A research team from Charité – Universitätsmedizin Berlin in Germany recently developed a new method that can read the time status of the human body’s internal biological clock with just a few hairs, thereby determining an individual’s “chronotype” and paving the way for “circadian medicine” that practices medicine based on circadian rhythms.
Researchers say that most people only realize its existence when their biological clock is disrupted, such as when switching to daylight saving time or experiencing jet lag after a long trip. The feeling of being groggy and out of state is the result of the body's approximately 24-hour rhythm being out of sync with the outside world. However, the biological clock goes far beyond just affecting sleep. It also regulates hormone secretion, digestive function, body temperature changes, and even changes the metabolism and efficacy of drugs in the body. In the treatment of certain diseases, differences in administration time may directly affect the efficacy.
"For example, studies have shown that certain cancer immunotherapies have significant differences in their efficacy when administered at different times of the day." Professor Achim Kramer, head of the Chronobiology Division of the Department of Anesthesia and Critical Care Medicine at Charité, pointed out, "This is likely because - like most organs - the immune system also follows an approximately 24-hour rhythm, and this rhythm is not the same between different individuals." The emerging rhythm medicine is trying to incorporate this kind of personalized time information in diagnosis and treatment.
At present, a major bottleneck in related fields is: how to measure an individual's biological clock time in a simple way. The current "gold standard" is to collect saliva under low-light conditions for several hours to measure the secretion time point of the so-called "dark hormone" melatonin. This process must be completed in the laboratory, and the operation is complicated and difficult to promote on a large scale.
The alternative proposed by Cramer's team is much simpler: reading the biological clock through hair follicle cells. The researchers detected the expression activity of 17 genes related to or regulated by the molecular clock from a small number of hair root cells, and used an algorithm to analyze the overall expression pattern of these genes to calculate the specific "time point" of the subject's own 24-hour rhythm, and only required one sampling to complete. In a study of about 4,000 participants, the hair-testing method was nearly as accurate as standard laboratory methods in assessing circadian rhythms, but was much simpler to perform.
"Hair analysis is easier to perform, which is where this approach is most valuable," Kramer said. The research team has verified this solution in a large sample: more than 4,000 participants collected hair samples at home and sent them to the laboratory. The results prove that the method is expected to be widely used in the population.
This study also systematically revealed the multiple factors that influence the timing of the biological clock and used biological data to confirm the patterns observed in past questionnaire surveys. Research shows that age is one of the important variables - people in their mid-20s fall asleep about an hour later on average than people over 50. Gender differences are also reflected: women's internal time is slightly earlier than men's, but the difference is only about 6 minutes, much smaller than previous estimates based on questionnaire data. Still, researchers believe gender affects the circadian clock because other studies have shown that sex hormones regulate biological rhythms.
Overall, an individual's diurnal pattern is shaped by multiple factors. "Genetic predisposition, age, gender and lifestyle all play a role, so differences in internal clocks between people can be quite significant," Cramer explains. In addition, a rather unexpected finding is that the impact of lifestyle is greater than expected: the data shows that the internal biological clock of subjects with regular jobs is about half an hour earlier on average than that of unemployed people.
In the next step, the research team plans to standardize this hair detection technology so that it can be applied as a routine laboratory project so that it can be promoted in clinical situations, such as for sleep consultation or assessment of abnormal sleep patterns, making rhythm medicine more operable. The researchers also hope to use this method to test whether arranging treatment time according to the individual's biological clock can indeed improve the efficacy and reduce side effects, which is more advantageous than treatment methods that do not consider time factors at all.
According to reports, this research was published in the Proceedings of the National Academy of Sciences (PNAS), and the paper is titled "HairTime: A noninvasive assay for estimating circadian phase from a single hair sample." In order to promote the transformation of results, Charité Medical School has hatched a start-up company BodyClock Technologies GmbH to market the test. Professor Kramer is one of the company's shareholders and patent holders; the company is also responsible for the data collection of approximately 4,000 samples in this study. Part of the research work was completed within the framework of the collaborative research center "Basics of Rhythm Medicine" (TRR 418) funded by the German Research Foundation (DFG).