Legend has it that Marie Antoinette's hair turned gray overnight just before her decapitation in 1791. While the legend is inaccurate — hair already grown out of the follicle doesn't change color — a new study from researchers from Columbia University Vagelos College of Physicians and Surgeons is the first to provide quantitative evidence linking psychological stress to graying hair in humans. And while it may seem intuitive that stress can accelerate graying, the researchers were surprised to find that hair color can be restored when stress is eliminated, a finding that contrasts with a recent study in mice that suggested that stress-induced gray hair. be permanent.
The study has broader meaning than confirming age-old speculation about the effects of stress on hair color, says 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 by which 'old' gray hairs return to their 'young' pigmented state could provide new clues about the malleability of aging in humans in general and how it is affected by stress,” says Picard.
“Our data adds to a growing body of evidence showing that human aging is not a linear, fixed biological process, but can be at least partially halted or even temporarily reversed.”
Studying hair as a way to investigate aging
“Just as the rings in a tree trunk contain information about the past decades in a tree's life, our hair contains information about our biological history,” says Picard. “When hairs are still under the skin as follicles, they are subject to the influence of stress hormones and other things that happen in our minds and bodies. Once hairs grow out of the scalp, they harden and these exposures permanently crystallize into a stable shape. ”
While people have long believed that psychological stress can accelerate gray hair, scientists have debated the link due to the lack of sensitive methods that can precisely correlate times of stress with hair pigmentation at a single follicle level.
Splitting hair to document hair pigmentation, Ayelet Rosenberg, lead author of the study and a student in Picard's lab, developed a new method for capturing highly detailed images of small pieces of human hair to measure the degree of pigment loss (greying) in each of them. to quantify those hairs. Each piece, about 1/20th of a millimeter wide, represents about an hour of hair growth.
“If you use your eyes to look at a hair, it looks like it's the same color everywhere, unless there's a big transition,” says Picard. “Under a high-resolution scanner, you'll see small, subtle variations in color, and that's what we're measuring.”
The researchers analyzed individual hairs from 14 volunteers. The results were compared to each volunteer's stress diary, in which individuals were asked to review their calendar and rate each week's stress level.
The researchers immediately noticed that some gray hairs naturally regain their original color, which has never been quantitatively documented, says Picard.
When hairs were aligned with stress diaries by Shannon Rausser, the paper's second author and a student in Picard's lab, striking associations between stress and hair graying were revealed and, in some cases, a reversal of graying with the removal of hair. stress.
“There was one person who went on vacation and five hairs on that person's head went dark again during the vacation, synchronized in time,” says Picard.
Blame the mind-mitochondria connection
To better understand how stress causes gray hair, the researchers also measured the levels of thousands of proteins in the hairs and how the protein levels changed over the length of each hair. Changes in 300 proteins occurred as hair color changed, and the researchers developed a mathematical model that suggests that stress-induced changes in mitochondria may explain how stress makes hair gray.
“We often hear that the mitochondria are the powerhouses of the cell, but that's not the only role they play,” says Picard. “Mitochondria are actually like little antennae in the cell that respond to a number of different signals, including psychological stress.”
The mitochondria connection between stress and hair color differs from that discovered in a recent study of mice, which found that stress-induced graying was caused by an irreversible loss of stem cells in the hair follicles.
“Our data shows that aging in humans is reversible, which involves a different mechanism,” said co-author Ralf Paus, PhD, a dermatologist professor at the University of Miami Miller School of Medicine. “Mice have a very different biology of hair follicles, and this could be a case where findings in mice don't translate well to humans.”
Hair pigmentation only possible for some
Reducing stress in your life is a good goal, but it won't necessarily give your hair a normal color.
“Based on our mathematical models, we think hair must reach a threshold before it turns gray,” says Picard. “In middle age, when the hair gets close to that threshold due to biological age and other factors, stress will push it over the threshold and transition into gray.
“But we don't think that reducing stress in a 70-year-old who has been gray for years will darken his hair or that increasing stress in a 10-year-old won't be enough to get his hair over the gray threshold.” fall.”
