Discuss the effect of the environment (light) on one seasonal affective disorder (SAD)

        Melatonin, produced in the pineal gland effects mood and energy levels (For example melatonin produces serotonin which causes sleep) and is suggested by research to be the cause of this disorder. It is produced most in the dark so production is therefore controlled by light stimulation to the eyes. It has been suggested that winter SAD is caused by too much melatonin production in the winter months due to earlier and later ending production of the hormone, because it is dark for more time in the winter.

        Inextricably linked the SAD is the amounts of light in ones environment, this is supported by the successfulness of phototherapy - where people suffering from the disorder are seated in front of a 1 metre square bright light to suppress production of melatonin. The success of this therapy in getting rid of the symptoms was so successful that it is widely accepted that light is a key external zeitgeber that causes SAD.

        Melatonin is not just linked to the circannual rhythm of SAD but also other bodily rhythms like the menstrual cycle. Reinburg (1967) studied a woman who had been in a cave for three months with no external zeitgeber’s at all, to see if light had an effect on this cycle. The results showed that her menstrual cycle did change without light effecting her. So this result further shows that light can effect physiological processes in many ways.

        So, in this example the environmental factor light effects the amount of melatonin secreted which in turn effects bodily and mind processes, becoming depressed and pessimistic about the future. It has interested scientists for many years that your environment can have such a direct link to your behaviour and thoughts. This direct link is shown by the fact that 9.5% of Finland’s population suffer from SAD, where they endure short sunlight hours and long winters.