Pre-Diabetes - Harvard Health

What is prediabetes?

In prediabetes, blood sugar levels are slightly higher than normal, but still not as high as in diabetes.

People almost always develop prediabetes before they get type 2 diabetes. The rise in blood sugar levels that is seen in prediabetes starts when the body begins to develop a problem called insulin resistance. Insulin is an important hormone that helps you to process glucose (blood sugar). If usual amounts of insulin can't trigger the body to move glucose out of the bloodstream and into your cells, then you have insulin resistance.

Once insulin resistance begins, it can worsen over time. When you have prediabetes, you make extra insulin to keep your sugar levels near to normal. Insulin resistance can worsen as you age, and it worsens with weight gain. If your insulin resistance progresses, eventually you can't compensate well enough by making extra insulin. When this occurs, your sugar levels will increase, and you will have diabetes.

Depending on what a blood sugar test finds, prediabetes can be more specifically called "impaired glucose (sugar) tolerance" or "impaired fasting glucose." Impaired fasting glucose means that blood sugar is higher than expected even after you haven't eaten for a while — for example, in the morning, before breakfast.

Impaired glucose tolerance means that blood sugar levels reach a surprisingly high level after eating. To diagnose impaired glucose tolerance, doctors may use what is called a glucose tolerance test. For this test you drink a sugary solution, and then you have blood drawn after a short time.

Having prediabetes does not automatically mean you will get diabetes, but it does put you at an increased risk. Prediabetes is also a risk factor for heart disease. Like people with type 2 diabetes, those with prediabetes tend to be overweight, have high blood pressure, and have unhealthy cholesterol levels.

Symptoms of prediabetes

Prediabetes is often called a "silent" condition because it usually has no symptoms. You can have prediabetes for several years without knowing it. Certain risk factors increase the chance that you have prediabetes. These risk factors include:

being overweight
being 45 years or older
a family history of diabetes
low levels of high-density lipoprotein (HDL) cholesterol (the "good" cholesterol)
high triglycerides
high blood pressure
a history of gestational diabetes
being African American, American Indian, Asian American, Pacific Islander, or Hispanic American/Latino.

If you have one or more of these risk factors, your doctor may recommend a blood sugar test. An abnormal result is likely to be the first sign that you have prediabetes.

Diagnosing prediabetes

The same blood sugar tests that are used for diabetes are used to diagnose prediabetes. For diagnosing prediabetes, your doctor can order one of the following:

a fasting blood glucose test
an oral glucose tolerance test
a hemoglobin A1C (HbA1C) blood test.

In a fasting glucose test, blood sugar levels are measured after at least eight hours of not eating.

In the oral glucose tolerance test, blood sugar levels are first measured after an overnight fast. You then drink a sugary solution (the “glucose challenge”), and two hours later another blood sample is drawn. In healthy people, the glucose challenge will cause blood sugar levels to rise slightly and fall quickly. In someone with prediabetes or diabetes, these levels may rise to a high level or fall slowly, so they will be abnormally high when checked two hours later.

A hemoglobin A1C blood test can be done at any time during the day. It does not require fasting. The result reflects an average of your blood sugar over the preceding three months.

Here is how to interpret the results of these tests (mg/dL = milligrams per deciliter):

Random glucose test

diabetes: 200 mg/dL or higher

Fasting glucose test

normal: Below 100 mg/dL
prediabetes: Between 100 and 125 mg/dL
diabetes: 126 mg/dL or higher

Oral glucose tolerance test

normal: Below 140 mg/dL
prediabetes: Between 140 mg/dL and 199 mg/dL
diabetes: 200 mg/dL or higher

Hemoglobin A1C test

normal: 5.6% or below
prediabetes: Between 5.7% and 6.4%
diabetes: 6.5% or higher.

Expected duration of prediabetes

Prediabetes sugar levels can remain slightly above normal, can return to normal, or can increase to a range that leads to a diagnosis of diabetes. As many as one in 10 people with impaired glucose tolerance will develop diabetes within one year. What happens to your prediabetes depends on whether you are able to prevent insulin resistance from progressing. If insulin resistance is kept in check, prediabetes may never become diabetes. If you do not adjust your lifestyle to maintain a healthy weight, increase exercise, and improve diet, there's a good chance that blood sugar levels will probably eventually rise to diabetic levels. Once this happens, medication is usually required to bring your blood sugar back to near-normal levels.

Preventing prediabetes

It surprises many people to learn that they may be able to prevent prediabetes and diabetes. To reduce your risk of both prediabetes and diabetes:

Maintain an ideal body weight. Aim for a body mass index (BMI) between 18.5 and 25. In some cases, a medication such as semaglutide (Ozempic, Wegovy, Rybelsus) or tirzepatide (Mounjaro, Zepbound) may be recommended, especially if you are obese or overweight with weight-related medical problems such as hypertension.
Exercise regularly. Both aerobic and strengthening exercises can reduce blood sugar. You should exercise for a minimum of 30 minutes daily.
Eat a balanced diet with just enough calories to maintain a healthy weight.

If you are overweight, aim to lose weight. Even modest weight loss of 10 or 15 pounds in a person who is 200 pounds can dramatically reduce the risk of diabetes.

Treating prediabetes

The purpose of treating prediabetes is to prevent diabetes. The same measures recommended for preventing prediabetes (see above) work for treating it, too.

The most effective treatment for prediabetes is to lose excess weight and exercise at least 30 minutes a day. Weight loss and exercise can improve insulin resistance, and can lower elevated blood sugar levels so that you don't progress to develop diabetes.

Additionally, the drug metformin (Glucophage) can lower the risk of getting diabetes, and it can add to the benefits of weight loss and exercise. Check with your doctor about whether taking metformin to prevent diabetes is a good idea for you. If your doctor feels that you have an especially high risk for progressing to diabetes, you may want to consider preventive treatment with this medication.

When to call a professional

Let your doctor know about symptoms that can suggest the development of new diabetes, such as:

excessive urination, thirst, and hunger
unexplained weight loss
increased susceptibility to infections, especially yeast or fungal infections of the skin and vagina
confused thinking, weakness, or nausea.

Prognosis

If you have prediabetes, you have about a 10% chance of developing type 2 diabetes within one year. People with prediabetes have a 50% to 70% lifetime risk of developing type 2 diabetes.

Fortunately, improvements in diet and exercise habits and loss of excess weight can help to delay or prevent type 2 diabetes. Research has shown that people with prediabetes who lose 5% to 7% of their body weight and exercise about 30 minutes a day can reduce their risk for diabetes during the next three years by almost 60%.

People with prediabetes have a higher than average risk of heart disease, even before diabetes develops. With the onset of diabetes, your risks for heart disease and stroke increase sharply. Diabetes also leads to complications such as blindness, kidney failure, foot ulcers, pain with walking due to poor circulation, and nerve damage. That's why it's important to take action to improve your health when you are diagnosed with prediabetes.