Many people eat and sleep slightly more in winter and dislike the dark mornings and short days. This is known as 'winter blues’. Others have more severe symptoms which such as sleep problems, withdrawal, overeating, depression, anxiety and lethargy. These often lead to difficulties at home, work and in relationships. This is a recognised problem known as Seasonal Affective Disorder (SAD).
SAD is caused by the lack of bright light in winter. Light entering our eyes stimulates our brain to control our daily rhythms through hormone production. In some people, the low levels of light in winter are insufficient to regulate the hormones that affect our waking up and sleeping, our feeling energised or depressed.
Treating SAD with light therapy
To treat SAD, most sufferers need light to their eyes as bright as a spring morning on a clear day, for around 30 minutes a day. The light must be at least 2,000 lux (the technical measure of brightness), which is roughly four times brighter than a well-lit office.
For more information, read the guide to SAD and the winter blues.