Scientists have been trying to find the maximum life span of a human and how to extend human lifetime for many years. But a new study finds that human life time is limited. Can the maximum life time span be extended further?
The oldest known person was Jeanne Calment, a French woman who died in 1997 at age122. Calment's longevity record is unlikely to be broken, the researchers said.
"In contrast to previous suggestions that human longevity can be extended ever further, our data strongly suggest that the duration of life is limited,"the researchers from the Albert Einstein College of Medicine wrote in their study, published in the journal Nature.
However,if there is no limit to how long people can live, then the greatest increases in survival rates over time should have occurred among those people who are the oldest, the researchers hypothesized. But the data showed that the greatest increase in survival rates among people in the oldest age groups in most countries peaked around 1980, and has not changed since. This may suggest that, after all, there may be a natural limit to how long people can live, the researchers said.
The scientists also looked to see how old the very oldest people were when they died. They focused on deaths between 1968 and 2006, in France, Japan, the United Kingdom and the United States, which are the four countries with the largest numbers of people who have lived longer than 110 years, according to the International Database on Longevity. The researchers also looked at the maximum reported age at death between 1972 and 2015 reported by another source, called the Gerontology Research Group.
However,the new findings don't mean that researchers know for sure that humans will never live longer than 122 years, said Steven Austad, a professor of biology and aging at the University of Alabama at Birmingham, who was not involved in the study. He said that scientists used to believe that the limit to the human life span was 110 years until somebody lived to be older than that, which shows that it is tough to predict what this limit can be for humans.
"Demographers as well as biologists have contended there is no reason to think that the ongoing increase in maximum lifespan will end soon," said senior authorJan Vijg, Ph.D., professor and chair of genetics, the Lola and Saul Kramer Chair in Molecular Genetics, and professor of ophthalmology & visualsciences at Einstein. "But our data strongly suggest that it has alreadybeen attained and that this happened in the 1990s."
In the new study, Dr. Vijg and his colleagues analyzed data from the Human Mortality Database, an international database with detailed mortality data that's maintained by researchers at the University of California, Berkeley and the Max Plank Institutes in Germany. The database contains information on how long people have lived in recent decades in many countries.
The researchers found that, in at least 40 countries and territories, the number of people surviving to age 70 and older has increased since 1900. This suggests that people's life expectancy,or the estimate of how long a person may expect to live, has increased.
The researchers found that, though the maximum reported age at death did increase until the 1990s, it has actually plateaued, and even slightly decreased since the time Jeanne Calment died.
"Further progress against infectious and chronic diseases may continue boosting average life expectancy, but not maximum lifespan," said Dr. Vijg. "While it's conceivable that therapeutic breakthroughs might extend human longevity beyond the limits we've calculated, such advances would need to overwhelm the many genetic variants that appear to collectively determine the human lifespan.Perhaps resources now being spent to increase lifespan should instead go to lengthening health span -- the duration of old age spent in good health."
But Steven Austadsaid that the human life span could likely still be extended. Experiments on mice have shown that these animals live longer if their calorie intake is restricted or if their genes are manipulated, he said.
If researchers found medications or lifestyle factors such as special diets that are better than the ones known today, that could allow humans to live longer, too, he said.