The specific cause of seasonal affective disorder remains unknown. It's likely, as with many mental health conditions, that genetics, age and, perhaps most importantly, your body's natural chemical makeup all play a role in developing the condition. A few specific factors that may come into play include:

  • Your biological clock (circadian rhythm). The reduced level of sunlight in fall and winter may disrupt your body's internal clock, which lets you know when you should sleep or be awake. This disruption of your circadian rhythm may lead to feelings of depression.
  • Serotonin levels. A drop in serotonin, a brain chemical (neurotransmitter) that affects mood, might play a role in seasonal affective disorder. Reduced sunlight can cause a drop in serotonin that may trigger depression.
  • Melatonin levels. The change in season can disrupt the balance of the natural hormone melatonin, which plays a role in sleep patterns and mood.
Sep. 22, 2011

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