The new federal data, drawn from all deaths recorded in the country in 2014, showed that life expectancy for whites dropped to 78.8 years in 2014 from 78.9 in 2013. Men and women had declines, but because of statistical rounding, the decline did not appear as sharp among men.

Life expectancy for women fell to 81.1 in 2014 from 81.2 in 2013. The average life span for men also fell, but not enough to sink below 76.5 years, their life expectancy in 2013.

“The increase in death in this segment of the population was great enough to affect life expectancy at birth for the whole group,” said Elizabeth Arias, the statistician at the National Center for Health Statistics who analyzed the data, referring to whites from their mid-20s to their mid-50s. “That is very unusual.”

Dr. Arias, who is preparing a larger study of mortality trends over the past 15 years, said drug overdoses, liver disease and suicide were the main drivers of the gloomy trends among whites in recent years, a pattern also found by other researchers.