Understanding Seasonal Affective Disorder and the Role of Vitamin D
As daylight decreases, many people notice their mood and energy change, even when their routines stay the same. This isn’t coincidence. It’s part of a well-documented pattern known as Seasonal Affective Disorder (SAD), a form of depression that follows a seasonal rhythm, most commonly appearing in late fall and winter.
What Is Seasonal Affective Disorder?
Seasonal Affective Disorder is a type of major depressive disorder that occurs predictably during specific months of the year.
Typical symptoms include:
Persistent low mood or irritability
Loss of interest or pleasure in usual activities
Changes in appetite or weight (often an increase in craving carbs and sweets)
Oversleeping or difficulty waking
Fatigue or slowed thinking
Difficulty concentrating
While many people experience mild “winter blues,” SAD represents a more significant and clinically recognizable shift that interferes with daily life.
Why It Happens
The primary driver is reduced sunlight exposure. Less daylight disrupts the body’s internal clock (circadian rhythm) and decreases both serotonin and melatonin; regulation neurotransmitters essential for mood stability and sleep.
This physiological change can lead to the symptoms above, even in people with no prior history of depression.
The Role of Vitamin D
Vitamin D, often referred to as the “sunshine vitamin,” is obtained through sunlight exposure. It plays a critical role in serotonin production and overall brain function. Low Vitamin D levels have been consistently linked to increased depressive symptoms and fatigue during winter months.
Because sunlight is limited from October through March, supplementation is often recommended. Most adults benefit from 1000–2000 IU daily, though individual needs vary. A simple blood test through your physician can confirm whether your levels are within the optimal range.
Evidence-Based Strategies That Help
Addressing SAD involves both physiological and psychological approaches:
Light Therapy:
Clinically validated light therapy boxes simulate natural daylight. Using a 10,000-lux light for 20–30 minutes each morning can improve mood within one to two weeks.Vitamin D Supplementation:
Regular supplementation helps support neurotransmitter balance. Always confirm dosage with your healthcare provider.Physical Activity:
Moderate aerobic exercise three times a week has been shown to have antidepressant effects comparable to medication in mild cases.Structured Routine:
Consistent sleep, nutrition, and exposure to natural light stabilize the circadian rhythm and reduce vulnerability to low mood.Psychotherapy:
Cognitive-behavioural therapy (CBT) and emotion-focused approaches help address thought patterns, behavioural withdrawal, and the isolation that often accompany seasonal depression.
When to Seek Support
If you notice that low mood, lack of motivation, or fatigue persist for more than two weeks, or if these symptoms recur every winter, professional support can help you assess whether you’re experiencing SAD or another form of depression. Early intervention prevents worsening symptoms and makes treatment more effective.
Bottom Line
Seasonal Affective Disorder is not a personal weakness, it’s a biological and environmental response that can be managed with the right strategies! Understanding your body’s seasonal rhythm, supplementing Vitamin D, and creating intentional structure through the darker months can significantly improve energy, focus, and overall mood.
Written by:
Haley Veronyak, MA, RP-Q
Registered Psychotherapist (Qualifying) | Haley Veronyak Counselling & Psychotherapy
If you’re interested in therapy support for mood, stress, or seasonal changes, you can learn more about my practice here.
