WE BECOME biologically older when our bodies are under stress, but younger again when we recover, according to a study that analysed people's DNA when they had emergency hip surgery, had severe covid-19 or were pregnant.
“This recovery suggests we have the machinery to be able to rewind the clock back at least a little bit,” says James White at Duke University in North Carolina, who co-led the study with Vadim Gladyshev at Harvard University.
We normally measure age by the number of birthdays – so-called chronological age. But people can be biologically older or younger than their chronological age depending on factors such as whether they smoke. We can measure this with “epigenetic clocks” that analyse patterns of markers on DNA called methyl groups that correlate with age.
White, Gladyshev and their colleagues used these clocks to assess the impact of three types of stressful event on biological age. They analysed DNA from blood samples that were collected at multiple points in time from participants in previous studies.
In the first analysis, the team found that the biological age of nine people with an average age of 81 rapidly rose after emergency surgery to repair a broken hip, but returned to pre-surgery levels over the following week.
Next, the team measured the biological age of 29 people with an average age of 60 while they were hospitalised with covid-19 and after they were discharged. The biological age of female participants fell after discharge, but that of male participants didn't, possibly because men take longer on average to fully recover from the disease, says White.
Finally, the team compiled data from four studies that included more than 200 women who were pregnant, which is known to put stress on the body. Their biological age increased over the course of the pregnancy, but, by six weeks after delivery, it had returned to below the levels seen in early pregnancy. No transgender men or non-binary people were included in this part of the study.
The researchers also used epigenetic clocks to measure the biological age of mice before, during and after pregnancy and found the same pattern (Cell Metabolism, doi.org/gr5z88).
The idea that biological ageing speeds up during stressful events but reverses afterwards is consistent with a previous study that found that people's grey hairs sometimes regain their original colour after they recover from psychologically stressful events.
However, Luigi Fontana at the University of Sydney in Australia says that even though there may be short-term fluctuations in biological age, the trend is still to become older. “Your grey hair may regain some colour, but it isn't going to revert to the hair you had as a 10-year-old,” he says.
Nevertheless, now we know that biological ageing can at least reverse slightly, it raises the possibility of being able to develop therapeutics to drive this reversal further, says White.