When the nights start getting crisp, and the leaves start turning yellow, some people start feeling the winter blues again. Called Seasonal Affective Disorder, this form of depression coincides with winter and occurs more frequently in higher lattitudes. Discovered by Norman Rosenthal in 1984, researchers believe it's caused by changing circadian rythms and serotonin levels.

Circadian derived from two Latin words: circa and diem. While circa means around, diem means day. When combined, the word means approximately one day. Consequently, circadian rythms are similar to internal alarm clock in which certain bilogical and physiological processes take place at a specific time each day. As winter approaches, your body senses the change in daylight. As light levels decrease, it causes increased levels of melatonin and decreased levels of serotonin.

Melatonin is linked to sleep. As the levels of melatonin increase, your body wants to sleep more. On the other hand, low levels of serotonin are linked to depression. Hence, as the number of daylight hours decrease, some people become more depressed and want to sleep more.

Affecting 10 million Americans, it is estimated 25% of the population suffers from a mild form while 5% suffer from a more severe form. Younger people are more likely to be diagnosed than older people, and the main age of onset is between 18 to 30 years of age. Women suffer from it more frequently than men. One reason for this may be because since some women are stay-at-home mothers, they are more socially isolated than men.

We already know two of the symptoms of SAD are depression and sleeping more. Other symptoms may be:

• Crying spells
• Lethargy
• Decreased activity level
• Irritability
• Poor sleep
• Loss of sex drive
• Changes in eating
• Difficulty concentrating
• Social isolation

Although SAD can be treated with antidepressants and counseling, researchers discovered SAD can be treated with a light therapy lamp. By the same way less daylight hours triggers SAD, the symptoms can be reversed by more daylignt hours. For some people, spending more time outside can help. However, for others that may not be enough.

Sitting or working by a bright light that mimics natural daylight can markedly improve the symptoms of SAD within a week. For it to be effective, a person needs to glance at the light but not stare since the change in light levels are sensed by the retina. Furthemore, the best time to use a light therapy lamp is in the morning. If you decide to purchase a light therapy lamp, any light bulb will not work; a "full spectrum" is the best..