Close to 10% of people experience seasonal affective disorder symptoms, including 15% of psychiatric patients.
Symptoms may include depression, inability to enjoy life, appetite change, sleep disruption, fatigue or cognitive dysfunction. The winter solstice approaches, however, at 1:20 a.m. Fairfield time, on Dec. 21. The precise moment of the solstice is 19:56 UTC (Coordinated Universal Time). UTC is based on atomic clocks, deriving from Greenwich Mean Time.
After the winter solstice, the time between sunrise and sunset lengthens. That is good news for sun worshipers. Since prehistoric times, human beings have been fascinated by solstices. What astronomical phenomenon are we really experiencing? The December solstice marks the moment when the sun passes over the Tropic of Capricorn. The summer solstice refers to the moment when the sun is over the Tropic of Cancer.
The winter solstice represents the first date of astronomical winter, at least in the Northern Hemisphere. The Earth tilts about 23.4 degrees, relative to the sun. Winter, with its shorter days, is the time of year when the Northern Hemisphere tilts away from the sun, leading to colder temperatures. The sun seems halted, as it reaches its most southerly latitude. After the winter solstice, the sun seems to mosey up north again, fostering longer days. Earth's relative location, of course, is what really changes. Earthlings are not the center of the solar system, although we feel that way at times.
In the Northern Hemisphere, we consider winter to be a season running from December to March. That means that the days get longer throughout winter, beginning as it does at the solstice. This reflects the concept of "seasonal lag." The world's temperatures lag the astronomical events giving rise to winter. The oceans, due to the capacity of water to absorb heat, tend to buffer temperature changes. By contrast, ocean-free Mars escapes that seasonal lag.
The shortest day of the year inspired traditional spiritual beliefs. Stonehenge, a prehistoric English stone structure begun in 3,100 BC, is a famous example. Numerous cultures developed holidays corresponding to the December solstice, after the Stone Age. In Ancient Rome, calendars marked Dec. 25 as winter solstice day. As far back as 274 AD, emperor Aurelian marked this as the date of the "Invincible Sun" festival, following on the heels of Saturnalia (Dec. 17-23), a period of feasting.
The decision to celebrate Christmas on Dec. 25, around the solstice, dovetailed with these traditions.
Is East Asian cultures, the winter solstice is one of 24 Chinese solar terms, representing important astronomical events. The Japanese goddess of the sun, Amaterasu, is depicted in ancient paintings as appearing from a cave of darkness. The Hindu calendar refers to the sun god, Surya, and celebrates the end of the winter solstice. For those identifying with pagan traditions, citing Norse and Celtic origins, winter solstice is reflected in "Yule" celebrations.
With respect to seasonal affective disorder, there may be a genetic component of causation, reflected in familial patterns of disease in up to two-thirds of sufferers. We also know that certain behaviors go along with SAD, including alcohol abuse, eating disorders and social anxiety. Prevention involves struggling to maintain sleep-wake schedules, irrespective of seasonal variations in sunlight exposure.
If the daylight periods in a northern latitude are quite short, it becomes challenging to go to sleep and get up at the same time. The converse experience is trying to sleep when the sun shines late into the evening, above the Arctic Circle. Ancient physicians, including Hippocrates, recognized seasonal patterns for disturbed mood.
Around the 1980s, artificial light therapies began to be systematically studied as remedies for the winter blues, achieving modest clinical utility.
Dr. Scott Anderson (standerson@ucdavis.edu) is a clinical professor at UC Davis Medical School. This column is informational and does not constitute medical advice.