A new study this week highlights a unique, long-spanning crisis among Americans. For decades, it suggests, the U.S. life expectancy has lagged behind similar countries. And for close to a decade, young to middle aged Americans have actually been dying more than in previous years, thanks in part to worsening rates of suicide, drug overdoses, and other chronic health problems.

Life expectancy at birth is considered an indirect measure of a country’s overall health. The higher it is, generally, the less people in a country are dying from preventable causes early on in life. And it’s no secret that the average life expectancy of Americans has gone down in recent years.

According to data from Centers for Disease Control and Prevention, the life expectancy at birth for someone born in 2017 was 78.6 years—the third straight annual decrease. But the authors of this new study, published Tuesday in JAMA, decided to take a longer look at life expectancy and morality trends, dating back to 1959.

Americans, they unsurprisingly found, have been living longer and longer over the years. In 1959, for example, someone’s life expectancy was 69.9 years. But since the 1990s, annual improvements in life expectancy has been slower compared to people living in similarly developed countries. And by 2010, life expectancy had started to stagnate in the U.S. until declining post-2014.

This lag, stagnation, and eventual decline in life expectancy, the authors found, can clearly be linked to people between the ages of 25 to 64 dying more often than their counterparts in other countries. And during the years 2010 to 2017, their overall mortality rate actually increased by six percent—an increase that amounted to around 33,000 extra deaths. Certain areas of the country have been hit much harder than others. The authors found that about a third of these excess deaths were concentrated in just four states: Ohio, Pennsylvania, Kentucky and Indiana.

“It’s supposed to be going down, as it is in other countries,” lead author Steven Woolf, director emeritus of the Center on Society and Health at Virginia Commonwealth University, told the Washington Post. “The fact that that number is climbing, there’s something terribly wrong.”

This study isn’t the first to suggest that increased rates of drug overdoses and suicide—which typically affect younger people more—are helping lower U.S. life expectancy in recent years. But the growing rise in obesity may also be playing a part, as more Americans have grown up overweight than ever before. This excess weight in adulthood can then raise the risk of developing high blood pressure and other conditions that could send people to an earlier grave.

The new study seems to lend more credence to a theory voiced by some researchers, who have theorized that working age Americans’ growing lack of purpose, loss of community, and financial problems are sending them into despair. But the authors also pointed to things like a weaker, yet more expensive health care system and less strict gun control laws in some states as factors, too.

Whatever is going on, though, it’s evident that the root causes lay deep.