Seasonal affective disorder

Seasonal affective disorder, usually shortened to SAD, is a form of depression linked to changes in the seasons. Symptoms tend to begin and improve at about the same times each year.

Most people with SAD develop depression during autumn or winter and feel better during spring or summer. A less common pattern begins during spring or summer and improves during autumn.

SAD is more than feeling disappointed about cold weather or shorter days. It can affect sleep, appetite, concentration, relationships, work, and the ability to enjoy life. Symptoms may last for several months.

Doctors usually describe SAD as major depression with a seasonal pattern. Seasonal depressive episodes can also occur as part of bipolar disorder, which causes periods of depression and periods of unusually high or irritable mood.

Effective treatments are available. Recognising the seasonal pattern can help you and your healthcare professional plan treatment before symptoms become more disruptive.

SAD includes the main symptoms of depression. These are present most days and interfere with everyday life. They may include:

• Persistent sadness, emptiness, or irritability
• Loss of interest or pleasure in usual activities
• Low energy or feeling slowed down
• Difficulty concentrating or making decisions
• Feelings of guilt, hopelessness, or worthlessness
• Changes in sleep, appetite, or weight
• Thoughts about death, self-harm, or suicide

Autumn and winter SAD often causes increased sleep, difficulty waking, overeating, carbohydrate cravings, weight gain, and social withdrawal. Some people describe feeling as though they want to “hibernate.”

Spring and summer SAD may cause insomnia, reduced appetite, weight loss, restlessness, anxiety, or agitation. These features are not exclusive to either pattern, so symptoms can look different from person to person.

In children and teenagers, depression may appear as irritability, falling school performance, withdrawal, or changes in sleep rather than obvious sadness.

If you have periods of needing very little sleep, racing thoughts, unusually high energy, impulsive behaviour, or an abnormally elevated or irritable mood, mention them during an assessment. These may be symptoms of mania or hypomania and can point to bipolar disorder.

The exact cause of SAD is not known. Researchers think reduced or changing daylight may affect the brain systems that control mood, sleep, and daily body rhythms.

Your circadian rhythm is the internal clock that helps regulate when you sleep and wake. Seasonal light changes can shift this clock. They may also affect melatonin, a hormone involved in sleep, and serotonin, a brain chemical involved in mood. These changes do not fully explain why some people develop SAD and others do not.

SAD can affect anyone, but it is associated with:

• Living farther from the equator, where seasonal daylight changes are greater
• A personal history of depression or bipolar disorder
• A family history of SAD or other mood conditions
• A pattern of symptoms beginning in early adulthood

These factors increase the possibility of SAD but do not prove that someone has it. Difficult events, loneliness, work patterns, physical illness, and sleep disruption can also affect mood during a particular season without being the underlying cause of SAD.

There is no blood test, brain scan, or questionnaire that can confirm SAD on its own. Diagnosis is based on a detailed assessment of your symptoms and their timing.

A healthcare professional will ask when symptoms start and end, how they affect daily life, and whether similar episodes occurred in earlier years. A seasonal pattern generally means that depressive episodes repeatedly begin during a particular season and improve or fully settle at another time of year. The seasonal episodes must be more common than depression occurring at other times.

You may be asked to complete a depression questionnaire. This can measure symptom severity, but it does not replace a clinical assessment.

The assessment should also check for bipolar disorder, anxiety, alcohol or drug use, medication effects, and your immediate safety. Blood tests may be used to look for other causes of similar symptoms, such as an underactive thyroid or anaemia. These tests rule out other conditions rather than confirm SAD.

Keeping a record of mood, sleep, appetite, and energy across the year can help identify a pattern. Diagnosis may take time if this is your first seasonal episode.

Treatment depends on symptom severity, the seasonal pattern, previous treatment responses, other health conditions, and your preferences. More than one approach may be used.

Light therapy involves sitting near a light box that produces bright visible light while you remain awake and continue an activity such as reading. It is mainly used for autumn and winter SAD, often in the morning. The device should be designed for treating SAD and should filter harmful ultraviolet light. Tanning lamps are not a substitute.

Light therapy can cause headache, eyestrain, nausea, sleep disturbance, or agitation. Speak with a healthcare professional before using it if you have an eye condition, take medicine that increases sensitivity to light, or may have bipolar disorder. Bright light can sometimes trigger mania or hypomania.

Talking therapy can help you manage depressive thoughts and behaviours. Cognitive behavioural therapy adapted for SAD, known as CBT-SAD, also addresses unhelpful responses to winter, reduced activity, and social withdrawal. Skills learned in therapy may help during later seasons.

Antidepressant medicines may be considered for moderate or severe symptoms or when other treatments have not been enough. Some are used during the affected season, while others may be started before symptoms usually begin. Benefits can take time to appear, and side effects differ between medicines. Antidepressants like sertraline or fluoxetine require particular care when bipolar disorder is possible because they can sometimes contribute to a high-mood episode.

Regular sleep and wake times, daytime outdoor activity, exercise, and staying socially connected may support treatment. They should not be presented as replacements for care when depression is significantly affecting your life.

Vitamin D supplements have not been shown to cure SAD. A clinician may recommend them for a confirmed deficiency or another health reason, but taking high doses without advice can be harmful.

Severe depression may require specialist mental healthcare. Hospital treatment or treatments such as electroconvulsive therapy may be considered when depression is life-threatening, causes profound loss of function, or has not improved with other approaches.

Without effective support, seasonal depression can disrupt work, education, finances, and relationships for several months each year. Withdrawal and inactivity may make isolation and low mood worse.

Other possible complications include harmful alcohol or drug use, poor self-care, worsening anxiety, and suicidal thoughts or behaviour. The risk is not the same for everyone, but any thoughts of self-harm deserve attention.

A person whose seasonal depression is part of bipolar disorder may develop mania or hypomania. Recognising this matters because bipolar disorder and major depression are managed differently.

SAD cannot always be prevented. Its cause is not fully understood, and ordinary lifestyle changes do not guarantee that another episode will not occur.

If your episodes follow a predictable pattern, a planned approach may reduce their severity or sometimes prevent a full episode. This might involve starting light therapy, talking therapy strategies, or prescribed medicine before the usual season begins. The timing should be agreed with a healthcare professional rather than estimated on your own.

Tracking symptoms across the year can help you notice early changes in sleep, energy, appetite, or interest. Maintaining regular routines and arranging social and practical support before a difficult season may also make symptoms easier to manage.

SAD often follows a repeated cycle. Symptoms may build gradually as daylight changes, continue through the affected season, and improve when the season changes. Some people have complete recovery between episodes, while others have milder symptoms at other times.

The pattern can change over the years. Episodes may become milder, more severe, less predictable, or stop recurring. Some people later experience depression without a seasonal pattern. SAD does not inevitably worsen, but previous episodes make future seasonal episodes more likely.

A written seasonal plan can be useful. It may record your early warning signs, treatments that helped, expected treatment timing, and people to contact if your mood declines. Continue any prescribed treatment as agreed rather than stopping as soon as the weather changes.

Most people can continue work, study, relationships, and usual activities with an effective treatment plan, although adjustments may be needed during symptomatic months. Routine follow-up is useful when symptoms return, treatment causes side effects, or your usual pattern changes.

Arrange a routine appointment if low mood, loss of interest, tiredness, or sleep changes persist for about two weeks, return during the same season, or interfere with everyday life. Seek earlier advice if you have a history of severe depression or bipolar disorder.

Contact a healthcare professional promptly if symptoms are rapidly worsening, you are struggling to eat or care for yourself, or you experience possible mania, such as very little need for sleep with unusually high energy or risky behaviour.

Get urgent or emergency help if:

• You intend to harm yourself or someone else
• You have made a suicide plan or taken steps to carry it out
• You cannot keep yourself safe
• You are hearing or seeing things others do not, or are losing touch with reality

Call your local emergency number or go to an emergency department. In the United States, you can call or text 988 for the Suicide & Crisis Lifeline. Elsewhere, use your local crisis service or emergency number. If possible, stay with a trusted person and move away from anything you could use to harm yourself.

Is SAD real, or is it just the winter blues?

SAD is a recognised pattern of depression. Winter blues may cause a temporary dip in mood but usually do not produce the persistent symptoms and loss of function seen with SAD.

Can you have seasonal affective disorder in summer?

Yes. Some people develop depression during spring or summer and improve during autumn. Sleep loss, reduced appetite, anxiety, and agitation may be more noticeable with this pattern.

How long does seasonal affective disorder last?

An episode often continues through the affected season and improves when the season changes. Its length and severity differ between people and may change from year to year.

Does vitamin D cure SAD?

No. Low vitamin D and SAD can occur at the same time, but supplements have not been shown to cure seasonal depression. Treating a confirmed deficiency may still be important for general health.

What kind of light should I use for SAD?

Use a purpose-made SAD light box that filters ultraviolet light, not a tanning lamp. Product quality and light output differ. Ask a healthcare professional about safe timing if you have an eye condition, take light-sensitive medicines, or could have bipolar disorder.

Can SAD turn into bipolar disorder?

SAD does not itself turn into bipolar disorder. However, seasonal depression can be one part of bipolar disorder. Periods of unusually high energy, reduced need for sleep, racing thoughts, or impulsive behaviour should be assessed.