Interestingly, when light hits the back of the eye messages go to the part of the brain that controls numerous bodily functions such as sleep, appe
Interestingly, when light hits the back of the eye messages go to the part of the brain that controls numerous bodily functions such as sleep, appetite, sex drive, temperature mood and activity. If there isn’t enough light, then these functions either slow down or stop.
Another way in which the lack of light during winter months affects the body is by disrupting the body clock. One theory is that if you experience SAD in the winter, the part of the brain that sets the body clock does not work in the same way.
This could mean the body clock is out of sync with daylight, leading to tiredness and depression. Some researchers think this is because your sleep pattern starts at a different time.
In darker light the brain also produces more of a hormone called melatonin, which helps your body get ready for sleep. Levels of another hormone, serotonin, which affects your mood, are also disturbed by how much sunlight an individual gets. Due to this it is thought that people who suffer from winter SAD seem to produce higher levels of melatonin and lower levels of serotonin during winter.