sciencetriffic

SAD (seasonal affective disorder) and 'winter blues'

Animals react to the changing seasons with changes in mood, metabolism and behaviour and human beings are just the same. Many people find they eat and sleep slightly more in winter and dislike the dark mornings and short days and this is commonly referred to as 'winter blues'. For some, however, symptoms are severe enough to disrupt their lives and to cause considerable distress. These people are suffering from SAD.

How does SAD affect people?

Symptoms tend to start from around September each year lasting until April, but are at their worst in the darkest months. Symptoms include:

• Sleep problems - oversleeping but not refreshed, cannot get out of bed, needing a nap in the afternoon
• Overeating - carbohydrate craving leading to weight gain
• Depression, despair, misery, guilt, anxiety - normal tasks become frustratingly difficult
• Family / social problems - avoiding company, irritability, loss of libido, loss of feeling
• Lethargy - too tired to cope, everything an effort
• Physical symptoms - often joint pain or stomach problems, lowered resistance to infection
• Behavioural problems - especially in young people

Who does it affect?

The standard figure says that around 2% of people in Northern Europe suffer badly, with many more (10%) putting up with milder symptoms (sub-syndromal SAD or winter blues). Across the world the incidence increases with distance from the equator, except where there is snow on the ground, when it becomes less common. More women than men are diagnosed as having SAD. Children and adolescents are also vulnerable.

What causes it?

The problem stems from the lack of bright light in winter. Researchers have proved that bright light makes a difference to the brain chemistry but why some people suffer and others don't is not clear.

Nerve centres in our brain controlling our daily rhythms and moods are stimulated by the amount of light entering the eyes. As night falls, the pineal gland starts to produce a substance called melatonin that tells our body clock it's night time; bright light at daybreak is the signal for the gland to stop producing this melatonin. But on dull winter days, especially indoors, not enough light is received to trigger this waking up process.Light is also linked to serotonin (also known as or 5HT), a neurotransmitter in the brain. This makes sense because low serotonin levels can cause depression and if you're depressed it can be difficult to concentrate and complete what would normally be simple tasks. Evidence has shown that serotonin levels increase with exposure to bright light - SSRI drugs such as Prozac have the same effect.

What treatment is there?

As the cause is lack of bright light, the treatment is to be in bright light every day. Going to a brightly-lit climate, whether that's skiing or somewhere hot, will relieve symptoms but if that's not possible you can use a bright light. The preferred level of light is about as bright as a spring morning on a clear day and for most people sitting in front of a light like this for around 30 minutes a day will be sufficient to alleviate the symptoms. You don't have to stare at the light, so you can watch TV or read or similar, just make sure that light reaches your eyes.

The light must be suitably bright. You need at least 2500lux (lux is the technical measure of brightness) which is roughly five times brighter than a well-lit office. Brighter 10,000lux lights take less time to use and allow you to sit further away. Simply using 'daylight' or 'full spectrum' lights at home will not work as they're not bright enough.

See all products for SAD including lightboxes, LED lights, desklamps and Bodyclock dawn simulators >

We encourage SAD sufferers to seek the support of their doctor. We can also supply comprehensive information packs for medical practitioners.

Please see your doctor if you believe you may be suffering from a depressive illness.

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