Seasonal Affective Disorder
Seasonal Affective Disorder (or SAD) is a mood disorder experienced by people living in areas where the changes in season are prominent. In the Northern United States, for instance, fall and winter are marked by shorter days and inclement weather or prolonged overcast skies, all of which limit the amount of natural sunlight exposure each day. Sunlight, however, plays an important role in the production of certain chemicals in the human body, most notably melatonin and serotonin.
Melatonin
Melatonin is a hormone secreted by a gland in the brain. Melatonin is made with the amino acid called tryptophan. After a particularly big dinner, you may have heard someone exclaim, "I'm ready for a nap! All that tryptophan is starting to kick in!" In fact, many meats do contain tryptophan, which can cause drowsiness as melatonin production is increased. However, large meals are not the only catalyst for increased melatonin production. Darkness also increases the production of melatonin. In most cases, this is a good thing. As daylight wanes, most people are preparing to sleep for the night. Darkness helps melatonin to aid in this natural process. However, when darkness persists without sufficient daylight, melatonin levels continue to increase, causing some people to feel perpetually drowsy or lethargic---factors contributing to depression.
Serotonin
Serotonin is a neurotransmitter. The prefix "neuro-" refers to the nervous system or nerves. To "transmit" means essentially to send across. The body's nerves are not one continuous strand, but rather a series of "relay runners." In order for messages to be transmitted properly, neurotransmitters must pass a sort of baton between these runners. If serotonin levels are low, certain messages cannot be sent correctly or quickly enough through the nervous system. As darkness aids in producing melatonin, sunlight aids in the production of the neurotransmitter serotonin. Without sufficient sunlight, the body may not produce enough serotonin. This can cause a drop in energy levels, a general sense of confusion or "fogginess" and other symptoms typically associated with depression.
Night Shift
For many, an increase in the sleep-inducing melatonin along with a decrease in serotonin causes SAD. Other factors besides the change in seasons may also cause light deprivation and depression; for instance, those who work nights and sleep days, or those who travel internationally for business and experience jet lag, may also have these symptoms of depression as exposure to sunlight becomes limited.
Light Therapy
The recognition of Seasonal Affective Disorder as a viable disorder is relatively new (first spoken about in 1985), and therefore research is also in relatively early stages. However, many doctors confidently prescribe "light therapy" as an alternative treatment to anti-depressant medications. Light therapy involves regular exposure during "low-light" times to artificial light which simulates sunlight.
Regular household light is not of the type or strength to replace natural sunlight. As distance may be measured in units of inches, feet or miles, light is measured in a unit called the "lux." During evenings or other times when sunlight is limited, the average living room lighting is only 400 lux---or just 4 percent as strong as the standard light therapy box (sometimes called a "SAD light") at 10,000 lux.
Light Therapy Boxes
The size, shape and construction of light therapy boxes will vary. The type of bulbs or screens used to emit the SAD light will also vary. The important commonality is that all light therapy boxes emit strong light that simulates natural sunlight.
Light Therapy Exposure Times
As with direct sunlight, you do not look directly into the SAD light source. Rather, the light therapy box is placed so that light reaches the eyes indirectly. Recommended light therapy exposure times will vary depending on the doctor, the severity of symptoms and the effectiveness of prior experimental exposure times. However, in general, recommended exposure to a 10,000 lux light therapy box is a half hour. If a patient has difficulty with the intensity of the light from such a box, a weaker light---as low as 2,500 lux---may be used for a longer period (in this case, two hours).
Recommendations
Most doctors recommend use of SAD light therapy in the morning to correlate with the body's natural waking rhythms. Though evening, or morning and evening, use of light therapy may be effective for some, using light therapy close to bed time often causes difficulty sleeping. Light therapy does not need to interrupt daily routines, since the light box can be placed nearby during breakfast, on a desk at work or any other place where exposure will be consistent during the recommended session time. The important thing is that SAD lighting must enter the eyes during that period; the light therapy is not effective on skin, but rather as the brain's receptors are stimulated by visual exposure.
Feeling Better
Light therapy does not work immediately. However, good results can be seen in only a few days or weeks, as levels of melatonin and serotonin regulate. As with anti-depressant medication, it is still important to stay on schedule with light therapy treatment and not skip treatments due to "feeling better" as symptoms decrease. Light therapy is usually continued on a regular schedule until exposure to natural sunlight becomes regularly and readily available (that is, until spring is well underway, until a night shift is changed for a day shift, or until other causal circumstances change).
