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Blood Sugar
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Checking blood sugar levels is a way of measuring how well the body uses glucose (GLOO-kose), a sugar that is the chief energy source for cells. After a meal, blood glucose rises. A hormone called insulin helps transport the sugar into cells, where it can be used as fuel. Blood sugar then gradually drops back to normal.

Blood sugar levels that remain higher than normal signal two problems: (1) cells are “starving” because they are not absorbing enough glucose and (2) the extra sugar circulating in the blood can damage the eyes, kidneys, nerves, heart and blood vessels.

Current guidelines establish two categories of higher-than-normal blood sugar:

  1. Prediabetes or “borderline diabetes.” Blood sugar is elevated but not high enough to meet criteria for diabetes. The formal terms for this condition are “impaired fasting glucose” or “impaired glucose tolerance,” depending on how blood sugar is measured. Those with prediabetes are at increased risk of developing cardiovascular disease and diabetes in the future.

  2. Diabetes. There are two main types

    • Type 1, in which specialized cells in the pancreas lose their ability to produce insulin. Type 1 diabetes is relatively uncommon and usually occurs in children and young adults.
    • Type 2, in which cells throughout the body lose their ability to respond to insulin

About 90 to 95 percent of individuals with diabetes have Type 2. The risk for Type 2 increases with age, although it is diagnosed with growing frequency in all age groups. Other risk factors for Type 2 diabetes include overweight, lack of exercise, high blood pressure, family history of diabetes, and being an African-American, Hispanic American, Native American, Asian American or Pacific Islander.

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Experts estimate many Americans with Type 2 diabetes have not been diagnosed. Although the early stages of Type 2 cause few symptoms, damage to the eyes, kidneys, blood vessels and nerves may already be occurring. New data also link diabetes to an increased risk of cognitive decline and dementia.

The Diabetes Prevention Program, a nationwide clinical trial enrolling 3,234 participants (including 45 percent from high-risk ethnic groups) found that overweight individuals with prediabetes could reduce their risk of developing diabetes by 58 percent (71 percent in participants over age 60) through:

  • Losing 5 – 7 percent of body weight (10 – 15 pounds in someone who weighs 200 pounds)
  • Walking or other moderate exercise 30 minutes on five days each week
  • Eating a healthy, low-fat diet

Current guidelines on blood sugar

  • Based on a “fasting” blood test taken at least 8 hours after eating
  • Regular testing should begin at age 45 or earlier in individuals with risk factors in addition to age

Fasting blood sugar


Health impact

Less than 100 milligrams per deciliter (mg/dL)


Healthy level

Between 100 and 125 mg/dL

Prediabetes or borderline diabetes

Increased risk of cardiovascular disease and future diabetes

126 mg/dL or higher, measured on two different days


Risk of damage to the eyes, kidneys, blood vessels, heart and nerves as well as cognitive decline and dementia

If your blood sugar is higher than normal, you should talk to your doctor about the best treatment strategy.

Additional resources


Alzheimer's Association

Our vision: A world without Alzheimer's disease®.
Formed in 1980, the Alzheimer's Association is the leading voluntary health organization in Alzheimer's care, support and research.