Nearly 26 million Americans have diabetes – and seven million of them don’t know it yet, according to new estimates from the Centers for Disease Control and Prevention (CDC).

In addition, an estimated 79 million U.S. adults have prediabetes, a condition in which blood sugar levels are higher than normal, but not high enough to be diagnosed as diabetes. Prediabetes raises a person's risk of type 2 diabetes, heart disease and stroke.

Those figures represent an increase from the CDC’s 2008 estimates, which put the total figure of diabetics in the U.S. at 23.6 million.

Diabetes is the seventh leading cause of death in the U.S. People with the disease – whether they’ve been diagnosed or not -- are more likely to suffer from complications such as heart attacks, strokes, high blood pressure, kidney failure, blindness and amputations of feet and legs. The annual cost of diabetes is $174 billion, which includes $116 billion in direct medical expenses.

"These distressing numbers show how important it is to prevent type 2 diabetes and to help those who have diabetes manage the disease to prevent serious complications such as kidney failure and blindness," said Ann Albright, Ph.D, R.D., director of CDC's Division of Diabetes Translation. "We know that a structured lifestyle program that includes losing weight and increasing physical activity can prevent or delay type 2 diabetes."

As part of the Affordable Care Act, the CDC is working on a National Diabetes Prevention Program aimed at helping people reduce their risk for developing type 2 diabetes, which accounts for 90 to 95 percent of diabetes cases. In that form of the disease, the body gradually loses its ability to use and produce insulin, the hormon that controls blood glucose levels. Risk factors for type 2 diabetes include older age, obesity, family history, having diabetes while pregnant (gestational diabetes), a sedentary lifestyle, and race/ethnicity. Groups at higher risk for the disease are African-Americans, Hispanics, American Indians/Alaska Natives, and some Asian-Americans and Pacific Islanders.

The CDC says that most of the 215,000 Americans under age 20 who are affected have type 1 diabetes, which develops when the body stops producing insulin altogether.

If current trends continue, the CDC predicts that as many as 1 in 3 U.S. adults could have diabetes by 2050.