Adults who look older than their years may be ageing at an accelerated pace, new research suggests.
A study of 38-year-olds in New Zealand found their "biological age" - the state of their organs, immune system, heart health and chromosomes - ranged from as young as 30 to as old as 60 years of age.
And the older their biological age, the older they looked, the researchers added.
"We looked at key markers for the integrity and health of different organs in the bodies of relatively young adults, in order to detect how their bodies were actually aging," said study author Daniel Belsky, an assistant professor of medicine at Duke University's School of Medicine and Center for Aging, in Durham, N.C.
"What we found is a clear relationship between looking older on the outside and ageing faster on the inside," said Belsky. "And also that it's possible to measure the kind of ageing process in young people that we usually only look for in old people."
For most young adults, biological age proceeds in sync with chronological age, the international research team found. But genetic and environmental influences can cause your biology to rack up signs of age much faster - or much slower - than your birth date might predict.
The findings were published July 6 in the Proceedings of the National Academy of Sciences.
The study authors noted that by 2050 the population of men and women aged 80 and older will hit 400 million globally, more than triple the current number.
That trend, the researchers said, highlights the importance of finding ways to spot signs of aging early in life, to fashion therapies that can prolong healthy living by preventing the onset of age-related disease.
The study team focused on roughly 1,000 men and women who had been participating in an ongoing New Zealand study since their birth in 1972-1973.
In 2011, the participants, then 38, underwent tests of kidney function, liver function, lung capacity and metabolic and immune system strength. Cholesterol, blood pressure, dental status, eye structure and heart health were also assessed, as was the length of chromosomal caps known as telomeres. Telomeres are known to shorten with age.
The researchers found a variance of up to 30 years in the different participants' biological age, although all were still free of any age-related disease.
The team conducted a secondary analysis, comparing biomarker information collected in 2011 with information gathered six and 12 years earlier.
That showed that between ages 26 and 38 most participants aged at an equal biological pace. But some were gaining three biological years for every one chronological year. Still others had essentially stopped getting older, as their biological age was essentially on "pause."
What's more, the older their biological age, the worse they fared on physical and mental acuity tests.
The fast-agers showed worse balance and poorer motor coordination, and reported having more trouble with tasks such as climbing stairs or carrying groceries.
"This showed that already early in life we can see symptoms of advanced age in young people, symptoms that correspond to declining physical and cognitive function, long before age-related disease actually develops," Belsky said.
Dr. Rosanne Leipzig, a professor of geriatric and palliative medicine at Icahn School of Medicine at Mount Sinai in New York City, described the investigation as a "landmark" effort to better understand the ageing process.
"If we can identify why some people have more rapid biological ageing, it may be possible to intervene and reduce the risks of complications and diseases related to ageing," said Leipzig, who was not involved in the study.
Belsky said the findings might propel scientists in a new direction. "This can help us as we start to come around to the idea that instead of trying to prevent individual illnesses like heart disease or cancer," he said, "we need to try to find ways to treat the common cause of all these things: ageing."
The research was funded by the New Zealand Health Research Council, the U.S. National Institute on Ageing, the U.K. Medical Research Council, the Jacobs Foundation and the Yad Hanadiv Rothschild Foundation.