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Every cell in your body needs a steady supply of glucose (blood sugar) to make energy, even hours after you've eaten. When blood glucose is too high—the hallmark of diabetes—the excess sugar can damage nerves, blood vessels, and other tissues. Low blood sugar can cause mental confusion, seizures, or loss of consciousness. Maintaining a Goldilocks glucose level that is that is not too high and not too low but just right is a remarkable balancing act.

In a healthy body, it happens automatically. During and after a meal or snack, the pancreas makes insulin, a hormone that cells must have in order to soak up sugar from the bloodstream. This gradually lowers the blood sugar level. When it reaches a certain lower limit, the pancreas produces another hormone called glucagon. It signals the liver to release a steady supply of stored sugar.

In people with diabetes, these tightly connected cycles don't work as they should. People with type 1 diabetes don't make enough insulin, so blood sugar stays dangerously high after eating and can drop dangerously low between meals. In people with type 2 diabetes, the pancreas makes insulin but muscle cells don't respond to this hormone's "open up for sugar" signal.

People with diabetes must use diet, exercise, and medications to regulate blood sugar. Several large studies have demonstrated that blood sugar control translates into developing fewer diabetes-related complications such as loss of vision, foot pain and other problems, heart attack, and more.

Knowing your blood sugar is a key step toward managing it. Glucose in the bloodstream is measured two ways. The hand-held meters used by millions of people with diabetes to test a drop of blood (see "Using a glucose meter" below) reveal the concentration of glucose in circulation at the moment the drop was taken. The results are given in milligrams of glucose per deciliter of blood, abbreviated as mg/dL. Target levels are listed in "Optimal blood sugar levels for people with diabetes." Blood sugar readings are great snapshots, but they don't tell you anything about an equally important value—the average daily blood sugar.

A test that evaluates the average blood sugar level over a several week period is the hemoglobin A1c (HbA1c) test. It measures the percentage of hemoglobin molecules (the oxygen-carrying protein in red blood cells) that have become coated with glucose. The higher the average daily blood sugar over a three-month period, the higher the HbA1c value. People who don't have diabetes typically have HbA1c readings of 6% or lower. For most people with diabetes, the American Diabetes Association recommends aiming for an HbA1c level less than 7%.

Although everyone with diabetes can benefit from routinely checking their blood glucose, it's more important for some than others. People who take insulin should test their blood sugar several times a day. Such monitoring helps them determine the timing and amount of insulin doses and when it's important to eat to prevent an episode of low blood sugar (hypoglycemia). Among people with type 2 diabetes, the use of oral diabetes medications such as sulfonylureas or meglitinides, can cause low blood sugar, so they may need to test their blood sugar several times a day.

Even if you aren't taking insulin or one of these other drugs, self-monitoring may be useful to show how you're doing. Your doctor can help you determine how often, and when, to check your blood sugar levels. Any of the following situations may warrant more frequent testing:

  • very high blood sugar level at diagnosis

  • recent weight loss or gain

  • exercising more or less than usual

  • change in diabetes medication

  • vomiting, diarrhea, or an illness such as stomach flu.

Optimal blood sugar levels for people with diabetes



Before a meal

70–130 mg/dL

About two hours after a meal (when blood sugar is usually at its peak)

Less than 180 mg/dL*

*Even lower levels may be desirable in certain situations, such as during pregnancy.

Reference: Diabetes section on Better Medicine

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60 – 70% of people with diabetes have some form of neuropathy.