LONDON
Humans are unlikely to ever blow out more than 125 candles on their birthday cake, according to research that suggests that our lifespan has already hit its natural limit.
The oldest human who ever lived, according to official records, was 122-year-old Frenchwoman Jeanne Louise Calment, who died in 1997.
Now a team of American researchers suggest Calment is unlikely to lose the top spot any time soon, as their research shows that though more people reach old age each year, the ceiling for human lifespan appears to be stuck at around 115 years.
“The chances are very high that we [have] really reached our maximum allotted lifespan for the first time,” said Jan Vijg, co-author of the research from the Albert Einstein College of Medicine in New York.
Figures such as Aubrey de Grey, chief scientific officer at the Strategies for Engineered Negligible Senescence (Sens) Research Foundation, have previously claimed that the first person to reach 1,000 years old is likely to be alive today.
But the new study suggests that is highly unlikely. The upshot, says Vijg, is that people should focus on enjoying life and staying healthy for as long as possible. “That’s where we have to invest our money,” he said.
The notion of extending the human lifespan has captured imaginations for millennia. Among scientists, enthusiasm for the idea has grown in recent years with a host of Silicon Valley companies springing up to join academic institutions in attempting to chip away at issue of longevity — among them Google’s California Life Company, or Calico, as it is known — with big-buck prizes such as the Palo Alto Longevity Prize adding to the clamour.
But the researchers, writing in the journal Nature, describe how analysis of records from a number of international databases suggests there is a limit to human lifespan, and that we have already hit it.
Using data for 41 countries and territories from the Human Mortality Database, the team found that life expectancy at birth has increased over the last century. That, says Vijg, is down to a number of factors, including advances in childbirth and maternity care, clean water, the development of antibiotics and vaccines and other health measures.
But while the proportion of people surviving to 70 and over has risen since 1900, the rate of improvements in survival differ greatly between levels of old age. Large gains are seen for ages 70 and up, but for ages 100 or more the rate of improvement drops rapidly. “[For] the oldest old people, we are still not very good at reducing their mortality rates,” said Vijg.
What’s more, in 88 per cent of the countries, the ages showing the greatest rate of improvement have not changed since 1980.
The researchers then turned to the International Database on Longevity and analysed data from France, UK, the US and Japan — four countries with a high proportion of those aged 110 or above — so-called “supercentenarians”.
The researchers found that the maximum reported age at death rapidly increased between 1970 and the early 1990s, rising by around 0.15 years every year. But in the mid-to-late 90s, a plateau was reached, with the yearly maximum reported age at death at around 115 years.
Modelling of the possibility of living beyond such an age offered further insights. “Based on the data we have now, the chance that you will ever see a person of 125 [years] in a given year is about 1 in 10,000,” said Vijg.
The apparent limit to human lifespan, the authors say, is not down to a set of biological processes specifically acting to call time on life. Rather, it is a by-product a range of genetic programmes that control processes such as growth and development.
Henne Holstege from VU University, Amsterdam works on ageing of centenarians, and previously led research into Dutch supercentenarian Hendrikje van Andel-Schipper, who died aged 115. She says the new study suggests “there seems to be a wall of mortality that modern medicine cannot overcome”.
“If you die from heart disease at 70, then the rest of your body might still be in relatively good health. So, a medical intervention to overcome heart disease can significantly prolong your lifespan,” she said. “However, in centenarians not just the heart, but all bodily systems, have become aged and frail. If you do not die from heart disease, you die from something else.”
Medical interventions, she says, cannot solve the problem of overall decline, with the only promising approach lying in slowing down the ageing process itself. But, she added, “It is however not yet clear if and how this can be accomplished.”
But Tom Kirkwood, associate dean for ageing at Newcastle University, is sanguine that the lifespan ceiling will continue to rise.
“There is no set programme for ageing and we know that the process, which is ultimately driven by the build-up of faults and damage in the cells and organs of the body, is to some degree malleable,” he said. “Even without any change in the biology of ageing, it is almost inevitable that the current record will be broken.”
Cynthia Kenyon, vice-president of ageing research at Calico, is also optimistic.
“No one, particularly not evolutionary theorists, predicted that single-gene mutations could slow the ageing process and double the lifespans of animals. But they can,” she said. “While we don’t have demographic data supporting the idea that the maximum human lifespan is now increasing, that certainly doesn’t mean it’s impossible.”
But scientists have found the most definitive evidence yet that some people are destined to age quicker and die younger than others — regardless of their lifestyle.
The findings could explain the seemingly random and unfair way that death is sometimes dealt out, and raise the intriguing future possibility of being able to extend the natural human lifespan.
“You get people who are vegan, sleep 10 hours a day, have a low-stress job, and still end up dying young,” said Steve Horvath, a biostatistician who led the research at the University of California, Los Angeles. “We’ve shown some people have a faster innate ageing rate.”
A higher biological age, regardless of actual age, was consistently linked to an earlier death, the study found. For the 5 per cent of the population who age fastest, this translated to a roughly 50% greater than average risk of death at any age.
Intriguingly, the biological changes linked to ageing are potentially reversible, raising the prospect of future treatments that could arrest the ageing process and extend the human lifespan.
“The great hope is that we find anti-ageing interventions that would slow your innate ageing rate,” said Horvath. “This is an important milestone to realising this dream.”
Horvath’s ageing “clock” relies on measuring subtle chemical changes, in which methyl compounds attach or detach from the genome without altering the underlying code of our DNA.
His team previously found that methyl levels at 353 specific sites on the genome rise and fall according to a very specific pattern as we age — and that the pattern is consistent across the population. The latest study, based on an analysis of blood samples from 13,000 people, showed that some people are propelled along life’s biological tramlines much quicker than others — regardless of lifestyle.
“We see people aged 20 who are fast agers and we look at them 20 years later and they are still fast agers,” said Horvath. “The big picture here is that this is an innate process.”
The scientists found that known health indicators, such as smoking, blood pressure and weight, were still more valuable in predicting life expectancy in the 2,700 participants who had died since the study began, but that their underlying ageing rate also had a significant effect.
This is not the first time that scientists have observed so-called epigenetic changes to the genome with age, but previously these were put down to wear-and-tear brought about by environmental factors, rather than indicating the ticking of an internal biological clock.
Wolf Reik, a professor of epigenetics at the University of Cambridge who was not involved in the work, said: “It now looks like you get a clock given to you when you’re young. It gets wound up and the pace it’s ticking at is dictated by this epigenetic machinery.”
