SAD is VERY REAL!...and I have lived with it for my entire life! I am a native of Cleveland, Ohio, now living in Columbus....The sun disappears about November and reappears in March or April. SAD is the body's primal urge to hibernate. As this urge is ignored longer and longer into periods of less and less sunshine (duration and intensity) the body and brain change their chemistry and you become depressed...clinically and chemically.
Typically, you want to sleep alot more and want to eat mostly large quantities of simple carbohydrates...which further stimulate your desire to sleep and become lethargic, irritable, a bit slower mentally, reclusive, etc.....The depression is also very real...and can range from almost none to suicidal.....mine has pushed me to suicidal 3 times, many years ago.....and is still fairly severe in the winter to this day.....
There is no one single answer to the disorder....rather a combination of treatments that varies by person and from year to year...To combat SAD, I have a light box of EXTREMELY bright , full spectrum lights that I sit with while I read or eat or watch TV, or surf the web, etc....this is special light that simulates the intensity and wavelength of natural sunlight....also get regular exercise and go outside even on the coldest days to get some natural daylight. Also eat a better diet with lower simple carbs and more complex carbs and lower fat and higher protein. I also have a number of medications that I can work through the fall and winter....Lexapro and Prozac both worked for me...I also try to schedule a few weeks around the winter solstice to go to central or south Florida to get a bit more sunshine and break the depressive situation and cycle....It takes a few days for the body to recalibrate to the increased sunshine (solar radiation) and make sure you are getting the right amount of sleep ....not too much or too little....all of these together help me through a lake effect winter on the Great Lakes...and Columbus is considerably less effected than Cleveland, but still, pretty bad....
I know that for me, I can start to notice a drop in solar intensity (and the beginning of my SAD) about August 1 each year and it is noticeable in the spring that it is starting to lessen around the 1st of March......For me, my doctors have calculated that I would need to live south of the latitude of Orlando, Florida to not have my SAD be the issue it is for me...... there is only a very small amount of the USA south of this latitude....that being in Florida, south Texas or Hawaii...There are several books on the topic and several studies and reports and article...but still not enough to really understand the way it works....so more research is needed.
one of the original studies was done by Norman E. Rosenthal, MD. (http://en.wikipedia.org/wiki/Norman_E._Rosenthal