >140 mg/dL after three hours. 

Some medications can result in impaired glucose intolerance as well. Corticosteroids (usually just referred to as steroids) are known to raise blood sugar levels. Steroids are a class of medications used to treat a variety of different health problems from skin rashes, asthma, COPD (chronic obstructive pulmonary disease), arthritis, and other inflammatory conditions. They can be applied topically, inhaled, taken orally, and administered through an injection.

Steroids mimic cortisol, which is a stress hormone. Cortisol raises blood sugar and blood pressure. Steroids can make the body more insulin-resistant over time, meaning the cells don’t respond to the hormone insulin the way they should. As a result, insulin resistance can occur because the liver is releasing too much sugar, making the pancreas release more insulin to compensate. Over time, this can cause the pancreas to stop making enough insulin, resulting in high blood sugar, which can become a chronic problem.


Prediabetes is a condition where blood sugar levels are higher than normal but not high enough to be considered diabetes. It is a major risk factor for developing type 2 diabetes later on. People with prediabetes suffer from impaired glucose tolerance due to insulin resistance. 

Prediabetes is usually diagnosed when the fasting blood sugar is between 100 and 125 mg/dL, with a hemoglobin A1c level of 5.7%-6.4%, or both.

Type 2 diabetes

Type 2 diabetes is a chronic disease resulting in impaired glucose tolerance. Cells require sugar (glucose) for energy. Insulin is a hormone produced by the pancreas and lowers blood sugar levels.

Cells have insulin receptors, which insulin attaches to in order to let the sugar in. Another way to think of it is that cells have doors, the insulin receptors are the doorknobs, and insulin is the key to open the doorknob to allow sugar in to feed the cells. Without enough insulin, the sugar stays in the bloodstream and accumulates, unable to enter the cell.

Diabetes results when the pancreas can’t make enough insulin or when the receptors on the cells don’t respond to insulin the way they should.

Symptoms of glucose intolerance

The signs and symptoms of glucose intolerance are similar to those of type 2 diabetes.

  • Increased urination: High blood glucose levels from glucose intolerance causes an imbalance of dissolved particles in the urine. When there is a lot of sugar in the urine, the body attempts to dilute the sugar by pulling fluid from the body. The result is increased urine volume due to less water being absorbed by the kidney and more being excreted through the bladder. People usually notice increased urination when they wake up several times per night to urinate, especially without increasing their fluid intake. Increased urination is one of the first symptoms noticed by people with glucose intolerance.

  • Increased thirst: Urinating more can cause dehydration, triggering you to feel thirsty. The more urine is lost, the more dehydrated you can get, which triggers the cycle to continue. If you have increased thirst without any obvious reason, such as increased exercise or hot weather, it may be a sign of glucose intolerance.

  • Feeling tired: If you have glucose intolerance, your cells aren’t able to take up sugar to use as energy. This can leave you feeling more fatigued than normal.

  • Feeling more hungry: When cells are starved of energy, it can trigger you to feel hungry. If you’re eating like normal but still feel hungry, it may be a sign of glucose intolerance.

  • Losing weight without trying: With glucose intolerance, sugar isn’t able to enter the cells to provide them with energy. When this happens, the body starts burning stored fat for energy instead of sugar, which results in weight (and sometimes muscle) loss.

  • Acanthosis nigricans:  Acanthosis nigricans is a skin condition characterized by dark, velvety patches of skin. These patches typically appear in skin folds, such as on the neck, groin, and armpits. The borders of the dark patches are usually not well-defined unless the patches of discolored skin become thickened. Acanthosis nigricans typically affects people who are overweight and is a sign of glucose intolerance. However, it can also occur in people without diabetes, but it’s much less common. Children can also develop acanthosis nigricans.

  • High blood sugar levels. A fasting blood sugar between 100 and 125 mg/dL is indicative of glucose intolerance, as is a hemoglobin A1c from 5.7%-6.4% or a failed glucose tolerance test (ogtt).

  • Polycystic ovarian syndrome (PCOS). PCOS is a common cause of infertility in women with symptoms such as irregular menstrual cycles, weight gain, unwanted facial hair, and acne. It’s often associated with insulin resistance and impaired glucose tolerance, but some women with PCOS don’t suffer from blood sugar issues. PCOS tends to affect women with bigger bodies but can also impact women who are lean. PCOS can be treated with medications and lifestyle changes.

Treatment options

Treatments for glucose intolerance depend on the severity. People with glucose intolerance and other risk factors for type 2 diabetes may choose to start on diabetes medications to help improve glucose tolerance, while some may choose to try lifestyle changes first. 

There are plenty of healthy habits you can implement to treat glucose intolerance. Some of the most effective lifestyle changes to combat glucose intolerance include:

  • Being physically active. 150 minutes per week of moderate to vigorous activity are recommended for people with and without glucose intolerance. Strength or resistance training a few days per week is also recommended as it can help reduce insulin resistance and improve blood sugars by increasing the amount of glucose absorbed by the muscles to use as fuel.

    The most important thing is to choose an activity that you enjoy and is sustainable, whether it’s horseback riding, walking, gardening, swimming, etc.

  • Follow a more plant-based diet. A more plant-based diet such as the Mediterranean diet includes more nutrient-dense foods and isn’t high in refined sugars or red meat. Plant-based diets have been associated with improved health outcomes, including reduced risk of developing diabetes and improved glucose tolerance.

  • Watch your sugar intake. Added sugars tend to spike blood sugar and insulin levels, worsening glucose tolerance. Women should consume no more than 24 grams of added sugar per day, and men should keep their added sugar intake below 36 grams per day. Foods and drinks high in added sugars include soda and other sweetened beverages and desserts. They can also hide in foods like cereals, yogurts, and granola bars. 

  • Try to lose a little weight. Losing 5-10% of your body weight can improve insulin sensitivity and improve blood sugar levels, reducing your risk of developing type 2 diabetes due to glucose intolerance.


Glucose intolerance is a term for conditions that result in higher than normal blood sugar levels. This includes impaired fasting glucose (high blood sugar after abstaining from food for 8-12 hours), impaired glucose tolerance (high blood sugar after consuming something high in sugar), prediabetes, and type 2 diabetes.

Having impaired glucose tolerance means that your body can’t lower your blood sugar as effectively as it should. The body uses a hormone called insulin to help lower blood sugar, so glucose intolerance occurs from insulin resistance or an insulin deficiency.

Common symptoms of glucose intolerance include:

  • Increased thirst, urination, and hunger.

  • Fatigue.

  • Acanthosis nigricans.

  • Unintentional weight loss.

  • High blood sugar levels and polycystic ovarian syndrome (PCOS). 

Glucose intolerance can be treated with diabetes medications and/or healthy lifestyle changes such as eating less sugar, losing weight, and being more active.

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Tita, Alan T N et al. “Predictive Characteristics of Elevated 1-Hour Glucose Challenge Test Results for Gestational Diabetes.” American journal of perinatology vol. 34,14 (2017): 1464-1469. doi:10.1055/s-0037-1604243

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