Skip to content
My WebMD Sign In, Sign Up

Diabetes Health Center

Font Size

How the Blood Sugar of Diabetes Affects the Body

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.

Recommended Related to Diabetes

Diabetes Complications: What's Your Risk?

Heart attack, stroke, blindness, amputation, kidney failure. When doctors describe these diabetes complications, it may sound melodramatic -- like an overblown worst-case scenario. The truth is, these things can happen when blood sugar, blood pressure, and cholesterol are out of control. "A lot of people don't really think it will happen to them," says David C. Ziemer, MD, director of the Diabetes Clinic at Grady Hospital in Atlanta. "For a lot of folks, the wake-up comes when they actually...

Read the Diabetes Complications: What's Your Risk? article > >

Diabetes and Normal Blood Sugar Levels

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.

Sugar Levels, Diabetes, and Prediabetes

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 a fasting plasma glucose test. 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 prediabetes.

According to the American Diabetes Association, 79 million people in the U.S. have prediabetes. People with prediabetes are five to six times more likely to develop diabetes over time. Prediabetes also increases the risk for cardiovascular disease, although not as much as diabetes does. It's possible to prevent the progression of prediabetes to diabetes, with diet and exercise.

WebMD Medical Reference

Is This Normal? Get the Facts Fast!

Check Your Blood Sugar Level Now
What type of diabetes do you have?
Your gender:

Get the latest Diabetes newsletter delivered to your inbox!


Your level is currently



Congratulations on taking steps to manage your health.





Did You Know Your Lifestyle Choices
Affect Your Blood Sugar?

Use the Blood Glucose Tracker to monitor
how well you manage your blood sugar over time.

Get Started

This tool is not intended for women who are pregnant.

Start Over

Step:  of 

Today on WebMD

Woman holding cake
man organizing pills
Close up of eye

Woman serving fast food from window
Can Vinegar Treat Diabetes
Middle aged person
are battery operated toothbrushes really better

Prediabetes How to Prevent Type 2 Diabetes
type 2 diabetes
food fitness planner
Are You at Risk for Dupuytrens Contracture