NEW YORK — The U.S. death rate has been falling for decades, but researchers have detected one group in which the rates have been steadily ticking up – middle-aged white people. Suicides and deaths from drug overdose and alcohol abuse are being blamed.

Deaths rates for other races have continued to fall, as they have for whites 65 and older. But while death rates for whites 35 to 44 have been level recently, they’re beginning to turn up for whites 55 to 64, and – most strikingly – death rates for whites ages 45 to 54 have risen by half a percent per year since 1998, said the authors, Anne Case and Angus Deaton of Princeton University.

The increase started in the late 1990s and probably is related to the increased availability around that time of certain prescription painkillers, they said.

“It certainly can’t be helping,” said Deaton, who last month was awarded a Nobel Prize in economics for unrelated work on consumer spending.

Their paper was published online Monday by the Proceedings of the National Academy of Sciences.

Federal researchers have reported – repeatedly – on worrisome increases in deaths from suicides and drug overdoses. And they have noted the bulk of those deaths have been white and middle-aged.

But the Princeton pair brought a new lens to the government’s statistics, breaking down death numbers by age and race in a way the government has not highlighted, he added.

“White Americans who are middle-aged were really doing worse,” Case summarized. “And that’s not news we were hearing.”

There has not been a similar increase in middle-aged people living in other affluent countries, the researchers said.

White death rates still are not nearly as bad as black rates – not even for those 45 to 54. The rate is about 415 deaths for every 100,000 white people in that age group. For blacks, it’s 582 per 100,000.

U.S. death rates have been on a general decline for more than century. In recent decades, the improvement has been driven by declines in death rates from heart disease and cancer – the nation’s two leading killers.

But from time to time, death rates for certain demographics have gone up. That’s generally happened in younger groups, who die in smaller numbers than the elderly and so have death rates that can be more easily swung. That happened with death rates for some age groups of white and black men during the height of the AIDS epidemic, Anderson said.

Of the 2.6 million deaths in 2013, about 123,000 – less than 5 percent – were in white, non-Hispanic people ages 45 to 54.

Studies have found white patients with pain are more likely to be prescribed opioid painkillers. And whites have been more likely to attempt suicide when faced with physical or mental hardships, for a range of possible reasons that include smaller networks of social support, say other experts.

Education is also a factor. The study found among whites with a college degree, the death rates were actually quite low. But for whites who achieved no more than a high school diploma, they were a whopping 736 per 100,000.