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The Science Behind Winter Depression

It’s that time of year of again. The air is getting colder and coats are being worn – winter has arrived.  The annual ‘fall back’ marking the end of daylight saving time not only sets the clocks back an hour,  but brings spirits down as well. The shorter, darker, and colder days are often accompanied by a lack of motivation and fatigue.

For about 15% of the United States’ population, these symptoms, along with many others, are so severe that they hinder people from completing their daily functions. This seasonal form of depression, known as Seasonal Affective Disorder (SAD), has the ability to overwhelm its victims with anxiety, mood swings, loneliness, social isolation, weight gain, excessive sleeping, and a general feeling of discontent. Women are four times more likely to have SAD than men, particularly around the age of 20.

SAD is a very complex and confusing disorder, which is why many theories have been brought about to explain it. One theory revolves around evolution. Due to the fact that SAD affects such a large portion of the population, many believe that SAD has something to do with energy conservation methods from the past.

Robert Levitan, a professor at the University of Toronto, said, “Ten thousand years ago, during the ice age, this biological tendency to slow down during the wintertime was useful, especially for women of reproductive age because pregnancy is very energy-intensive. But now we have a 24-hour society, we’re expected to be active all the time and it’s a nuisance. However, as to why a small proportion of people experience it so severely that it’s completely disabling, we don’t know.”

Evolutionary theorists also believe that light plays an important role in the daily behaviors and functions of animals and that through evolution, humans became dependent on light. In winter, the Northern Hemisphere tilts away from the sun, resulting in fewer daylight hours. Theorists have hypothesized that this  deprivation of sunlight in the winter affects people’s abilities to function properly.

The most common explanation for SAD involves serotonin, a mood-regulating transmitter produced in the human body. Various studies suggest that serotonin is influenced by light, especially light emitted by the sun. When the blue light of the sun comes into contact with cells in a person’s retina, the cells transmit a hub in the brain called the suprachiasmatic nucleus which is connected to another hub called the raphe nucleus. Located in the brain stem, the raphe nucleus is the primary source of serotonin neurons within the brain. A decreased amount of light in the winter time prevents this network in the brain from functioning properly, causing a significant serotonin deficiency in many individuals.

In addition to explaining the emotional symptoms of SAD, the serotonin theory provides an explanation for why women are more susceptible to the disorder than men. Estradiol is a female sex hormone that has a direct connection with serotonin. According to Brenda McMahon, a psychiatry researcher at the University of Copenhagen, the varying levels of estradiol in a woman’s body throughout their life can affect the way serotonin is made.

There are various solutions available for those suffering from the SAD symptoms. Similar to other kinds of depression, SAD can be treated with prescribed drugs. Antidepressants are often used for SAD patients. Prozac, in particular, is distributed to SAD patients because it is a Selective Serotonin Reuptake Inhibitor, which alters the behavior of neurotransmitters in the brain.

The most common treatment for SAD is light therapy (phototherapy). The light involved in this kind of treatment is brighter than typical indoor lighting but does not compare to the brightness of direct sunlight. The light therapy treatment compensates for  decreased exposure to sunlight and maintains the body’s internal clock, regulating sleep. Light therapy is most effective when used first thing in the morning and when it is used two  to four times a day.  Symptoms of SAD are typically relieved after three weeks of light therapy.

Like all forms of treatment, light therapy comes with its share of side effects. Among many other side effects, eye strain, nausea, headaches, and agitation are the most prominent. These symptoms can be relieved by reducing the duration of time spent under the light.  

About the author

Amanda Weinberg