The life expectancy of the average American born in 2011 was 78.7 years, according to the US Centers for Disease Control and Prevention. The average lifespan has increased by more than a decade since 1950, but rising obesity rates threaten to take a toll on this progress.

“In studying the rate of death among adults younger than age 50, we found that there was no improvement among men who were overweight or obese as teenagers,” said one of the study’s authors, Amir Tirosh, of the Division of Endocrinology at the Brigham and Women’s Hospital in Boston. “In fact, the mortality rate among overweight and obese teenagers in the years 2000 to 2010 was as high as the rate observed in the 1960s and 1970s.”

The nationwide longitudinal cohort study analyzed records for more than 2.1 million teenagers who were evaluated for compulsory military service in Israel. The study subjects were born between the years 1950 and 1993. Each was between the ages of 16 and 20 when they were evaluated for military service.

Researchers calculated the teenagers’ body mass index at the time of the evaluation. The study also combed death records to determine mortality rates among the study population.

Researchers found mortality rates were 41 percent lower among normal weight teenagers who were born in the 1980s than teens of a similar weight who were born thirty years earlier. But among those who were overweight or obese as teenagers, there was no significant improvement in the survival rate over the course of four decades.

In addition, the study found overweight and obese teenagers had a higher risk of death before the age of 50. Among boys, even those with weights at the upper end of the normal range faced a greater risk of dying relatively early in adulthood.

While the causes of death weren’t available to researchers performing the analysis, obesity can raise the risk of death from cardiovascular disease, cancer and even motor vehicle crashes linked to sleep apnea, Tirosh said.

“Public health officials have known all along that obesity contributes to chronic illness, but this study clearly illustrates that it can raise the risk of death in early adulthood,” he said. “This has enormous implications for families, public health and society as a whole.”