Life expectancy declining in high-income countries, especially in the US: Study This pattern is even more dramatic in the United States.

For the first time in recent decades, life expectancy across high-income countries is declining and this pattern is even more dramatic in the United States, according to a study published in The British Medical Journal Wednesday.

“It’s really striking that we saw so many high-income countries simultaneously experience life expectancy declines in one year,” Jessica Y. Ho, lead author and assistant professor of Gerontology and Sociology at the University of Southern California, said in an interview with ABC News.

Researchers from the University of Southern California examined trends in life expectancy across 18 high-income countries from 2014-2016. Information from the majority of these countries from 2014-2015 showed that people, on average, didn’t live as long. The average decline in longevity was 0.21 years for women and 0.18 years for men. Increasing deaths related to a severe season of influenza was thought to be a contributing cause for this decline, especially in those 65 and older.

In contrast to the other higher income countries, declines in life expectancy in the United States were because more people were dying in their 20s and 30s. Authors suggested the ongoing opioid epidemic may be acting as a primary driver in this decline -- particularly for men, for whom drug overdose increased significantly in the past two years, according to data from the National Center for Health Statistics.

Between 2015-2016, there was an increase in life expectancy in most countries, making up for the decline from the previous year. The United States and the United Kingdom were the exceptions, as they continued to show a decline or simply showed stagnation. Drug overdose, as well as other external causes of death, were suggested by authors to be contributing factors.

This decline in U.S. life expectancy is troubling, as it’s seen as a measure of the health and well-being of a population. Declines may signal problems in a nation's social and economic conditions, quality of its health care services or worsening behavioral factors.

Though life expectancy is a commonly used measure of population health, other measures of health that may be relevant were not included in this study (eg. disability-adjusted life expectancy, health-adjusted life expectancy). It is possible that trends in these other measures may not correspond to trends in life expectancy that are depicted in this study.

“We need to keep a sharp eye on mortality events, and understand what is happening,” Ho stated.

The authors feel that the earlier we can have access to data that can inform us of life expectancy, and causes for possible declines, the quicker we can mobilize resources in the most proactive way to improve these numbers.

Ho suggested that reducing influenza mortality, increasing awareness and continuing to improve programs to aid with substance abuse would be a good focus, given the information in this study.

Richa Kalra, M.D., is a resident physician specializing in psychiatry and working in the ABC News Medical Unit.

Ryan Guinness, M.D., MPH, is an internal and preventive medicine resident physician, currently working the ABC News Medical Unit.