Dark Days, Low Vibes: Understanding Seasonal Affective Disorder

Do you notice yourself feeling more tired, sluggish, or down when fall begins, then feeling better again in the spring or summer? You may be experiencing symptoms of Seasonal Affective Disorder (SAD), a form of depression that follows a predictable seasonal pattern. SAD most commonly occurs during the fall and winter months when daylight is shorter.

Reduced sunlight during these months is believed to disrupt the body’s internal clock (circadian rhythm) and alter levels of key brain chemicals such as melatonin, which regulates sleep, and serotonin, which affects mood. These changes can contribute to depressive symptoms, including:

• Low mood or feelings of hopelessness
• Low energy and fatigue
• Sleeping more than usual
• Craving carbohydrates and gaining weight
• Withdrawing from others or losing interest in usual activities

Although SAD is sometimes dismissed as “winter blues,” it can significantly affect your daily life, relationships, and work performance. The good news is that SAD is treatable.

When and Where SAD Occurs

Onset: Symptoms typically begin in late fall or early winter and improve in spring or summer as daylight increases.

Age of Onset: SAD most commonly begins between ages 15 and 30, but it can appear earlier or later in life.

Geographic Influence:

• SAD is more prevalent in northern latitudes, where winter days are shorter and darker.
• Rates begin to decline south of Columbia, South Carolina, where seasonal light changes are less dramatic.
• SAD is rare in tropical or equatorial regions like southern Florida, where sunlight exposure is more consistent year-round.

Common Symptoms

SAD shares many symptoms with major depressive disorder, but the timing and pattern are seasonal. Symptoms typically develop gradually as daylight decreases and are most intense during the winter months.

Common symptoms include:

• Persistent sadness or low mood
• Constant fatigue or low energy despite adequate sleep
• Excessive sleeping (hypersomnia) and difficulty waking
• Increased appetite, especially for carbohydrates and sweets
• Weight gain
• Difficulty concentrating or making decisions
• Loss of interest in previously enjoyable activities
• Social withdrawal or “hibernation” behavior

What Causes SAD?

The exact cause of SAD is not fully understood, but several biological mechanisms are believed to be involved:

• Reduced sunlight exposure disrupts the body’s circadian rhythm, leading to sleep disturbances and mood changes.
• Melatonin imbalance: Decreased sunlight may increase melatonin production, leading to excessive drowsiness.
• Reduced serotonin levels: Less sunlight may lower serotonin, a neurotransmitter involved in mood regulation, contributing to symptoms of depression.

Who Is at Risk?

You may be more likely to develop SAD if you have:

• A family history of depression or bipolar disorder
• A personal history of depression or other mood disorders
• A biological sex of female (women are diagnosed more frequently, although men may experience more severe symptoms)
• Residence in higher latitudes or regions with long, dark winters

How Is SAD Diagnosed?

To be diagnosed with Seasonal Affective Disorder, the following criteria generally must be met:

• Symptoms meet the diagnostic criteria for major depressive disorder
• Depressive episodes occur during a specific season, typically fall or winter, for at least two consecutive years
• Symptoms improve or fully remit during the spring and summer

Treatment Options for Seasonal Affective Disorder (SAD)

SAD is a highly treatable condition. Several evidence-based strategies can significantly reduce symptoms and improve quality of life. Treatment may involve one or a combination of the following approaches:

• Light Therapy (Phototherapy)
  • Light therapy is the first-line treatment for winter-pattern SAD. It involves sitting near a 10,000-lux light box every morning, ideally within an hour of waking.
  • Sessions typically last 30 to 60 minutes
  • The light mimics natural outdoor light, helping reset circadian rhythms and boost mood
  • Most individuals notice improvement within a few days to a few weeks
  • A clinically tested, properly sized light box is essential (see our related blog post on Light Therapy for recommended light box models
• Vitamin D Supplementation
  • Vitamin D levels are often low during the winter months, especially in individuals with SAD.
  • A blood test can determine your vitamin D level
  • Supplementation may support mood, especially when combined with other treatments
  • Although evidence is mixed on its use as a standalone treatment, it is a reasonable adjunct for those with low levels
• Antidepressant Medications
  •  For more moderate to severe symptoms, antidepressants may be recommended.
  • Bupropion has an FDA approval for the treatment of SAD
  • Other antidepressants, such as sertraline or fluoxetine have shown effectiveness in treating SAD
  • Medications may be beneficial for individuals with a history of major depressive disorder or those who do not respond to light therapy alone
• Cognitive Behavioral Therapy (CBT)
  • A form of CBT specifically adapted for SAD: CBT-SAD focuses on the thoughts and behaviors that contribute to seasonal depression.
  • Helps individuals identify and reframe negative thinking patterns
  • Teaches coping skills for managing seasonal changes
  • Research indicates that CBT-SAD can be as effective as light therapy, with longer-lasting results for some patients
• Lifestyle and Behavioral Strategies
  • Simple daily routines can help minimize symptoms and support recovery
  • Spend time outdoors, especially in the morning even on cloudy days
  • Engage in regular physical activity, which supports mood regulation through increased serotonin and endorphin levels
  • Maintain a consistent sleep–wake schedule, including weekends
  • Increase indoor light exposure by opening blinds, sitting near windows, and using daylight-spectrum bulbs
• Dawn Simulators
  • Dawn simulators are specialized alarm clocks that gradually increase light intensity to mimic a natural sunrise.
  • Can help regulate circadian rhythms
  • May be especially helpful for people with severe morning grogginess or difficulty waking during dark winter mornings

Other Seasonal Patterns: Summer-Pattern SAD

While winter-pattern SAD is the most common form, some individuals experience depression in the spring or summer. This is known as summer-pattern SAD, and it affects an estimated 10% of people with SAD.

Common symptoms of summer-pattern SAD include:

• Insomnia or disrupted sleep
• Decreased appetite, sometimes leading to weight loss
• Agitation, irritability, or restlessness
• Anxiety or increased emotional sensitivity

Although its causes are less well understood, summer SAD is a clinically recognized and impairing subtype of seasonal depression. Accurate diagnosis is important, especially since symptoms may resemble those of other mood or anxiety disorders.

Prognosis

With appropriate treatment and self-care, most individuals with Seasonal Affective Disorder can successfully manage their symptoms and lead fulfilling lives throughout the year. Recognizing early warning signs, beginning treatment before symptoms worsen, and working closely with your healthcare provider can significantly improve outcomes.

If You Suspect SAD

If you believe you may be experiencing symptoms of Seasonal Affective Disorder, talk to your healthcare provider or contact us for further evaluation and treatment. Early diagnosis and treatment can significantly improve your symptoms and help maintain year-round mental wellness.