Thanks for the interesting question, I had actually never heard of
Seasonal Affective Disorder before. Below I have listed a number of
sites which contain detailed information about causes, diagnosis and
treatment for SAD.
"SAD is a type of seasonal depression, usually occurring in the
winter, which affects millions of people a year between September and
April with the peak occurring in the winter months of December,
January, and February. True SAD is a seriously disabling illness,
preventing people from functioning normally. In addition, millions of
others suffer from a milder version called "subsyndromal SAD" or
"winter blues," less disabling but still impairing and uncomfortable.
There is a more rare form of summer SAD in which symptoms occur in the
summer and remit in the winter."
"Light is an important factor for maintaining biological rhythms. The
circadian clock relies heavily on changes in light to determine
transitions from night to day. During periods of darkness the SCN
clock sends out the hormone melatonin, which induces sleep. It is
plain to see how changing work schedules from the day shift to the
night shift would create the need to reverse this process, which takes
time and will in turn disrupt normal rhythmic patterns. Circadian
rhythms in shift workers were shown to adjust an hour or two per day
(Hedge, 1999). This means that it could take over one week for an
individual to fully adjust to an 8-hour shift change.
Another major disruptive factor related to the circadian clock's
interpretation of light is season changes. During winter months there
are fewer daylight hours, as a result the level of melatonin secretion
increases along with the number of hours of darkness."
"The two hormones that are affected by the sunlight, and are thought
to be the cause of SAD, are melatonin and serotonin. Both of these
chemicals "are influenced by photoperiodism, the earth's daily
dark-light cycle" (Wurtman 1989). Melatonin is the chemical that
effects mood and energy levels. In the human body melatonin is at its
highest at night and is lowest in the day. There has been a study done
to see if sunlight has a direct effect on suppressing melatonin. It is
known that melatonin levels in urine are five times higher at night
than they are in the day. It was not until a 1980 study that it was
known that melatonin levels could be directly suppressed with light."
"Despite the therapeutic effects of light on mood and sleep,
surprisingly little is known about the underlying mechanisms through
which bright light exerts its effects. Presumably, the antidepressant
and mood-energizing effect of light on mood is due in part to the
neurobiological effects of light on an area of the brain called the
suprachiasmatic nucleus, which is located in the hypothalamus of the
brain. This nucleus contains a circadian pacemaker that acts as a
"clock for all seasons" by being tuned to seasonal changes in light.
For mammals, changes in light and darkness play an important role as a
chemical mediator of the effects of season on breeding and other
behaviors such as eating, sleeping, and weight. In many animals,
including humans, the circadian pacemaker is able to take seasonal
variations in the duration of darkness and light into account by
detecting seasonal changes in day length and making corresponding
changes in the brain."
Other links you may be interested in...
Seasonal Affective Disorder -- Bryn Mawr
How Fertility is Affected by Sleep and Sunlight
The Role of Light in health
Can Sunlight help elderly nursing home residents sleep better?
Seasonal Affective Disorder in Detail
Yale Researcher sheds light on winter depression
Hope this answers your question. If you need anything cleared up
please request a clarification before rating this answer.
Have a great day and enjoy the sun!
sunlight effects mood research
possible ways sunlight influence mood
Clarification of Answer by
26 Apr 2005 22:35 PDT
I found a number of sites which are more research oriented on the
subject of SAD, hopefully these are more in line with what you are
"Background: The goal of this study was to evaluate the role of
genetic variation in the coding sequence of tryptophan hydroxylase
(TPH) in the pathogenesis of several psychiatric diseases in which
altered serotonin function has been implicated: bipolar affective
disorder (BP), obsessive?compulsive disorder (OCD), anorexia nervosa
(AN), seasonal affective disorder (SAD), panic disorder (PD), and
A look at how SAD was first identified...
"Bright light suppresses the hormone melatonin. Melatonin is released
in the evening time as a signal for the body to withdraw and prepare
for sleep. Melatonin is converted from serotonin, and so lowers
available serotonin. It also causes feelings of irritablity, withdrawl
and sadness. Melatonin is important as a nighttime hormone but daytime
or too much melatonin can cause mood problems."
The Lancet: Effect of Sunlight and season on serotonin turnover in the brain
"Alterations in monoaminergic neurotransmission in the brain are
thought to underlie seasonal variations in mood, behaviour, and
affective disorders. We took blood samples from internal jugular veins
in 101 healthy men, to assess the relation between concentration of
serotonin metabolite in these samples and weather conditions and
season. We showed that turnover of serotonin by the brain was lowest
in winter (p=0·013). Moreover, the rate of production of serotonin by
the brain was directly related to the prevailing duration of bright
sunlight (r=0·294, p=0·010), and rose rapidly with increased
luminosity. Our findings are further evidence for the notion that
changes in release of serotonin by the brain underlie mood seasonality
and seasonal affective disorder. "
"Since the first study of light therapy in winter seasonal affective
disorder (SAD) (Rosenthal et al., 1984), a syndrome in which
depression developed during fall or winter and remitted the following
spring or summer for at least two successive years, numerous studies
have concluded that bright light therapy is an effective treatment for
SAD (Lam et al., 1999b; Magnusson and Boivin, 2003; Oren and
Rosenthal, 1992; Partonen, 2001)."
How to Help Patients Beat the Winter Blues
I would especially look at the Lancet paper which seems to have a lot
of detailed information. From what I have read it seems that there is
little to no question about the existence of SAD and most research
being conducted at this point goes towards treatment.
Have a Great Evening/Morning. If you have any questions, feel free to ask.