Higher mortality rates among Americans younger than 50 are responsible for much of why life expectancy is lower in the United States than most of the world’s most developed nations.

The research, by Jessica Ho, a University of Pennsylvania doctoral candidate in demography and sociology, found that excess mortality  among Americans younger than 50 accounted for two-thirds of the gap in life expectancy at birth between American males and their counterparts and two-fifths between females and their counterparts in the comparison countries.

The study, “Mortality Under Age 50 Accounts for Much of the Fact That U.S. Life Expectancy Lags That of Other High-Income Countries,” is published in the March issue of Health Affairs. 

Ho used cross-national mortality data from 2006-2008 to identify the key age groups and causes of death responsible for the U.S. life-expectancy shortfall.

Most of the excess mortality of those younger than 50 was caused by noncommunicable diseases, including perinatal conditions, such as pregnancy complications and birth trauma, and homicide and unintentional injuries including drug overdose, a fact that she said constitutes a striking finding of the study.

“These deaths have flown under the radar until recently,” Ho said. “This study shows that they are an important factor in our life expectancy shortfall relative to other countries.”

She said that the majority of the drug overdose deaths stemmed from prescription drug use.

Ho said her study underscores the importance of focusing on policies to prevent the major causes of deaths below age 50 and to reduce the social inequalities that lead to them.   

She is a recipient of the National Science Foundation Graduate Research Fellowship and has consulted for the National Academy of Sciences Panel on Understanding International Health Differences in High-Income Countries.