Seasonal Affective Disorder Pt.1: What’s happening in the brain?

While a lot of us deal with mood shifts when the seasons change and winter creeps ever closer, some of us can feel them on a deeper level, leading to a more disruptive form of depression called SAD, or Seasonal Affective Disorder. In previous posts, we’ve touched on the impact of various weather conditions on our cognition and mental well-being, but in our next two, we’ll be zooming into the specific science of SAD. We’ll explore how the brain reacts to seasonal changes, explain why some are more susceptible, and offer advice on managing the condition.

SAD and its symptoms

SAD is triggered by changes in seasons and light levels. Although it’s most commonly experienced during the darker winter months, it can also occur during summer. It affects approximately 5% of adults in the US, often starting in young adulthood, and it affects a higher proportion of women than men. Common symptoms include:

• Feelings of low mood, helplessness, and worthlessness

• Fatigue and low energy levels

• Difficulty concentrating

• Loss of interest in previously enjoyed activities

• Sleep disturbances, ranging from insomnia to oversleeping

• Appetite changes.

SAD and the brain

There are three key things affecting the brains of SAD sufferers:

• Light factors

  The body’s internal clock, or circadian rhythm, influences our sleep cycles, energy levels and mood by controlling the production of specific hormones and neurotransmitters. There are two chemicals that are really important here:

  • Melatonin. Produced by the pineal gland in response to darkness, it helps the body prepare for sleep. During the darker months, those with SAD tend to produce higher levels than usual, leading to feelings of drowsiness and lethargy during the day. 

  • Serotonin. Sunlight boosts the production of this feel-good chemical, so darker days mean reduced serotonin activity and therefore a higher likelihood of lower moods. 

• Vitamin D Levels

  Another crucial contributing factor to SAD is declining levels of vitamin D, which are synthesized by the skin during the sunnier months. Reduced amounts of vitamin D is not only an issue for immune health, but can also cause impaired cognitive function and a higher risk of depressive symptoms. 

• The Limbic System 

  This is a set of structures within the brain that plays an important role in how we experience stress and emotions. Certain parts of the limbic system, such as the hypothalamus, influence mood, sleep-wake cycles, and appetite. Reduced light exposure in winter can affect the hypothalamus's careful regulation of these processes.

  For example, dysregulation of the body’s central stress response system, known as the HPA, or hypothalamic-pituitary-adrenal axis, can cause increased levels of the stress hormone cortisol to be released, exacerbating those tell-tale feelings of anxiety and depression present in SAD. 

Now you know what’s going on up there in the brain of someone with SAD, keep your eyes peeled for our next post detailing why some people are more likely to experience the condition, and what can be done to treat it.