The adage “age is just a number” has some scientific truth to it. Not only can a person look or act a different age than they are, but the organs in their body can vary too.
The concept of “biological age” has developed as an alternative to strict chronological age, and researchers who study aging say that it is a better way to assess disease and mortality risk (1). Today, the proportion of older people is higher than it has been at any point in human history; this growth has prompted research into the genes and behaviors that influence biological age.
Although the concept has existed since the mid-20th century, it took advances in sequencing and big data processing to turn biological age into a metric. Scientists now compute biological age by measuring epigenetic changes to DNA (2, 3). This research has focused on body-wide or organ-specific aging, but no one has clocked multiple organ systems at once.
“Your biologic age is the actual rate at which your body is aging,” said Brian Kennedy, a biochemist and director of the Center for Healthy Longevity at National University of Singapore. “But that's led to a different question, which is how does that rate that you can calculate compare to different systems in your body — organs? And are they all aging at the same rate?”
Kennedy led a recent study published in Cell Reports to address these questions (4). He collaborated with scientists in China and Russia to take blood and stool samples, conduct physical exams, and run facial imaging on more than 4,000 adults in Shenzhen. From these samples, the team calculated biological ages specific to each organ system. For example, the age of a person’s liver corresponded with the concentration of various metabolic markers that indicate liver dysfunction, such as bilirubin.
Kennedy and his colleagues found that for any given person, different organ systems aged at different rates. This means, theoretically, that a participant might have the kidneys of a 25-year-old but the skin of a 40-year-old. When correlated with chronological age, the researchers found that cardiovascular age had the lowest variance from chronological age, while liver age varied the most. This finding came as a surprise to Kennedy, who is following up on the research by measuring biological age for the organ systems of Chinese, Malay, and Indian adults.
Unlike other healthy aging studies, this one looked at younger individuals to test whether it might be possible to identify healthy agers before they outlive their peers.
“We know these people exist, but typically we call them centenarians,” Kennedy said. “What this is trying to do is to identify those people earlier, so that we can study them earlier in their lives to figure out what's happening throughout the process, not just, ‘What do they look like at 100?’”
Because centenarians cannot be compared in any meaningful way to “controls,” aging research has instead focused on their children, but their longevity is not always a given (5).
This study “brings a new perspective and advances our understanding of aging,” said Vadim Gladyshev, a biologist at Brigham and Women’s Hospital and Harvard Medical School, who was not involved in the research. The integration of many different metabolite and protein levels into the calculation of each organ’s biological clock, and the use of a large, young cohort represents an exciting trend in the field, he added.
Future studies might look at wider age ranges — both older and younger — to see if these systems continue aging at different rates. But even as processing power to analyze vast amounts of data increases, collecting so many different kinds of samples from thousands of participants is no easy task.
Based on this methodology, research could become even more fine-grained, Gladyshev said. One could conduct a study comparing the aging rate of a single cell’s mitochondria to its nucleus, for instance.
- Kennedy, B.K. et al. Geroscience: linking aging to chronic disease. Cell 159, 709-13 (2014).
- Burch, J.B. et al. Advances in geroscience: impact on healthspan and chronic disease. J Gerontol A Biol Sci Med Sci 69 Suppl 1(Suppl 1), S1-3 (2014).
- Horvath, S. DNA methylation age of human tissues and cell types. Genome Biol 14, 3156 (2013).
- Nie, C. et al. Distinct biological ages of organs and systems identified from a multi-omics study. Cell Rep 38, 110459 (2022).
- Andersen, S.L. et al. Reduced Prevalence and Incidence of Cognitive Impairment Among Centenarian Offspring. J Gerontol A Biol Sci Med Sci 74, 108-113 (2019).