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What a stellar interview!
One question I was left with is regarding chronotypes. Dr. Walker mentioned that many people think they are of one chronotype, but genetically they are not.
How does someone determine which chronotype they are? Is this identifiable in standard genetic testing?
There are certain genes that code for chronotype, also named ‘clock genes’ as they activate processes in our biological clock. These are mainly the genes PER1, PER2 and PER3 (which are most often investigated in scientific research). Chronotype itself, however, is examined with a questionnaire in most scientific studies. A famous (and validated!) questionnaire used for is the Munich Chronotype Questionnaire (MCTQ). You can find the questionnaire and calculation of the score here: https://www.thewep.org/documentations/mctq The score is based on self-reported average bedtimes, sleep times, and wake times on working days and free days.
That said, I do not fully agree with what Matthew Walker is saying about “you cannot do something about your chronotype, it is genetic”. I totally believe that there is a genetic component in your chronotype, but based on what I have read (I am a postdoc researcher studying the effects of light on alertness, performance, and sleep myself) I think the environment is basically creating ‘late chronotypes’ nowadays. Take a look at this study for example: https://www.sciencedirect.com/science/article/pii/S0960982213007641 They investigated chronotypes (circadian phase) in people who were ‘forced’ to go camping under natural light only for one week (no artificial light sources were allowed or present). The timing of the internal clocks of the late chronotypes in this study became more similar to the internal clocks of the early chronotypes, just after one week of camping under natural light exposure. I think the variation in chronotypes would be much smaller if we would have continued living under natural light exposure only. Light pollution at night and too low levels of light during the day are creating late chronotypes.
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