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Reaching the limits of the human lifespan

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The longest any human being has ever lived was 122 years. Jeanne Calment of France, who rode a bicycle until age 100, passed away in 1997. Since then, no one has been recorded to live past 120 years.

A paper published in the Oct. 2016 issue of Nature claims to have found an age limit to the human lifespan. The researchers compared the death of the oldest person against calendar years and found that the rate of maximal lifespan growth seems to have hit a plateau.

These results are consistent with the idea that the limit of an organism’s lifespan is encoded in its genetics. For example, fruit flies live for about 40 days, while the Giant Galapagos Tortoise can live for over 170 years. The imposition of a genetic constraint on maximum lifespan may also apply to humans.

However, the exact mechanisms of the aging process are still unclear, though many theories exist. From a physical perspective, the “general wear and tear” mechanism states that aging is the phenomenon of overuse, in the same sense as old cars accumulate problems as their mileage increases.

In the case of progeria—an extremely rare genetic disorder where patients age eight to ten times faster than the normal aging process—general wear and tear damage, such as cataracts and osteoarthritis, is not observed. While overuse is likely a contributing factor to aging, there are other genetic influences at play.

Another theory of aging is genomic instability from mutations and DNA damage. During cellular respiration—the process wherein cells derive their energy—cells produce unstable modecules called free radicals resulting in harmful oxidation. Free radicals are incredibly reactive and can cause extensive damage to proteins and DNA. As more damage is incurred, there will be an increased likelihood of cancer and cell mutation arising from abnormal protein production.

There is some good news when it comes to aging. Globally, the average human lifespan is rising over two years per decade. Better health care and nutrition improve the average life expectancy in developing and developed countries like the United States, Canada, and Germany. There are also drugs going to clinical trial that target cellular aging pathways, which have demonstrated promising results in laboratory animals.

One such drug is metformin, a U.S. Food and Drug Administration (FDA)-approved medication for the treatment of type II diabetes. The drug has slowed down the aging process in laboratory model organisms. However, researchers will likely have a hard time receiving funding from pharmaceutical companies as metformin is a low-cost drug and therefore not very profitable.

As of now, there is only one agreed-upon method to slow down the aging process: Caloric restriction. In model organisms, restricting the caloric intake while still supplying essential nutrients such as iron and calcium, led to reproducible results that extended an organism’s maximum lifespan. While the underlying mechanism of this process is still unclear, physiological changes such as increased insulin sensitivity, reduced metabolism and oxidation have been reported. Dietary intake restriction is an area of intense research and could yield promising discoveries in the near future.

While it appears that the maximum amount of time any human being could stay on this planet is predetermined by DNA, there is also something to be said about the quality of these years: As the millennials say, “You Only Live Once.”

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