A new study for the first time provides quantitative evidence linking psychological stress to greying hair in people.
Greying of hair, a phenomenon still poorly understood in humans, first starts in white individuals at 34, while black individuals only start greying around 44. While it may seem intuitive that stress can accelerate greying, the researchers were surprised to discover that hair colour can actually be restored when stress is eliminated, a finding that contrasts with a recent study in mice that suggested that stressed-induced grey hairs are permanent.
The study holds clues to understanding ageing beyond just confirming the old tale about stress and ageing, said the study’s senior author Martin Picard, PhD, associate professor of behavioral medicine (in psychiatry and neurology) at Columbia University Vagelos College of Physicians and Surgeons.
“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,” Prof Picard said.
“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.”
Hair can help understand ageing
“Just as the rings in a tree trunk hold information about past decades in the life of a tree, our hair contains information about our biological history,” Picard said. “When hairs are still under the skin as follicles, they are subject to the influence of stress hormones and other things happening in our mind and body. Once hairs grow out of the scalp, they harden and permanently crystallise these exposures into a stable form.”
Though it has long been believed by people that psychological stress can increase grey hairs, it has remained a matter of scientific debate due to a lack of sensitive methods that can precisely correlate times of stress with hair pigmentation at a single-follicle level.
Splitting hairs to document hair pigmentation
Ayelet Rosenberg, first author on the study and a student in Picard’s laboratory, developed a new method for making high resolution images of tiny slices of human hairs to measure the extent of pigment loss — greying — in each of those slices. Each slice, about 1/20th of a millimetre wide, represents about an hour of hair growth.
“If you use your eyes to look at a hair, it will seem like it’s the same color throughout unless there is a major transition,” Picard says. “Under a high-resolution scanner, you see small, subtle variations in color, and that’s what we’re measuring.”
For the study 14 volunteers were asked to review their calendars and rate each week’s level of stress in a stress diary. Analysing individual hair samples, the researchers compared the results with each volunteer’s stress diary.
Right away, it was noticed that some grey hairs naturally regain their original color, which had never been quantitatively documented, Picard said.
When hairs were aligned with stress diaries, it revealed striking associations between stress and hair greying and, in some cases, a reversal of greying with the lifting of stress.
“There was one individual who went on vacation, and five hairs on that person’s head reverted back to dark during the vacation, synchronized in time,” Picard said.
Blame the mind-mitochondria connection
Measuring levels of different proteins in the hairs and how protein levels changed over the length of each hair, the researchers came up with a model showing that mitochondria were responsible for greying.
“We often hear that the mitochondria are the powerhouses of the cell, but that’s not the only role they play,” Picard said. “Mitochondria are actually like little antennas inside the cell that respond to a number of different signals, including psychological stress.”
The mitochondria connection between stress and hair colour is a different mechanism than found in a recent study of mice, where stress-induced greying was caused by an irreversible loss of stem cells in the hair follicle.
“Our data show that greying is reversible in people, which implicates a different mechanism,” said co-author Ralf Paus, PhD, professor of dermatology at 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.”
Hair re-pigmentation possible only for some
Stress reduction is a good idea, but it won’t necessarily get rid of your grey hairs.
“Based on our mathematical modeling, 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.
“But 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.”
Source: Columbia University Irving Medical Center
Journal information: Ayelet M. Rosenberg et al, Quantitative mapping of human hair greying and reversal in relation to life stress, eLife (2021). DOI: 10.7554/eLife.67437
