(CNN) Life expectancy at birth -- the average length of time that you are expected to live -- continues to drop for Americans, a new study finds. Drug overdoses, suicides, alcohol-related illnesses and obesity are largely to blame. These problems have been building since the 1980s, according to the study's authors.

The US had been making steady progress. Life expectancy increased by nearly 10 years over the last half century -- from 69.9 years in 1959, to 78.9 years in 2016.

But the pace of this increase slowed over time, while other high income countries continued to show a steady rise in life expectancy.

After 2010, US life expectancy plateaued and in 2014 it began reversing, dropping for three consecutive years -- from 78.9 years in 2014, to 78.6 in 2017. This is despite the US spending the most on health care per capita than any other country in the world.

Of all age groups, adults 25 to 64 years old saw the largest increase in mortality rates -- 6% -- according to the study, published Tuesday in the medical journal JAMA.