People living up to the age of 65 live six years longer than their grandparents, a new study finds.
Researchers at Stanford University in California say they have discovered that the life span of those who retire increases by three years each generation.
Previous research has suggested that humans are approaching the limit of their longevity.
But the team says its results show that there can be no natural limit to the time when humans can live and that the rising trend of life is likely to continue.
A new study found that the lifespan of those living up to the age of 65 increases every generation three years (file image)
For the study, researchers looked at birth and death records in 20 countries from 1960 to 2010 for those who lived to be over 65.
The results showed that the lifespan for those over 65 has increased by three years in each 25-year period.
This means that, on average, people are likely to live about three years longer than their parents and about six years older than their grandparents.
While there are factors that cause fluctuations in the way life span has increased, including the advent of some antibiotics and vaccines, the changes are mediated over time.
"The data show that we can expect longer lives and there is no sign of a slowdown in this trend," said lead researcher Dr Shripad Tuljapurkar, a professor of biology at Stanford University.
"There is no limit to the life we can see, so what we can say with certainty is that it is not close enough to see the effect."
The dott. Tuljapurkar says the problem with most longevity studies is that research focuses on abnormal values, or people who live longer than anyone else.
This includes studies on the so-called "blue zones": five geographical areas with low rates of chronic diseases and home to some of the world's oldest people.
However, because few people live this long, the data can be misleading and dr. Tuljapurkar wanted to look at an age at which most people live: 65 years.
"Our method is innovative because it allows us to get rid of the confusion," he said. "We focus on the age group where we have a precise idea of what's going on."
The team says that if we approach a limit to human lifespan, the data should stabilize. However, survival rates of old age have continued to increase as a "traveling wave".
The dott. Tuljapurkar admits to being surprised that the average age of death has increased at a constant rate.
He says he expected that certain lifestyle factors would allow some to live longer than others.
"There were a lot of publicity about how people could live longer, for example, eating yogurt," said Dr. Tuljapurkar.
Although yogurt may not be the key to a longer life, Dr. Tuljapurkar suspected at the beginning of the study that those who are richer would live longer.
If this were the case, the distribution of data would widen while the rich lived beyond 65 – but the data were consistent during the 50-year study period.
Dr Tuljapurkar added that when most people reached age 65, they overcame many factors that reduce lifespan including early violence and disease.
"As someone who would like to be one percent, but it is not, I am certainly very happy to know that my chances of living longer are as good as the millionaire down the road," he said.