The effects of SAD on a person's life can be catastrophic including severely disrupted education, careers and relationships. The exact causes of SAD are still unclear. But everyone has an internal body clock which is controlled by nerve centres in the brain. Lack of light, for example night time, causes the pineal gland to secrete a chemical called melatonin . The increase of light at dawn tells the gland to switch off this secretion so that we can wake up.
SAD sufferers appear to have something wrong with their internal body clock.
Firstly, there are indications that SAD is inherited so a sufferer has a genetic vulnerability . Secondly, someone with the SAD genetic make-up may not show symptoms until they experience lack of light . Obviously, in this part of the world, light levels are low in winter. But a sufferer may also experience symptoms during very cloudy summers or when spending large amounts of time in a windowless or badly lit environment or if they have eye conditions which reduce the amount of light entering the eyes, eg cataracts. Thirdly, stress seems to be a major trigger.