US researchers believe they've found evidence of the absolute limit of human lifespan, and it's about 125 years.

History's oldest documented person died aged 122 years, according to new research - and it's unlikely the record will be broken.

This is despite human life expectancy increasing throughout the 20th Century thanks to advances in medicine.

Using data from the Human Mortality Database, reseachers at Albert Einstein College of Medicine found the age at death plateaued about 1997, close to the time of death of Jeanne Calment - the oldest person documented.

While life expectancy has increased significantly over the years, the rate of survival declines significantly after the age of 100, analysis of global demographics showed.

In France, the number of individuals per 100,000 surviving to old age (70 and up) has increased since 1900. This pattern is very similar across the other 40 countries and territories included in the database.

However, the rate of improvement in survival peaks and then declines for very old age levels.

The results, published in journal Nature, strongly suggest human lifespan is subject to natural constraints, the authors said.

Simply put, there is a limit to human life.

"The idea ageing is a purposeful, programmed series of events that evolved under the direct force of natural selection to cause death has now been all but discredited," the authors concluded.

They believe this 'natural limit' to the human lifespan is encoded in our DNA and that without specific intervention will remain unchanged.

The scientists came up with a modelling tool using global data to approximate the absolute limit of human lifespan.

They believe it's about 125 years.

The likelihood of a person exceeding this age in any given year is less than one in 10,000.