Are human lifespans still getting longer?

A new study published on Wednesday finds that humans are unlikely to ever live much longer than 115 years old, although some researchers dispute the finding. 

As average American lifespans continue to lengthen, scientists are curious about just how long we can live. A new study published in Nature offers some answers.

Researchers based their studies on decades of longevity data from around the world, eventually concluding that although average lifespans are still rising, the ceiling for long life may rest at around 115 years old.

But debate over human longevity continues, and some researchers argue that the new study’s conclusion is flawed. Nevertheless, study author Jan Vijg remains staunch in his conclusion.

"We cannot break through that ceiling," said Dr. Vijg, according to National Public Radio (NPR). "The take-home message essentially is this whole ever-increasing life expectancy of humans cannot go on."

Vijg, a molecular geneticist at the Albert Einstein College of Medicine in New York, and his co-authors argue that advances in modern medicine and genetic intervention will continue to help lower mortality rates over time, leading to longer lifespans, but that on the whole, people won't live much past 115. 

Currently, longevity data indicates a positive trend. A baby boy born in the United States in 1913 was expected to live to be just over 50 years old. If that same baby boy were born in 2012 the expectation for his lifespan is about 76 years.

Yet although life expectancies are rising across the board, study authors say, it is important to note that the world’s oldest residents are living to approximately the same age. Vijg and his team came to their conclusion by measuring both live expectancy increases across the board, and by calculating changes in the maximum reported age of death in countries around the world.

Using these two measurements, scientists found that although average life expectancies are increasing, even supercentenarians are plateauing – age-based records stand for years before they are broken.  

For example, the oldest woman who ever lived, Jeanne Louise Calment, died in France in 1997. She was 122. The oldest man who ever lived, a Japanese citizen named Jiroemon Kimura, died at the age of 116 in 2013.

Beginning in the 1990s, Vijg says, the age of the oldest people dying ceased rising. Mrs. Calment’s record-setting life is an outlier – while study authors calculated that the maximum human lifespan could reach 125 years old, they say that the odds of living that long are worse than one in 10,000.

While some scientists, such as MIT aging researcher Leonard P. Guarente, say that the study confirms their suspicions about human potential lifespans, others maintain that the longevity study is flawed.

"It is disheartening how many times the same mistake can be made in science and published in respectable journals," director of the Max-Planck Odense Center on the Biodemography of Aging, James Vaupel, told The New York Times.

Dr. Vaupel says that with life spans increasing since 1900, there is little reason to believe in a ceiling. Furthermore, he says that researchers did not use the most powerful statistical tools to analyze age data, and notes that in some countries (like Japan), more people are living to an older age.