Scientists Shed Light on the Winter Blues When a case of the winter blues feels more like depression, you may be suffering from SAD. SAD stands for Seasonal Affective Disorder. SAD is a seasonal disruption of mood that occurs during the winter months and ceases with the beginning of spring. Symptoms usually begin in September when days begin to shorten, and last through the winter into March when the days begin to lengthen again. The symptoms of SAD usually include episodes of depression, hypersomnia, increased appetite, and weight gain. Light plays a big part in its origin and in its treatment. To better understand winter depression, think of it as four months of jet lag. The human body has hundreds of 24-hour biological rhythms all controlled by one "internal clock." The sleep cycle is one rhythm. Body temperature is another. The brain's production of certain chemicals, like the nighttime hormone melatonin, is another. Melatonin is a hormone produced by a gland in the brain called the pineal gland. High levels of this hormone can adversely affect our mood. Very little melatonin is secreted in daytime light and its peak production is usually at night, between 2 and 3 a.m. Due to their longer nights, winter months cause extra production of melatonin in the body. In the summer, most of us wake up when it is light outside. The morning light decreases the levels of melatonin in the body. In winter, however, most of us force ourselves to wake up while it's still dark outside. The darkness causes increased levels of melatonin, which cause some people to become depressed. Seasonal Affective Disorder causes many symptoms of depression. It can cause a diminished interest or enthusiasm in all, or almost all, activities. Overeating, especially of carbohydrates, leads to significant weight gain. SAD causes sleep problems such as oversleeping, but not feeling refreshed; and a feeling of lethargy or an overall sluggishness durin...