Seasonal affective disorder (SAD) is a form of depression that affects people during the winter months. It generally begins as the days shorten in September and begins to go away as spring begins in April. Also known as winter depression, seasonal affective disorder is responsible for around 10% of all cases of major depression. Research has also shown that SAD is more prevalent and lasts longer in the higher latitudes. It is not disorder that is found in more tropical latitudes.

The symptoms of seasonal affective disorder are much the same as major depression and include:

• Sleep disorders – Chronic fatigue, oversleeping but not feeling rested and needing afternoon naps.

• Depression and anxiety – Daily tasks that are typically easily accomplished becoming frustrating to do.

• Weight gain – Cravings for sugar and carbohydrates leads to weight gain.

• Family and social withdrawal – Sufferer becomes increasingly anti-social and irritable.

• Physical symptoms – Stomach and digestive problems, muscle pain and joint pain and headaches.

As spring approaches some individuals who suffer from seasonal affective disorder may begin to exhibit signs of mania and have boundless energy and creativity. If these seasonal episodes of depression and mania are sufficient enough the sufferer may diagnosed with Bipolar Disorder.

The cause of SAD according to most research is a lack of bright light. It is thought that bright light sends signals to the brain suppressing the release of melatonin. Melatonin is released during periods of dim light or darkness and helps the body relax and sleep. Research has also found that while an increase in melatonin exists in the brain chemistry serotonin is not properly being accessed across neurons in the brain. Serotonin is considered the happy hormone and depressed individuals nearly always have low levels of it.

The treatment for seasonal affective disorder is exposure to bright light. During the winter months with cold temperatures and short days those afflicted with this type of depression do not get enough light exposure. Although outdoor light is the best treatment sitting in front of a 2500 to 10,000 lux light for 15 to 45 minutes per day will normally alleviate the symptoms.

Just how bright is 2500 lux light? It's five times brighter then a normally lit office and most living room lights are normally around 100 lux. So simply sitting in your home with all the lights turned on will not be enough to banish the symptoms.

For more severe cases of SAD light therapy may need to be augmented with anti-depressant medications and psychological therapy. It is important that anyone who thinks they may suffer from seasonal affective disorder to seek treatment from their doctor or therapist.