The authors suggest that "aging processes can be quantified in people still young enough for prevention of age-related disease, opening a new door for anti-aging therapies."
The study, published in the Proceedings of the National Academy of Sciences, examined signs of aging in 954 people born in 1972-73 from birth until the age of 38.
"We set out to measure aging in these relatively young people," states first author Dan Belsky, an assistant professor of geriatrics at Duke University's Center for Aging. "Most studies of aging look at seniors, but if we want to be able to prevent age-related disease, we're going to have to start studying aging in young people."
As the global population gets older, the prevalence of age-related diseases also increases. With the burden of these diseases growing, anti-aging interventions become more important. Young people are the ideal target for interventions as with them it is still possible to prevent age-related disease.
There is a skepticism, however, around whether the rate of aging can be detected in young adults who are yet to develop chronic diseases, the authors explain.
Aging can be seen through physical changes on the outside of the body - in the eyes, hair and the mobility of the joints - but it can also be observed in the human organs. And so, alongside interviews, the researchers measured the participants' kidney, liver, lung, metabolic and immune functions.
Other health factors the researchers measured included cholesterol levels, dental health, the condition of blood vessels at the back of the eyes (associated with the brain) and the length of telomeres - protective caps found at the end of chromosomes whose shortening is associated with aging.
The researchers used a selection of these biomarkers to assign a "biological age" for each of the participants now at the age of 38. These biological ages ranged from below 30 to almost 60 in some individuals.
They then looked back at data collected during the longitudinal study, analyzing the biomarker measurements taken when the participants were aged 26, 32 and 38. For each of these variables, a slope was drawn to reflect change during the study, and these measurements were used to calculate each participant's pace of aging.
Biological age reflected participants' ability to complete certain tasks
Most participants aged at a rate of 1 biological year per year, although some were aging as much as 3 biological years per chronological year and some as little as zero biological years per year.
The researchers found that the participants who had the highest biological age at 38 also appeared to be aging at a quicker pace.
Participants also had to complete a number of tests typically given to people over the age of 60. These included problem solving and tests of balance and coordination. Participants who were biologically older fared worse at these tests and reported having more physical difficulties than the biologically younger peers.
Additionally, undergraduate students were asked to rate how old or young the participants appeared in photos taken at the age of 38. The participants with the highest biological ages also appeared older on the outside to the students.
Previous research involving twins has demonstrated that only around 20% of aging is influenced by genes, meaning that environmental factors play an important role. "That gives us some hope that medicine might be able to slow aging and give people more healthy active years," says senior author Terrie Moffitt, a professor of psychology and neuroscience at Duke University.
According to Prof. Belsky, the findings of the study indicate that aging can be quantified in young people through a combination of multiple measures, although "the measures and methods need refinement to be 'better, faster and cheaper.'"
The team hope that one day it might be possible for clinicians to actively interfere in the aging process, rather than targeting individual diseases such as cancer and heart disease that are more prevalent in older populations.
"As we get older, our risk grows for all kinds of different diseases," Prof. Belsky concludes. "To prevent multiple diseases simultaneously, aging itself has to be the target. Otherwise, it's a game of whack-a-mole."
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