Seasonal affective disorder (SAD) kicks in as soon as days turn shorter during winter with loss of natural light triggering lethargy, lack of interest in sex and sleep problems. But intense bright light can counteract SADness.
Stockholm, for instance, gets only five hours of daylight during winter. But the city's commuters can stop off in cafes and sit bathed in lighting to the strength of 3,000 lux (measure of brightness).
This intense light simulates natural light and is thought to correct the hormone imbalance that causes SAD, although its effectiveness has not been conclusively proved.
Victoria Revell, expert in chronobiology (the study of circadian rhythms) at the University of Surrey, says the cafes would benefit SAD sufferers, the Telegraph reports.
"They are beneficial both physiologically and socially. Using light therapy in this way can help our sleep patterns, energy levels and performance."
An estimated seven percent of Britain's population suffer from SAD, with a further 17 percent experiencing a milder form of the condition, commonly known as the "winter blues".
Revell explains: "One key role of light is to synchronise our circadian body clock to the 24-hour day." SAD sufferers, she says, require a higher light intensity to regulate their body clocks.
In the winter, when light levels are lower, they produce too much melatonin -- the hormone which helps us sleep -- and less of the "feel-good" hormone, serotonin.
The latest thinking is that the disorder has genetic origins. In the US, for example, research suggests that mutations in a gene associated with melanopsin -- a light-sensitive pigment in the retina of the eye thought to help regulate our circadian rhythms -- may be involved.
SAD sufferers are also advised to spend as much time as possible outside in natural daylight and to keep active.
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