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Researchers say there is a limit to the human lifespan, and we have already hit it

Almost for thousands of years, throughout known history, people have searched for a method to live longer. And we have made remarkable steps, particularly in the past century and a half or so. But we may now be striking against a natural limit to the human lifetime, according to a study published October 5 in Nature. The authors of the study say that their data shows that even if we carry on curing diseases that affect people in old age, no one is likely to significantly live longer than the Frenchwoman who holds the record of the human with the longest known age, Jeanne Calment.

She was 122 years old when she died, in 1997. The important question, according to authors Brandon Milholland, Xiao Dong and Jan Vijg, is whether or not our maximum lifetime is flexible, like that of some creatures, or whether biological elements mean that limit is fixed. Even though they write that the data they have analyzed "strongly recommend that human lifetime has a natural limit", that does not mean human race could never find a way to outlive that limit.

Ikaria, a Greek island renowned for the longevity of its residents. Credit: iStock/3quarks

To answer that essential question, the authors of the paper analyzed demographic information from 41 countries around the world. In history, life expectancy first started to extremely shoot up in the past hundred years or so because we had eliminated many deaths that happened early in life.

The overview of antibiotics, aggressive vaccination promotions, and actions to reduce infant and maternal death ensured that countless people were able to reach old age. In recent years, there were slower but major developments in late-life mortality, meaning that more and more old people lived longer. But those variations appeared to plateau around 1980, the authors write, which they say shows the prospect of a limit on human life.

To further solve this question, the authors analyzed the death rates of super-centenarians (people 110 years of age or more) in the US, the UK, Japan, and France. However limited numbers of super-centenarians exist, which means that the data on their death rates is not certain, the maximum informed age of death in this group appears to have plateaued as well around 1995, just two years before the death of Jeanne Calment.

Even the healthiest people who appear to have the best genes for longevity have not lived longer since then. The authors write that the chances of somebody living past 125 in any known year are less than 1 in 10,000. In many ways the important question right now, among tech billionaires working to defeat death or among scientists and philosophers convinced we can "slay the dragon" of age, is whether or not a human being can outlive whatever natural boundaries we might have.

The authors of the Nature study write that they think the limits on human life are not certainly set by the diseases that kill us when we are old, but by the procedures through which our bodies develop throughout our life. We need to change and develop and become able to reproduce, but along the way these physical changes will start a process that has a natural endpoint.

After that, our cells and bodies will be incapable of continuing. Even curing diseases like cancer and Alzheimer's might not help humans live longer, however, the ends of our lives might certainly be better. For that purpose, many of present anti-aging scientists are more focused on the idea of improving what's called health-span as well as on improving lifespan. Who would desire to live forever if their bodies and minds continued to decline, like Tithonus of Greek myths?

Scientists know that aging itself is far more difficult and intertwined with humans' simple biology than just being an unexpected result of the individual diseases that generally end our lives. That high-point the challenge of trying to treat aging but it also means they know the difficulty of the problem.

Valter Longo, a professor of gerontology and biological science and the director of the University of Southern California Longevity Institute, told in an interview, "Treating aging used to be just an impression that was provoked with skepticism."

But now Longo trusts that there might be enough care for research that helps us work out how to take the science of life extension extra further, though he approves that health-span must be improved at the same time. He has established a diet that he says he believes could increase normal lifespan by about 10% (normal lifetime still being far less than the lifetime of centenarians but more significant to a normal person), but that could also keep people much healthier during the course of that life.

Jan Vijg, genetics and aging scientist and one of the authors of the paper, tells Andrew Joseph and Natalia Bronshtein of Stat News that he does not think it's possible we will figure out how to treat all the details of aging: "What are you planning to do? Develop a drug for all of them?"

And at the moment, it might be difficult to imagine an answer to that.

But 200 years ago it may have been unbearable for most people to imagine living to 80 years of age or to conceive of the idea that humans would be preparing to send people to Mars. Vijg tells Stat that what he thinks is impossible could surely change. It is that amazing challenge that sent Longo and others down the track of trying to 'solve' aging in the first place.

Longo says, "It was the strangest thing you could possibly study". And a final answer may reveal ways to cross even those natural limits we may have.

This article was initially published by Business Insider.

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