For the first time in more than two decades, U.S. life expectancy has dropped.

This week, the Centers for Disease Control and Prevention reported that in 2015, U.S. life expectancy at birth was 78.8 years — that’s a decrease of 0.1 year from 78.9 years in 2014. Among males, life expectancy went from 76.5 years to 76.3 years; among females, it went from 81.3 years to 81.2 years. According to news reports on the findings, no one single factor caused the drop, but it’s still a cause for concern. Over at The New York Times, Katie Rogers reports:

Dr. Peter Muennig, a professor of health policy and management at Columbia University’s Mailman School of Public Health, said in an interview that the decline was a “uniquely American phenomenon” in comparison with other developed countries, like Japan or Sweden.

“A 0.1 decrease is huge,” Dr. Muennig said. “Life expectancy increases, and that’s very consistent and predictable, so to see it decrease, that’s very alarming.”

The CDC report, “Mortality in the United States, 2015,” finds that the 10 leading causes of death, which are responsible for more than 74 percent of all deaths in the country, are: heart disease, cancer, chronic lower respiratory diseases, unintentional injuries, stroke, Alzheimer’s disease, diabetes, influenza and pneumonia, kidney disease and suicide. Those are the same leading causes as 2014, however death rates associated with eight of those causes increased between 2014 and 2015, driving the overall life expectancy decline.

In particular, the death rates went up 0.9 percent for heart disease, 2.7 percent for chronic lower respiratory diseases, 6.7 percent for unintentional injuries, 3 percent for stroke, 15.7 percent for Alzheimer’s, 1.9 percent for diabetes, 1.5 percent for kidney disease and 2.3 percent for suicide. Mortality rates decreased 1.7 percent for cancer and stayed the same for influenza and pneumonia.

Other findings from the report include an update on the nation’s infant mortality rate. That rate shifted from 582.1 infant deaths per 100,000 live births in 2014 to 589.5 deaths per 100,000 in 2015. While the change is technically an increase, the report described it as “not statistically significant.” Also, the age-adjusted death rate for the overall U.S. population increased 1.2 percent from 724.6 deaths per 100,000 people in 2014 to 733.1 deaths in 2015. In 2015, the death rate increased among black males, white males and white women.

Back to the life expectancy drop, researchers are also noted that the 2015 finding could be an anomaly, though they warn it’s still troublesome. At NPR, Rob Stein reports:

Now, there’s a chance that the latest data, from 2015, could be just a one-time blip. In fact, a preliminary analysis from the first two quarters of 2016 suggests that may be the case, says Robert Anderson, chief of the mortality statistics branch at the National Center for Health Statistics, which released the new report.

Anderson says government analysts are awaiting more data before reaching any definitive conclusions.

“We’ll have to see what happens in the second half of 2016,” he says.

Still, he believes the data from 2015 are worth paying attention to.

To read the full mortality findings, visit CDC’s National Center for Health Statistics.

Kim Krisberg is a freelance public health writer living in Austin, Texas, and has been writing about public health for 15 years.