The primary fuel your body runs on is a form of sugar called glucose. Virtually everything you eat—proteins, carbohydrates, fats— eventually gets converted by your digestive system to this sugar compound. As is the case with so many of the delicate balances at work in the human body, you need to have enough glucose in your bloodstream to remain healthy, but if you have too much it can adversely affect your health.

Precisely how much glucose gets absorbed from your bloodstream by the cells in your body at any given moment is regulated by a hormone called insulin that’s produced by the pancreas. It helps to think of insulin as a key that unlocks a sort of gate in the walls of every cell through which the glucose passes to provide energy to the cell.

When this system malfunctions—that is, when insulin is not succeeding in helping your cells absorb glucose—the cells become starved for energy and you begin to feel weak, tired, hungry, and often irritable. At the same time, because it’s not getting to the cells, the sugar level rises in your bloodstream.

This condition is called diabetes. More than 10 million Americans are suffering from diagnosed diabetes. Another 5 million have the disease and don’t know it. It’s a condition that, if poorly controlled, damages blood vessels and eventually can cause a wide range of other problems.

Damage to smaller blood vessels can and often does harm your eyes, kidneys, and nerves. Damage to larger blood vessels can lead to heart disease and high blood pressure. Diabetes can also cause impotence in men and increase the risk of infections of all kinds.

Until as recently as the 1920s, the “sugar disease,” as it was long known, was inevitably fatal. Their bodies starved for energy, patients with the disease slipped into a coma and quickly died. Then, in 1921 a Canadian researcher, Fred Banting, and his student assistant, Charles Best, extracted insulin from a pancreas and injected it into ten diabetic dogs, saving their lives.

Subsequent human experiments were equally successful. Their discovery led to a Nobel Prize for Banting (many think that Best also deserved it) and made it possible for diabetics to live long and productive lives. Since then, scientists have identified two kinds of diabetes.

In the case of Type I diabetes, the problem is that the pancreas doesn’t produce enough insulin to let the glucose pass into the body’s cells. This form of diabetes is typically inherited, usually appears in people at a young age, and is relatively uncommon.

Insulin injections, to augment what the pancreas is producing, are the treatment for Type I diabetes. In Type II diabetes, it’s not that the body isn’t producing enough insulin, it’s that the cell walls have become resistant to it and therefore don’t absorb the glucose they need.

Type II diabetes typically appears later in life and is far more common than Type I; in fact, 90 percent of the people who are diagnosed with diabetes have the Type II form. Typically, this kind of diabetes is treated with drugs that cause the pancreas to create extra insulin to supply those cells that have not yet become resistant or by increasing the sensitivity of cells to insulin.

But over a long enough time the pancreas can get overworked and these patients, too, may require insulin injections. Researchers are not yet certain about what causes Type II diabetes, but it seems clear that, as with Type I, there is a strong genetic connection. That is, if someone in your family has had Type II diabetes, there is a greater likelihood that you will, too.

Yet it is also increasingly clear that dietary and lifestyle choices play a significant role. People who are overweight or obese have a much higher likelihood of developing Type II diabetes than people who are not. Unhealthy eating not only contributes to weight gain, but it also can put a much greater strain on your blood sugar/insulin balance.

Overeating, especially eating a lot of simple carbohydrates (sweets, sweetened foods and drinks, chips, fries, and the like) that the body converts quickly to sugar, overloads the bloodstream with glucose, puts a strain on the insulin-production system, and appears to be connected to the development of insulin resistance.

Chronic high blood sugar levels exact a significant toll on many parts of the body. They can cause loss of eyesight, kidney damage, and nerve disease, among other things. There is a third blood sugar condition called “borderline” high glucose, or “impaired glucose tolerance,” in which glucose remains in the bloodstream longer than is the case with people with normal glucose/insulin function.

Researchers suspect that people with borderline high glucose already have developed some insulin resistance in their cell walls but have not yet reached the level of Type II diabetes. But that doesn’t mean it’s not a serious condition; borderline high glucose often develops into diabetes.

Testing for High Blood Sugar

How do you know whether your blood sugar levels are too high? A simple series of blood tests will tell you. To be certain the results are reliable, these tests typically are done on two separate occasions. You are diabetic if:

• Your “fasting blood glucose” level is at least 126 mg/dL
• You have a blood glucose level of at least 200 mg/dL two hours after a meal
• You have a random blood glucose level of at least 200 mg/dL and have symptoms such as excess thirst and frequent urination.

The Guidelines

The American Diabetes Association guidelines say that if you do not yet have diabetes you should have your blood glucose levels checked at least every three years starting at age forty-five. But you should have it checked even more frequently if any of the following apply to you:

• You have any disease of the blood vessels, such as heart disease, stroke, or atherosclerosis
• Your body mass index (BMI) is 25 or greater
• Your blood pressure is higher than 140/90
• Your HDL (good) cholesterol measures 35 mg/dL or less
• You have a triglyceride level of 250 mg/dL or more
• You have parents or siblings with diabetes
• You have been told at any time in the past that you have “borderline” high blood sugar
• You are habitually inactive
• You are a member of an ethnic group with a high risk for diabetes (African-American, Hispanic-American, Native American, Asian-American, or Pacific Islander)
• you are a woman who has delivered a baby of more than nine pounds or has been diagnosed with gestational diabetes
• You have been diagnosed with polycystic ovarian syndrome.

On the other hand, if you do have diabetes already the guidelines urge you to have your blood glucose tested every three months, or even more often depending upon the type and severity of the diabetes you have, what treatments you are receiving, and how well the disease is being controlled.

In addition, your doctor should be ordering a “hemoglobin A1c (HbA1c) level” test for you (also called glycosylated hemoglobin). Hemoglobin is a molecule that exists in red blood cells and carries oxygen. HbA1c forms when excess blood sugar attaches to the hemoglobin in those cells.

The more glucose in your bloodstream, the more HbA1c will be present. And because HbA1c stays in your bloodstream for a long time, this test makes it possible for your doctor to get a kind of overall average of the glucose that’s been in your bloodstream during the past three months, not just the past day or two.

This not only provides a more reliable indication of your long-term condition but also makes it possible for the doctor to know whether you have been following your treatment program regularly or have simply fasted the day before your blood glucose test to get a good result a not uncommon practice. To stay healthy, you need to keep the HbA1c level in your bloodstream below 7 percent. You should know your sugar test results.