There may be a limit to how long humans can live, according to a new study.
The oldest known person was Jeanne Calment, a French woman who died in 1997 at age 122. 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 wrote in their study, published today (Oct. 5) in the journal Nature.
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. [Extending Life: 7 Ways to Live Past 100]
In the new study, the researchers looked at 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.
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.
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.
But Austad said 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.
Originally published on Live Science.