An international research team from the US, UK, Israel and New Zealand has found a way to measure the aging process in young adults -- a younger population than is usually tested in aging studies. Working with study participants age 26 to 38, the scientists identified factors that can determine whether people are aging faster or slower than their peers, and to quantify both their biological age and how quickly they are aging.
In a paper appearing today in the Proceedings of the National Academy of Sciences, the researchers showed that even among young adults, a person's biological age may differ by many years from their actual chronological age. For example, among 38-year-olds studied, the participants' biological age was found to range from under 30 years old, to nearly 60 years old. That means that some participants' biological age was more than 20 years older than their birth certificates indicated.
"This research shows that age-related decline is already happening in young adults who are decades away from developing age-related diseases, and that we can measure it," said Dr. Salomon Israel, a researcher and senior lecturer in the Hebrew University of Jerusalem's Department of Psychology, and a co-author of the study. Dr. Israel joined the Hebrew University's faculty in January 2015 after completing a postdoctoral fellowship in psychology of neuroscience at Duke University.
The data comes from the Dunedin Study, a long-term health study in New Zealand that seeks clues to the aging process. The study tracks over a thousand people born in 1972-73 from birth to the present, using health measures like blood pressure, liver function, and interviews.
As part of their regular reassessment of the study population in 2011, the team measured the functions of kidneys, liver, lungs, metabolic and immune systems. They also measured HDL cholesterol, cardiorespiratory fitness, lung function and the length of the telomeres -- protective caps at the end of chromosomes that have been found to shorten with age. The study also measures dental health and the condition of the tiny blood vessels at the back of the eyes, a proxy for the brain's blood vessels.
Based on a subset of these biomarkers, the research team determined a biological age for each participant. The researchers then looked at 18 biomarkers that were measured when the participants were age 26, and again when they were 32 and 38. From this, they drew a slope for each variable, and then the 18 slopes were added for each study subject to determine that individual's pace of aging.
Most participants clustered around an aging rate of one year per year, but others were found to be aging as fast as three years per chronological year. Many were aging at zero years per year, in effect staying younger than their age.
As the team expected, those who were biologically older at age 38 also appeared to have been aging at a faster pace. A biological age of 40, for example, meant that person was aging at a rate of 1.2 years per year over the 12 years the study examined.
Study members who appeared to be more advanced in biological aging scored worse on tests typically given to people over 60, including tests of balance and coordination and solving unfamiliar problems. The biologically older individuals also reported having more difficulties with physical functioning than their peers, such as walking up stairs.
As an added measure, the researchers asked Duke University undergraduate students to assess facial photos of the study participants taken at age 38 and rate how young or old they appeared. Again, the participants who were biologically older on the inside also appeared older to the college students.
"We set out to measure aging in these relatively young people," said Dan Belsky, an assistant professor of geriatrics in Duke University's Center for Aging and the study's first author. "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."
"That gives us some hope that medicine might be able to slow aging and give people more healthy active years," said Terrie Moffitt, the Nannerl O. Keohane professor of psychology and neuroscience at Duke and the study's senior author.
The ultimate goal is to be able to intervene in the aging process itself, rather than addressing killers like heart disease or cancer in isolation.
"Accelerated aging in young adults predicts the symptoms of advanced aging that we see in older adults: deficits in cognitive and physical functioning, feelings of ill-health, and even an older appearance. The ability to measure how quickly a young person is aging may in the future enable us to engage in interventions that slow aging or target specific diseases," the Hebrew University's Dr. Israel said.
Dr. Israel's research at the Hebrew University focuses on the biological mechanisms that give rise to individual differences in personality and social behavior; and conversely, how enduring differences in personality and social behavior unfold over time to contribute to physical health and economic well-being. To address these topics, he applies methods from fields including molecular genetics, neuroendocrinology, behavioral economics, social psychology, and life-course epidemiology.