Researchers at Inserm have conducted a study under real conditions on the body clocks of members of the international polar research station Concordia. Led by Claude Gronfier (Inserm Unit 846: Stem Cell and Brain Institute), the researchers have shown that a particular kind of artificial light—short wavelengths (blue) light—is capable of ensuring biological rhythms are correctly synchronized 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, the researchers say.
These results, published in PLOS ONE, could be rapidly transformed into practical applications for working environments that are dimly to moderately lit, including offices without windows, polar research stations, thermal and nuclear power stations, and space missions. They could enable the design of lighting strategies intended to maintain the health, productivity, and safety of staff, the researchers say.
Located deep within the brain, the body clock consists of 20,000 neurons whose pulsatile activity controls the sleep/wake cycle, body temperature, heart rate, the release of hormones, etc. The cycle determined by the internal clock lasts spontaneously between 23.5 and 24.5 hours, depending on the individual. In order to function correctly, it refers to the signals that it receives from the external world and that it interprets as indicators for the purpose of constantly resynchronizing itself every 24 hours.
For 9 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.
On a general level, the study shows that an optimized light spectrum enriched with short wavelengths (blue) can enable the circadian system to synchronize correctly and non-visual functions to be activated in extreme situations where sunlight is not available for long stretches 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” centers in the brain.
“Although the benefits of blue light for the biological clock have already been demonstrated in the past, all the studies were conducted under conditions that are difficult to reproduce under real conditions,” says Gronfier in a release. “Beyond a professional context, we envisage this strategy more broadly as a practical approach to the treatment of problems with the circadian rhythms of sleep and non-visual functions in conditions where the lighting is not optimal.”
Gronfier says the research takeaways are as follows:
- White light enriched with blue is more effective than the standard white light that is found in offices and homes for the purpose of synchronizing the biological clock and activating the non-visual functions that are essential to the correct functioning of the body. It is thus not necessary to use blue lights or even LEDs to obtain positive effects.
- The effectiveness of this light does not require high levels of illumination as is the case in the photic approaches to the treatment of problems with the circadian rhythms of sleep or seasonal affective disorder (5,000 to 10,000 lux are recommended in these approaches).
- Due to its effectiveness, this light does not require sessions of exposure to it (between 30 minutes and 2 hours are recommended in the photic approaches previously mentioned). In this study, the light comes from the lighting of the rooms being used.
- The effects of this lighting approach do not disappear with the passage of time. This study shows that the effects are the same from the first to the ninth week of observation.