Seasonal affective disorder (SAD) is a type of depression that comes and goes with the seasons. It usually starts in the late fall and early winter and goes away during the spring and summer. Some people do have episodes of depression that start in the spring or summer, but that is a lot less common. Symptoms of SAD may include

• Sadness
• Gloomy outlook
• Feeling hopeless, worthless, and irritable
• Loss of interest or pleasure in activities you used to enjoy
• Low energy
• Difficulty sleeping or oversleeping
• Carbohydrate cravings and weight gain
• Thoughts of death or suicide

SAD is more common in women, young people, and those who live far from the equator. You are also more likely to have SAD if you or your family members have depression.

The exact causes of SAD are unknown. Researchers have found that people with SAD may have an imbalance of serotonin, a brain chemical that affects your mood. Their bodies also make too much melatonin, a hormone that regulates sleep, and not enough vitamin D.

The main treatment for SAD is light therapy. The idea behind light therapy is to replace the sunshine that you miss during the fall and winter months. You sit in front of a light therapy box every morning to get daily exposure to bright, artificial light. But some people with SAD do not respond to light therapy alone. Antidepressant medicines and talk therapy can reduce SAD symptoms, either alone or combined with light therapy.

Seasonal affective disorder is a mental health condition that is triggered by the changing of the seasons. This condition is a subtype of major depressive disorder and bipolar disorder. Major depressive disorder is characterized by prolonged sadness and a general lack of interest, while bipolar disorder is characterized by similar depressive episodes alternating with periods of abnormally high energy and activity (hypomania or mania). People with seasonal affective disorder have signs and symptoms of either major depressive disorder or bipolar disorder only during certain months of the year. Major depressive disorder is more common than bipolar disorder among people with seasonal affective disorder. This condition usually begins in a person's twenties or thirties.

The signs and symptoms that occur during depressive episodes in people with seasonal affective disorder are similar to those of major depressive disorder, including a loss of interest or enjoyment in activities, a decrease in energy, a depressed mood, and low self-esteem. In most people with seasonal affective disorder, depression and other features appear in the fall and winter months and subside in the spring and summer months. In these individuals, additional symptoms often include weight gain due to increased cravings for carbohydrates and an increase in sleep (hypersomnia). Affected individuals with underlying bipolar disorder typically have alternating episodes of depression in the fall and winter months and mania during the spring and summer months.

In about 10 percent of people with seasonal affective disorder, the condition has the opposite seasonal pattern, occurring in the spring and summer months and stopping during the fall and winter months. These individuals usually have a loss of appetite and sleep, unlike those with symptoms in the fall and winter.

For those affected, it is estimated that symptoms of seasonal affective disorder are present during 40 percent of the year. In some individuals, seasonal affective disorder does not recur every year. Thirty to 50 percent of affected individuals do not show symptoms of the disorder in consecutive winters. In about 40 percent of individuals with seasonal affective disorder, depressive episodes continue after winter and do not alleviate in the summer months, leading to a change in diagnosis to either major depressive disorder or bipolar disorder.

Individuals with seasonal affective disorder tend to have another psychological condition, such as attention-deficit/hyperactivity disorder (ADHD), an eating disorder, anxiety disorder, or panic disorder.

Seasonal affective disorder occurs in 0.5 to 3 percent of individuals in the general population; it affects 10 to 20 percent of people with major depressive disorder and about 25 percent of people with bipolar disorder.

Some individuals have a condition known as subsyndromal seasonal affective disorder or seasonality, which is more common than seasonal affective disorder. These individuals have only mild changes in mood that correspond with the changes in seasons.

As the days get shorter, many people find themselves feeling sad. You might feel blue around the winter holidays, or get into a slump after the fun and festivities have ended. Some people have more serious mood changes year after year, lasting throughout the fall and winter when there’s less natural sunlight. What is it about the darkening days that can leave us down in the dumps? And what can we do about it?

NIH-funded researchers have been studying the “winter blues” and a more severe type of depression called seasonal affective disorder, or SAD, for more than 3 decades. They’ve learned about possible causes and found treatments that seem to help most people. Still, much remains unknown about these winter-related shifts in mood.

“Winter blues is a general term, not a medical diagnosis. It’s fairly common, and it’s more mild than serious. It usually clears up on its own in a fairly short amount of time,” says Dr. Matthew Rudorfer, a mental health expert at NIH. The so-called winter blues are often linked to something specific, such as stressful holidays or reminders of absent loved ones.

“Seasonal affective disorder, though, is different. It’s a well-defined clinical diagnosis that’s related to the shortening of daylight hours,” says Rudorfer. “It interferes with daily functioning over a significant period of time.” A key feature of SAD is that it follows a regular pattern. It appears each year as the seasons change, and it goes away several months later, usually during spring and summer.

SAD is more common in northern than in southern parts of the United States, where winter days last longer. “In Florida only about 1% of the population is likely to suffer from SAD. But in the northernmost parts of the U.S, about 10% of people in Alaska may be affected,” says Rudorfer.

As with other forms of depression, SAD can lead to a gloomy outlook and make people feel hopeless, worthless and irritable. They may lose interest in activities they used to enjoy, such as hobbies and spending time with friends.

“Some people say that SAD can look like a kind of hibernation,” says Rudorfer. “People with SAD tend to be withdrawn, have low energy, oversleep and put on weight. They might crave carbohydrates,” such as cakes, candies and cookies. Without treatment, these symptoms generally last until the days start getting longer.

Shorter days seem to be a main trigger for SAD. Reduced sunlight in fall and winter can disrupt your body’s internal clock, or circadian rhythm. This 24-hour “master clock” responds to cues in your surroundings, especially light and darkness. During the day, your brain sends signals to other parts of the body to help keep you awake and ready for action. At night, a tiny gland in the brain produces a chemical called melatonin, which helps you sleep. Shortened daylight hours in winter can alter this natural rhythm and lead to SAD in certain people.

NIH researchers first recognized the link between light and seasonal depression back in the early 1980s. These scientists pioneered the use of light therapy, which has since become a standard treatment for SAD. “Light therapy is meant to replace the missing daylight hours with an artificial substitute,” says Rudorfer.

In light therapy, patients generally sit in front of a light box every morning for 30 minutes or more, depending on the doctor’s recommendation. The box shines light much brighter than ordinary indoor lighting.

Studies have shown that light therapy relieves SAD symptoms for as much as 70% of patients after a few weeks of treatment. Some improvement can be detected even sooner. “Our research has found that patients report an improvement in depression scores after even the first administration of light,” says Dr. Teodor Postolache, who treats anxiety and mood disorders at the University of Maryland School of Medicine. “Still, a sizable proportion of patients improve but do not fully respond to light treatment alone.”

Once started, light therapy should continue every day well into spring. “Sitting 30 minutes or more in front of a light box every day can put a strain on some schedules,” says Postolache. So some people tend to stop using the light boxes after a while. Other options have been tested, such as light-emitting visors that allow patients to move around during therapy. “But results with visors for treating SAD haven’t been as promising as hoped,” Postolache says.

Light therapy is usually considered a first line treatment for SAD, but it doesn’t work for everyone. Studies show that certain antidepressant drugs can be effective in many cases of SAD. The antidepressant bupropion (Wellbutrin) has been approved by the U.S. Food and Drug Administration for treating SAD and for preventing winter depression. Doctors sometimes prescribe other antidepressants as well.

Growing evidence suggests that cognitive behavioral therapy (CBT)—a type of talk therapy—can also help patients who have SAD. “For the ‘cognitive’ part of CBT, we work with patients to identify negative self-defeating thoughts they have,” says Dr. Kelly Rohan, a SAD specialist at the University of Vermont. “We try to look objectively at the thought and then reframe it into something that’s more accurate, less negative, and maybe even a little more positive. The ‘behavioral’ part of CBT tries to teach people new behaviors to engage in when they’re feeling depressed, to help them feel better.”

Behavioral changes might include having lunch with friends, going out for a walk or volunteering in the community. “We try to identify activities that are engaging and pleasurable, and we work with patients to try to schedule them into their daily routine,” says Rohan.

A preliminary study by Rohan and colleagues compared CBT to light therapy. Both were found effective at relieving SAD symptoms over 6 weeks in the winter. “We also found that people treated with CBT have less depression and less return of SAD the following winter compared to people who were treated with light therapy,” Rohan says. A larger NIH-funded study is now under way to compare CBT to light therapy over 2 years of follow up.

If you’re feeling blue this winter, and if the feelings last for several weeks, talk to a health care provider. “It’s true that SAD goes away on its own, but that could take 5 months or more. Five months of every year is a long time to be impaired and suffering,” says Rudorfer. “SAD is generally quite treatable, and the treatment options keep increasing and improving.”

Lift Your Mood

These “self-care” tips might help with seasonal depression. See a mental health professional if sadness doesn’t go away or interferes with your daily life:

• Go to a movie, take a walk, go ice-skating or do other activities you normally enjoy.
• Get out in the sunlight or brightly lit spaces, especially early in the day.
• Try to spend time with other people and confide in a trusted friend or relative.
• Eat nutritious foods, and avoid overloading on carbohydrates like cookies and candies.
• Be patient. You won’t suddenly “snap out of” depression. Your mood will improve gradually.
• If you have thoughts of suicide, get help right away. Call the toll-free National Suicide Prevention Lifeline at 1-800-273-TALK (8255).

Millions of American adults may suffer from SAD, although many may not know they have the condition. SAD occurs much more often in women than in men, and it is more common in those living farther north, where there are shorter daylight hours in the winter. For example, people living in Alaska or New England may be more likely to develop SAD than people living in Florida. In most cases, SAD begins in young adulthood.

SAD is more common in people with major depressive disorder or bipolar disorder, especially bipolar II disorder, which is associated with recurrent depressive and hypomanic episodes (less severe than the full-blown manic episodes typical of bipolar I disorder). Additionally, people with SAD tend to have other mental disorders, such as attention-deficit/hyperactivity disorder, an eating disorder, an anxiety disorder, or panic disorder.

SAD sometimes runs in families. SAD is more common in people who have relatives with other mental illnesses, such as major depression or schizophrenia.

Scientists do not fully understand what causes SAD. Research indicates that people with SAD may have reduced activity of the brain chemical (neurotransmitter) serotonin, which helps regulate mood. Research also suggests that sunlight controls the levels of molecules that help maintain normal serotonin levels, but in people with SAD, this regulation does not function properly, resulting in decreased serotonin levels in the winter.

Other findings suggest that people with SAD produce too much melatonin—a hormone that is central for maintaining the normal sleep-wake cycle. Overproduction of melatonin can increase sleepiness.

Both serotonin and melatonin help maintain the body’s daily rhythm that is tied to the seasonal night-day cycle. In people with SAD, the changes in serotonin and melatonin levels disrupt the normal daily rhythms. As a result, they can no longer adjust to the seasonal changes in day length, leading to sleep, mood, and behavior changes.

Deficits in vitamin D may exacerbate these problems because vitamin D is believed to promote serotonin activity. In addition to vitamin D consumed with diet, the body produces vitamin D when exposed to sunlight on the skin. With less daylight in the winter, people with SAD may have lower vitamin D levels, which may further hinder serotonin activity.

Negative thoughts and feelings about the winter and its associated limitations and stresses are common among people with SAD (as well as others). It is unclear whether these are "causes" or "effects" of the mood disorder, but they can be a useful focus of treatment.

Seasonal affective disorder does not have a clear pattern of inheritance in families. Overall, the risk of developing this condition is greater for first-degree relatives (such as parents or siblings) of affected individuals compared to the general public. Studies have found that approximately 15 percent of individuals with seasonal affective disorder have a first-degree relative who also has the condition.

Many individuals with seasonal affective disorder have relatives with other mood or psychological disorders (such as major depressive disorder or schizophrenia). Studies show that 25 to 67 percent of people with seasonal affective disorder have one or more relatives with such a disorder. These other disorders may run in families in part because they share some genetic risk factors with seasonal affective disorder. However, these conditions are relatively common in the general population, and so they may occur in multiple people in a family by chance.

SAD is not considered a separate disorder but is a type of depression characterized by its recurrent seasonal pattern, with symptoms lasting about 4 to 5 months per year. Therefore, the signs and symptoms of SAD include those associated with major depression, and some specific symptoms that differ for winter-pattern and summer-pattern SAD. Not every person with SAD will experience all of the symptoms listed below.

Symptoms of major depression may include:

• Feeling depressed most of the day, nearly every day
• Losing interest in activities you once enjoyed
• Experiencing changes in appetite or weight
• Having problems with sleep
• Feeling sluggish or agitated
• Having low energy
• Feeling hopeless or worthless
• Having difficulty concentrating
• Having frequent thoughts of death or suicide

For winter-pattern SAD, additional specific symptoms may include:

• Oversleeping (hypersomnia)
• Overeating, particularly with a craving for carbohydrates
• Weight gain
• Social withdrawal (feeling like “hibernating”)

Specific symptoms for summer-pattern SAD may include:

• Trouble sleeping (insomnia)
• Poor appetite, leading to weight loss
• Restlessness and agitation
• Anxiety
• Episodes of violent behavior

Get Immediate Help

If you or someone you know is in immediate distress or is thinking about hurting themselves, call the National Suicide Prevention Lifeline toll-free at 1-800-273-TALK (8255). You also can text the Crisis Text Line (HELLO to 741741) or use the Lifeline Chat on the National Suicide Prevention Lifeline website.

As the days get shorter and there is less daylight, you may start to feel sad. While many people experience the “winter blues,” some people may have a type of depression called seasonal affective disorder (SAD).

The first step is to determine how much your symptoms interfere with your daily life.

Do you have mild symptoms that have lasted less than 2 weeks?

• Feeling down but still able to take care of yourself and others
• Having some trouble sleeping
• Having less energy than usual but still able to do your job, schoolwork, or housework

These activities can make you feel better

• Doing something you enjoy
• Going outside in the sunlight
• Spending time with family and friends
• Eating healthy and avoiding foods with lots of sugar

If these activities do not help or your symptoms are getting worse, talk to a health care provider.

Do you have more severe symptoms that have lasted more than 2 weeks?

• Social withdrawal
• Oversleeping
• Gaining weight
• Craving foods with lots of sugar like cakes, candies, and cookies

Seek professional help

• Light therapy
• Psychotherapy (talk therapy)
• Medications
• Vitamin D supplements

If you think you may be suffering from SAD, talk to your health care provider or a mental health specialist about your concerns. They may have you fill out specific questionnaires to determine if your symptoms meet the criteria for SAD.

To be diagnosed with SAD, a person must meet the following criteria:

• They must have symptoms of major depression or the more specific symptoms listed above.
• The depressive episodes must occur during specific seasons (i.e., only during the winter months or the summer months) for at least 2 consecutive years. However, not all people with SAD do experience symptoms every year.
• The episodes must be much more frequent than other depressive episodes that the person may have had at other times of the year during their lifetime.

Treatments are available that can help many people with SAD. They fall into four main categories that may be used alone or in combination:

• Light therapy
• Psychotherapy
• Antidepressant medications
• Vitamin D

Talk to your health care provider about which treatment, or combination of treatments, is best for you. For tips for talking with your health care provider, refer to the NIMH fact sheet, Taking Control of Your Mental Health: Tips for Talking With Your Health Care Provider.

Light Therapy

Since the 1980s, light therapy has been a mainstay for the treatment of SAD. It aims to expose people with SAD to a bright light every day to make up for the diminished natural sunshine in the darker months.

For this treatment, the person sits in front of a very bright light box (10,000 lux) every day for about 30 to 45 minutes, usually first thing in the morning, from fall to spring. The light boxes, which are about 20 times brighter than ordinary indoor light, filter out the potentially damaging UV light, making this a safe treatment for most. However, people with certain eye diseases or people taking certain medications that increase sensitivity to sunlight may need to use alternative treatments or use light therapy under medical supervision.

Psychotherapy or “Talk Therapy”

Cognitive behavioral therapy (CBT) is a type of talk therapy aimed at helping people learn how to cope with difficult situations; CBT also has been adapted for people with SAD (CBT-SAD). It is typically conducted in two weekly group sessions for 6 weeks and focuses on replacing negative thoughts related to the winter season (e.g., about the darkness of winter) with more positive thoughts. CBT-SAD also uses a process called behavioral activation, which helps individuals identify and schedule pleasant, engaging indoor or outdoor activities to combat the loss of interest they typically experience in the winter.

When researchers directly compared CBT with light therapy, both treatments were equally effective in improving SAD symptoms. Some symptoms seemed to get better a little faster with light therapy than with CBT. However, a long-term study that followed SAD patients for two winters found that the positive effects of CBT seemed to last longer over time.

Medications

Because SAD, like other types of depression, is associated with disturbances in serotonin activity, antidepressant medications called selective serotonin reuptake inhibitors (SSRIs) are also used to treat SAD when symptoms occur. These agents can significantly enhance patients' moods. Commonly used SSRIs include fluoxetine, citalopram, sertraline, paroxetine, and escitalopram.

The U.S. Food and Drug Administration (FDA) also has approved another type of antidepressant, bupropion, in an extended-release form, that can prevent recurrence of seasonal major depressive episodes when taken daily from the fall until the following early spring.

All medications can have side effects. Talk to your doctor about the possible risk of using these medications for your condition. You may need to try several different antidepressant medications before finding one that improves your symptoms without causing problematic side effects. For basic information about SSRIs, bupropion, and other mental health medications, visit the NIMH Mental Health Medications page. Also, visit the FDA website for the most up-to-date information on medications, side effects, and warnings.

Vitamin D

Because many people with SAD often have vitamin D deficiency, nutritional supplements of vitamin D may help improve their symptoms. However, studies testing whether vitamin D is effective in SAD treatment have produced mixed findings, with some results indicating that it is as effective as light therapy but others detecting no effect.

Seasonal affective disorder (SAD) is a type of depression with a recurring seasonal pattern, with symptoms most often starting in the late fall and early winter and going away in the spring and summer. The risk of SAD is higher in people who live far from the equator and those with a personal or family history of depression. Women are more likely than men to develop SAD, and younger people have a higher risk than older ones.

Types of treatment that have been studied for SAD include medication (antidepressants), psychotherapy (such as cognitive behavioral therapy, CBT), light therapy, and dietary supplements (such as vitamin D).

Bottom Line

• Antidepressant medications, including selective serotonin reuptake inhibitors (SSRIs) or bupropion, may be used for SAD.
• A type of CBT adapted for use with SAD patients helps to relieve symptoms, and its effects may continue into subsequent winters, even without additional sessions with a therapist.
• Light therapy involves daily exposure to bright artificial light, usually from early fall until spring. It typically requires sitting for 20 to 60 minutes each morning in front of a light box that produces much more light than ordinary indoor lighting. The idea behind light therapy is to replace the diminished sunlight of the fall and winter months. In several studies, light therapy has had beneficial effects on SAD symptoms similar to those of medication or CBT.
• Low levels of vitamin D, caused by low dietary intake of the vitamin or not enough exposure to sunshine, have been found in people with SAD. However, it’s unclear whether vitamin D supplementation can help to relieve SAD symptoms.
• Very little research has been done on dietary supplements other than vitamin D for SAD. A few studies involving very small numbers of people have looked at melatonin and St. John’s wort for treatment of SAD, with unclear or inconsistent results. Single small studies of vitamin B12 for treatment of SAD and Ginkgo biloba for prevention of SAD did not find that the supplements were beneficial.

Safety

• Like other medications, those used for SAD may have side effects. Sometimes, it’s necessary to try several medications to identify one that works well without too many undesired effects.
• CBT is generally considered safe.
• Light therapy sometimes has side effects such as dizziness, nausea, headaches, or tired eyes. This form of treatment may not be appropriate for people with diseases of the retina, recent eye surgery, or bipolar disorder or those who are taking medicines that increase sensitivity to light.
• Some dietary supplements may have side effects or interact with medicines. St. John’s wort is known to interact in harmful ways with a large number of medicines. Some vitamins, including vitamin D, may be toxic if taken in excessive doses. It’s a good idea to talk with your health care provider about any dietary supplement you’re considering or taking, especially if you take medicine.

Because the timing of the onset of winter pattern-SAD is so predictable, people with a history of SAD might benefit from starting the treatments mentioned above before the fall to help prevent or reduce the depression. To date, very few studies have investigated this question, and existing studies have found no convincing evidence that starting light therapy or psychotherapy ahead of time could prevent the onset of depression. Only preventive treatment with the antidepressant bupropion prevented SAD in study participants, but it also had a higher risk of side effects. Therefore, people with SAD should discuss with their health care providers if they want to initiate treatment early to prevent depressive episodes.