Saturday, October 22, 2016

On the idea that the human life expectancy is limited to 115 years

The theme of longevity is one that Demography Matters has touched upon in the past. I've written about two interesting case studies, in February 2010 about the Abkhaz of the Caucasus and their mythic longevity, and then in June 2014 about the factors behind the extended life expectancy of the inhabitants of the Greek Aegean island of Icaria. I've also written about broader trends, in December 2014 noting the remarkable global trends which have seen global life expectancy rise substantially. The news, announced earlier this month, that built-in biological failings might limit the human life expectancy to 115 years or so, definitely caught my attention. The study--available here--was outlined by Linda Geddes at Nature.

To investigate, Jan Vijg, a geneticist at Albert Einstein College of Medicine in New York City and his colleagues turned to the Human Mortality Database, which spans 38 countries and is jointly run by US and German demographers. They reasoned that if there’s no upper limit on lifespan, then the biggest increase in survival should be experienced by ever-older age groups as the years pass and medicine improves. Instead, they found that the age with the greatest improvement in survival got steadily higher since the early twentieth century, but then started to plateau at about 99 in 1980. (The age has since increased by a very small amount).

The researchers went on to look at the International Database on Longevity, which focuses on the oldest people and is run by an international team. They found that the maximum reported age of death — the age of the oldest person to die in a given year — in France, Japan, the United States and the United Kingdom (the countries with the largest numbers of supercentenarians) increased rapidly between the 1970s and early 1990s but plateaued in the mid-1990s at 114.9 years. The researchers observed the same trend when they considered the second, third, fourth and fifth oldest person who died in a given year — and a similar peak age of 115 years old when they tracked the maximum annual age of death using another database run by the international Gerontology Research Group, which validates supercentenarian claims.

Vijg’s team concludes that there is a natural limit to human lifespan of about 115 years old. There will still be occasional outliers like Calment, but he calculates that the probability of a person exceeding 125 in any given year is less than 1 in 10,000.

The limit is surprising, says Vijg, given that the world’s population is increasing — supplying an ever-increasing pool of people who could live longer — and that nutrition and general health have improved. “If anything you would have expected more Jeanne Calments in recent years, but there aren’t."

But not everyone agrees with his team's interpretation. The age experiencing the greatest increase in survival may have plateaued in many countries, says James Vaupel, founding director of the Max Planck Institute for Demographic Research in Rostock, Germany. But it has not yet plateaued in some that are particularly relevant to this research, namely Japan, which has the world’s highest life expectancy — 83.7 years for those born in 2015, nor in France or Italy, which have large populations and high life expectancies.

Vijg’s paper includes “one-sided conclusions”, says Vaupel. But Vijg argues that the increase in the survival age in even these three countries has significantly slowed down in recent years and so seems to be trending towards no increase.

This report garnered a lot of attention from the mainstream media, The Guardian, NPR, and The Atlantic providing some insightful commentary. The Atlantic notes the arguments that frailties inherent in the human organism make it unlikely that this ceiling will be raised, not without unforeseen technological advances.

The ceiling is probably hardwired into our biology. As we grow older, we slowly accumulate damage to our DNA and other molecules, which turns the intricate machinery of our cells into a creaky, dysfunctional mess. In most cases, that decline leads to diseases of old age, like cancer, heart disease, or Alzheimer’s. But if people live past their 80s or 90s, their odds of getting such illnesses actually start to fall—perhaps because they have protective genes. Supercentenarians don’t tend to die of major diseases—Jeanne Calment died of natural causes—and many of them are physically independent even at the end of their lives. But they still die, “simply because too many of their bodily functions fail,” says Vijg. “They can no longer continue to live.”

[. . . I]f early development and childhood experiences are so important to our future health, it’s notable that today’s centenarians were born in the 1900s. It might be that longevity records “haven’t yet seen the impact of the improved sanitation, healthcare, vaccinations, and hygiene advances that took place in the 1930s and later,” says Holly Brown-Borg from the University of North Dakota. Or perhaps, “our poor diets and lack of exercise have countered those gains.”

That’s unlikely to matter much, says Vijg. “Once you survive your childhood, you’re really more likely to survive over long periods of time. And there have been enormous advances in keeping older people alive much longer. We’ve continued to make progress in medical care and safety standards, and there are more and more people. You can’t explain the fact that there aren’t older people that Jeanne Clement except to say that we’ve hit a ceiling.”

We have pushed that ceiling upward for laboratory animals, like worms, flies, and rodents. But these creatures were specifically bred by scientists to grow fast and reproduce rapidly. Many of the techniques for extending their lives, from drugs to calorie restriction, probably work by simply slowing their artificially inflated growth.

Similar tricks might increase our healthspan, and raise our average life expectancy. But Vijg believes that the most we can hope for is to be very healthy for around 115 years, after which our bodies will just collapse.

“There’s no question that we have postponed aging,” adds Judith Campisi, from the Buck Institute for Research on Aging. “But to engineer an increase in maximum lifespan, we’ll probably have to modify so many genes that it won’t be possible within our lifespan—or even our grandchildren’s lifespan.”

Even granting the arguments of Campisi and others that--assuming this limit does exist--this limit of 115 years cannot be breached in the foreseeable future, there's still much that can be done. Most obviously, in no country does the average life expectancy actually reach 115 years, or come close to it. Moreover, as noted by many of the people interviewed, there is still much that can be conceivably done to make the human process easier. Biomedical interventions into the aging process and specific diseases aside, I noted in my treatments of the Abkhaz and the Icarians specific things that can be done--inclusive social structures, for instance, and relatively healthy diets--that can do much to extend not only longevity but healthy lifespans. The commentary at Forbes, concentrating on the specific case of Japan, provides stil another example. In a generation's time--perhaps even in my generation--decline and death may end up being postponed and not so nearly drawn out.

The consequences of any scenario involving extended longevity are notably significant. A worst-case scenario might involve an extension of human life expectancy towards supercentenarian territory without a corresponding increase in a person's active and healthy lifespans. The financial costs of supporting these people for additional decades would be extreme, to say nothing of the human cost to specific individuals who might well not relish added years of suffering. The Greek mythological figure of Tithonus, who suffered the tragic consequences of being granted immortality but not eternal youth, comes to mind. Conversely, a scenario where longevity and health are extended could have very positive consequences.

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