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In 2015, for the first time in 10 years, the death rate in the United States went up. According to preliminary data from the National Center for Health Statistics, in 2015 there were 729.5 deaths per 100,000 people, compared to 723.5 in 2014. (This is the age-adjusted death rate, by the way, so it accounts for the increasing likelihood of death as people age.)

The last time the death rate went up, in 2005, it was by a smaller amount—from 813.7 in 2004 to 815—and it seems to have been due to a rough bout of the flu. Bumps aside, generally, the trend since 1999 (and since the 1930s, really) has been downward.

This, too, could be a blip. Or it could be a sign of a serious issue that’s turning the tide. Or several serious issues. It’s not clear exactly what caused the increase. Many different causes of death also increased during the 2014-2015 period—Parkinson’s disease, strokes, homicide, Alzheimer’s, chronic liver disease, and firearm injuries among them.

Suicide deaths also increased from 2014 to 2015, continuing a troubling upward trend. Between 1999 and 2014, the suicide rate in the U.S. went up by 24 percent, according to the Centers for Disease Control and Prevention.

Another prime suspect is drug overdoses, deaths from which have gone up by 137 percent since 2000 (and which also increased in this new analysis). This is largely driven by the opioid addiction epidemic; overdose deaths from opioids specifically have gone up by 200 percent since 2000.

Drug overdoses are deeply tied to another surprising trend in the U.S.: the rising death rates among middle-aged white Americans. As my colleague Olga Khazan has reported, many of these are what have been called “despair deaths”—drug overdoses, yes, but also suicide and liver disease. And this demographic is also starting to get diseases that usually cause death in older people, like heart disease and diabetes.

Exactly which of these trends, or what combination thereof, can account for the recent death rate rise remains to be seen, but when an entire country’s population reverses direction like this, it merits investigating.

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