Understanding Seasonal Affective Disorder

Many people have difficulty dealing with the darker, shorter days of winter. They struggle to get out of bed in the morning, have less energy, feel down, and gain weight. For people with seasonal affective disorder (SAD), these changes are severe enough to cause significant problems in their everyday lives. But what exactly is SAD? And how can it be treated?

What Is Seasonal Affective Disorder?

SAD is a type of seasonal depression that is thought to be caused by changes in daylight. The most common kind of SAD occurs during the winter months. The symptoms may begin in the fall and last until the early spring. Winter-onset SAD is more common in people who live at higher latitudes.

While less frequent, some people experience seasonal depression during the summer months. It is not clear why summer SAD occurs, but it may be due higher temperatures and humidity.

Who Gets SAD?

Women experience SAD more often than men. It can occur at any age—though it is mostly seen in people in their twenties and thirties. Even children can be affected by SAD. But, they may experience different symptoms than adults. For example, children may be irritable instead of sad.

What Are the Symptoms?

The following symptoms typically begin in the fall, intensify in winter, and subside in spring:

  • Depressed mood, feelings of sadness
  • Cravings for sweet or starchy foods
  • Overeating
  • Significant weight gain or loss
  • Lack of energy
  • Oversleeping or insomnia
  • Fatigue
  • Irritability
  • Social withdrawal
  • Difficulty concentrating
  • Decreased sexual desire

Symptoms of summer-onset SAD may include:

  • Anxiety
  • Insomnia
  • Agitation
  • Weight loss
  • Poor appetite
  • Increased sexual desire

The symptoms of SAD can range from mild to severe. If you are experiencing any of these symptoms, talk to your doctor to get the help that you need.

How Does SAD Differ From Other Types of Depression?

The main difference between SAD and other types of depression is that SAD occurs seasonally, usually during the winter months. In many types of depression, people generally eat and sleep less and lose weight; people with SAD usually eat and sleep more and gain weight when it is cold and dark outside.

SAD, like other types of clinical depression, is not caused by psychological or social factors, although such stresses can aggravate it. Normal sadness tends to be situational and does not generally include these physical symptoms.

The “holiday blues” can be distinguished from SAD because they are generally not accompanied by physical symptoms. They are caused by the typical stresses of the December holiday season and occur only around the holidays.

What Causes SAD?

Lack of exposure to light seems to be the main trigger of SAD symptoms. There are a variety of hypotheses as to the underlying biochemical process that is affected by the lack of light. Also, SAD appears to run in families. Most people with the disorder have at least one close relative who has had bouts of depression (often SAD), other mood disorders, or alcohol use disorder.

An abnormality in one or more neurotransmitters and/or hormones is the suspected cause of SAD. Neurotransmitters are the chemicals that carry messages between nerve cells. A deficiency of the neurotransmitter serotonin is considered to be a likely cause of SAD. Its concentration in the brain varies with the seasons, the smallest amount occurring during the winter.

Other chemicals under investigation include the neurotransmitters norepinephrine and dopamine, and the hormone melatonin. The female sex hormones estrogen and progesterone may also be involved, since women are more vulnerable to SAD than men—especially in the years between puberty and menopause.

How Can SAD Be Treated?

Light Therapy

In this treatment, a person is exposed to light that is 5-20 times brighter than regular indoor lighting by sitting close to a light box for 15 minutes to a few hours a day. Since looking directly at the light is not recommended, usual activities such as reading, writing, and eating can be carried out. The length of time and intensity of the light can vary depending on a person’s needs and the equipment used. Initial evaluation and ongoing supervision of treatment should be provided by a healthcare professional who has experience with light therapy.

Although light therapy is safe for most people, it can cause eyestrain, headaches, insomnia, and feelings of restlessness or irritability. These problems can often be resolved by reducing the length of exposure or sitting farther from the light box. People with certain types of eye disease or those taking medicines that increase light sensitivity may not be able to use light therapy. Talk to your doctor first before you buy a light box. There are many different kinds and, if you need to use a light box, you will want to be sure that you are buying a good quality one.

Lifestyle Changes

There are also lifestyle changes that may be beneficial. You may want to increase your exposure to outdoor light by taking daily walks during the morning or afternoon. Getting regular aerobic exercise can also help improve your mood. In addition, exercise and diet can be used to control the weight gain common in SAD. Since stress can exacerbate SAD, stress management is important, especially during the winter months. Psychotherapy may be useful in coping with problems that are causing stress.


Antidepressant medicines can be used to treat SAD. These medicines may be used along with light therapy. Use of light therapy in conjunction with medicine may also make it possible to take smaller doses of medicine and to reduce medicine side effects. In addition, taking medicine can decrease the amount of time that is needed in front of lights.

Common medicines used to treat SAD include:

  • Bupropion (Wellbutrin)
  • Sertraline (Zoloft)
  • Fluoxetine (Prozac)

Other Potential Treatments

While more research is needed, the hormone melatonin, which plays a role in the biological clock, may help improve sleep and feelings of well-being in people with SAD. Researchers are also studying whether increasing vitamin D levels can be beneficial.

What Is the First Step in Treating SAD?

If you have mild SAD symptoms, increase your exposure to regular indoor and outdoor light. Start a walking program or a daily exercise regime. If you have symptoms that are interfering with your quality of life, talk to your doctor and/or a mental health professional. He or she can determine whether you do have SAD and discuss available treatments. Remember, there are a number of different treatment options that can be used alone or in combination that can help you feel better and keep a brighter outlook.


Golden RN, Gaynes BN, Ekstrom RD, et al. The efficacy of light therapy in the treatment of mood disorders: a review and meta-analysis of the evidence. Am J Psychiatry. 2005;162:656-662.

Information sheet on seasonal affective disorder and light therapy. National Institute of Mental Health, Clinical Psychobiology Branch.Bethesda,MD; August 1996.

Lam RW, Levitt AJ, Levitan RD, et al. The Can-SAD study: a randomized controlled trial of the effectiveness of light therapy and fluoxetine in patients with winter seasonal affective disorder. American Journal of Psychiatry. 2006;163:805-812

NationalInstituteofMental Healthwebsite. The National Organization for Seasonal Affective Disorder (NOSAD) website.


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