There are many statistics found in the USA which show a nation with some serious issues to grapple with: since 1999 its suicide rate has increased by 24%; the mortality rate of middle-aged white Americans is rapidly rising and the mortality rate for the population overall is also increasing. With suicide, gun deaths and drug and alcohol deaths increasing, it has surely something to do with what Michael Cook termed “ghost legions of idle men” (those men no longer actively looking for work). With these in mind, it is perhaps not surprising that the life expectancy of the average American declined slightly from 2014 to 2015. As the BBC reports, the average American born in 2015 can expect to live 78.8 years (81.2 years for women and 76.5 years for men). This is a decrease of about 0.1 years from 2014, slightly more than that for men. While not a large drop (and smaller than the last two drops in the past thirty years – 0.2 years in 1980 and 0.3 years in 1993) it is the first drop in 23 years. It is also concerning health experts in that it has come after a flat trend in life expectancy for the past three years. Since the 1970s there has been a steady increase in life expectancy (barring those two years mentioned earlier, 1980 and 1993). The question now will be whether the plateau will continue, or whether 2015 is a harbinger of further decreases in American life expectancy.
What's causing this decrease? Well, a mixture of many things:

"The figures show a mixture of factors. Death rates have risen for eight out of 10 of the leading causes of death: heart disease (0.9% rise), chronic lower respiratory diseases (2.7% rise), unintentional injuries (6.7% rise), stroke (3% rise), Alzheimer's disease (15.7% rise), diabetes (1.9% rise), kidney disease (1.5% rise) and suicide (2.3% rise)."  While the figures based on those killed by opiates have not yet been released for 2015, the 2014 was 28,000. The medical director at Northwell Health's Huntington Hospital in New York, Michael Grosso, stated that there has been a “dramatic upswing in the use of opiates and narcotic use across our country” and the 6.7% increase in “unintentional injuries” could be at least partly related to this upswing.
On the positive side, the death rate for cancer has gone down 1.7% and, as cancer is the second-largest cause of death after heart disease, this can only have a large positive effect on the life expectancy rates. Overall, the USA ranks 28 out of 43 OECD countries and is just behind Costa Rica, Chile and the Czech Republic. However, if 2015's trend continues, then it could start sliding down past Turkey, Poland and Estonia. Time will tell.