Seasonal Affective Disorder (SAD)

What seasonal affective disorder is

SAD is not a separate illness but a pattern of major depression (or, less often, bipolar disorder) in which episodes start and end at about the same time each year. Doctors diagnose it when:

• depressive episodes have started and ended at a characteristic time of year for at least 2 consecutive years
• there have been no non-seasonal episodes during that time
• seasonal episodes clearly outnumber non-seasonal ones over the person's lifetime

Episodes typically begin in October or November and lift by March or April. Many more people have milder "winter blues" that do not meet the criteria for depression but still lower energy and mood.

Symptoms

Symptoms of depression

• feeling sad, empty or hopeless most of the day, nearly every day
• losing interest in activities you used to enjoy
• feeling worthless or guilty
• trouble concentrating
• thoughts of death or suicide

Typical of winter-pattern SAD

• oversleeping (hypersomnia) and difficulty getting up
• low energy and heavy, leaden limbs
• cravings for carbohydrates and sweets, overeating
• weight gain
• withdrawing from friends and activities, sometimes described as "hibernating"

Summer-pattern SAD

Less common. It tends to cause:

• trouble sleeping (insomnia)
• poor appetite and weight loss
• restlessness, agitation and anxiety

Seasonal affective disorder vs winter blues

Causes and risk factors

The exact cause is not fully understood. Contributing factors include:

• Disrupted body clock: less morning light shifts the circadian rhythm, the internal 24-hour clock, out of sync with the day.
• Serotonin: brain levels of this mood-regulating chemical may fall with less sunlight.
• Melatonin: longer nights increase production of this sleep hormone, which can cause sleepiness and low energy.
• Vitamin D: lower levels in winter, or outright vitamin D deficiency, may play a role, though evidence is mixed.

Risk factors:

• living farther from the equator, such as in Alaska, Canada, the northern US or northern Europe
• female sex
• young adulthood. SAD often starts between ages 18 and 30
• a personal or family history of depression or bipolar disorder
• working indoors or night shifts with little daylight

Diagnosis

A primary care doctor or mental health professional will ask about your symptoms, when they start and stop each year, and how they affect daily life. They may use a depression questionnaire such as the PHQ-9 and ask about past episodes of high energy or mania to check for bipolar disorder. Blood tests may check thyroid function, vitamin D and anemia, which can cause similar tiredness.

Treatment

Light therapy

Bright light therapy is a first-line treatment for winter-pattern SAD. It works for many people within 1 to 2 weeks.

• Use a light box that gives 10,000 lux of light and filters out UV.
• Sit with it about 16 to 24 inches (40 to 60 cm) from your face, at an angle, eyes open but not staring at it.
• Use it for 20 to 30 minutes each morning, ideally soon after waking.
• Start in early fall, or when symptoms begin, and continue until spring.

Side effects are usually mild: headache, eye strain, nausea or feeling jittery. Using it late in the day can cause insomnia. Check with a doctor before starting if you have bipolar disorder (light can trigger mania), eye disease such as macular degeneration or diabetic retinopathy, or take medicines that increase light sensitivity.

Dawn simulators, which gradually brighten the bedroom before you wake, help some people.

Talking therapy

Cognitive behavioral therapy adapted for SAD (CBT-SAD) helps you replace negative thoughts about winter and schedule enjoyable, energizing activities. Studies suggest its benefits may last longer into future winters than light therapy alone.

Medicines

• SSRIs such as sertraline or fluoxetine are commonly used.
• Bupropion XL is FDA approved to prevent seasonal depressive episodes when started in early fall in people with a history of SAD.

Antidepressants take several weeks to work, so starting before your usual onset helps.

Vitamin D

If your vitamin D level is low, supplements are reasonable for general health. Evidence that vitamin D alone treats SAD is limited, so it should not replace other treatment.

Self-help that makes a difference

• Get outside in daylight every morning, even on cloudy days. Outdoor winter light is usually far brighter than indoor light.
• Sit near windows at home and work.
• Exercise regularly, ideally outdoors.
• Keep a consistent sleep and wake time, including weekends.
• Plan social contact and enjoyable activities in winter.
• Limit alcohol, which worsens mood and sleep.
• Mark your expected onset on a calendar and start light therapy or other prevention ahead of time.

Outlook

SAD tends to recur each year if untreated. With light therapy, therapy or medicine, most people feel substantially better within weeks. Some people find symptoms ease as they age or after moving to a sunnier place. Low mood that persists year-round is a different pattern, such as ongoing depression or dysthymia, and needs its own assessment.

Frequently asked questions

What are the main symptoms of seasonal depression?

The main symptoms are low mood and loss of interest for most of the day, plus oversleeping, low energy, heavy limbs, carbohydrate cravings, weight gain and withdrawal from people. These start around the same time each fall or winter and lift in spring.

Does light therapy really work for SAD?

Yes. Bright light therapy using a 10,000-lux light box for 20 to 30 minutes each morning improves symptoms in many people with winter-pattern SAD, often within 1 to 2 weeks. It needs to be used daily through the season. Ordinary household lamps are not bright enough.

Can you get seasonal affective disorder in summer?

Yes. Summer-pattern SAD is less common. It usually brings insomnia, poor appetite, weight loss, restlessness and anxiety rather than oversleeping and cravings. It may be linked to heat, humidity or long daylight hours. Treatment uses therapy and medicines; light therapy is not used.

How do I know if I have SAD or just the winter blues?

The winter blues cause mild low mood and tiredness but you still enjoy things and function normally. SAD is a form of depression: low mood and loss of interest last most days for weeks, affect work or relationships, and recur every year. If in doubt, a doctor can assess you.

When should I start treatment for seasonal affective disorder?

Ideally, start before your symptoms usually begin, often in early fall. Light therapy and preventive bupropion work best when started early. If symptoms have already begun, start treatment as soon as possible and continue through winter until your usual recovery time in spring.