But now those gains are slowing down. That's the conclusion of a sobering new study published October 27 in the Journal of the American Medical Association (JAMA).
"Decade after decade, mortality rates have declined - until now," said David Ludwig, the director of the New Balance Foundation Obesity Prevention Center at Boston Children's Hospital. "We're likely at the tipping point."
The paper's findings, while preliminary, seem to reveal something deeply troubling. Eileen Crimmins, a gerontologist at the University of Southern California who co-chaired a National Research Council committee on trends in life expectancy, put it bluntly: "Things are not getting better in the US."
The JAMA study's authors - all researchers at the American Cancer Society - looked at deaths in the United States between 1969 and 2013. The rate at which people in this country are dying each year shows a steady downward trend until about 2010, when something alarming happens: It plateaus.
Previous slowdowns have occurred, the researchers told The New York Times, but a plateau has never before been so pronounced. The paper notes that the biggest slowdowns in declining death rates were for heart disease, stroke, and diabetes - leading causes of death that are all associated, though not exclusively, with obesity.
The 2010-2013 plateau "may reflect the lagged consequences of increased obesity prevalence since the 1980s," the researchers suggest. Smoking is now less common, and it has held us back in previous years, which is why obesity may what's driving the latest slowdown.
These aren't problems we can solve with pharmaceutical breakthroughs we can currently imagine. Reversing the worrisome new trend will require painstaking efforts in public health and public policy. "Further improvements in life expectancy are going to have to depend upon transforming our lifestyle beyond what can be done by drugs," Ludwig said.
And obesity-related diseases don't strike all Americans equally; last year a study found that while obesity rates are actually declining among high-income teenagers, they are still rising among poor Americans in the same age group. "The privileged are continuing to do better, and the underprivileged are doing ever worse," Ludwig said.
While the JAMA finding could mean an end to our ever-improving health, the authors emphasized that it was observed over too short a time period to qualify as a bona fide trend; we'll need more years of data to see whether it continues, worsens, or reverses.
But the finding is not entirely surprising. Ten years ago, Ludwig and colleagues predicted this might happen in a report published in the New England Journal of Medicine.
"From our analysis of the effect of obesity on longevity," they wrote in 2005, "we conclude that the steady rise in life expectancy during the past two centuries may soon come to an end."