In a recent study, researchers from Salk Institute for Biological Studies, the University of Southern California, and the University of California Irvine discovered the hair of mice has a circadian clock: a 24 hour cycle of growth followed by restorative repair. They worked out the precise timing of the hairs’ circadian clock, uncovering the biology behind it in the molecules that tells hair when to grow and repair damage. This information was then studied to reveal the hair loss effects from medical treatments like targeted radiation.
The researchers tested the circadian clock using radiotherapy on two groups of mice: one group received the therapy in the morning and the other at night. The mice who received the therapy in the morning lost 85 percent of their hair. However, the mice who received radiation therapy in the evening only lost 17 percent.
The reason for this drastic disparity in the percentage of hair loss in nighttime radiation treatment mice and those treated in the daytime begins by understanding the process of radiation itself. Radiotherapy damages DNA in cells that divide rapidly, such as cancer cells. The mice’s hair loss was caused because DNA damage to hair cells from radiotherapy occurred during a time when the hair was in a non-repair portion of the circadian cycle (i.e., the radiation delivered in the mornings was not repaired until the evening; however, the hair on the mice treated at night was already mid-repair. )
The study’s evidence makes researchers suspect that human hair loss from chemotherapy and radiotherapy may be minimized if treatments are administered late in the day. However, scientists have not yet tested the theory on human models. Researchers have made the preliminary comparison of the mouse hair circadian clock to the male “5 o’clock shadow,” which only grows in the day. There is no 5 AM shadow if you shave at night.
Investigative research on the circadian rhythms of the body indicate that they are present in body organs and tissues—which could mean they could be utilized to time drug therapy for maximum benefit. Notably, researchers found that cancer cells do not have circadian clocks because they are constantly dividing. The study and continuing research has potential to change the way therapy is given and diminish the drastic hair loss effects that often accompany it.
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