An international team of researchers has developed a new way to track the biological ageing process – and the results suggest that humans can live to a maximum of 150 years old.
Why do we age?
Ageing is a gradual process that happens over our whole life, as our normal body functions slow down.
There are at least nine markers of ageing, but a common one is when our cells slowly lose the ability to produce new and healthy cells to repair damage. It is marked by a decline in physical functionality and an increased risk of chronic disease.
Researchers distinguish between chronological age, which is exactly how many years a person has been alive, and biological age, which is how old a person seems at a cellular level – that is, how close their cells are to completely ceasing all function. These two numbers are not always the same for any given person, nor is biological age always linear.
Since biological age is influenced by a range of factors such as diet, exercise, sleeping habits, genetics and more, it’s difficult to calculate – but researchers are interested in measuring it in order to develop effective anti-ageing interventions.
What did this new research find about biological ageing?
This new study, published in the journal Nature Communications, reports a method that converts data from an ordinary blood test into a single statistic to determine biological age, as well as understand how it can fluctuate over time in the same person.
The research team from Singapore-based biotech company Gero drew on longitudinal human blood count data from the National Health and Nutrition Examination Survey and UK Biobank. This resulted in a single variable to describe biological age, called the dynamic organism state indicator (DOSI).
Basically, the DOSI is derived from biomarkers in blood and it indicates the resilience of individuals over time. One of the major factors of resilience is the ability to make new cells to repair damage, both regular wear and tear and to overcome diseases and injuries.
The study found that healthy people were very resilient to stresses, while people who had chronic diseases and an elevated risk of mortality were less resilient.
The recovery time also grew longer with age – two weeks for a healthy 40-year-old to six weeks for an 80-year-old. This finding from blood test parameters was compared to and confirmed by physical activity levels recorded by wearable devices.
By extrapolating this trend out, the team found that people will completely lose their ability to recover – that is, their resilience – by the age of 120–150, even if they are otherwise healthy and not suffering from major disease.
“This work indicates that the apparent human lifespan limit is not likely to be improved by therapies aimed against specific chronic diseases or frailty syndrome,” the authors write in their paper.
“Thus, no dramatic improvement of the maximum lifespan and hence strong life extension is possible by preventing or curing diseases without interception of the aging process, the root cause of the underlying loss of resilience.”
Does this agree with what we previously knew about biological ageing?
Kylie Quinn, leader of the Ageing and Immunotherapies Group at RMIT University in Melbourne, says “it’s a really cool idea using accessible information”.
But Quinn – who was not involved in the study – notes that it would be challenging to use this method across a whole population, because some of the variables can change in a person’s normal daily life.
“For example, if they got an infection…that that could change their complete blood counts quite a bit,” she explains. “A one-time sampling might not be enough – we might have to have a couple of different samples from an individual if we were going to use this as a health tool.”
But as a tool to understand biological ageing, she says this research an intriguing addition to the field and agrees well with previous findings – even the estimation of the maximum human lifespan.
“It pans out when we look at what happens within the human population,” Quinn points out. “The oldest individual that is known to have ever lived, lived to the age of 122, but we know that person is a bit of an outlier – the next person after that is only 119. So we know that there’s something about that 120 years of age, which is a real challenge in terms of getting past that.”
How does this compare to other methods of determining biological age?
Lindsay Wu, another independent researcher at the University of New South Wales, explains that there have been many previous attempts to determine a “clock” for biological age, including several based on composite measures from blood biochemistry.
“However, these are highly sensitive to fluctuations in blood markers of metabolism, for example glycosylated haemoglobin (HbA1c) which is a stable measure of long-term glucose levels,” he says.
This means that anti-diabetic medication, fasting and exercise can all affect the age measure.
“While all of these interventions are well-accepted measures to maintain late-life health and possibly to extend overall lifespan, the degree of “age-reversal” observed from these algorithms just is not realistic – by fasting for a day you can reverse a predicted biological age by 20 years,” Wu says. “The trick would be maintaining this level of fasting for the rest of a lifetime!”
“The only situation in humans where you can observe a “reversal” of a predicted biological age according to this clock is in individuals who go from being regular smokers to then quitting smoking – again, this seems reasonable,” Wu says.
He agrees with Quinn that the mathematical prediction from this recent research – of a maximum human life span of 150 years – seems to line up with observations that “the rate of mortality exponentially increases beyond a certain age”.
“There has been this idea that individuals could achieve an “escape velocity” whereby if they get to a certain age and escape most of the common diseases, there is no reason for drastically increased longevity,” he says.
“Given all the data of centenarians and their health and lifespan we just don’t see this – rather, we see the exponential decay in further lifespan.”