One of the best ways to prevent diabetes is to spot blood sugar (glucose) problems before the full-blown disease develops. But most people don't realize that diabetes-and its precursor, prediabetes-can cause no symptoms at all or a wide range of symptoms that often are misinterpreted.

Common mistake: Because type 2 diabetes is strongly linked to excess body weight, many people who are a normal weight assume that they won't develop the disease. But that's not always true. About 15% of people who are diagnosed with diabetes are not overweight. And paradoxically, even weight loss can be a symptom of this complex disorder in people (normal weight or overweight) who have uncontrolled high glucose levels.

Shocking recent finding: The Centers for Disease Control and Prevention now estimates that 40% of Americans ages 40 to 74 have prediabetes, and nearly two out of three Americans over age 65 have prediabetes or diabetes-most likely due to the increasing numbers of people who are overweight and inactive, both of which boost diabetes risk.

However, most primary care doctors aren't diagnosing and treating prediabetes early enough in their patients-often because they fail to order the necessary screening tests (see the next page). And because the symptoms of prediabetes can be subtle, especially in its early stages, most people are not reporting potential red flags to their doctors.

Fortunately, prediabetes can virtually always be prevented from progressing to diabetes if the condition is identified and treated in its early stages (by following a healthful diet, exercising regularly and taking nutritional supplements and medications, if necessary).

What Is Prediabetes?

Prediabetes occurs when the body's cells no longer respond correctly to insulin, a hormone that regulates blood sugar. With prediabetes, blood sugar levels are higher than normal but not high enough to warrant a diagnosis of diabetes.

Prediabetes affects about 57 million Americans-most of whom are unaware that they have the condition.

Red Flags For Diabetes

Being overweight (defined as having a body mass index, or BMI, of 25 or higher) is perhaps the best-known risk factor for type 2 diabetes.* The more excess body weight you have, the more resistant your cells become to the blood sugar-regulating effects of the hormone insulin, ultimately causing blood glucose levels to rise.

Greatest danger: Abdominal fat, in particular, further boosts diabetes risk. That's because belly (visceral) fat hinders the processing of insulin. The single biggest risk factor for prediabetes is having a waistline of 40 inches or more if you're a man... or 35 inches or more if you're a woman. Lesser-known red flags for prediabetes (and diabetes)-if you have one of these symptoms, see your doctor...

• Increased thirst and need to urinate. Because excess blood glucose draws water from the body's tissues, people with elevated blood glucose levels feel thirsty much of the time. Even when they drink fluids, their thirst is rarely quenched. Therefore, they drink even more, causing them to urinate more often than is normal for them.

• Unexplained weight loss. While being overweight is a significant risk factor for prediabetes, the condition also can paradoxically lead to unexplained weight loss resulting from a lack of energy supply to the body's cells and a loss of glucose-related calories due to excessive urination.

• Dry, itchy skin. Excess blood glucose also draws moisture from the skin, leaving it dry and prone to itching and cracking-especially on the legs, feet and elbows.

• Blurred vision. Glucose can change the shape of the eye lens, making it difficult to focus properly.

• Slow-healing cuts, sores or bruises and frequent infections. For unknown reasons, excess blood glucose appears to interfere with the body's healing processes and its ability to fight off infection. In particular, women with prediabetes and diabetes are prone to urinary tract and vaginal infections.

• Red, swollen and tender gums. Because the body's ability to heal can be compromised by prediabetes, gum inflammation, involving red, swollen, tender and/or bleeding gums, may develop.

• Persistent feelings of hunger. When the body's cells don't get enough glucose due to prediabetes, the cells send signals to the brain that are interpreted as hunger, typically about one hour after consuming a meal.

• Lack of energy. Because their cells are starved of energy-boosting glucose, people with prediabetes tend to tire quickly after even mild physical effort. Dehydration due to excess blood glucose also can contribute to fatigue.

• Falling asleep after eating. An hour or so after eating, our digestive systems convert the food we've eaten into glucose. In people with prediabetes, the process is exaggerated-blood glucose levels spike, triggering a surge of insulin as the body attempts to stabilize high glucose levels. This insulin surge is ineffective in lowering blood glucose, causing the person to become drowsy. If you feel sleepy after meals, it can be a sign that your blood glucose levels are riding this prediabetic roller coaster.

• Moodiness and irritability. Lack of energy production in your cells, together with sharp rises and dips in blood glucose levels, can trigger feelings of restlessness, irritability and exaggerated emotional responses to stress.

• Tingling or numbness in the hands and feet. Excess blood glucose can damage small blood vessels feeding the body's peripheral nerves, often causing tingling, loss of sensation or burning pain in the hands, arms, legs or feet.

• Loss of sex drive and erectile dysfunction in men. Prediabetes is associated with low testosterone in men, which often reduces libido. In addition, glucose-related damage to the body's small blood vessels often impairs the ability of prediabetic men to have an erection.

Three Key Diabetes Tests

If you suspect that you may have prediabetes, ask your doctor to order the following tests...

• Fasting blood glucose. This traditional blood test for diabetes is usually part of a standard physical. Until recently, a result over 125 mg/dL was considered a sign of diabetes, while 100 mg/dL to 125 mg/dL indicated prediabetes.

Standard guidelines established by the American Diabetes Association have not changed, but recent data suggest that a person who has a fasting blood glucose reading over 90 mg/dL should be evaluated by a physician.

• Hemoglobin A1C. This blood test, also included in many annual checkups, measures the average blood glucose level over a two- to three-month period. An A1C result of 4.5% to 5.9% is considered normal... 6% to 6.5% indicates prediabetes... and two separate readings of 6.5% or above indicate diabetes.

Standard guidelines still use 6% as the lower end of the prediabetes range, but recent data suggest that results as low as 5.6% or 5.7% may signal prediabetes.

• Oral glucose tolerance test. Administered over two hours in your doctor's office, this test can spot problems with blood-sugar regulation that may not show up in the other tests. For the oral glucose tolerance test, blood levels of glucose are checked immediately before drinking a premixed glucose formula and two hours afterward.

A result of 140 mg/dL to 159 mg/dL is a sign of increased risk for diabetes... 160 mg/dL to 200 mg/dL indicates high risk for diabetes... and over 200 mg/dL signals full-blown diabetes. Also ask your doctor to measure your insulin levels-insulin fluctuations can be an even earlier predictor of prediabetes than the tests described above.

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