Most babies born in 1900 didn't live to see 50, but most Americans born this year will reach the upper end of the 70s, and a record number of us will hit the century mark. The steady gains in human lifespans over the past century have caused some people to wonder if lifespans of 1,000 years — or even physical immortality — may one day be possible.
New government data, however, is raining on the longevity parade. Life expectancy in America declined by a fraction in 2015, worrying some health officials who fear the change may mark the beginning of an ominous trend.
"I think we should be very concerned. This is singular. This doesn't happen," Princeton University economist Anne Case said in The Washington Post.
In the Centers for Disease Control and Prevention's most recent mortality report, released Dec. 8, life expectancy fell from 78.9 years in 2014 to 78.8 in 2015.
The last time life expectancy dropped in the U.S. was in 1993, when the HIV/AIDS epidemic and an outbreak of flu contributed to a decline from 75.7 to 75.4.
This year's drop is even smaller and could be a statistical blip. But some health professionals have been predicting a downward turn because of the obesity epidemic and wonder if this could be it.
Also at play could be the increasing number of Americans suffering from "diseases of despair" — suicide and addiction.
No single cause
Case, the Princeton economist, made headlines last year for research that found a startling increase in mortality among middle-aged whites.
The newest data confirm that trend. The only groups for whom life expectancy held steady were Hispanics, and African-American women. For everyone else, life expectancy fell.
The number of deaths from cancer declined, a drop which health experts attribute to earlier detection and more effective treatments. But that was the only good news. The mortality rate increased in eight out of the 10 leading causes of death in the U.S., the CDC said. These include heart disease, respiratory disease, stroke, diabetes, kidney disease and suicide.
The biggest increase was in the number of people whose deaths were attributed to Alzheimer's disease, up 15.7 percent from 2014.
More than 2.7 million Americans died in 2015 — 86,212 more than the previous year.
The infant mortality rate — the ratio of infant deaths to births — ticked upward, too: from 582.1 infant deaths per 100,000 live births in 2014 to 589.5 in 2015.
The change was largely due to an increase in unintentional injuries and sudden infant death syndrome; however, the CDC deemed the change "statistically insignificant."
For all Americans, the mortality rate went from 724.6 per 100,000 people to 733.1 per 100,000. But physical health wasn't the only reason for the decline; mental health figures into it, too.
"Diseases of despair" — such as alcoholism and drug abuse — are on the rise, and helped contribute to a 2.6 percent increase in suicide in 2015. One in six Americans took a drug for mental health in 2013.
The CDC reported the data without speculating on the reasons for the change. "When you see increases in so many of the leading causes of death, it's difficult to pinpoint one particular cause as the culprit," Robert Anderson, chief of the mortality statistics branch at the National Center for Health Statistics, told Rob Stein of NPR.
One thing that didn't change: As in previous years, women can generally expect to live longer than men. A 65-year-old woman can expect to live 20.6 more years, compared to 18 years for a 65-year-old man. The difference is generally attributed to men being less likely to take care of themselves and more likely to engage in risky behavior, but a new study published Dec. 13 posits that viruses have evolved to be more dangerous to men than women.
The limits of longevity
The data challenge not just the assumption that Americans will continue to live longer as health care and technology improve, but also raise questions about whether the human lifespan has a ceiling — and if so, what it is.
If we eventually eradicate all forms of disease, or find ways to treat them, and if we can find ways to replace aging body parts, the human body could be immortal, some people say.
A more realistic view is taken by Jan Vijg of Albert Einstein College of Medicine in New York, who has analyzed longevity records around the world and concluded that, Methuselah notwithstanding, humans seem to have an age ceiling of about 115 years.
In a study published in October in the journal Nature, Vijg and colleagues said that the ages of the oldest people dying around the world increased between the 1960s and 1970s, but the numbers have remained flat since then.
"The take-home message essentially is this whole ever-increasing life expectancy of humans cannot go on," Vijg told Stein, in another report for NPR.
That, however, was before the news broke Dec. 15 that researchers had found a way to rejuvenate the cells of aging mice, not only making them look younger and heal from injury faster, but extending their lives by 30 percent.
"Our study shows that aging may not have to proceed in one single direction. With careful modulation, aging might be reversed," co-author Juan Carlos Izpisua Belmonte told Hannah Devlin, science correspondent for The Guardian in the U.K.
The findings could lead to some forms of human trials within 10 years, the researchers said.
The toll of obesity
Even if anti-aging therapies are developed for humans, it's unclear if they could counter the damage that humans do to their own health with sedentary lifestyles and poor eating habits. While some doctors believe it's possible to be both fit and fat, the obesity epidemic in America has likely contributed to this year's decline in longevity, as well as anemic gains in previous years, analysts said.
"Heart disease, stroke, diabetes — the impact of obesity is across the board. And people are living long enough to show the long-term effects," S. Jay Olshansky, a researcher at the University of Illinois School of Public Health, said in USA Today.
A study of obesity and mortality on four continents, published in the journal Lancet in July, showed that about one in five premature deaths in North America might have been prevented if the people had not been obese.
America is not the only nation with an obesity problem. In fact, when compared to other countries, it's not even in the top 10. (Samoa, Kuwait and Qatar all rank ahead of the U.S. in obesity.)
And being underweight is dangerous, too, which is one reason (along with unsanitary conditions and poor access to health care) that many undeveloped nations have life expectancies that resemble America's in 1900.
The most worrisome thing about the life expectancy decline isn't its size. It's that other comparable nations aren't seeing their longevity slip, and the U.S. already lags behind countries that include Germany, Spain, Greece, Ireland and Canada.
In The World Factbook published by the CIA, the U.S. ranks No. 42 in longevity. The top three — Monaco, Singapore and Japan — have lifespan average of 89.5, 85 and 85, respectively.
If the decline does continue, Olshansky, of the University of Illinois, will seem like a prophet. In 2005, he and other colleagues wrote in the New England Journal of Medicine that obese Americans portend "a threatening storm … that will, if unchecked, have a negative effect on life expectancy."
