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Can biology explain the “winter blues” mood disorder?

Does winter give you the blues? Biology might be able to explain why.
Diedre Ribbens

With the recent decrease in temperatures, waning daylight, and growing snow banks it’s becoming apparent that winter is coming to Minnesota. While many people look forward to the change in seasons, a portion of the population also experiences a change in their mood. Seasonal Affective Disorder, or SAD, is “a type of depression that occurs at the same time every year,” according to the Mayo Clinic website. Many of us in Minneapolis are familiar with SAD, but what are the biological reasons behind this mood disorder?

Some evidence suggests that the prevalence of SAD depends on latitude – the farther north, the greater incidence of the mood disorder. There are theories that this correlation is actually caused by the amount of daylight, as regions to the north have a greater reduction in the amount of daylight hours. Support for this idea comes from the fact that patients with SAD are often prescribed early morning bright light therapy to alleviate the symptoms of their mood disorder. The light therapy is thought to adjust for the delay in dawn and therefore put the patient’s sleep/wake cycle back on track with a more summer-like time of year.

One population that defies this latitude-SAD correlation is the people of Iceland. Icelanders and their descendents have a comparatively low incidence of SAD. Some researchers think that this is due to the large amount of omega-3 fatty acids in their diet (Icelanders eat a lot of fish that contain these fatty acids), but other studies have suggested a genetic variation present among the Icelandic population that shows somewhat of an “adaptation” to long, dark winter days. There has been support for both of these ideas, and it could be that the combination of good genes and lots of fish makes the people of Iceland less susceptible to SAD.

An important conclusion that scientists have made about SAD is that your genetics and your natural circadian rhythm play a large part in your chances of experiencing this mood disorder. Circadian rhythm is a natural system present in your body that regulates your daily cycle. Over the course of a day, your circadian rhythm impacts when you feel tired or hungry, and is largely controlled by your genes. Circadian rhythm can be impacted by the environment, which is why bright light therapy can help SAD patients, but several studies have shown that your genes can predispose you to developing SAD. Several genes involved in circadian rhythm were shown to have slight genetic changes in patients with SAD when compared to a control group of patients without SAD. The two groups were matched for age, gender, and geographic location, so the researchers were confident that the occurrence of SAD was influenced by the genetic changes they observed. These changes were minor, but consistent, making a strong argument for a genetic component to SAD.

If you want to learn more about SAD, or if you are concerned that you might have this mood disorder, visit the Mayo Clinic website or talk to your doctor for more information. The “winter blues” are no fun, but it’s important to know that there are ways to combat these feelings and enjoy the beautiful winters of Minnesota.

Horrocks, L.A., Yeo, Y.K. “Heath benefits of docosahexaneoic acid (DHA).” (1999) Pharmacological Research 40: 211-225
Johansson, C., et al. “Circadian clock-related polymorphisms in Seasonal Affective Disorder and their relevance to diurnal preference.” (2003) Neuropsychopharmacology 28: 734-739
Magnusson, A., Axelsson, J. “The prevalence of seasonal affective disorder is low among descendents of Icelandic emigrants in Canada.” (1993) Arch Gen Psychiatry 50: 947-951
Magnusson, A., Axelsson, J., Karlsson, M.M., Oskarsson, H. “Lack of seasonal mood changes in the Icelandic population: results of a cross-sectional study.” (2000) American Journal of Psychiatry 157: 234-238
Mayo Clinic Website Information on SAD
McClung, C.A. “Circadian genes, rhythms, and the biology of mood disorders.” (2007) Pharmacology & Therapeutics 114: 222-232

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