Blog Post #6: Seasonal Affective Disorder: How Changing Daylight Affects Mood and Sleep — and What You Can Do
As the days shorten and nights lengthen, many people notice their energy, mood, and sleep patterns change. For some, these shifts are mild and manageable; for others, they can develop into a recurrent mood condition known as seasonal affective disorder (SAD). Below is a clear, evidence-based explanation of how changing daylight hours affect our brains and sleep — plus practical steps to protect your mental health this season.
What is seasonal affective disorder (SAD)?
SAD is a pattern of depressive symptoms that reliably recurs with seasonal change, most commonly in fall and winter when daylight hours decrease. People with SAD typically report low mood, low energy, social withdrawal, increased sleep, and changes in appetite or weight during the affected season. SAD is recognized clinically as a seasonal pattern of major depressive episodes. NCBI+1
How daylight (or lack of it) changes your biology
Light is the strongest cue for the body’s internal clock (circadian rhythm). Exposure to morning daylight helps set the timing of hormones and brain systems that regulate alertness, sleep, appetite, and mood. When daylight shortens, that timing can shift — causing later sleep and wake times, changes in melatonin (the sleep hormone) production, and downstream effects on mood-regulating neurotransmitters such as serotonin. These biological shifts help explain why mood and sleep often worsen in the darker months. PMC+1
Sleep changes commonly seen with SAD
People with winter-onset SAD often report sleeping more (hypersomnolence) and experiencing delayed sleep timing or difficulty waking in the morning. Altered sleep timing and increased daytime sleepiness both worsen functioning and can amplify low mood and cognitive fog. Addressing sleep timing is therefore a key part of treating seasonal symptoms. PMC
The evidence for light as treatment
Because lack of natural light is central to SAD, controlled bright light therapy (using a light box that emits a specified intensity of white light, typically used early in the morning) has been studied extensively. Meta-analyses of randomized trials show that bright light therapy is effective in reducing depressive symptoms in SAD and is considered a first-line, non-pharmacological treatment option. Early morning exposure to appropriately bright light helps shift circadian timing earlier and can reduce both sleep-related symptoms and low mood. PubMed+1
Practical, evidence-informed steps you can take now
Seek morning light exposure. Spend 20–30 minutes outside early in the day when possible (even on overcast days) or consider a clinically tested light box used per instructions. Morning light helps reset your circadian clock and improves alertness. PMC+1
Stabilize sleep timing. Go to bed and wake up at consistent times every day, aiming to get up with daylight or shortly after. Avoid late-evening bright screens that can delay melatonin production. PMC+1
Prioritize activity and schedule. Behavioral activation — deliberately scheduling pleasant or meaningful activities — combats withdrawal and low motivation that often accompany SAD. Light + activity together can produce better outcomes than either alone. PubMed
Talk to your provider about treatment options. For many people, a combination of light therapy, cognitive-behavioral approaches tailored to SAD (CBT-SAD), and, when appropriate, medication offers the best results. Your clinician can help you decide which combination fits your symptoms and lifestyle. PubMed+1
Check medical contributors. Low vitamin D or thyroid problems can worsen energy and mood; coordinate with your primary care clinician as needed. (Evidence on vitamin D supplementation for SAD is mixed, so testing and individual medical advice are recommended.)
When to seek professional help
If seasonal changes cause persistent depressive symptoms, significant sleep disruption, difficulty caring for yourself or your family, or thoughts of harming yourself, seek professional help promptly. Early intervention reduces suffering and prevents worsening of symptoms.
If you’re in Lincoln or the surrounding area and seasonal changes are affecting your mood or sleep, Power of the Mind Psychology can help. We provide assessment and evidence-based treatment for SAD and seasonal mood problems — including CBT tailored for seasonal depression, guidance on safe and effective light therapy, and coordinated care with medical providers when needed.
Call us at 402-413-5425 or visit powerofthemindpsychology.com to schedule an evaluation or learn more. If symptoms are severe or you’re thinking about hurting yourself, call 988 (U.S. Suicide & Crisis Lifeline) or go to your nearest emergency room immediately.