Any school or university reunion - when the 'class of '85' all meet up again - will tell you that each of us seems to age differently and at a different rate. The value of extremely large, well-done, longitudinal studies is that they can pick apart this phenomenon and study it properly and infomatively. Avshalom Caspi and Terrie Moffett have been at the heart of this study for decades and have just released their findings on differential aging. As this article says: "The researchers developed a method to determine the pace of ageing in individuals by looking at a range of biomarkers – including blood pressure and gum health. The study participants, all aged 38, varied widely in "biological age" and those ageing more quickly also looked older and reported more health problems."
This companion article in Medical Express adds further detail on how the study was done, according to another of its authors, Dan Belsky:
""We set out to measure aging in these relatively young people," said first author Dan Belsky, an assistant professor of geriatrics in 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."
Belsky said the progress of aging shows in human organs just as it does in eyes, joints and hair, but sooner. So as part of their regular reassessment of the study population at age 38 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, which are a proxy for the brain's blood vessels. Based on a subset of these biomarkers, the research team set a "biological age" for each participant, which ranged from under 30 to nearly 60 in the 38-year-olds.
The researchers then went back into the archival data for each subject and 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."
The source paper for these articles, titled "Quantification of biological aging in young adults" is open access in PNAS at the following link