Average life expectancy in the United States fell between 2016 and 2017, fueled by increasing drug overdoses and suicides and continuing a declining trend seen since 2014.

Life expectancy at birth for the U.S. population in 2017 was 78.6 years – a decline from 78.7 the previous year, according to a report released Thursday by the National Center for Health Statistics, part of the Centers for Disease Control and Prevention.

The drop also marks a decline of three-tenths of a year from the peak American life expectancy of 78.9 years in 2014.

“The latest CDC data show that the U.S. life expectancy has declined over the past few years. Tragically, this troubling trend is largely driven by deaths from drug overdose and suicide," CDC Director Dr. Robert Redfield said in a statement. "These sobering statistics are a wakeup call that we are losing too many Americans, too early and too often, to conditions that are preventable."

The U.S. last experienced a life-expectancy dip over a similar multiyear period around the time of the 1918 Spanish flu pandemic, says Robert Anderson, chief of the Mortality Statistics Branch at the National Center for Health Statistics.

And while three-tenths of a year is nowhere near the dramatic decline witnessed a century ago – the pandemic spurred a drop in average life expectancy of about 12 years for both sexes over just a year – Anderson says it's "concerning."

"We’re living in a developed country with a fairly sophisticated health care system and lots of resources ... and we’ve had this increasing trend in life expectancy over the course of 100 years, and now all of the sudden it seems to (have) reversed,” Anderson says.

For the report, researchers analyzed data from death certificates filed in all 50 states and the District of Columbia for 2016 and 2017. Report authors noted that "changes in life expectancy, computed using figures rounded to one decimal, may slightly overestimate or underestimate the actual change," and that "changes ... from 2016 to 2017 using unrounded estimates were less than 0.1 year."

Researchers found that female life expectancy remained unchanged between 2016 and 2017 at 81.1 years, while male life expectancy dropped from 76.2 in 2016 to 76.1 in 2017. And as overall life expectancy declined in the U.S., the country's age-adjusted mortality rate increased from 728.8 deaths per 100,000 population in 2016 to 731.9 in 2017.

Non-Hispanic white males and females both saw a significant increase in their age-adjusted death rates, while non-Hispanic black females saw a significant decrease. At 1,083.3 deaths per 100,000 population, non-Hispanic black males continued to have the highest age-adjusted death rate in 2017.

By age group, people between the ages of 25 to 34, 35 to 44, and those 85 and older saw significant death rate increases.

Meanwhile, the top 10 causes of death in the country – with heart disease and cancer topping the list – remained unchanged between 2016 and 2017. Cancer was the only cause of death within the top 10 to see a significant decrease in its age-adjusted death rate, which ticked down by 2.1 percent to 152.5 per 100,000 standard population. Death rates significantly increased for seven of the 10 leading causes, with influenza and pneumonia (5.9 percent), unintentional injuries (4.2 percent) – a category including unintentional drug overdoses – and suicide (3.7 percent) seeing the largest increases.

The flu was tied to the deaths of nearly 80,000 people during the 2017-2018 season – more than the average number of people who attend the Super Bowl each year, according to recent CDC estimates.

"The flu can affect a lot of causes of death – it tends to affect people whose health is compromised, and may push unhealthy people over the edge and kill them," Anderson says. "It was a bad flu season, and that accounts for the rise in the pneumonia and influenza, but it also probably is putting upward pressure on some of the other causes of death as well, like the heart disease category and stroke.”

A companion CDC report released Thursday showed that drug overdoses – the main driver behind the increased death rate of unintentional injuries, Anderson says – killed 70,237 Americans in 2017, up from 63,632 in 2016.

As the nation continues to grapple with the opioid crisis, West Virginia (57.8 deaths per 100,000 population), Ohio (46.3), Pennsylvania (44.3) and the District of Columbia (44.0) had the highest observed age-adjusted drug overdose death rates in 2017, while Texas (10.5), North Dakota (9.2), South Dakota (8.5) and Nebraska (8.1) had the lowest.

"The drug overdose issue has been a problem for a while now, and those rates have been going up very steadily, and they’re quite high now – higher than they have been," Anderson says. "However, our provisional data for 2018 seem to suggest that that may be reversing, and we may be reaching peak and maybe even declining. But we only have data for the first quarter of 2018, so it’s hard to say."

A third CDC report out Thursday showed the U.S. suicide rate has continued to increase, from 10.5 suicides per 100,000 population in 1999 to 14.0 in 2017.

Suicide rates were even starker for people living in more remote areas: The most rural U.S. counties experienced a suicide rate nearly two times higher than those in the most urban counties, according to the report.