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How Sugar Affects Diabetes

Diabetes mellitus leads to persistently elevated blood sugar levels. Over time, high sugar levels damage the body and can lead to the multiple health problems associated with diabetes.

But why are high blood sugars so bad for you? How much sugar in the blood is too much? And what are good sugar levels, anyway? WebMD takes a look at how your sugar level affects diabetes and your health.

Diabetes and sugar levels: What's normal?

At present, the diagnosis of diabetes or prediabetes is based in an arbitrary cut-off point for a normal blood sugar level. A normal sugar level is currently considered to be less than 100 mg/dL when fasting and less than 140 mg/dL two hours after eating. But in most healthy people, sugar levels are even lower.

During the day, blood glucose levels tend to be at their lowest just before meals. For most people without diabetes, blood sugar levels before meals hover around 70 to 80 mg/dL. In some, 60 is normal; in others, 90. Again, anything less than 100 mg/dL while fasting is considered normal by today's standards.

What's a low sugar level? It varies widely, too. Many people's sugar levels won't ever fall below 60 mg/dL, even with prolonged fasting. When you diet or fast, the liver keeps sugar levels normal by turning fat and muscle into sugar. A few people's sugar levels may fall somewhat lower. Without taking diabetes medicine, though, or having uncommon medical problems, it's difficult to drop sugar levels to an unsafe point.

Higher sugar levels: Diabetes and pre-diabetes

Sugar levels higher than normal mean either diabetes or pre-diabetes is present.

There are several ways diabetes is diagnosed.

The first is known as fasting plasma glucose. A person is said to have diabetes if his or her fasting blood sugar level is higher than 126 mg/dL after not eating -- fasting -- for eight hours.
The second method is with an oral glucose tolerance test. After fasting for eight hours, a person is given a special sugary drink. That person is said to have diabetes if two hours after the drink he or she has a sugar level higher than 200.
The third way is with a randomly checked blood sugar level. If it is greater than 200, with symptoms of increased urination, thirst, and/or weight loss, that person is said to have diabetes. A fasting sugar level or oral glucose tolerance test will be needed to confirm the diagnosis.

But diabetes is not like a switch that gets turned on and off -- healthy one day, diabetic the next. Any sugar levels higher than normal are unhealthy. A blood sugar higher than normal, but not meeting the above criteria for full-blown diabetes, is called pre-diabetes.

Fifty seven million people in the United States have pre-diabetes. People with pre-diabetes are five- to six-fold more likely to develop diabetes over time. Pre-diabetes also increases the risk for cardiovascular disease, although not as much as diabetes does. It's possible to prevent the progression of pre-diabetes to diabetes, with diet and exercise.

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