More than 1 in 10 adults over age 20 has diabetes, but about 40% of them don’t know they have the disease, according to a large national survey. In addition, nearly 1 in 3 adults has pre-diabetes.

Diabetes is the most common cause of blindness, kidney failure and amputations in adults. It’s also a leading cause of heart disease and stroke. People with diabetes have unusually high levels of a sugar called glucose in the blood. When blood glucose gets too high, it can damage your tissues and organs.

Researchers have collected data on diabetes for several decades as part of the National Health and Nutrition Examination Survey. For this survey, people were given a 2-hour oral glucose tolerance test during 2 time periods—from 1988 to 1994 and again from 2005 to 2006. This test is more sensitive in detecting diabetes and pre-diabetes than a more common and less expensive test called fasting plasma glucose.

By comparing data from the 2 time periods, scientists found that the percentage of people with diabetes rose from about 5% in 1988-1994 to nearly 8% a decade later. By 2006 more than 40% of adults had either diabetes or pre-diabetes.

“It’s important to know if you have diabetes or pre-diabetes, because there’s so much you can do to preserve your health,” said Joanne Gallivan, director of NIH’s National Diabetes Education Program. “Talk to your health care professional about your risk.”

Cleaner air may be adding months to our lives, according to a new study.

To see how air pollution affects lifespan, NIH-funded scientists looked at fine-particle pollution in 51 U.S. cities. These particles are only about 1/30th the width of a human hair. Fine-particle air pollution usually comes from power plants, industry and car exhaust.

The researchers analyzed pollution levels from around the early 1980s and again from around the early 2000s. They then calculated the lifespans of the cities’ residents during those years.

The researchers found that air pollution levels dropped in all 51 cities during the 20-year study period, and life expectancy rose on average by nearly 3 years. After the scientists adjusted for income, smoking and other factors that affect lifespan, they found that improved air quality accounted for up to 15% of the overall increase in longevity. That’s an average gain of nearly 5 months of life.

“We’re getting a substantial return on our investments in improving our air quality,” said lead researcher Dr. C. Arden Pope III of Brigham Young University.