Treating Seasonal Affective Disorder, Understanding Knowledge Gaps

January 10, 2023 - According to the Cleveland Clinic, roughly 5% of adults in the United States experience seasonal affective disorder (SAD), starting between 18 and 30 years old. Mental Health America notes that 80% of people with seasonal affective disorder are women. While this experience affects a relatively small population, up to 20% of people in the US may experience a milder version of SAD. With the number of people affected by SAD, understanding the available treatments and existing knowledge gaps can improve patient outcomes and help direct future research.

What Is SAD?

Seasonal affective disorder (SAD) — sometimes referred to as seasonal depressive disorder — is a mood disorder experienced during a particular season of the year. It is more likely to happen in the colder seasons, such as fall and winter, when there is less sunlight; however, it is not unheard of to have SAD in the spring and summer.

According to StatPearls, “Seasonal affective disorder is classified as depression related to climate and seasonal weather changes. It shares similar symptoms with other modes of depression. Most factors pertaining to the cause-and-effect mechanisms of SAD are yet to be unearthed.”

Symptoms

According to StatPearls, SAD is associated with symptoms such as inattentiveness, depression, social withdrawal, and fatigue. For a patient to be diagnosed with SAD, they must experience these symptoms during a specific time of year and then experience a recovery period for two consecutive years.

Early signs of SAD may include headache, difficulty concentrating, and irritability — common symptoms of mild depression. Poor school performance in certain seasons may also be an indicator of SAD. Although SAD is more common in the winter, it may occur in the summer. However, summer symptoms may differ slightly, presenting as insomnia, weight loss, agitation, and appetite changes.

Causes and Risk Factors of SAD

While there is no definitive cause of SAD, many hypothesize that it is caused by sunlight deficiency and hormonal changes that occur with changes in the climate. Researchers know that changes in sunlight can affect the concentration of serotonin and melatonin in the body, which alters circadian rhythms.

In most patients, SAD is associated with higher levels of melatonin due to lower levels of sunlight. Higher levels of melatonin trigger fatigue, relaxation, and sleep.

Besides causing higher levels of melatonin production, a lack of sunlight is linked to lower levels of vitamin D, which is essential in the active synthesis of serotonin.

SAD is more common in areas that experience all four seasons, as people living in places with sunlight year-round typically don’t experience the effects of low serotonin and high melatonin.

Beyond geographical location, age and gender can also be risk factors for SAD. Many sources note that women are more likely to experience SAD. Additionally, individuals, such as young adults, who are at peak hormone production are more likely to have SAD.

A history of depression may also contribute to the development of SAD. StatPearls says, “A history of depression makes one’s body an easy target for hormonal imbalances and fluctuations. Therefore, any changes in the hormonal concentration of a particular hormone result in a vicious cycle of other hormonal imbalances leading to hormonal depressions.”

Treating SAD

Treatments for SAD can vary dramatically depending on the patient. Like the treatments for many other cognitive conditions, deciding the proper treatment may take multiple tries and can depend on many factors. Some treatments for SAD may include light therapy, hormonal therapy, antidepressants, dietary changes, physical activity, ECT therapy, and vitamin D supplementation.

While all these treatments and many others are available and may be explored, the most common kinds of treatments fall into four categories: light therapy, psychotherapy, antidepressant medication, and vitamin D supplementation.

Light Therapy

According to the National Institute of Mental Health (NIMH), light therapy has been explored since the 1980s and has quickly become a preferred treatment for SAD. Light therapy requires the patient to sit in front of a bright box, emitting approximately 10,000 lux of light, for up to 45 minutes. Often this process occurs first thing in the morning from fall to spring, when exposure to sunlight is reduced. This light is significantly brighter than indoor light but is safe as they filter out UV light.

It is thought that this kind of therapy could simulate the effects of sunlight, providing a source of vitamin D. Looking back at the theory that SAD can be triggered by low vitamin D — which prevents the production of serotonin — light therapy may be an obvious treatment for some patients. Additionally, light exposure at the start of the day may be beneficial for preventing excessive melatonin production until the evening.

One caveat is that light therapy is not advised for people with light sensitivity due to eye disease or as a side effect of medication.

Cognitive Behavioral Therapy

Psychotherapy, also referred to as cognitive behavioral therapy (CBT), is another option for treating SAD. The NIMH notes that traditional CBT has been adapted for people with SAD, referred to as CBT-SAD. This kind of cognitive behavioral therapy is often done in group sessions twice a week for six weeks, focusing on replacing negative thoughts with positive ones. CBT-SAD may also concentrate on scheduling pleasant activities to discourage the typical loss of interest associated with SAD.

Researchers have noted that light therapy and CBT have similar efficacy for people with SAD, but light therapy achieves slightly faster results. Providers who are urgently concerned about patients with SAD may choose to prescribe light therapy instead of CBT. However, other studies suggest that CBT has better long-term impacts on SAD.

Antidepressants

Another potential option for treating SAD is to prescribe antidepressants to increase the concentration of serotonin. The most common antidepressants for SAD are selective serotonin reuptake inhibitors (SSRIs) such as fluoxetine, citalopram, sertraline, paroxetine, and escitalopram. Bupropion is another antidepressant commonly prescribed. While medications may be beneficial for some patients, they are associated with more significant side effects than other SAD treatments.

Vitamin D Supplementation

The final typical therapy is vitamin D supplementation. Vitamin D supplementation can address the low serotonin levels associated with seasonal affective disorder. Taking vitamin D in the morning can help facilitate the active synthesis of serotonin. While evidence supporting vitamin D supplementation is mixed, it is an effective way to address SAD for some patients.

Some sources also suggest starting SAD treatments before its expected onset to minimize the symptoms when it is triggered. Although the jury is still out on whether CBT or light therapy could be utilized as a preventative treatment, bupropion has been an effective preventive SAD therapy. 

Despite multiple options acting as the current standard of care, it is clear that there are many gaps in the understanding of seasonal affective disorder. Future research directions may aim to better understand the cause of SAD and why treatment efficacy varies between patients.