Light therapy is a treatment for certain induced or spontaneous circadian sleep rhythm disorders. Who are the people affected by these disorders and how to treat them?
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The effects of light on the body and on sleep
We get up at approximately the same time, except for the end of sleep, after sunrise in summer and before in winter, and we usually retire after sunset in summer and winter. This is due to the rhythm city of the circadian oscillator or “biological clock” located in the suprachiasmatic nucleus of the anterior hypothalamus (central nervous system structure of only a few centimeters, located on the ventral surface of the brain). The period of this biological clock is slightly greater than 24 hours, exactly 24 hours 18 min. It is daily adjusted to that of the environment thanks to exposure in the morning to light. Acting through the retinohypothalamic bundle between the retina and the hypothalamus.
Circadian rhythm disturbances in waking and sleeping
There are two types, provoked and spontaneous, provoked in the case of shift workers and persons carrying out trans-meridian flights (east-west or west-east), spontaneous in the case of disturbances of the biological clock, delay syndromes, or phase advance of circadian rhythms.
What is happening with these subjects?
1) In the shift worker, the inertia of the circadian wake/sleep rhythm causes his biological clock to tend to remain in phase with environmental synchronizer and adaptation to changes in sleep schedules (the synchronization of sleep (biological clock with environmental synchronizers) requires at least several days during which the subject will still want to sleep at night, while he is at work, and want to be awake during the day when he would like to sleep.
As for the traveler of trans-meridian flights, his biological clock is no longer in phase with the local synchronizers of the environment at his place of arrival, in phase advance during a flight towards the west (Paris-Los Angeles) and late in phase during an eastward flight (Paris-Hong Kong), and as in the previous case, it will take several days for its biological clock to synchronize with the synchronizers of the new environment, hence a generalized discomfort while waiting for re-synchronization.
2) In subjects with spontaneous circadian sleep rhythm disturbances, the biological clock lags behind the environmental synchronizer in the case of delayed sleep phase syndrome, subjects fall asleep at a late hour of the night and wake up in the late morning or early afternoon, or ahead of the environmental synchronizer in the case of advanced sleep phase syndrome, with
subjects falling asleep at the end of the day. ‘afternoon and waking up around 4 or 5 in the morning
How to treat these disorders?
1) In the former, by light
Taking into account the action of light on the biological clock via the retina and the retinohypothalamic bundle, lightly applied at a certain point in the 24 hours will be able to accelerate the re-synchronization of the biological clock with the environment synchronizers:
In the case of the night worker, exposure to light during the night, and protection against the light on return home and before going to bed in the morning are recommended.
In the case of the trans-meridian traveler, we recommend exposure to sunlight upon arrival at the place of destination that is to say not to sleep when it is daylight.
2) In the latter, by light therapy
Light therapy corresponds to exposure to bright light (= 2000 lox) delivered by special lamps. Exposure occurs in the morning in the subject with delayed sleep phase syndrome and in the evening in the subject with advanced sleep phase syndrome. The time and duration of exposure to light must be calculated carefully to avoid an effect opposite to the desired effect.
If light therapy has already proven its worth, it is however necessary to remain vigilant, especially for lamps, which are still the most used. Watch out for scams! It is important to pay attention to the quality of the product: check that the CE 0459 logo appears on the device. If it does not appear, the lamp is not considered a light therapy lamp by the European community. Some companies offer lamps without an efficient filter or without light diffusions, such as the small blue and white light therapy LEDs. If these lamps have been very successful, they are nevertheless really harmful to the eyes. Also, pay attention to the light therapy application on smartphones: it is not effective and the creators have been condemned.
