The Science Behind Seasonal Depression

As the days get shorter and the nights get longer, you may feel yourself acting a bit off—a bit ‘blue’, if you will. In the United States, roughly 5% of adults, which translates into millions of Americans, suffer from seasonal depression. So, today, let’s uncover the various types of seasonal depression, its causes, who is typically affected by it, diagnosis, and treatment options.

First, what is seasonal depression? Seasonal depression, also known as Seasonal Affective Disorder (SAD), was first coined in the 1980s, its recency underscoring the lack of research conducted on this topic. Although some may believe that individuals with SAD are merely complaining about the environment on a whim, SAD is triggered by a disruption in the body’s natural circadian rhythm, the natural cycle of physical changes, such as sleep. SAD is linked to seasonal changes, typically beginning in late fall and improving in spring. It is also classified as a major depressive disorder by the American Psychiatric Association. As a result, SAD can significantly affect a person’s daily life, how they think, and how they feel. Common symptoms include feelings of sadness (hopelessness and worthlessness), lack of energy, loss of interest in usual activities, oversleeping, and weight gain.

However, there are also other forms of SAD. One type is winter-pattern SAD, often called the ‘winter blues’. This is a mild version of SAD, and it occurs during the cold months. Its symptoms include overeating, social withdrawal (hibernating), and oversleeping. Roughly 10-20% of Americans may experience a milder form of the winter blues. Rather than predictable seasonal challenges, the holiday blues are feelings of sadness or anxiety brought on by seasonal stressors, particularly during the holidays. There is also summer-pattern SAD or summer depression. This is a rare form of SAD that starts in late spring or early summer and ends in fall. There is very little research done, but common symptoms include agitation, anxiety, decreased appetite, episodes of violent behavior, and trouble sleeping.

Now, what causes SAD? Unfortunately, due to the overarching lack of research on the topic, the exact cause of SAD remains unknown. Yet, there are several theories. In particular, scientists believe that a lack of sunlight may trigger the condition as it shifts individuals' biological clocks. Since one’s internal clock regulates their mood, sleep, and hormones, the daylight changes shift the clock and trick the body into thinking that it’s nighttime, which continues melatonin secretion. This overproduction of melatonin causes sluggish and sleepy behavior. Another potential cause of SAD is a brain chemical imbalance. Serotonin is a chemical messenger that typically regulates mood, and with less sunlight, serotonin levels drop, which increases one’s inclination towards depression. Additionally, sunlight helps produce vitamin D, and reduced sunlight in the winter months can result in a vitamin D deficiency, which affects serotonin and mood. In particular, there is evidence that this brain chemical imbalance causes SAD, as individuals with SAD frequently desire carbohydrate-rich foods, which are known to increase mood-enhancing chemicals.

Moving beyond its causes, who is typically affected by SAD? The demographics commonly associated with this condition are individuals aged 18-30 and women. Individuals with another major depressive disorder or who have relatives diagnosed with mental conditions are at a higher risk for SAD. Geographically, those who live at latitudes that are far north or south of the equator receive less sunlight and are at a greater risk.

Despite those traits, how is SAD diagnosed? As with many mental conditions, health professionals discourage patients from self-diagnosing with SAD. This is because there may be another reason for their depression, or the condition that they’re presenting may have an atypical form, making their diagnosis more complex. The United States Preventive Services Task Force recommends that all adults be screened for major depressive disorders using the Patient Health Questionnaire or Geriatric Depression Scale at least once. However, there is no blood test or scan specific to SAD. So, physicians will ask patients about their symptoms and have them fill out a questionnaire. Then, if patients meet the criteria of having depressive episodes occur during specific seasons for at least 2 consecutive years and have their episodes happen more frequently during specific seasons, then they will be diagnosed with SAD.

Finally, what are the treatment options for SAD? One treatment option is phototherapy, also known as light therapy. This consists of a light therapy box or special lamp with fluorescent light tubes and a plastic screen to block UV rays. This box mimics natural outdoor light. This indirect exposure helps individuals recalibrate their body clock and relieve symptoms of SAD. As such, it is best to implement this therapy for about 15-30 minutes in the morning and throughout the entire winter season.

Another option is psychotherapy or talk therapy, specifically cognitive behavior therapy (CBT). CBT-SAD teaches people with SAD how to challenge and change unhelpful depressive thoughts. This form of therapy is commonly implemented through 2 weekly group sessions over the course of 6 weeks. CBT also utilizes behavioral activation by helping people identify activities to offset the loss of interest associated with SAD. According to Cambridge University, CBT was found to be more effective than light therapy in reducing depressive symptoms, and it may provide longer-term remission.

In terms of medication, individuals with SAD may be prescribed vitamin D supplements or antidepressants to enhance their mood.

There are also behavioral or lifestyle modifications that can be made. For those with SAD, making the effort to spend more time outdoors for more sun exposure or simply exercising can be worthwhile in reducing symptoms. While there is no strong evidence supporting a particular diet to alleviate SAD, individuals should consume nutritious meals that include minerals, vitamins, whole grains, and unprocessed foods. However, people with SAD should not isolate themselves as this commonly worsens symptoms, and should instead stay in contact with friends and family.No matter the length of the day or night, it’s important to keep in mind that seasonal depression or SAD is a legitimate mental health condition. While there are several variations of SAD, and its causes remain unknown, it is still highly treatable through interventions and daily habit improvements, revealing the science behind seasonal depression.

Amber Liwanag: State Vice President (2025-2026)