Nov. 1, 2018 -- Along the Virginia-Tennessee border, near Virginia’s southwestern tip, you can find a mirror image: twin cities named Bristol that straddle the state line. State Street, the main artery of both cities, forms the dividing line between the two cities, and a sign in lights that frames the street points out the state boundary: “Bristol VA | TENN, A good place to live.”

But that’s where the similarities end between the two Bristols, including on the most basic of health measures: If you live on the Virginia side, you can expect to live 2 years less than your Tennessee neighbors.

Americans living in adjacent counties and even census tracts are finding different health outcomes -- meaning that where you live can determine how long you might live. The news isn’t uplifting for many Americans, either: According to a study done by the Institute for Health Metrics and Evaluation (IHME), almost 40% of counties in the United States had a decline in life expectancy between 2010 and 2014, the most recent data available at the county level.

That decline is significant because life expectancy reflects a sea of issues -- genetics, social and economic status, and access to health care, to name a few.

“As human beings, we've been tracking our life expectancy forever, and it's always pretty much been good news,” says Georges Benjamin, MD, executive director of the American Public Health Association. “I think we have just assumed that we’re going to live longer.”

Nationally, American life expectancy has gone down for the second year in a row, according to the CDC’s annual report on 2016 deaths, and experts say a third year of decline is likely. Americans can now expect to live 78.6 years, down from 78.9 in 2014. The country ranks 46th in the world for life expectancy and is expected to drop to 64th by 2040, a new study shows.