Joint ESRS-SRS Seminar Spring Edition – Circadian Biology: Converging Pathways from Bench to Bedside – 20 March, Q&A Highlights (Part 2)

PZ: There is no easy way to get accurate melatonin levels. You may consider inferring DLMO from actigraphy and light exposure timing.

Cheng P, Walch O, Huang Y, Mayer C, Sagong C, Cuamatzi Castelan A, Burgess HJ, Roth T, Forger DB, Drake CL. Predicting circadian misalignment with wearable technology: validation of wrist-worn actigraphy and photometry in night shift workers. Sleep. 2021 Feb 12;44

Murray et al..Andrew J. K. Phillips. Scientific Reports volume 11, Article number: 10878 (2021)

PZ: If you mean countries with low amounts of daylight, then consider light devices that emit solar similar light wavelength.

PZ: Absolutely. I think modelling that allows us to look at phase relationships (between external with internal, but also among internal rhythm at different times of the day) will be more informative that phase of a single rhythm.

MM: Oh that is an interesting question, indeed! That would hypothesise non-sinusoidal or unusual shaped oscillations which is likely but regarding which we have little experience. I recall that Päl Westermark has been working on this problem (how to evaluate and analyse e.g. sawtooth oscillations). See here: doi: 10.1177/0748730414553029 Further, he has developed other methods. How to think of the basis for such an idea? When you look at phase plots for transcriptomes, you often see a dominant phase where the majority of genes are phased within 3-6 h of each other. But then there can be a second peak and if that is regulated by a different clock-regulated output pathway, perhaps even a different zeitgeber, then it is possible to imagine that one set is on one phase while the other wavers.

PZ: It will depend on what you intend to use this data for-as far as accuracy, scalability, light accuracy etc. There are research grade actigraphy/light sensors, as well as consumer (like Oura-which has been used mainly for sleep-but also can infer sleep wake and cardiovascular rhythms. For people with diabetes -there are ambulatory glucose sensors and for cardiovascular disorders, heart rate and blood pressure. All of these can be used outside of the clinic for many days.

MM: I guess that if you hypothesise that most people’s chronotypes are within a few hours of each other, then you can apply the methods used by among others Chen, … and McClung (https://doi.org/10.1073/pnas.150824911) broadly. With a large enough N, you can see markers that are rhythmic with a high enough amplitude. All of these devices/tests will have time stamps, thus it will give a nice time series for analysis.

MM: There is epidemiological level data showing more social jetlag at the extreme western side of the time zone and higher incidences of some cancers also at the western edges. For an individual, it is not critical, except life is easier on the eastern side where the alarm clock is cutting off less sleep. But the increased risk for certain conditions is significant and measurable. See here for instance: doi 10.3109/07420528.2010.541312.

MM: Practice regular behaviours (same time getting up and going to bed), make your days very light and your nights very dark and quiet. SO this may sound like folk wisdom, but I am describing increasing the amplitude of your zeitgeber cycles (light/dark and feeding/fasting), which should stabilise your circadian clock to a given phase.