For many people, shorter days and less sunlight can lead to seasonal affective disorder, or SAD. Also referred to as seasonal depression, WebMD defines as a mood disorder that happens every year at about the same time. It usually starts in fall or winter and ends in spring or early summer.

Courtney Shaw, nurse practitioner at Aspirus St. Luke’s healthcare, in Duluth, says that while anyone can affected, research indicates that SAD is more prevalent in the northern states.

The Yale School of Medicine concurs, saying SAD is more common in latitudes further from the equator. Within the United States, SAD is rare in Florida, more common in Mid-Atlantic States, and most common in the northern US or Canada. One study using questionnaires estimated an incidence of SAD of 1% in Florida, around 5% at the latitude of New York, and around 10% at the latitude of New Hampshire. Some patients report that they did not have trouble with the winter when they lived in southerly latitudes but did have significant seasonal symptoms when they moved further north.

The American Psychiatric Association (APA)reports that approximately 5% of adults in the U.S. experience SAD and it typically lasts about 40% of the year. If 5% sounds low, keep in mind that SAD is most prevalent in the northern states.

“The most difficult months for people with SAD in the United States tend to be January and February,” the APA states.

According to the National Institute of Mental Health (NIH),studies indicate that people with winter-pattern SAD, have reduced levels of the brain chemical serotonin, which helps regulate mood. Research also suggests that sunlight affects levels of molecules that help maintain normal serotonin levels. Shorter daylight hours may prevent these molecules from functioning properly, contributing to decreased serotonin levels in the winter.

Symptom of SAD can include:

Persistent sad, anxious, or “empty” mood most of the day, nearly every day, for at least 2 weeks

    • Feelings of hopelessness or pessimism

    • Feelings of irritability, frustration, or restlessness

    • Feelings of guilt, worthlessness, or helplessness

    • Loss of interest or pleasure in hobbies and activities

    • Decreased energy, fatigue, or feeling slowed down

    • Difficulty concentrating, remembering, or making decisions

    • Changes in sleep or appetite or unplanned weight changes

    • Physical aches or pains, headaches, cramps, or digestive problems that do not have a clear physical cause and do not go away with treatment

    • Thoughts of death or suicide or suicide attempts

For winter-pattern SAD, additional symptoms can include:

    • Oversleeping (hypersomnia)

    • Overeating, particularly with a craving for carbohydrates, leading to weight gain

    • Social withdrawal (feeling like “hibernating”)

While not everyone who experiences SAD may experience all symptoms, it can range from mild to severe.

There are treatment options to reduce or even eliminate SAD symptoms. The APA reports that SAD can be effectively treated in several ways, including light therapy, antidepressant medications, talk therapy or some combination of these. While symptoms will generally improve on their own with the change of season, symptoms can improve more quickly with treatment, especially if they have become severe.

Light therapy involves sitting in front of a light therapy box that emits a very bright light (and filters out harmful ultraviolet (UV) rays). It usually requires 20 minutes or more per day, typically first thing in the morning, during the winter months. Most people see some improvements from light therapy within one or two weeks of beginning treatment. To maintain the benefits and prevent relapse, treatment is usually continued through the winter. Because of the anticipated return of symptoms in late fall, some people may begin light therapy in early fall to prevent symptoms.

The NHS says that many people with winter-pattern SAD have vitamin D deficiency. Vitamin D supplements may help improve symptoms. However, the NHS cautions, studies testing vitamin D as a treatment for SAD have produced mixed results, with some studies indicating that it is as effective as light therapy and other studies finding no effect.

NHS UK, the United Kingdom’s government-funded healthcare system, also recommends getting as much natural sunlight as possible, and getting physical exercise.

If symptoms do not improve, or begin to increase, experts recommend talking with a healthcare provider, who can properly determine if the symptoms meet the criteria for SAD.