Researcher ContactClaude Gronfier Chargé de recherche Inserm Unité Inserm 846 "Institut cellule souche et cerveau"
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Researchers at Inserm, led by Claude Gronfier (Inserm Unit 846: Stem Cell and Brain Institute), have, for the first time, conducted a study under real conditions on the body clocks of members of the international polar research station Concordia. The researchers have shown that a particular kind of artificial light is capable of ensuring that their biological rhythms are correctly synchronised despite the absence of sunlight. The full significance of this result can be appreciated with the knowledge that disturbance to this biological clock causes problems with sleep, alertness, cardiovascular problems and even depression.
These results, published in Plos-One, could be rapidly transformed into practical applications for working environments that are dimly to moderately lighted (polar research stations, thermal and nuclear power stations, space missions, offices with no windows, etc.). They could enable the design of lighting strategies intended to maintain the health, productivity and safety of staff.
For the first time, scientists have been able to study under real conditions how various types of artificial light influence the way the biological clock behaves in situations where the natural light is insufficient. For nine weeks of the polar winter (no sunlight during the day), the staff of the international polar station Concordia were alternately exposed to a standard white light and a white light enriched with blue wavelengths (a particular kind of fluorescent light that is perceived as white by the visual system). For the purposes of the study, the researchers asked the staff not to change their day-to-day habits, particularly the times they got up and went to bed.
Once a week, samples of saliva were taken in order to measure the rates of melatonin (central hormone) secreted by each of the individuals.
The details of the results show that an increase in sleep, better reactions and more motivation were observed during the ‘blue’ weeks. Moreover, while the circadian rhythm tended to shift during the ‘white’ weeks, no disturbance in rhythm was observed during the ‘blue’ weeks. In addition, the effects did not disappear with the passage of time.
The effectiveness of such lighting is due to the activation of melanopsin-containing ganglion cells discovered in 2002 in the retina. These photoreceptor cells are basically essential to the transmission of light information to a large number of so-called ‘non-visual’ centres in the brain.
What should be remembered from this work is as follows:
Composition of standard white light and light enriched with blue
On the left, the spectrum of the white light consists of roughly equal parts of red and green (about 40%), then blue (12%) and infra-red waves (4%). On the right, the proportions are different (42% blue and 14% red). Nevertheless, with the naked eye, a human will perceive a white light in both cases.
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