who spends part of the year in a cold climate knows that it’s not
unusual for people to feel a little more “down” in the winter than
in the summer — an experience some have described
as a kind of “emotional hibernation.” But for others winter can
bring on a much more acute form of the common winter blues, a condition
that triggers severe depression and sometimes even suicide. It
has recently acquired a name: Seasonal Affective Disorder, or SAD.
Since there are differences in opinion about how severe the symptoms
need to be to qualify as SAD, figures for the prevalence of the disorder
vary. A middle-of-the-road estimate would place the rate of severe
winter depression sufferers in America at about four to six percent,
with mild SAD ranging from 10 to 20 percent of the population. The
further north or south of the equator one travels, the higher the
prevalence of SAD. It is much more common in Minnesota and Alaska
than it is in Florida and Arizona. This is not due to cold temperatures,
but to a reduction in the amount of sunlight reaching the brain through
As the hours of daylight in high-latitude climates drop, the brain
responds by increasing production of a hormone called melatonin —
a brain chemical that helps you fall asleep, and stay asleep until
morning. Levels of melatonin (marketed in pill form to frequent fliers
who often have to reset their internal clock to a new time zone)
typically rise in the evening, and peak at about 2 to 3 am.
Another central player in the SAD saga is the pineal (literally
“pine cone”) gland, a pea-sized structure located deep in the center
of the brain. This gland acts as a sort of light meter for the brain
and body, receiving information from the eyes and producing the melatonin
hormone in response to that information. By producing and sending
out higher or lower levels of melatonin according to the amount of
light the eyes receive, the pineal gland sets and regulates the brain’s
Many animals besides humans produce melatonin. Squirrels produce
extra amounts as the summer solstice passes and the days begin to
shorten. For them, high levels of melatonin trigger their food-hoarding
behavior, prodding their nut-gathering activities into high gear.
For most furry mammals, a seasonal melatonin surge also causes a
thickening of the fur in preparation for the cold winter months.
With the approach of winter and the corresponding increase in melatonin
levels, humans will also exhibit “hibernation”-type responses, such
as eating more food, putting on weight, and sleeping longer hours.
However, when the psychological symptoms become too extreme and develop
into severe depression, they can seriously interfere with an individual’s
day-to-day functioning and overall health.
One of the remarkable things about SAD is that women have it more
than men by a ratio of about four to one. And younger people suffer
from SAD much more frequently than the elderly. The gender difference
may result from a greater sensitivity of a woman’s pineal gland to
changes in daylight hours, while men’s brains are apparently tricked
by artificial light into thinking that summer never ends. In order
to experience the hormonal fluctuation that women do, men must be
isolated from the yellow glow of electric bulbs and the shifting
blue light of the television set.
Moreover, some population groups appear to have some kind of genetic
protection against SAD. A recent Icelandic study turned up very little
evidence of winter depression in that country — despite its extreme
northern latitude and short winter days.
How not to be SAD
Many experiments have shown that light therapy
— daily exposure to intense artificial light emitted by a “light
box” — works well to alleviate winter depression in most people.
The beneficial effect of light therapy doesn’t derive from the
kind of ultraviolet radiation emitted by the sun, but rather from
sheer brightness. The standard well-lit home or office provides
about 300 to 600 lux (with one lux about equivalent to the brightness
of a single candle), while a light box offers about 10,000 lux
— less bright than the 100,000 lux provided by a sunny summer day,
but still enough to alleviate symptoms of SAD. The therapeutic
effect of bright light works through the eyes, not the skin. In
experiments, people who are naked but blindfolded show no beneficial
response to light therapy, while people wrapped like mummies except
for their eyes respond well. Light box therapy has to be maintained
for an hour or so every day during the entire winter season; otherwise
a relapse is all but inevitable.
Antidepressants such as Prozac and Zoloft alleviate the sadness
of severe winter blues. These are SSRI (serotonin-increasing) drugs
that work by raising brain levels of the transmitter serotonin, the
very chemical that the pineal gland converts into melatonin. This
interaction seems to be a paradox. For some reason, while high serotonin
levels have an antidepressant effect, for most people high melatonin
levels appear to cause depression despite the fact that melatonin
is created by the release of serotonin in the brain.
One issue that also needs to be investigated is whether or not SAD
is a modern phenomenon resulting from the combination of an ancient
brain response to shorter daylight hours with the more complex demands
of modern life. If left to follow their internal adjustments to seasonal
rhythms, it is quite possible that almost everyone would fall quite
naturally into an appropriate winter pattern of long nightly slumbers
and reasonable weight gain. In our modern world, however, SAD sufferers
must force their bodies to adhere to what is in effect a year-round
summer pattern of long days and short nights.