Some people suffer from symptoms of depression during the winter months, with symptoms subsiding during the spring and summer months. This may be a sign of Seasonal Affective Disorder (SAD). SAD is a mood disorder associated with depression episodes and related to seasonal variations of light.

SAD was first noted before 1845, but was not officially named until the early 1980’s. As sunlight has affected the seasonal activities of animals (i.e., reproductive cycles and hibernation), SAD may be an effect of this seasonal light variation in humans. As seasons change, there is a shift in our “biological internal clocks” or circadian rhythm, due partly to these changes in sunlight patterns. This can cause our biological clocks to be out of “step” with our daily schedules. The most difficult months for SAD sufferers are January and February, and younger persons and women are at higher risk.

SAD (Seasonal Affective Disorder) is a type of winter depression that affects an estimated half a million people every Winter between September and April, in particular during December, January and February.

It is caused by a biochemical imbalance in the hypothalamus due to the shortening of daylight hours and the lack of sunlight in winter.

For many people SAD is a seriously disabling illness, preventing them from functioning normally without continuous medical treatment.

For others, it is a mild but debilitating condition causing discomfort but not severe suffering. We call this subsyndromal SAD or 'winter blues.'

The symptoms of SAD usually recur regularly each Winter, starting between September and November and continuing until March or April. A diagnosis can be made after three or more consecutive Winters of symptoms, which include a number of the following

• regularly occurring symptoms of depression (excessive eating and sleeping, weight gain) during the fall or winter months.
• full remission from depression occur in the spring and summer months.
• symptoms have occurred in the past two years, with no nonseasonal depression episodes.
• seasonal episodes substantially outnumber nonseasonal depression episodes.
• a craving for sugary and/or starchy foods.

Most sufferers show signs of a weakened immune, system during the Winter, and are more vulnerable to infections and other illnesses.

SAD symptoms disappear in Spring, either suddenly with a short period (e.g., four weeks) of hypomania or hyperactivity, or gradually, depending on the intensity of sunlight in the Spring and early Summer.

In sub-syndromal SAD, symptoms such as tiredness, lethargy, sleep and eating problems occur, but depression and anxiety are absent or mild.

SAD may begin at any age but the main age of onset is between 18 and 30 years.

It occurs throughout the northern and southern hemispheres but is extremely rare in those living within 30 degrees of the Equator, where daylight hours are long, constant and extremely bright.

Melatonin, a sleep-related hormone secreted by the pineal gland in the brain, has been linked to SAD. This hormone, which may cause symptoms of depression, is produced at increased levels in the dark. Therefore, when the days are shorter and darker the production of this hormone increases.

Light therapy has been shown to be effective in up to 85 per cent of diagnosed cases. That is, exposure, for up to four hours per day (average 1-2 hours) to very bright light, at least ten times the intensity of ordinary domestic lighting.

Ordinary light bulbs and fittings are not strong enough. Average domestic or office lighting emits an intensity of 200-500 lux but the minimum dose, necessary to treat SAD is 2500 lux, The intensity of a bright summer day can be 100,000 lux!

Light treatment should be used daily in Winter (and dull periods in summer) starting in early Autumn when the first symptoms appear. It consists of sitting two to three feet away from a specially designed light box, usually on a table, allowing the light to shine directly through the eyes.

The user can carry out normal activity such as reading, working, eating and knitting while stationary in front of the box. It is not necessary to stare at the light although it has been proved safe.

Treatment is usually effective within three or four days and the effect continues provided it is used every day. Tinted lenses, or any device that blocks the light to the retina of the eye, should not be worn,

Some light boxes emit higher intensity of light, up to 10,000 lux, which can cut treatment time down to half an hour a day.

Light boxes are not available on the NHS and have to be bought from specialist retailers; they are now free of VAT and start at less than £100.

SADA recommends trying before buying; several companies offer a home trial or hire scheme and SADA has a number of boxes for short-term hire.