Although it is the richest nation in the world and the sole remaining superpower, life expectancy at birth in the United States is among the lowest of all high-income countries.

In 2007, the life expectancy of American males was 75.6 years—the lowest among a set of 17 high-income countries and 3.7 years less than the world leader, Switzerland. American females had the second-lowest life expectancy at birth at 80.8 years—5.2 years less than the world leader, Japan.

Recent comparative research on life expectancy and mortality rates has focused on Americans 50 years and older, showing that they have a lower life expectancy and experience higher levels of disease and disability than do their counterparts in other industrialized nations.

A new study by Jessica Ho, a doctoral candidate in demography and sociology in the School of Arts & Sciences, focuses on the mortality of Americans 50 years and younger, and found that these ages contribute to the bulk of American males’ overall life expectancy shortfall and make a substantial contribution to the shortfall for American females.

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 in the March issue of Health Affairs.

“It turns out that a large part of the story is that we die more at the younger ages— below 50—than people in other high-income countries,” Ho says. “For men, two-thirds of our life expectancy shortfall can be attributed to deaths occurring below age 50. For women, that number is two-fifths.”

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. Drug overdoses constitute a striking finding of the study, with the majority of these unintentional deaths stemming from prescription drug use.

“What I did here was quantify how much of that shortfall [in life expectancy] is coming from chronic disease, how much of it is coming from homicide, and so on,” Ho says. “It turns out that five major causes are behind why we’re doing poorly at younger ages: car accidents, chronic diseases, perinatal conditions, homicide, and drug overdose.”

On Tuesday, March 26, Ho will discuss “Why Does U.S. Life Expectancy Rank So Low?” as part of the Penn Lightbulb Café lecture series. The talk takes place at 6 p.m. at World Cafe Live.

Ho’s research of international comparisons of the U.S. life expectancy disadvantage began more than five years ago while she was an undergrad at Penn. Her latest study highlights the importance of focusing on policies to prevent the major causes of death for Americans 50 and under, and to reduce the social inequalities that lead to them.

“To me, it’s a very intriguing puzzle,” Ho says. “I think trying to unpack our health and longevity disadvantage is very exciting and has many important implications.”