Why Some Get SAD and Others Don't

Find out why seasonal affective disorder only affects some of the population

Why Some Get SAD and Others Don't

By Danielle Cronquist Published at December 20, 2017 Views 1,452

The risk of getting depression increases for many in the winter and can often be due to seasonal affective disorder (SAD). SAD generally sets in during fall and continues until the end of the winter months. Approximately a half a million people in the US suffer from SAD and another 10–20% suffer from winter blues (a mild, subclinical form of SAD). It might be easy to see how cold temperatures that keep you indoors and shorter days could affect your mood, but why do some people get full depression with seasonal affective disorder and some don’t?

The science behind SAD

A study done by the University of Copenhagen in Denmark showed that there is a significant difference in the way that people with SAD regulate the neurotransmitter serotonin. In a study of 11 SAD patients and 23 individuals who were not affected by SAD, there was a significant difference in levels of their serotonin transporter (SERT) protein. Higher levels of SERT activity mean lower activity of serotonin, which helps regulate mood. Those affected by SAD on average had a 5% higher SERT level in the winter compared with the summer, while the patients not affected by SAD had no major changes in their SERT level.

Many studies have been able to show a correlation between SAD and SERT levels, but this is the first study to track patients during both the winter and the summer.

SAD and sunlight

Many people draw a relationship between SAD and the short days and long nights of winter. According to lead researcher Brenda McMahon, M.D./Ph.D. student, “Sunlight keeps [SERT] settings naturally low, but when the nights grow longer during the autumn, the SERT levels increase, resulting in diminishing active serotonin levels. Many individuals are not really affected by SAD, and we have found that these people do not have increase in SERT activity, so their active serotonin levels remain high throughout the winter.”

This is also supported by evidence from numbers of people with SAD in various locations. In New Hampshire about 10% of people suffer from SAD, while in Florida only 1% are affected.

Be sure to soak in all the sunshine you can, get regular exercise, and do your best to stay healthy during chilly winter months to prevent SAD. But, if you do think you are affected, see your doctor so that you can get proper treatment and help.

For more on seasonal depression:

Sustain Your Energy, Stave Off Fatigue
Understanding the "Winter Blues"
Understanding and Dealing with Depression During Summer

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