Many people are affected by the change in seasons during the year. It seems quite natural to feel more energised and cheerful when there is more daylight and the days are longer over the summer, while the "winter blues" lead to many of us hibernating later on in the year.
However, if you are severely affected by the longer nights and shorter days, there is a possibility you are suffering from seasonal affective disorder (SAD), which is a recognised mental health condition. Countries like the UK are more susceptible to SAD, as we are in the higher latitudes of the northern hemisphere. This means we see large changes in the amount of daylight as summer turns into winter, and dark and gloomy weather reduces daylight even further.
The causes of SAD
At this stage, we don't fully understand why people develop SAD. We do know that it is linked to reduced exposure to sunlight. One theory is that the reduced sunlight stops the hypothalamus in our brain from working properly. This can alter the levels of melatonin and serotonin our body produces, as well as affecting our body clock. People with SAD often sleep longer in the winter thanks to a higher amount of melatonin in their body, while lower serotonin impacts mood and appetite.
Another theory is that SAD is influenced by our genetic make-up, as there have been reported cases of it running in some families. However, there is more research required before we have a definitive answer to the causes of the disorder.