A new study from researchers at Columbia University is the first to offer quantitative evidence
linking psychological stress to graying hair in people.
And while it may seem intuitive that stress can accelerate graying, the researchers were
surprised to discover that hair color can be restored when stress is eliminated, a finding
that contrasts with a recent study in mice that suggested that stressed-induced gray
hairs are permanent.
The study, published in the journal eLife has broader significance than confirming age-old
speculation about the effects of stress on hair color.
The researcher says that understanding the mechanisms that allow ‘old’ gray hairs
to return to their ‘young’ pigmented states could yield new clues about the malleability
of human aging in general and how it is influenced by stress.
Also, the researcher says that their data add to a growing body of evidence demonstrating
that human aging is not a linear, fixed biological process but may, at least in part, be halted
or even temporarily reversed.
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.
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 crystallize these exposures
into a stable form.
Though people have long believed that psychological stress can accelerate gray hair, scientists
have debated the connection due to the lack of sensitive methods that can precisely correlate
times of stress with hair pigmentation at a single-follicle level.
The researchers developed a new method for capturing highly detailed images of tiny slices
of human hairs to quantify the extent of pigment loss (graying) in each of those slices.
Each slice, about 1/20th of a millimeter wide, represents about an hour of hair growth.
The researchers analyzed individual hairs from 14 volunteers.
The results were compared with each volunteer’s stress diary, in which individuals were asked
to review their calendars and rate each week’s level of stress.
The investigators immediately noticed that some gray hairs naturally regain their original
color, which had never been quantitatively documented.
When hairs were aligned with stress diaries, striking associations between stress and hair
graying were revealed and, in some cases, a reversal of graying with the lifting of
stress.
The researcher says that 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.
To better understand how stress causes gray hair, the researchers also measured levels
of thousands of proteins in the hairs and how protein levels changed over the length
of each hair.
Changes in 300 proteins occurred when hair color changed, and the researchers developed
a mathematical model that suggests stress-induced changes in mitochondria may explain how stress
turns hair gray.
We often hear that the mitochondria are the powerhouses of the cell, but that’s not
the only role they play.
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 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 follicle.
The researcher says that their data show that graying is reversible in people, which implicates
a different mechanism.
Mice have very different hair follicle biology, and this may be an instance where findings
in mice don’t translate well to people.
Reducing stress in your life is a good goal, but it won’t necessarily turn your hair
to a normal color.
Based on their mathematical modeling, the researchers think hair needs to reach a threshold
before it turns gray.
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 gray.
But reducing stress in a 70-year-old who’s been gray for years will not darken their
hair or increasing stress in a 10-year-old will not be enough to tip their hair over
the gray threshold.