This demonstrates that human biological ageing may not be a fixed process, researchers say.
It’s long been said that stress can turn your hair prematurely grey. A study by researchers at Columbia University Vagelos College of Physicians and Surgeons has provided the first quantitative evidence that this is in fact the case – and not only that, but hair can go back to its original colour if the stress is removed.
“Understanding the mechanisms that allow ‘old’ grey hairs to return to their ‘young’ pigmented states could yield new clues about the malleability of human ageing in general and how it is influenced by stress,” said Dr Martin Picard, Herbert Irving Associate Professor of Behavioral Medicine at Columbia University.
“Our data add to a growing body of evidence demonstrating that human ageing is not a linear, fixed biological process but may, at least in part, be halted or even temporarily reversed.”
In the past, scientists had struggled to quantify the relationship between stress and hair going grey. It’s tricky to keep track of how much stress a person feels at a certain time and compare that with individual hairs.
The team got around this by developing a method that allowed them to study the colour of individual hairs in fine detail. They captured images of tiny slices, each only a fraction of a millimetre wide and representing about an hour of hair growth.
“If you use your eyes to look at a hair, it will seem like it’s the same colour throughout unless there is a major transition,” said Picard. “Under a high-resolution scanner, you see small, subtle variations in colour, and that’s what we’re measuring.”
A group of 14 participants wrote a ‘stress diary’, rating their level of stress each week. The researchers then compared this with the colour data from their hair. The researchers noticed a strong correlation between the stressful periods and hair greying.
They were also shocked to find that some hairs had regained their pigmentation when the stress was lifted. “There was one individual who went on vacation, and five hairs on that person’s head reverted back to dark during the vacation, synchronised in time,” Picard said.
A 2020 study of mice suggested that stress-related greying was an irreversible process caused by the loss of stem cells in hair follicles. However, the researchers believe that the process must be different in humans.
“Our data show that greying is reversible in people, which implicates a different mechanism,” said co-author Prof Ralf Paus of the University of Miami Miller School of Medicine. “Mice have very different hair follicle biology, and this may be an instance where findings in mice don’t translate well to people.”
The team studied the levels of thousands of proteins in the hairs, and found 300 that changed as the hair lost its pigment. They believe these changes are caused by mitochondria, the structures inside the cell that produce most of its energy.
“Based on our mathematical modelling, we think hair needs to reach a threshold before it turns grey,” Picard said. “In middle age, when the hair is near that threshold because of biological age and other factors, stress will push it over the threshold and it transitions to grey.”
Unfortunately, this doesn’t mean that all greying is reversible. “We don’t think that reducing stress in a 70-year-old who’s been grey for years will darken their hair or increasing stress in a 10-year-old will be enough to tip their hair over the grey threshold,” said Picard.