Old before their time? Why do people age at different rates?
When English poet John Milton wrote of "Time, the subtle thief of youth" in the 17th century, he probably wasn't thinking of a high school reunion.
But if you've ever been to such an event, Milton's words may have crossed your mind as you walked around the room shaking hands with classmates who had become bald and fat before their time and those who looked like they hadn't aged a day since you last saw them.
A team of researchers led by Duke University assistant professor Daniel Belsky believes that some of the secrets to the aging process may lie in understanding the phenomenon of why people grow "old" at such differing rates.
"By slowing down the aging process, we could prevent not just one disease, but many simultaneously," Belsky, a researcher at Duke's Center for the Study of Aging and Human Development, said.
Scientists have long known that what happens at the very beginning of life, in the womb, can have powerful effects on a person's health. But what about in the interim?
In a study published this month in the Proceedings of the National Academy of Sciences, the scientists tracked 1,000 people born in 1972-73 in the coastal city of Dunedin in New Zealand and calculated their "biological age" 20 years after their 18th birthdays based on a wide range of biomarkers.
The measurements included:
• Kidneys, liver, lungs, metabolic and immune systems
• HDL cholesterol, cardiorespiratory fitness, lung function
• Length of the telomeres (protective caps at the end of chromosomes that have been found to shorten with age)
• Dental health like the condition of the gums
• Condition of the tiny blood vessels at the back of the eyes, (which are a proxy for the brain's blood vessels)
• Cognitive function
They looked at the volunteers at age 26, 32 and 38 and found that while most of them aged at a normal pace - one year's worth of physiological changes for each chronological year - some of them aged surprisingly slower or faster.
In fact, researchers calculated, the "biological ages" of the 38-year-olds ranged from 30 to nearly 60 years.
The fastest-aging study participants experienced two to three years of changes with the passage of a single calendar year. They tended to have worse balance and motor coordination and were physically weaker.
Belsky and his colleagues said that these volunteers reported having more trouble with basic tasks like climbing stairs or carrying groceries.
Moreover, those who were aging fast also showed evidence of cognitive decline. Their IQ scores, which according to previous studies have been shown to remain relatively constant throughout a person's life, were lower by age 38.
One particularly interesting finding of the study was that the people who were physiologically older looked older, at least according to Duke undergraduates who were asked to guess their ages from their pictures.
The study, which was funded in part by the National Institute on Aging, is significant because it looked at young adults. Most previous aging research is focused on the second half of the average person's life, in the 50s, 60s, and 70s.
"Our findings indicate 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 researchers wrote. "The science of healthspan extension may be focused on the wrong end of the life span; rather than only studying old humans, geoscience should also study the young."
Belsky said that in the future a person's biological age could serve as a simple measure of a person's health that may help patients better understand the battery of numbers they get from their doctors today.
"A single number would be much easier to process," Belsky said.
He said the measurement could also help with assessing the health of a community. Right now we look at things like disease end points, new diagnoses, hospitalizations and death, but all are imperfect because they don't give us a picture of the health of a whole person.