With the arrival of colder temperatures, shorter days and the prospect of inclement weather, the winter months carry forth an entire rucksack of characteristics inherent to their place in the march of seasons. As the sun rises late and sets early, winter ushers in something else: an increase in the prevalence of depressive disorders. Characterized by the same symptoms of major depression, this cyclic phenomenon is known as seasonal affective disorder (SAD), and it can lead to harmful and isolating effects.

While SAD affects some people in the spring and summer months, 90 percent of the cases occur during the wintertime, commencing typically after the onset of fall — October or November — and persisting until spring. For some, according to the National Alliance on Mental Illness (NAMI), symptoms will begin in August, and in others they will not present until January.

Specific variables, including the area of the country in which one resides, are determining factors in who develops the disorder. “It affects people who live at the northern latitudes,” says Dr. Paul Arbisi. “The farther away from the equator you get during shorter light periods, the greater the percentage of the population who will report these symptoms.”

Dr. Arbisi, a psychologist at the Minneapolis VA Medical Center and an assistant clinical professor at the University of Minnesota, points out that SAD affectsjust 1-2 percent of the population in Florida, while peaking at about 10 percent of the population in latitudes as far north as New Hampshire. The reason has to do with sunlight, and specifically how much time someone is exposed to it. Research suggests that the reduced level of sunlight in the fall and winter months upsets the body’s circadian rhythm, an inborn process that serves as a keeper of time and an arbiter of the cycles governing sleep and wakefulness.

“From an evolutionary perspective, we are diurnal creatures — that is, we are active during the daytime and at night we sleep — so our circadian rhythms are tied to signals indicating daylight and night,” Arbisi explains. “People who get slowed down and tired and want to sleep a lot more during the winter end up having some fairly significant social and perhaps occupational consequences for that.”

Indeed, this seasonal depression shares the same symptoms as standard depression: hopelessness, anxiety, loss of energy, social withdrawal, weight gain, changes in appetite, oversleeping, and a loss of interest in activities once considered pleasurable.

“The difference is that most people learn that by early or late spring the condition will significantly improve, if not disappear,” says Arbisi.

A psychiatric illness in the family is another predominant risk factor, with 55 percent of people reporting a family history of depression and another 34 percent reporting alcohol abuse, according to NAMI.

Let There Be Light

Dr. Arbisi, along with the National Alliance on Mental Illness, advocate the use of light therapy for the treatment of seasonal affective disorder. NAMI’s guidelines say that light therapy, which involves sitting in front of a full-spectrum light for anywhere between 15-45 minutes per day, “is now considered the first-line treatment intervention, and if properly dosed can produce relief within days.”

The luminous therapy is intended to make up for the absence of daylight. “What you’re doing is fooling your body into thinking it’s summer,” says Arbisi. While antidepressants may also provide relief, light therapy is better supported by empirical studies, he says. “Pills are convenient,” he says. “But I’m not convinced they work as well as light, and they come with certain side effects that light doesn’t have.”