But there are signs that diabetes is present, although they are easily ignored. In fact, of the nearly 21 million Americans with type 2 diabetes, about six million don’t know they have it.

Type 2 Diabetes: Red Flags

Possible symptoms of type 2 diabetes include:

• Being more thirsty than usual
• Feeling more hungry than usual
• Feeling more tired than usual
• Needing to urinate more than usual, especially at night
• Blurry vision
• Unplanned weight loss
• Sores that don’t go away

"There are a lot of people who don’t have symptoms," says Vivian Fonseca, MD, professor of medicine and pharmacology and chief of the section of endocrinology at Tulane University Health Sciences Center in New Orleans.

Type 2 Diabetes: Silent Condition, Serious Damage

Dr. Fonseca says that many people believe a "silent" condition like diabetes is nothing to worry about because they don’t feel any different. However, higher-than-normal blood sugar levels do damage at the microvascular level (affecting the smallest of your blood vessels), even if you can’t feel it.

"Even milder diabetes with no symptoms can continuously do damage over the years, so that’s where the problem lies," says Fonseca. "When sugar goes from 115 to 130 [mg/dL], you have diabetes. So for example, you can have eye damage, but no knowledge of that happening."

Diabetic retinopathy, which is the result of damage to the blood vessels in the eye that causes progressive vision loss, is one physical change that is most closely linked to the onset of type 2 diabetes. Data from the Diabetes Prevention Program suggest that this gradual damage to the eye occurs in about 12 percent of people within three years of the diagnosis of diabetes.

Although early damage to your eye can be seen using the equipment at your eye doctor’s office, many people will not know they have diabetic retinopathy until it has progressed far enough to interfere with their vision.

Type 2 Diabetes: Getting the Message

This is why understanding your risk factors and getting screened for diabetes, even if you don’t feel any different, is so important, says Fonseca.

The good news is that efforts to get people screened for type 2 diabetes appear to be working.

According to a study of 7,300 people, the number of adults with diagnosed diabetes is on the rise, but the proportion of those who have undiagnosed diabetes is stable. This means that national efforts to spread the word about the importance of screening are successful — although there is more work to be done.

Type 2 Diabetes: Who Should Get Screened?

The American Diabetes Association recommends that all adults age 45 or older be screened for diabetes. If you are younger than age 45, talk to your doctor about diabetes screening if you are overweight or obese and you have one or more of the following risk factors:

• You exercise fewer than three times a week.
• A close relative (sibling or parent) has type 2 diabetes.
• You had diabetes during pregnancy (gestational diabetes).
• You gave birth to a baby weighing more than nine pounds.
• You come from a Native American, Hispanic, African-American, Alaska Native, Pacific Islander, or Asian-American background.
• You were diagnosed with polycystic ovarian syndrome — a hormone imbalance in women.
• You’ve been told you had higher-than-normal blood sugar levels before.
• You have a history of heart disease.
• You have high blood pressure at 140/90 mm Hg or above (or are taking medication to lower blood pressure).
• You have HDL "good" cholesterol below 35 mg/dL.
• Your triglyceride level is above 250 mg/dL.

Because diabetes can damage your body for a while before you even realize you have it, it is important in order to make good choices about your long-term health. Ask for a screening if you are at risk.

For more diabetes news, follow @diabetesfacts on Twitter from the editors of @EverydayHealth.