LOS ANGELES, Calif.–On average, Americans live about a year-and-a-half less than Western Europeans–a disparity that stems from higher levels of obesity among United States residents, according to new study from University of Southern California, the Harvard School of Public Health and the RAND Corp.

The study–which appears in the July issue of Social Science & Medicine–also indicated Americans live less than the residents of most other developed nations.

In the first half of the last century, average life expectancy increased by saving more babies, said author Dana Goldman, director of the Schaeffer Center for Health Policy and Economics at USC and the Norman Topping/National Medical Enterprises Chair in Medicine and Public Policy at USC.

“But now it is reduction in mortality among the elderly, rather than the young, that propels increases in life expectancy,” he said. “The question is whether ‘being American’ is an independent mortality risk factor.’”

Researchers found that the life-expectancy disparity–which begins around the age of 50–stems from higher levels of middle-age obesity and obesity-related chronic diseases, such as hypertension and diabetes.

The study calculates the fiscal consequences of the growing life-expectancy gap over the next few decades.

Though the transition to better health initially raises expenditures, the researchers estimate that by 2050 healthcare savings fromhealth improvements among the middle age could total more than $1.1 trillion, of which $632 billion would accrue to the U.S. government in the form of Medicare and Medicaid savings.