You’re only as old as you feel, the saying goes, but what if different parts of your body aged at different speeds? It turns out they do. A system for studying the age of our bodies has been developed, and it shows that different tissues inside us are effectively different ages. Scientists have used several systems before, such as the levels of hormones in our bodies, to study biological age. But in 2012 Professor Steve Horvath at the University of California, Los Angeles, looked at something new – DNA methylation, a naturally occurring process in which DNA is chemically changed over time.
Horvath analysed the DNA in 8,000 tissue samples from different parts of the body in different people to study these ‘epigenetic markers’. What he found was striking – the amount of methylation in cells from most parts of the body were a good predictor of the person’s age. But there were inconsistencies. Breast tissue, for instance, ages rapidly, whereas muscle ages slowly. The rates of ageing are also different in men and women. “There are many medical implications, from cancer to premature ageing diseases,” Horvath says. It has already been established that tissue that looks significantly younger or older could be cancerous. Horvath’s study found that cancerous tissue has a biological age on average 36 years older than a subject’s actual age.
Could this knowledge help us live longer? “If the epigenetic clock relates to a process that causes ageing, then it would be theoretically possible to slow down ageing by carefully targeting DNA methylation,” says Horvath. But before scientists get to work meddling with methylation, they first needed to establish whether these changes were the cause of ageing or just a byproduct of another process. Now, a 2023 study from the University of Michigan has backed up Professor Horvath’s findings. “Our main aim was… to see whether biological age acceleration as measured from DNA methylation was predictive of health outcomes and mortality,” said research associate professor Jessica Faul. “It turned out that is largely the case. You can use certain DNA methylation markers to predict age and age-related outcomes quite well.”