“Don’t stress, you get gray hair.” How many times have we heard this? It is a belief strongly rooted in the popular imagination, but there are few scientific studies that clearly demonstrate this relationship.
We know that the appearance of gray hair is a natural consequence of the aging process, and that some people experience premature gray hair due to genetic components and even as a consequence of some diseases or nutritional deficiencies. Now, a new study done in mice and published in Nature has found the connection between stress and hair bleaching. But let’s go in parts.
Why are gray hairs coming out?
Hair color is determined by cells called melanocytes, which are the ones that produce the corresponding pigments. In turn, melanocytes come from a specific type of stem cells that are located in the hair follicle.
As we age, the melanocyte stem cells are depleted, producing a progressive loss of pigments. In this way, the new hair produced in the regeneration process loses color.
To relate this mechanism of gray appearance, mediated by the depletion of melanocyte stem cells, with the physiological response that triggers stress in the body, the researchers had to descend from the larger-scale processes to the more local ones. And, since stress is a factor that affects the whole body, the question was to deduce what specific mechanism was the one that connected it with hair pigmentation.
Neither autoimmune response nor cortisol
The first hypothesis put forward was that stress causes an autoimmune attack on pigment-producing cells. However, in a test with mice lacking immune system cells, the scientists observed no differences from the control group, and mice subjected to physiological stress were not spared gray either.
Another of the failed tests tried to link graying with the ‘queen hormone’ of stress: ” We think that cortisol could play an important role ,” explains Chieh Hsu, a researcher at Harvard and one of the authors of the work. “So we removed the adrenal gland from the mice so they couldn’t make it, but there were no differences, and when they were stressed, they still gray.”
The key is in the norepinephrine
After rejecting several hypotheses, the team of researchers finally managed to hit the mark. As they were able to show, the activation of the sympathetic nervous system, involved in automatic responses to stress, seems to enhance the loss of stem cells from melanocytes that leads to the appearance of gray hair.
And it is that the stem cells of melanocytes have specific receptors for norepinephrine, another of the neurotransmitters involved in the flight response to a situation of stress or danger. This molecule produces a superactivation of the melanocyte stem cells, and as a consequence the reservoir is depleted prematurely and the hair turns white.
When scientists blocked these receptors for norepinephrine, the gray hair stopped appearing as a result of stress. Furthermore, the results revealed that the areas with more sympathetic innervation were more prone to graying. “When we started this line of research, I already expected that stress would produce negative effects on the body, but its impact goes far beyond what I imagined.”, Hsu explains. “ After a few days, the mice in the experiment lost all the stem cells that regenerate the pigment. The damage is permanent ”, he concludes.
The evolutionary advantages of having white hair
Digging into this topic a bit, one wonders whether stress-induced premature aging could have an evolutionary advantage. As Shayla A. Clark and Christopher D. Deppmann explain in a review of the article offered by the journal Nature, gray hair could be associated with greater experience and leadership. For example, the back of male mountain gorillas ( Gorilla beringei beringei ) becomes gray when they reach adulthood (hence the nickname ‘silver back’), and at that time they can occupy the upper link of the hierarchy . An animal that has had to deal with many stressful situations throughout its life, and has survived, may have deserved that leadership position.
Applications beyond anti-gray therapies
“The neurons of the peripheral nervous system modulate the function of organs and blood vessels, as well as the mechanisms of immune response, but less was known about their role in the regulation of stem cells,” says the researcher. ” We have shown that neurons can control stem cells and their functions, and explain how they interact at the cellular and molecular level to link stress with aging hair .”
Perhaps many find it hopeful that this research can open up new avenues for the development of hair treatments that delay the appearance of the dreaded gray hair, something that is still far away because, remember, it is a very basic and preliminary research.
However, beyond this application, the research marks a line to continue to deepen the understanding of how stress affects, through the modulation of stem cells, other organs and tissues, and thus seek to block its most damaging effects on the general health.
Referencia: Zhang et al. 2020. Hyperactivation of sympathetic nerves drives depletion of melanocyte stem cells. Nature doi.org/10.1038/s41586-020-1935-3
