Declining life expectancies in the U.S. include Gen X and Y Americans, in addition to the older Baby Boomers. But the causes of premature mortality vary by race, gender and ethnicity, according to a new study from Duke University.

"We identified late-Gen X (38- to 45-year-olds) and early-Gen Y (27- to 37-year-olds) as age cohorts with elevated mortality patterns, particularly for non-Hispanic whites, said study co-author Emma Zang, a Ph.D. candidate at the Sanford School of Public Policy. "That is in addition to the rise among the already much-discussed Baby Boomer generation."

To study cause of death for Americans born from 1946 to 1992, the researchers used data from the Centers for Disease Control and Prevention Mortality Multiple Cause Files for the years 1990-2016.

Late Gen X and early Gen Y Americans were aged 25 to 43 during the Great Recession and faced greater difficulty finding jobs, which may have contributed to greater health impacts.

"Social scientists and policymakers are aware of the financial burden for the younger generation, but the elevated mortality rate among them has largely been ignored," the authors say in a paper that appears in the December issue of the International Journal of Epidemiology.

The study examined death rates in five different age cohorts, comparing men and women, as well as whites, blacks and Hispanics.

"Few studies have looked at Hispanics when considering disparities in mortality," Zang said.

The researchers examined nine leading causes of death for each age cohort, finding that the underlying causes for increased mortality vary for the different ethnic groups and also between genders in the cohorts and ethnicities.

For Baby Boomers, five causes of death drove the rising mortality rates.

"Drug overdoses, external causes -- such as traffic accidents and homicides, suicides, COPD (chronic obstructive pulmonary disease) and HIV/AIDS have contributed to the increase in mortality trends among Baby Boomers across all race, ethnic, and gender groups," Zang said.

For the late Gen X (born 1973-1980) and early Gen Y (born 1981-1991) age cohorts, leading causes of death vary by ethnicity:

For Hispanics, overdoses and suicides are the leading causes of death.

For non-Hispanic whites, both men and women, overdoses and alcohol-related diseases appear to drive increased mortality.

For non-Hispanic black women, diabetes-related mortality is increasing.

For non-Hispanic black men, leading causes are cancer, alcohol-related diseases and external causes, such as traffic accidents.

The time period of the study spans the opioid abuse crisis and the Great Recession. Some of the disparities may reflect different access to opioid prescriptions among blacks, whites and Hispanics, Zang said.