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. Over that year, the overall death rate increased from 724.6 per 100,000 people to 733.1 per 100,000.
While that's not a lot, it was enough to cause the overall life expectancy to fall slightly. That's only happened a few times in the past 50 years. The dip in 1993, for example, was due to high death rates from AIDS, flu, homicide and accidental deaths that year.
On average, the overall life expectancy, for someone born in 2015, fell from 78.9 years to 78.8 years. The life expectancy for the average American man fell two-tenths of a year — from 76.5 to 76.3. For women, it dropped one-tenth — from 81.3 to 81.2 years.
"It's remarkable," Morgan says. "There are lots of things about this that are unexpected."
Most notably, the overall death rate for Americans increased because mortality from heart disease and stroke increased after declining for years. Deaths were also up from Alzheimer's disease, respiratory disease, kidney disease and diabetes. More Americans also died from unintentional injuries and suicide. In all, the decline was driven by increases in deaths from eight of the top 10 leading causes of death in the U.S.
"When you see increases in so many of the leading causes of death, it's difficult to pinpoint one particular cause as the culprit," Anderson says.
The obesity epidemic could be playing a role in the increase in deaths from heart disease, strokes, diabetes and possibly Alzheimer's. It could also be that doctors have reached the limit of what they can do to fight heart disease with current treatments.
The epidemic of prescription opioid painkillers and heroin abuse is probably fueling the increase in unintentional injuries, Arun Hendi, a demographer at Duke University, wrote in an email. The rise in drug abuse and suicide could be due to economic factors causing despair.
"Clearly, that could be related to the economic circumstances that many Americans have experienced in the last eight years, or so, since the recession," says Irma Elo, a sociologist at the University of Pennsylvania.
Whatever the cause, the trend is concerning, especially when the death rate is continuing to drop and life expectancy is still on the rise in most other industrialized countries.