Seasonal Affective Disorder (SAD) is a kind of depression that begins and ends at roughly the same times every year. Generally this starts in the fall and continues through the winter months. SAD can also emerge in the spring or early summer months as well.


Most commonly SAD symptoms arise during late fall or early winter and tend to diminish as the days become more sunny during spring and summer. A less frequent pattern of SAD can also appear in the reverse pattern:  symptoms that begin in spring or summer. SAD, in either pattern often starts out very mild but can continue to progress in severity as the season wears on.

Signs and symptoms of SAD may include:

  • Depressed mood, low self-esteem
  • Loss of interest or pleasure in activities you used to enjoy
  • Appetite and weight changes
  • Feeling angry, irritable, stressed, or anxious
  • Unexplained aches and pains
  • Changes in sleeping pattern
  • Difficulty concentrating
  • Fatigue and lack of energy; reduced sex drive
  • Use of drugs or alcohol for comfort
  • Feelings of sadness, hopelessness, and despair

Just as with other forms of depression, SAD symptoms vary from person to person—appearing to be related to genetic vulnerability and geographic location. To be diagnosed with seasonal affective disorder a person must have experienced these cyclical symptoms for two or more consecutive years.

What are the causes of seasonal affective disorder?

The exact causes of seasonal affective disorder are not fully understood, most theories attribute the disorder to the decreasing amount of daylight hours in winter. Shorter days and a reduction of exposure to sunlight that occurs in winter are thought to affect a person by disrupting the following:

Circadian rhythms.

The internal clock – the natural sleep-wake cycle responds to changes between light and dark to regulate sleep, mood, and appetite. The longer periods of dark and decreased amount of daylight is thought to disrupt this “internal clock”. This disruption can result in feeling groggy, disoriented, and sleepy at inappropriate times.

Production of melatonin.

At night when it’s dark, the brain produces the hormone melatonin. This helps sleep and then sunlight during the day signals the brain to stop melatonin production. This results in feeling awake and alert. However, the short days and long nights of winter can result in an over production of melatonin. The result of this can include feeling drowsy and low on energy.

Production of serotonin.

Exposure to the reduced sunlight of winter can lower your body’s production of serotonin, a neurotransmitter that plays a key role in the brains ability to regulate mood.  A deficit in serotonin often is linked to depression, dysregulation of sleep, appetite, memory, and sexual desire.

Risk factors

While Seasonal affective disorder can affect anyone it’s most common in people who live far north or south of the equator. Other risk factors include:


While 3 out of 4 sufferers of SAD are women, men often experience more severe symptoms.


Winter SAD is first diagnosed in people aged 18 to 30 and less frequent with increasing age.

Family history

Having relatives who’ve experienced SAD or another type of depression puts you at greater risk.

Treatment for seasonal affective disorder: Light therapy

The most common form of winter SAD treatment is light therapy, also called phototherapy. Light therapy is thought to work by replacing the missing daylight of winter via exposure to bright light that mimics natural outdoor light. Suppressing the brain’s secretion of melatonin with exposure to the light can lead to feeling more awake and alert. The light can also help decrease feelings of tiredness and sadness.

Light therapy has been shown to be an effective treatment for SAD, approaching an 85% effective treatment rate in some studies. The timing and length of exposure needed varies according to the severity of the symptoms and an individual’s unique circadian rhythm.

Light therapy has to be continued daily throughout the winter months to be effective. Starting light therapy before the onset of symptoms in the fall may even help prevent seasonal affective disorder.

Two different ways of administering light therapy.

A light box. This device delivers intense light, with up to ten times the intensity of normal household lighting. Treatment is relatively simple, simply sit about 12 inches in front of a 10,000-lux light box for 15 to 30 minutes each morning. The light box emits a metered amount of white light. The harmful ultraviolet (UV) rays filtered out. Although light needs to enter the eyes staring directly at the light box is not advised. For the best results continue on with a normal morning routine. Generally most people notice an improvement in their SAD symptoms with in the first few days and experience a near complete reduction of symptoms in as few as two weeks.

Although a light box can be purchased without a prescription it is advisable to work with a professional to achieve the maximum possible benefit. There are very few negative side effects of light therapy however it is best to consult your doctor if any odd symptoms are observed.  For those suffering bipolar disorder beware that light therapy may trigger a manic episode.

A dawn simulator. Think of this a “rising sun alarm”. It is a device that slowly increases the amount of light in the bedroom. This simulates the rising sun and gently wakes you. The effect is that of the sun beaming through open curtains on a cloudless morning. This can help reset circadian rhythm and improve mood. Unlike light boxes that may trigger hypomania or mania in those with bipolar disorder, a dawn simulator does not appear to have this effect.

For more details on selecting a light box visit this guide from the Mayo Clinic: Light Box