The report found that life expectancy for this group fell from 81.2 to 81.1 years between 2013 and 2014. Overall, U.S. life expectancy remained unchanged at 81.2 years for women and 76.4 years for men.
The annual report does not speculate on what caused the decline, but the authors note that the findings are an aberration from the overall trend toward longer life expectancy.
"The trend in life expectancy at birth has been one of improvement since national estimates were first published with 1900 data," the researchers said.
Laudan Yvett Aron, a senior fellow at the Urban Institute, has published studies looking at the possible reasons why U.S. residents have a lower life expectancy rate compared to other high-income nations. Aron said this study may reflect a wide range of factors including increasing rates of suicide, drug use and cirrhosis of the liver.
"We know what the specific causes of death are that may explain this particular increase," she said. "Really it’s a bigger conversation we need to be having."
Aron, who was not involved in this report, said it's key to look at these problems more holistically to address what is happening in specific communities. She pointed out that people with poor health often live in economically-depressed communities.
"This dip is kind of important, it catches our attention," Aron explained. "We’ll see if downward slide continues for next several years."