U.S. life expectancy rose in 2018 for the first time in four years, the Centers for Disease Control and Prevention announced back at the end of January. This got some attention but not a huge amount, which was understandable given that the rise was only from 78.6 years to 78.7 years, and life expectancy remains below its 2014 peak of 78.9 years. Since 2010, life expectancy in the U.S. has more or less flatlined.

That ominous one-year drop in the second decade of the 20th century was due mainly to the influenza pandemic of 1918. It is conceivable that the Covid-19 coronavirus now spreading around the U.S. will also make a noticeable dent in life expectancy, but it’s unlikely to be nearly as big. Covid-19 seems relatively benign for those under 50, while the 1918 flu was especially hard on young adults, and a bunch of 25-year-olds dying puts a lot more downward pressure on average life expectancy than an equal number of 65-year-olds.

In any case, the coronavirus impact will be temporary. The stall in U.S. life expectancy may not be. As a group of doctors and public health experts wrote in the New England Journal of Medicine in 2005, “we conclude that the steady rise in life expectancy during the past two centuries may soon come to an end.” One reason was simply that “past gains in life expectancy have largely been a product of saving the young,” and that with those mostly played out, “future gains must result from extending life among the old.” Another was that, due to rising obesity and the resulting “elevated risk of type 2 diabetes, coronary heart disease, cancer, and other complications,” extending life among the old was getting harder and harder.

When life expectancy did drop in 2015 — the first such decline since the AIDS epidemic in the mid-1990s — the proximate cause turned out to be something else: opioid use, which led to a quadrupling of drug-overdose deaths (and a slightly smaller rise in death rates) from 1999 to 2017.

In 2015, economists Anne Case and Angus Deaton famously linked these drug-overdose deaths to suicides and deaths from alcohol-related diseases, later describing them as “deaths of despair” that were “triggered by progressively worsening labor market opportunities at the time of entry for whites with low levels of education.” That in turn inspired a lot of research investigating whether more-dangerous drugs, overprescription by doctors and other factors might explain more of the overdose rise than worsening labor market opportunities could.

I’m not going to try to officiate that debate here, but it is clear that the rise in drug-overdose deaths was much steeper than that for suicides and alcoholic-related ailments. If the opioid epidemic keeps easing — the 2018 drop was driven by declines in overdose deaths related to heroin and prescription opioids; deaths from the illegal synthetic opioid fentanyl were still on the rise — we may see more small increases in life expectancy. But the underlying economic challenges described by Case and Deaton (who have a book on the subject, “Deaths of Despair and the Future of Capitalism,” coming out in two weeks) haven’t really gone away, and neither have the obesity-related ones that were the focus of that 2005 New England Journal of Medicine article (the CDC estimates that 42.4% of U.S. adults were obese in 2017-2018, up from 34.3% in 2005-2006). Life expectancy gains will most likely continue to be excruciatingly slow.

What might change that? It’s clear that life expectancy can go higher in the U.S., given that it is now several years longer in just about every other rich country on earth. To keep it simple I’ve just put the combined average life expectancy of the euro-zone countries in the following chart for comparison, but lots of others show a similar divergence.

Why is life expectancy so much lower in the U.S.? Most explanations focus on economic inequality, although lifestyle and diet probably play a role, too. The U.S. has seen a huge divergence in life expectancy by income group, with 50-year-olds in the top income quintile now expected to live about 13 years longer than their peers in the bottom income quintile (three decades ago the gap was only five years for men and four for women). There’s some evidence of similar disparities starting to open up outside the U.S., but the income gaps generally aren’t as big in other rich democracies, and access to health care there is less dependent on economic status. This is clearly a problem that could be fixed, given that other countries seem to have succeeded in mostly fixing it. The U.S. has been failing to do so for almost four decades, though, so it’s maybe not something we should count on happening soon.

There’s also the possibility of a technological fix, which has captivated people in Silicon Valley in particular. “Silicon Valley is right that the biological aging process is modifiable, and we will modify it,” says S. Jay Olshansky, a professor at the University of Illinois at Chicago’s School of Public Health and lead author of that 2005 paper that predicted a life expectancy plateau. “What I don’t believe is claims of a radical rise of life expectancy.” That is, the diabetes drug metformin, senolytics and other anti-aging treatments now being researched and developed may well keep people healthier in their 80s and 90s and extend their lives by a few years, but “there’s a limit imposed by our basic body design.”

One of these days, of course, someone may figure out how to redesign the human body. Someone may figure out how to redesign U.S. politics, economics, lifestyles and eating habits too. Until then, though, it’s looking like we may be stuck with a life expectancy in the high 70s.

This article was provided by Bloomberg News.