SAD, or seasonal affective disorder, is a specific type of depression that affects people at the same time each year - autumn and winter. During spring and summer, people with SAD feel well.
Dr Gill Jenkins last medically reviewed this article in July 2011.
Experts believe SAD is related to a lack of daylight exposure, which explains why people feel well during spring and summer and only start experiencing problems when the days get shorter.
Many people experience symptoms such as:
Some also find their sleep is disturbed, they eat less or more than usual and they have no sex drive although in SAD, more unusual symptoms such as a craving for sweet things, increased appetite, weight gain and increased sleepiness may also occur.
Symptoms usually start between September and November and almost always spontaneously disappear with the arrival of spring and the longer daylight hours.
Up to one in 20 people is believed to be affected by SAD, with women three times more likely to be affected than men. Younger people, particularly those between the ages of 18 and 40, are more likely to suffer. There's a familial tendency so may be some sort of genetic link, with one in seven first-degree relatives (parents, siblings or children) also being affected.
Because days get shorter the further north you go, SAD is more common in northern countries.
Worrying about work, relationships or money make SAD more likely.
Ensure exposure to plenty of daylight as this is the best source of light.
Alternatively, light boxes provide a regular dose of artificial light each day and help many people. Ordinary light bulbs aren’t strong enough as they only give out 200-500 lux but to treat SAD you need a light source about ten times that of ordinary light bulbs, of at least 2,500 lux. The device will come with instructions but generally you need to sit under the light for 30 minutes to two hours a day, starting in the autumn before your symptoms begin.
It's not well understood why it works but it's possible that bright light on the retina sends nerve signals to parts of the brain, affecting the level of certain mood-altering chemicals and hormones in parts of the brain.
Counselling, exercising and spending time outdoors can help. Boost mood with rest, relaxation, regular exercise and a healthy diet.
Treatment with antidepressants may help to relieve symptoms.
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