(Reuters Health) - Life expectancy is declining in high-income countries worldwide, driven in part by the effects of the opioid epidemic on younger adults in the U.S. and the impact of a severe flu season on older adults in other nations, two new studies suggest.

A man is seen in silhouette walking a dog at Cunningham Park in the Queens borough of New York U.S., January 26, 2017. REUTERS/Shannon Stapleton

Life expectancy is a measure of the health and wellbeing of a population. Widespread or sustained declines in life expectancy may signal problems in a nation’s social and economic conditions or in the provision or quality of its healthcare services, researchers write in The BMJ.

The first study looked at trends across 18 high-income countries and found that most countries experienced declines in life expectancy in 2015. This is the first time in recent decades that so many high-income countries simultaneously experienced declines in life expectancy for both men and women.

Out of 18 countries in the study, 12 experienced life expectancy declines among men and 11 experienced life expectancy declines among women.

“This hasn’t occurred in decades, and the size of these most recent declines were larger than prior declines,” said study co-author Jessica Ho of the University of Southern California in Los Angeles.

A particularly severe influenza season drove declines outside the U.S. in 2014-2015, primarily among adults 65 and older, the study found. In addition to flu and pneumonia, the main causes of death in these countries were associated with an aging population and included other respiratory diseases, cardiovascular disease and Alzheimer’s disease as well as other mental and nervous system disorders.

Most of these countries reversed their life-expectancy decline in the 2015-2016 period, but in the U.S. and the UK, the declines continued, the authors note.

In the U.S., the source of reduced life-expectancy was concentrated at younger ages, particularly deaths among those in their 20s and 30s, and largely driven by increases in drug-overdose deaths related to the nation’s ongoing opioid epidemic.

A second study in The BMJ suggests, however, that the problems driving life expectancy declines in the U.S. are broader than just the opioid crisis and may extend to a wide range of causes unrelated to drug use or substance abuse.

“A leading cause is fatal drug overdoses - fueled by the opioid epidemic - but we make a mistake if we focus only on the drug problem, which is just the tip of the iceberg,” said lead study author Dr. Steven H. Woolf of Virginia Commonwealth University in Richmond.

“Deaths from alcoholism and suicides have also increased, what some call deaths of despair,” Woolf said by email.

Even worse, the study found rising midlife death rates from dozens of diseases of the heart, lungs, digestive systems and other organs. It even found rising death rates during pregnancy and early childhood, Woolf said.

“Something far-reaching is affecting the health of Americans in the prime of their lives,” Woolf said.

Neither study was a controlled experiment designed to prove what specific factors might be influencing declines in health or life expectancy in the U.S. and other countries.

Still, taken together, these studies highlight a need for high-income countries to invest more in preventing disease outbreaks and addressing persistent social and health inequalities, said Domantas Jasilionis of the Max Planck Institute for Demographic Research in Rostock, Germany.

“Although a part of this health disadvantage of lower socioeconomic classes is explained by ‘traditional’ risk factors such as poor diet, alcohol and smoking, the question remains why these people have a higher risk of choosing such health damaging behaviors,” Jasilionis, author of an editorial accompanying the studies, said by email.

“There is strong evidence that psychological factors, often having social origins including social exclusion, poor prospects for social mobility, and high income inequality are the main contributors to these ‘bad choices,’ especially in the lowest socioeconomic groups,” Jasilionis added.

At the population level, maintaining steady gains in life expectancy is challenging because it requires reductions in mortality at increasingly advanced ages, Jasilionis writes in the editorial.

“At the individual level, life span also depends on a range of lifestyle choices, including continuous education throughout the whole life,” Jasilionis added by email. “Good knowledge of health risks and awareness about our own health status is a key for a longer life.”

SOURCE: bit.ly/2wgHAkN, bit.ly/2Mtl57a and bit.ly/2N9EMgA The BMJ, online August 22, 2018.