White Americans have been dying more often in middle age over the past 15 years, and the causes are mostly self-inflicted, according to a new study.

This signals a reverse of a long-term trend of declining death rates among this age group in the United States.

The authors of the study link this reversal to a rise in deaths due to drug and alcohol use, suicide, chronic liver disease, and cirrhosis.

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Several Factors Driving Rise in Death Rates

Between 1970 and 2013 the overall death rates for 45- to 54-year-old Americans fell by 44 percent.

The authors attribute this decline to improvements in disease prevention and treatment, along with public health efforts like anti-smoking campaigns.

After 1998, though, white middle-aged Americans started to die more often, their mortality rate rising by half a percent each year.

Researchers identified several factors that may be driving this increase.

“Accidental poisonings are the largest part of the increase,” study author Angus Deaton, PhD, a professor of economics at Princeton University, wrote in an email to Healthline. “But that is both (legal) opioids and (illegal) opiates, as well as alcohol. And suicides and liver disease are also important.”

In 2011, deaths from drug or alcohol overdoses overtook lung cancer as a top cause of death among this group. Suicide follows closely behind.

As death rates went up among Caucasians in the United States, however, death rates among middle-aged Hispanics and African Americans continued to go down.

The study was published today in the online early edition of the Proceedings of the National Academy of Sciences. The authors used a variety of reports and surveys covering 1999 to 2013, including death records and data from the Centers for Disease Control and Prevention.

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Those With Lowest Education Most Likely to Die

Between 1999 and 2013, middle-aged whites with less than a high school degree had the largest increase in overall death rates, while the rate for those with more education went down

Middle-aged whites with the least education also had larger increases in deaths due to drug or alcohol overdoses, suicides, and chronic liver disease.

The authors did not study differences in death rates by gender in this age group.

Previous research, though, has shown that men may be at higher risk than woman of many of the factors identified in this study.

“The main factors that the authors identify as contributors to this midlife risk—such as suicide, heavy drinking, and drug use—are all significantly greater risks for men than for women,” Will Courtenay, PhD, an Oakland, California, psychotherapist and researcher, told Healthline.

, men have long had higher rates of substance abuse than women, including among 45- to 54-year-olds.

One of the leading causes of drug overdoses in the United States are opioid painkillers, such as OxyContin. These became widely available in the late 1990s. After OxyContin was changed in 2010 to make it harder for people to abuse it, the number of heroin users increased.

Middle-aged men are also more likely than women to .

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Role of Social Factors and Economy

The new study doesn’t identify the social causes behind the rising death rates among middle-aged whites, but the authors provide some possibilities.

“You could ask why are people taking so many painkillers, or so many illegal drugs, or so much alcohol,” said Deaton. “And then you get back into deeper social and economic factors about which we can only speculate.”

The last recession—which started in 2007 in the United States—may have played a role in the increased mortality.

A 2013 paper found that drunkenness and alcohol abuse increased among middle-aged Americans during that economic downturn.

Some of the differences seen between middle-aged men and women in earlier research may also be linked to the faltering economy.

“There is a lot of previous research that showed a spike in suicides among middle-aged men during this same time period, which is likely linked to economic downturns,” said Courtenay.

A study earlier this year points to a possible link between the recession and an increase in suicides among people aged 40 to 64 between 2005 and 2010.

That study also found that suicides among men were more likely to be related to job and financial problems, as compared to women.

Together, the increases in death rates among middle-aged whites represent a missed opportunity to save lives, the authors say.

They estimate that had the death rate among middle-aged whites continued to decline at its previous rate, nearly half a million lives might have been saved. Even if it had held at its 1998 level, almost 100,000 lives would have been saved.

In addition, as middle-aged Americans approach retirement, they may be bringing along many problems that will affect their health throughout their later years.

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