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A study by Salk Institute, recently published in the Proceedings of the National Academy of Sciences, found that hair follicles rest during the circadian cycle. The study was preformed on mice, and showed dramatic reduction in hair loss by delivering gamma radiation when follicular cells were least rapidly dividing. During radiation and chemotherapy, the fast growing cells—those that rapidly divide, are the cells targeted to be killed. The problem with this is, normal rapidly dividing cells are killed along with cancerous ones, creating all sorts of unpleasant side effects like hair loss, nausea and loss of taste to name a few.
It isn’t known if hair of mice and men share the similar circadian clock, but it is known that facial hair on men grows during the day, thus the 5 o’clock shadow. In a Salk news release, Satchidananda Panda, a Salk Institute researcher said, “There’s no 5 a.m. shadow if you shave at night.”
The study stated, “These findings parallel daily changes in sensitivity of epidermis to external UV genotoxicity and can have important implications for designing radiation therapy and possibly chemotherapy protocols. More immediately, radiation treatment can be administered during the mitotic depression phase to minimize hair loss said effect.”
Some cancers have shortened circadian cycles that would need to be factored into treatment by cancer chronotherapy. In the study, mice were given 400 -700 rads. One group received radiation during a circadian time known as CT50 (when their hair cells were most actively dividing.) The other group of mice received radiation at CT58 (when their hair cells were least actively dividing.)
The study showed a dramatic difference between the two groups. The group irradiated when their cells were actively dividing were almost completely bald. The other group maintained most of their hair. Once levels of rads increased to 600 or more, both groups of mice had nearly total hair loss, which the study suggests was caused by prolonged effects of high cytotoxic radiation levels.
A third group of mice was tested to see if circadian cycles were truly responsible for the differences. This group consisted of mutant mice whose circadian cycles had been disrupted. At 500 rads, this third group had nearly total hair loss, irrelevant of the time of day they were irradiated.
Source: U-T San Diego, May 21, 2013