Seasonal Depression: Why Shorter Days Can Pull Your Mood Down
Every year around this time, some people notice the same slide. Getting out of bed takes more effort, the afternoons feel heavy, cravings for bread and sweets get stronger, and plans with friends start to feel like too much. By spring, it lifts. If that pattern sounds familiar, you may be dealing with seasonal depression, also called seasonal affective disorder or SAD. It is a real form of depression, and it has real causes.
Winter Blues or Seasonal Depression?
Plenty of people feel a little flatter when the days get short. That is common and usually mild. Seasonal depression is different: it meets the criteria for major depression, it shows up at the same time of year, and it gets in the way of work, relationships or daily life. Clinicians usually look for this pattern for at least two years in a row, with the mood lifting when the season changes.
Typical winter symptoms include:
Sleeping more, and still feeling tired
Craving carbohydrates, often with weight gain
Low energy, heaviness in the body and trouble concentrating
Pulling away from people, sometimes described as wanting to hibernate
Low mood, hopelessness or losing interest in things you usually enjoy
Why It Happens
No single cause explains seasonal depression. Researchers have found several pieces that seem to work together, and they all start with light.
Less light throws off your body clock
Your brain keeps time using light, especially morning light. When sunrise comes later and the days are short, that internal clock can drift later than the clock on your wall. You end up trying to wake and work at a time your body still treats as night. The mismatch shows up as grogginess, low energy and low mood.
Melatonin runs longer
Melatonin is the hormone that signals night to the body. Long nights mean a longer melatonin signal, and people with winter depression may produce more of it, or produce it at the wrong time. That can add to sleepiness and sluggishness during the day.
Serotonin activity drops
Serotonin is one of the brain chemicals involved in mood. Studies suggest serotonin activity is lower in winter, partly because the brain clears serotonin away faster in the darker months. This is one reason some antidepressants help.
Vitamin D may play a part
Your skin makes vitamin D from sunlight, and levels often fall in winter. Vitamin D is involved in serotonin activity, so low levels may make symptoms worse. The research on vitamin D supplements as a treatment is mixed, though, so it is worth checking a level rather than assuming it is the answer.
Genes and family history
Seasonal depression tends to run in families, and twin studies point to a genetic piece. Some people are simply more sensitive to changes in light than others.
Where you live and when the clocks change
Seasonal depression is more common farther from the equator, where winter days are shortest. In St. Louis, the shortest day of the year has about 9.5 hours of daylight, compared with nearly 15 hours in June. The end of daylight saving time in early November makes the change feel sudden, because evenings go dark an hour earlier overnight.
Who Is More Likely to Get It
Women, who are diagnosed more often than men
Young adults, since it often starts between about 18 and 30
People with a family history of depression or seasonal depression
People who already have depression or bipolar disorder, whose symptoms may follow the seasons
People who get little daylight, such as those who work night shifts or spend most daylight hours indoors
It Can Happen in Summer, Too
A less common summer pattern exists. It tends to look different: trouble sleeping, poor appetite, weight loss, restlessness, anxiety and irritability. The causes are less well understood, but the same idea applies. If your mood reliably shifts with one season, that pattern is worth mentioning to your clinician.
What Helps
Bright light therapy. A 10,000-lux light box used in the morning is one of the best-studied treatments. The details matter, so we wrote a separate guide on how to use a light box so it actually works.
Therapy built for seasonal depression. A version of cognitive behavioral therapy designed for SAD works about as well as light therapy and may do a better job of preventing the next winter's episode.
Medication. Antidepressants can help. Extended-release bupropion is FDA-approved to prevent seasonal depression when it is started in the fall, before symptoms usually begin.
Daily habits that support your clock. A consistent wake time, time outside in the morning, regular movement and limiting alcohol all help. They rarely fix moderate or severe depression on their own, but they make other treatment work better.
When to Talk to a Psychiatrist
Reach out if your symptoms make it hard to work, care for yourself or connect with people, or if they come back every year. It is also worth a careful evaluation if you have ever had periods of unusually high energy, little need for sleep or racing thoughts. Bipolar disorder can follow a seasonal pattern, and both antidepressants and light therapy need to be used differently in that case.
If you have thoughts of harming yourself, call or text 988 right away, or go to the nearest emergency room.
Worth a Conversation
Seasonal depression is predictable, and that is good news: it means you can plan for it. SANA Psychiatry provides psychiatric evaluation and treatment for adults in Missouri, Illinois and Florida, in person and by video. Current patients can message us through the patient portal. New patients can join our waitlist.
Sources
Written by Sindhura Saini, board-certified psychiatrist (American Board of Psychiatry and Neurology). Last reviewed November 2026. This article is for education and is not a substitute for an individual medical evaluation. If you are in crisis, call or text 988 or go to the nearest emergency room.
Comments