We have shown that light levels influences the life in animals and humans immensely. Scientists have performed experiments to determine how animals will react if they are deprived of light. Of particular interest was to determine, whether they can perceive the seasons in the absence of light. These studies have shown that, the animals perceived the arrival of seasons without the aid of the light. This result led them to the conclusions that the animals, and humans too, possess a biological clock in their body that can keep the approximate time in the absence of the external stimuli such as sunlight.
The interesting thing they noticed was that, this biological clock was, at best, approximate. It was not meant to keep time over a longer period of time. (This can be illustrated with the example of our spare tire in cars. Most of new cars come with a spare tire which is smaller in size. It is meant to be used, in case their tire has to puncture, to go to the nearest service station to get the main one fixed. Because the spare tire is smaller, it cannot be used to drive for extended period of time.) For example, the body clock sensed the day more than 24 hours. (The cycle was anywhere from 24 to 48 hours in the absence of light.) What we do is to use the natural daylight to "fine-tune" our body clock (or to apply a correction), so that the body clock is in synch with the external environment. The result of going for an extended period of time without having our body clocks "reset" with natural light is that we get sick with problems such as hormonal imbalances, sleep disorders, and mood disturbances.
Just as animals rely on signals from the sun to keep their body clocks exact and to synchronize their activities, so humans need sufficient daylight to synchronize their circadian and circannual rhythms (See Rhythms and Body Clock for an explanation). It has been suggested that a number of illnesses which result from hormonal imbalances - sleep, appetite, mood and reproductive disorders - could be linked to a disruption of circadian rhythms and ultimately to a lack of sufficient sunlight. SAD is an example of disturbed sleep patterns, appetite and weight disorders and depression, all of which manifest in a yearly and daily cycle: the symptoms peak at the height of winter and are at their worst in the evening. Giving SAD patients artificial daylight (light therapy) has proved successful in correcting these disorders, which suggests that SAD is directly associated with a lack of sufficient light.
There are other diseases that are influenced by the circadian rhythm disturbances. Classical depression has a daily rhythm. It worsens in the morning and improves in the evening. The result of this swing is the appearance of mood swings, along with insomnia or disturbed sleep patterns. Today, classical depression is often treated with drugs which exert an influence on circadian rhythms. Research is being carried out to determine the effectiveness of treating it with light therapy. Menstrual disturbances in women, such as irregular menstrual cycles or premenstrual syndrome are further examples of disturbances in the body's biological clocks. Again research is looking at the possibility of treatment with light therapy.
Next Topic: Brain, Hormones, Biological Cycles and Clocks
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