Seasonal affective disorder (SAD)

Seasonal affective disorder is a pattern of depression that recurs at about the same time each year. In clinical terms, it is a form of major depression with a seasonal pattern. The most common type is winter depression, which tends to appear as days get shorter. A less common summer pattern also exists.

Many people feel a bit flatter or more tired in the darker months. These winter blues are mild and don't stop you from functioning. Seasonal depression is different: the low mood is persistent, and it affects work, relationships and self-care.

SAD tends to be more frequent in places far from the equator, where winter daylight is short, and it often starts in young adulthood. People with a history of depression or bipolar disorder, or a family history of mood problems, may be more vulnerable.

Symptoms usually build gradually and follow the season. Common signs of winter-pattern SAD include:

• Persistent low mood, sadness or emptiness for most of the day
• Loss of interest in things you normally enjoy
• Low energy and feeling heavy or sluggish
• Sleeping much more than usual and struggling to get up
• Craving carbohydrates and gaining weight
• Difficulty concentrating
• Withdrawing from friends and activities
• Feelings of hopelessness or worthlessness

Summer-pattern SAD more often involves trouble sleeping, poor appetite, restlessness and anxiety.

If you have thoughts of death or suicide, this is not something to wait out until spring. Reach out for help right away: in the US, call or text 988; in the UK and Ireland, call Samaritans at 116 123; or call your local emergency number.

Researchers think several mechanisms contribute:

• Less daylight can disrupt the body's internal clock (circadian rhythm), which affects sleep, energy and mood.
• Changes in brain chemicals, such as serotonin, may be linked to reduced sunlight.
• Melatonin, the hormone that signals sleep, may be produced at the wrong times or in greater amounts during dark months.
• Lower vitamin D levels in winter have been studied as a possible factor, although the evidence is mixed.

Psychological and social factors matter too. Colder weather often means less exercise, less time outdoors and more isolation, which can deepen low mood and loneliness. Thinking patterns, such as dreading winter in advance, can also play a role.

Seasonal depression is not a character flaw or a lack of willpower. It reflects real biological and psychological changes, which is why structured treatment, not just "toughing it out," tends to work best.

SAD is treatable, and many people do best with a combination of approaches.

• Light therapy: sitting near a special light box (often called a SAD lamp) for a set time each morning mimics daylight. It is one of the most studied treatments for winter depression. It's best to start it with guidance from a health professional, especially if you have eye conditions, take photosensitizing medication or have a history of bipolar disorder.
• Cognitive behavioral therapy (CBT): a version adapted for SAD helps people challenge negative thoughts about winter and plan enjoyable, active routines. Some research suggests its effects may last into following years.
• Medication: a psychiatrist or physician may recommend an antidepressant, sometimes started before the season begins for people with a clear yearly pattern.

A psychologist or clinical psychologist can assess your symptoms, while a psychiatrist can evaluate whether medication is appropriate. In the first appointment, expect questions about timing, sleep, appetite, mood history and family history.

Alongside professional care, these habits often help:

• Get outside in the morning, even on cloudy days.
• Keep a regular sleep and wake time.
• Exercise, ideally outdoors or near a window.
• Plan social contact and enjoyable activities in advance for the darker months.
• Make your home and workspace brighter.
• Limit alcohol, which can worsen mood and sleep.
• Eat regular, balanced meals to keep energy steady.

If you know that symptoms tend to return each year, talk to a professional before the season starts. Planning ahead can make the difference between a hard winter and a manageable one. Some people also find it useful to keep a simple mood diary to spot early warning signs. Seek help sooner if low mood lasts more than two weeks or makes daily life difficult.