by Dr. Megan Britton

As the days grow shorter and the sunlight fades, many people notice a shift in their energy, motivation, and mood. Seasonal Affective Disorder, or SAD, is a form of depression that follows a seasonal pattern, most commonly appearing in late fall and winter. SAD affects a wide range of individuals across industries and can have a real impact on work performance, emotional resilience, and daily functioning.

This article explains what SAD is, why it happens, what symptoms to watch for, and how evidence-based treatments, including light therapy, can help. 

What Is Seasonal Affective Disorder?

Seasonal Affective Disorder is a type of depression that follows a predictable seasonal pattern. The most common form is winter-pattern SAD, which begins in late fall and resolves in spring as sunlight returns. Reduced daylight disrupts the body’s circadian rhythm, affects serotonin and melatonin regulation, and contributes to changes in energy, sleep, and mood.

SAD is very common. Estimates suggest that about 5% of adults in the U.S. experience full SAD each year, while another 10 to 20% experience a milder but noticeable winter slump. People working long indoor hours, living in northern climates, or managing intense workloads may be especially vulnerable.

Key Symptoms to Watch For

SAD shares many symptoms with depression, but its timing and seasonal pattern set it apart.

Common symptoms include:

• Low mood or persistent sadness
  
• Difficulty concentrating or staying motivated
  
• Fatigue or low energy levels
  
• Increased sleep or difficulty waking up
  
• Cravings for carbohydrates or weight changes
  
• Feeling socially withdrawn or less engaged
  
• Loss of interest in activities that are normally enjoyable
  

These symptoms can affect productivity, collaboration, creativity, and overall wellbeing. Recognizing them early allows for timely, effective intervention.

Why SAD Happens: The Role of Light and Circadian Rhythm

Sunlight plays a major role in regulating mood, energy, and sleep. When daylight decreases, the body’s internal clock can drift out of alignment. Several mechanisms help explain why SAD occurs:

• Reduced sunlight may lower serotonin levels, which affects mood
  
• Shorter days can disrupt circadian rhythms, making it harder to maintain consistent energy and sleep
  
• Increased darkness can elevate melatonin, leading to fatigue or oversleeping
  
• People who work indoors or long hours may get even less natural light, increasing risk
  

Understanding these factors helps explain why one of the most effective treatments involves recreating sunlight through light therapy lamps.

Evidence-Based Treatments That Work

Multiple treatments have been shown to alleviate SAD symptoms and help people feel and function better during the winter season.

Many individuals use a combination of the following approaches:

Light Therapy: A First-Line Treatment

Light therapy is one of the most extensively studied treatments for SAD. It involves sitting near a specialized light box that mimics the intensity of natural outdoor light. These devices deliver bright, full-spectrum light without harmful UV rays.

How light therapy works:

• Helps reset circadian rhythms by signaling to the brain that it is morning and time to be awake and alert
  
• Boosts serotonin activity, supporting mood and wellbeing
  
• Reduces melatonin production during morning hours, improving energy
  

Evidence-based recommendations for effectiveness:

• Choose a 10,000 lux light therapy lamp – this is the intensity supported by research
  
• Sit about 16 to 24 inches from the lamp
  
• Use the lamp for 20 to 30 minutes each morning, ideally within an hour of waking
  
• Keep your eyes open but do not look directly at the light
  
• Continue daily use through late fall and winter for best results

Most people begin to feel improvement within one to two weeks. Light therapy is safe for most individuals, though people with certain conditions or those on photosensitizing medications should consult their healthcare provider.

Cognitive Behavioral Therapy for SAD (CBT-SAD)

CBT-SAD is a structured form of talk therapy that focuses on understanding negative thought patterns, building coping strategies, and adjusting behaviors that worsen seasonal mood changes. It can be delivered by a therapist in person or virtually.

Key elements include:

• Identifying thought patterns that arise during darker months
  
• Developing behavioral strategies to maintain structure and activity
  
• Increasing engagement in energizing or meaningful experiences
  
• Building resilience and reducing avoidance behaviors
  

Studies show that CBT-SAD is as effective as light therapy in the short term and may have longer-lasting effects.

Antidepressant Medication

Some individuals benefit from antidepressants, especially selective serotonin reuptake inhibitors (SSRIs). These medications can help regulate mood and energy during the winter season. They are typically prescribed when symptoms are moderate to severe, or when other interventions have not provided enough relief.

Only a clinician can determine whether medication is appropriate, but it is one of the well-established options for treating SAD.

Vitamin D Supplementation

Vitamin D levels often drop during winter months due to decreased sun exposure. Low vitamin D has been associated with fatigue, low mood, and decreased immune function. Supplementation may help individuals who are deficient, although it is not a sole treatment for SAD.

People who live in northern regions or spend most of their time indoors may want to discuss vitamin D testing with their provider.

Lifestyle Strategies That Support Wellbeing

Lifestyle factors can meaningfully impact energy, mood, and focus during the winter season. Helpful strategies include:

• Maximizing natural light exposure by opening blinds, working near windows, or taking midday walks
  
• Maintaining a consistent sleep schedule to stabilize circadian rhythms
  
• Engaging in regular physical activity, which has strong mood-enhancing effects
  
• Staying socially connected, even if motivation is lower than usual
  
• Spending time outdoors, especially during daylight hours
  
• Organizing tasks and deadlines to reduce unnecessary stress
  

These steps support resilience and can amplify the benefits of other treatments.

How Employers and Organizations Can Support Individuals

SAD can influence workplace performance, attendance, and collaboration. Organizations that acknowledge seasonal wellbeing challenges often see improvements in morale and productivity.

Supportive approaches may include:

• Offering flexible scheduling to allow for morning daylight exposure
  
• Encouraging or providing access to mental health benefits
  
• Educating teams about SAD and available resources
  
• Supporting hybrid or outdoor work options when possible
  
• Improving office lighting to mimic more natural brightness
  

Small environmental changes can have a meaningful impact on wellbeing during the winter months.

When to Seek Professional Help

Anyone experiencing persistent low mood, significant loss of motivation, or difficulty functioning should consider talking with a healthcare provider. Early support can prevent symptoms from escalating and help maintain overall wellbeing and performance.

If stress or fatigue feel overwhelming, or if symptoms seem out of proportion to seasonal changes, it is important to check in with a primary care provider to rule out other underlying health issues and determine whether additional support, including medication, could be helpful.

Key Takeaways

Seasonal Affective Disorder is a real and treatable condition that affects many people during the winter months. Understanding the signs, recognizing the role of light and circadian rhythms, and using evidence-based strategies can help individuals stay productive, balanced, and emotionally healthy even when daylight is limited.

For many individuals, light therapy offers substantial relief, especially when used consistently. Combined with CBT-SAD, lifestyle adjustments, and professional support when needed, it is possible to navigate the winter season with far greater ease.

Supporting wellness is an investment in resilience and long-term wellbeing. With the right tools, people and organizations can create healthier routines and environments that help everyone thrive, no matter the season.