Latest insight – How the human biological clock responds to light

July 18, 2022

A new publication in PNAS by BioClock researchers shows how the SCN responds to different colors of light. In the remarkable study, led by BioClock coordinator Joke Meijer (Leiden University Medical Center, LUMC), it was discovered that not only blue light triggers activity of the biological clock. This is a groundbreaking discovery because until now it was generally thought that blue light stimulates our biological clocks the most. Now Meijer and colleagues found that other colors can affect the clock as well.

“This means, for example, that the use of blue light filters in the evening is therefore not sufficient to avoid disturbance to our sleep rhythm!” says Meijer.

Robin Schoonderwoerd, PhD candidate at LUMC executed the study in which she used MRI scans to identify and image the human SCN. Since the SCN is only 2 mm3, they had to increase the spatial resolution of the area as such to be able to measure it. This is unique because the SCN now is the smallest brain area ever measured with the MRI scan technique.

Schoonderwoerd, Meijer and colleagues state that this study offers new insights into the effect of light on the biological clock. For instance, current strategies to prevent harmful effects in the evening must be revised. “Because we now know that that multiple colours can affect our internal clock, we advise to also dim the light in the evening, instead of just filtering blue light out. The good news is this works the other way around: all colours are effective to stimulate the clock during the day, which is especially important for nursing homes, clinical settings and even for children’s bedrooms.”

The full article can be found here.


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The BioClock Consortium is funded by the NWA-ORC programme of the Dutch Research Council (NWO; project number 1292.19.077).