They were able to pinpoint 18 bio-markers which, when combined, could indicate whether they would biologically age faster or slower than their peers. When the participants reached the age of 38, the researchers were able to set biological ages for each of them, which ranged from under 30 to nearly 60 years.
This was then compared to their previous measures at age 26 and 32, allowing the researchers to draw slopes for each of the 18 variables and determine the hidden pace of biological ageing in all of the individuals.
While most were found to be ageing on the inside at a rate roughly in step with their years, some were found to be ageing at three times that - and others weren't ageing at all.
"As we expected, those who were biologically older at age 38 also appeared to have been ageing at a faster pace," said the study's director, Professor Richie Poulton of Otago University.
"A biological age of 40, for example, meant that person was ageing at a rate of 1.2 years per year over the 12 years the study examined."
People who were ageing more rapidly were less physically able, showed cognitive decline and brain ageing, reported worse health, and, based on the estimates of students who judged their ages by looking at photographs of them, looked older.
Being able to detect accelerated ageing at an early stage paved the way for applying therapies that slowed ageing and reduced age-related ailments, Dr Poulton said.
In New Zealand, the number of people aged 85 years and over was projected to rise from 67,000 in 2009 to 144,000 in 2031, then more than double to about 330,000 by 2061.
The global population of people aged over 80 would be near 400 million by 2050, bringing the risk of an "enormous global burden" of disease and disability if we couldn't find a way to extend healthy lifespans, Professor Poulton said.
The paper's lead author, Dr Dan Belsky of Duke University in the US, noted the new findings had only gone as far as establishing a proof of concept that an "ageing trajectory" could be mapped out.
The method would need to be refined to make it faster and cheaper, he said, but the ultimate goal was to intervene in the ageing process itself, instead of separately tackling different killers such as cancer and heart disease.
The study was published in the scientific journal Proceedings of the National Academy of Sciences.
Scientist with skin in the game
Findings of a study which explores what makes us age are particularly fascinating to Nava Fedaeff - and not just because casual modelling work makes appearance important.
As a fulltime scientist, the 26-year-old says she can appreciate the complex challenges researchers face in trying to slow rates of ageing globally - and why it's so crucial they tackle the issue.
"I follow these studies from a distance and this particular study is quite interesting," the Niwa climate scientist said.
"There is a lot of pressure on health facilities, and with an ageing population, that's only going to increase."
The Russian-born Aucklander was especially interested in the different rates at which the study participants aged compared with their actual years.
As for her own rate, she believed it was either in step, or perhaps slower.
"I've always been told that I look younger than I am throughout my life and I'd still say that's the case - maybe I'm one of the lucky ones.
"My parents are both quite youthful looking, so maybe it's genetics, but you can always speculate."
Ms Fedaeff believed basic lifestyle choices - especially being smokefree and shielding her skin from the harsh sun - were crucial too.
As well as this, she kept healthy through regular exercise, sleeping and eating well but, with the exception of basic cosmetics, didn't use anti-ageing treatments.
"I haven't gone down that route too much and just try to focus more on diet and exercise. I try to keep it as natural as possible."
Finding the hidden age
• A study based on data from the 40-year Dunedin Multidisciplinary Study has unveiled a new method to determine biological ageing in people still in their 20s and 30s.
• After recording a large number of health measures, including blood pressure, cholesterol, gum health, white blood cell count, liver and kidney function, the researchers identified 18 "bio-markers" that could be combined to determine whether people are ageing faster or slower than their peers.
• The "biological ages" calculated for each of the individuals when they reached a chronological age of 38 ranged from under 30 to nearly 60 years.
• Individuals who were ageing more rapidly were less physically able, showed cognitive decline and brain ageing, reported worse health, and looked older.
• The researchers believe being able to detect accelerated ageing at an early stage paves the way for applying therapies that slow ageing and lessen age-related ailments.
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