Each year, 6% of northern populations are affected with Seasonal Affective Disorder
(SAD) and another 14% have a milder form of SAD, called the winter blues.
Surprisingly, SAD may occur at any time of year and in equatorial regions although the
ratio of northerners with SAD as compared to those living in the tropics is about 10-1.
People in the southern USA experience SAD in the summer from staying indoors where
air conditioning allows them to escape the unbearable summer heat. People have also
experienced SAD moving into a basement suite or an office on the north side of a
building or after painting the interior of their home a darker shade of color. People have
experienced SAD following the development of cataracts or after wearing sunglasses for
an extended period of time and during overcast, rainy periods (Rosenthal, 1993).
The common symptoms are depression, anxiety, extreme fatigue, hypersomnia,
carbohydrate cravings, and weight gain. Women between the ages of 20 to 40, their
sexually reproductive years, are most susceptible (Rosenthal, 1993). The first controlled
study using light therapy to treat SAD was published in 1984. SAD was officially
accepted as a clinical malady in 1987 by the American Psychiatric Association and
described in its then current diagnostic manual, the DSM-III-R. Since that time, a great
number of studies on the topic have been completed.
Animals are more sensitive to the seasons than humans, as they go through migration,
mating, molting and hibernation. For instance, hamsters can sense the difference between
a 12-hour day when their gonads don’t grow versus a 12-hour and 15 minute day when
their gonads begin growth. It is thought that humans aren’t as sensitive as animals
because humans originated in and around Africa where solar fluctuations are much more
minimal than those near the Earth’s poles (Wright, 2002).