(CNN) It's a midlife crisis of a different sort: "Deaths of despair" -- due to drugs, alcohol and suicide -- are largely responsible for rising mortality rates among middle-age white Americans. And a new analysis by Princeton economists delves into what they believe is behind this trend.

The prescription of opioids, which may predict who gets hooked , only "added fuel to the flames," according to husband and wife researchers Anne Case and Angus Deaton. The new analysis builds on their 2015 study that identified an upward trend in mortality for white 45- to 54-year-olds starting in 1998.

"It's not just ... the baby boomers," said Case. "It really has spread into Gen X, as well."

The economy and other social factors may be playing even larger roles, meaning we're in it for the long haul, according to the researchers. These factors may include a shortage of steady jobs for people without a college degree.

"And when the jobs just aren't there, they sink into depression or that feeling of general hopelessness ," according to Shannon Monnat, a professor of rural sociology from Penn State University.

Monnat published a study (PDF) in December showing that counties with the highest rates of "deaths of despair" voted more heavily for Donald Trump in the last election than they did for Mitt Romney in 2012.

A number of experts have pointed out the contrast between voting behavior and health interests . For example, a number of poor, white communities voted for Trump hoping to bounce back from poverty and escape the throes of addiction. However, the current Republican health care proposal, which the President backs, could result in dramatic cuts to addiction treatment and mental health services. The bill could end an existing requirement under the Affordable Care Act that these services be covered by Medicaid in the 31 states that expanded the program.

Thomas' most recent study , released in January, also showed that premature death was on the rise for Native and white Americans, with drug overdose and suicide contributing heavily to the increase.

Thomas previously told CNN that opioid abuse is "an unusual epidemic" in that it affects predominantly white people and started in rural areas.

"I don't think we have a complete understanding of why it's happening that way," he said. "There's not just one simple answer."

However, the Princeton researchers say that the uptick in "deaths of despair" is now countrywide, in both urban and rural areas, even if it didn't start out so widespread. The trend can be traced back to the Southwest in 2000, after which it spread to Florida, Appalachia and the West Coast a few years later.

The Princeton economists also identified a useful proxy to break down the numbers: a college degree.

"The job opportunities available to people with a college degree just put them on a different trajectory," said Case, adding that jobs and education also affect people's social circles, including who they marry and how stable their home lives are.

In 1999, the mortality rate of middle-age white Americans without a college degree was 30% lower than that of all black Americans regardless of degree status. Now, it's 30% higher, said Case. When comparing only those without a college degree, death rates for middle-age white and black Americans' have converged.

"There used to be quite a staggering amount of daylight between them," she said.

This level of detail may get overlooked when looking at the country as a whole. Overall, white Americans still live longer on average than black Americans. But this life expectancy gap has been closing, from 5.9 years in 1999 to 3.6 years in 2013 , according to the US Centers for Disease Control and Prevention.

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The CDC has also previously studied the link between health and education. Those without a college education are more likely be obese and smokers, while those with a bachelor's degree live about nine years longer on average.

Case said that there is no easy fix, and the connections between economy, education and health could take a long time to thoroughly understand.

"Exactly how we take diplomas and pin them to people and make them healthier is a really deep and abiding question," she said. "We really don't know the answer to that."