Seasonal depression, often called seasonal affective disorder (SAD), is a depression that occurs each year at the same time, usually starting in fall or winter and ending in spring or early summer. It is more than just "the winter blues" or "cabin fever." A rare form of SAD known as "summer depression," begins in late spring or early summer and ends in fall. 


People who suffer from SAD have many of the common signs of depression: Sadness, anxiety, irritability, loss of interest in their usual activities, withdrawal from social activities, and inability to concentrate. They often have symptoms such as extreme fatigue and lack of energy, increased need for sleep, craving for carbohydrates, and increased appetite and weight gain. 

Symptoms of winter SAD include:

  • Fatigue
  • Increased need for sleep
  • Decreased levels of energy
  • Weight gain
  • Increase in appetite
  • Difficulty concentrating
  • Increased desire to be alone

Symptoms of summer SAD include:

  • Weight loss
  • Trouble sleeping
  • Decreased appetite

How Common is SAD?

Between 4 and 6 percent of the U.S. population suffers from SAD, while 10 to 20 percent may suffer from a more mild form of winter blues. Three-quarters of the sufferers are women, most of whom are in their 20s, 30s, and 40s. Though SAD is most common during these ages, it can also occur in children and adolescents. Older adults are less likely to experience SAD. 

This illness is more commonly seen in people who live at high latitudes (geographic locations farther north or south of the equator), where seasonal changes are more extreme. It is estimated that 1% of Florida residents, 4% of Washington, D.C. residents, and nearly 10% of Alaska residents suffer from SAD. 

What Causes SAD?

The exact cause of this condition is not known, but the influence of latitude on SAD strongly suggests that it is caused by changes in the availability of sunlight. One theory is that with decreased exposure to sunlight, the biological clock that regulates mood, sleep, and hormones is delayed, running more slowly in winter. Exposure to light may reset the biological clock. 

Another theory is that brain chemicals that transmit information between nerves, called neurotransmitters (for example, serotonin), may be altered in individuals with SAD. It is believed that exposure to light can correct these imbalances. 

How Can I Tell if I Have SAD?

It is very important that you do not diagnose yourself. If you have symptoms of depression, see your doctor for a thorough assessment. Sometimes physical problems can cause depression. But other times, symptoms of SAD are part of a more complex psychiatric problem. A health professional should be the person to determine the level of depression and recommend the right form of treatment. 

How is SAD Treated?

Research now shows that light therapy is an effective treatment for SAD. Sometimes antidepressant medicine is used alone or in combination with light therapy. Spending time outdoors during the day can be helpful, as well as maximizing the amount of sunlight you're exposed to at home and in the office.

What Is Light Therapy, and Is It Safe?

Light therapy, sometimes called phototherapy, is administered by a device that contains white fluorescent light tubes covered with a plastic screen to block ultraviolet rays. The intensity of light emitted (Lux) should be at least 10,000 Lux. The patient does not need to look directly into the light, but reads or eats while sitting in front of the device at a distance of 2 to 3 feet. Light therapy is safe and generally well tolerated. 

Minor side effects of light therapy include:

  • Eye strain
  • Headache
  • Irritability
  • Fatigue
  • Insomnia

At What Time of the Day and for How Long Should I Use Light Therapy?

Recent studies suggest that morning light therapy is more effective than evening treatments. Using this treatment too late in the day may also produce insomnia.

Many health professionals today prefer to treat SAD with 10,000 Lux for 30 minutes every morning. Patients have shown some improvement within 2 to 4 days and reach full benefits within 2 to 4 weeks. The symptoms of SAD return quickly after discontinuation of light therapy, so light treatment should be continued throughout the entire season of low sunlight. 

Even though they generate enough light, tanning beds should not be used to treat SAD. The amount of ultraviolet (UV) rays they produce is harmful to the skin and eyes. 

Can I Prevent the Onset of SAD?

If you think you have symptoms of SAD, see your doctor for a thorough examination. Your doctor will want to make sure that these symptoms are not caused by another form of depression or major medical illness. 

If you have been diagnosed with SAD, here are some things you can do to help to prevent it from coming back: 

  • Try to spend some amount of time outside every day, even when it's very cloudy. The effects of daylight are still beneficial.
  • Begin using a light box upon the onset of low sunlight (fall season), even before you feel the onset of winter SAD.
  • Eat a well-balanced diet and include sufficient amounts of vitamins and minerals as recommended by the FDA. This will help you have more energy even though your body is craving starchy and sweet foods.
  • Try exercising for 30 minutes a day, three times a week.
  • Seek professional counseling, if needed, during the winter months.
  • Stay involved with your social circle and regular activities. This can be a tremendous means of support during winter months.

xox, Dr. G