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Sunshine is an effective mood-lifter – most of us notice that a sunny day makes it easier to be cheerful, while grey days can contribute to a gloomy mood. It’s normal for the weather to have an effect on your mood, but in some people, this is a deeper problem called Seasonal Affective Disorder, which was first described in the 1980s. SAD, which affects as many as 10 million Americans, is considered a form of depression.

Here’s more information about this common problem, including how it’s treated.

Symptoms of SAD

During wintertime, many people are less energetic and long for the sunny days of summer, but SAD is more than just “winter blues.” SAD symptoms are similar or identical to the symptoms of clinical depression – the only difference is that they’re linked to season.

Typically, symptoms show up when daylight hours are more limited, during fall and winter, and dissipate during spring and summer. January and February are often the worst months for SAD. Symptoms include:

• Persistent depression that doesn’t go away
• Loss of interest in favorite activities
• Feelings of hopelessness or worthlessness
• Low energy, tiredness, and sleep disturbances such as trouble sleeping or oversleeping
• Increased appetite, especially for carbohydrate-rich foods, and weight gain
• Persistent thoughts of suicide or death

Who is likely to develop SAD?

No one knows why, but younger adults are more prone to SAD, and women are four times more likely to develop it than men.

People who are prone to depression generally may be more prone to develop SAD. Summer-onset SAD is also possible, although it is much more unusual. Some people with bipolar disorder may experience mania symptoms in spring and summer, and depression in fall and winter.

As with many mental health conditions, if your family has a history of SAD, you may be more likely to develop the problem. Many people with SAD have family members with a mental illness.

Geography can play a role, too. People living furthest from the equator experience the fewest hours of sunlight in fall and winter, and are more likely to develop SAD as a result. For example, SAD is much more common in Scandinavian countries.

What causes SAD?

Exactly why some people develop SAD is unknown, but it seems to be related to our circadian clock , which is the combination of behavior and biology that gives us cues on how to structure our daily and nightly routine – when to get up, go about our daily activities, eat, and go back to bed, in 24-hour cycles.

Researchers believe that a neurotransmitter called serotonin, which is important in regulating mood, may play a role in SAD. People with SAD seem to have trouble regulating serotonin in winter.

Vitamin D is believed to play a role in seratonin activity, and Vitamin D insufficiency is common in winter, especially in northern climates. However, a link between Vitamin D and SAD has not been proven.

Melatonin, a hormone that regulates sleep, may also be involved. Your melatonin level increases naturally when it’s dark, which helps cue your body that it’s time to go to sleep. The shorter days associated with winter triggers your body to produce more melatonin naturally, leading to feelings of sluggishness and lethargy. This effect may be exaggerated in people with SAD.

How is SAD treated?

SAD can be treated by medication, light therapy, or psychotherapy, alone or in combination.

Forms of medication for SAD include a type of drug called Selective Serotonin Reuptake Inhibitors (SSRIs). These help the body more effectively regulate serotonin. In addition, Vitamin D supplementation is sometimes used, although researchers disagree on how effective this is.

Light therapy is a proven treatment for SAD, helping replace the lost sunlight hours. Light boxes that filter out ultraviolet rays and provide 10,000 lux of florescent light are used, and light visors are also available as well.

A form cognitive behavioral therapy, or CBT, can be effective in helping people cope with SAD. CBT-SAD helps people learn to replace the negative, gloomy thoughts associated with SAD and instead focus on more positive thoughts through behavioral activation. Behavioral activation means that the person focuses on engaging in activities they enjoy to help them cope.

For anyone who is prone to any form of depression, including SAD, self-care is important. Plan to take advantage of available sunny days and sunlight hours, and take part in physical activities whenever you can. But if this isn’t enough, seek help.