What Is Seasonal Affective Disorder?

Learn about SAD, how it may impact your sleep, and what you can do to combat symptoms

Lonely young woman feeling alone and negative emotion.
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Seasonal affective disorder, also known as seasonal depression, is a type of depression that typically occurs and resolves at the same time each year. Commonly known as SAD, the condition is treatable and usually lasts for a few months of the year.

For many people, cold, dark days trigger their SAD. “It typically occurs during the fall and winter months when days become shorter,” explains owner and director of New York’s Suffolk DBT (Dialectical Behavioral Therapy), Jeanette Lorandini. “However, it can also happen during summertime.”

Like other forms of depression, SAD can affect your sleep, but you can take steps to support your sleep health and your mental health throughout whatever season triggers your depression.

How does SAD impact your sleep?

If you have SAD, you may experience sleep disturbances, as well as episodes of prolonged fatigue or extended sleep. People with SAD often experience hypersomnia, feeling sleepy during the day or sleeping longer than usual at night. You may have difficulty waking from a long sleep or feel the need to nap. Napping may not provide relief from feeling sleepy, though, and SAD may also lead to insomnia due to disrupted sleep patterns.

“Even if someone with SAD gets a full night’s sleep,” explains Jordan Bierbrauer of Thriveworks in Colorado Springs, Colorado, “they could still awaken feeling restless and fatigued due to the impact that depression has on the body.”

According to some research, people with SAD may sleep two or more hours longer on weekends in the fall and winter compared with weekends in the spring and summer. However, it’s important to note that increased sleep in cooler seasons is common for people without SAD, too, though to a lesser degree.

In an older survey of 293 people with SAD, 80% of respondents reported winter hypersomnia. That’s in comparison to 10% who reported insomnia and 5% who reported hypersomnia in combination with insomnia. About 5% reported no sleep issues.

A more recent survey of nearly 5,000 participants found that almost 7% met the criteria for SAD. Of those with SAD, 25% experienced insomnia. That’s compared to just over 7% of respondents without SAD who experienced trouble falling or staying asleep. Although more research is needed, insomnia may be more prevalent in people who experience SAD in the summertime.

As with other forms of depression, seasonal depression may trigger nightmares. “Studies have found that 16% of people with SAD had frequent nightmares, compared to 2.4% of people without SAD,” adds Bierbrauer.

What causes seasonal affective disorder?

Researchers don’t yet know the exact cause or causes of SAD, but based on research, they have a few theories.

“There are a number of factors that can influence the development of seasonal affective disorder,” says Lorandini. “These include genetics, stress, circadian rhythms, and changes in hormones with the seasons. Additionally, some experts believe that people who live further away from the equator may be more likely to experience SAD due to a lack of sunlight during winter months.” Colder temperatures also make people less inclined to spend time outside, limiting their exposure to the natural light that is available.

Several mental health disorders are associated with circadian-rhythm misalignment, including SAD, which is a type of depression. Your master clock is your suprachiasmatic nucleus (SCN), located in your hypothalamus. It syncs with the mini clocks located in all your cells, and all together, these control your sleep-wake cycle. The SCN does this through exposure to environmental cues, like light in the morning and darkness at night. But the days get shorter in late fall and early winter.

Darkness, via your eyes’ photoreceptors, kicks of a process that eventually signals the pineal gland to release the hormone melatonin, which helps relax you for sleep. Research suggests that some people may be more sensitive to melatonin release.

Likewise, light in the morning is key for syncing our sleep-wake cycle. “Our bodies are programmed to stop producing melatonin — a natural chemical that aids in sleep — when they are exposed to sunlight,” says Megan Ford of Relief Mental Health, which has 10 locations in Illinois and New Jersey. “With less sunlight available in the winter months, you may find that you have an increased desire to stay in bed.”

For those who experience SAD in spring or summer, too much light may be hindering melatonin production, which can delay sleep or prevent someone from getting enough sleep. And a lack of sleep can affect mood and energy levels.

Light signaling the SCN — again via a chain reaction that starts with our eyes — also helps set in motion a host of other hormone-signaling processes. The changes to light and darkness that occur as the seasons change disrupt this signaling.

“During the winter months, when days are shorter and nights are longer,” says Colleen Wenner, founder and clinical director of New Heights Counseling of Fort Walton Beach, Florida, “our bodies produce less serotonin — a hormone that helps regulate mood and energy levels. This decrease in serotonin can lead to feelings of depression, anxiety, and fatigue.”

Many people also experience a drop in vitamin D levels during the winter months from reduced sunlight exposure and being bundled up when outdoors. Sunlight hitting your skin kicks off the process of vitamin D synthesis within the body. That’s why the micronutrient is called the sunshine vitamin. This vitamin plays roles for mood and sleep, likely through its regulation of melatonin and serotonin.

One more thing to consider is that some research indicates that evening chronotypes, meaning those who lean more toward being a night owl, may be more at risk for SAD, according to research, though scientists don’t know the exact reasons for this.

Symptoms of seasonal affective disorder

Symptoms of seasonal affective disorder are much like those of other forms of depression. Bierbrauer says to be on the lookout for “social withdrawal, isolation, fatigue, a lack of interest in typically pleasurable activities, hopelessness, irritability, significant weight loss, insomnia, a diminished ability to think or concentrate, and recurring thoughts of death.”

Also monitor yourself for other sleep disturbances, such as not wanting to get out of bed, as well as changes in appetite, such as a lack of interest in eating or increased cravings for “comfort foods,” like carbohydrates.

“Additionally, if you are someone who experiences anxiety at your baseline,” Ford adds, “SAD can exacerbate those symptoms as well.”

How to fight symptoms of SAD

An important thing to remember is that SAD is a temporary form of depression. Some strategies from the experts we interviewed can help you cope with this difficult period and ease your symptoms.

  • Get natural sunlight when possible. “Make an effort to get outside during the day,” Wenner says, “even if it’s just for a few minutes. Natural sunlight helps regulate your body’s circadian rhythm and can help boost your mood.”
  • Invest in a SAD light. “These extra bright lights can mimic sunshine and have been said to improve your mood in just a few minutes a day,” Ford says.
  • Practice good sleep hygiene. “Establish a regular sleep schedule and stick to it,” Wenner says, “even on weekends. Avoid caffeine and alcohol in the evening, and limit screen time before bed.”
  • Get tested for vitamin D deficiency. “Adding vitamin D to your diet could improve your mood and make you feel better overall,” Ford says. But talk to your doctor before adding supplements.
  • Eat a healthy diet. “Eating a balanced diet full of fruits, vegetables, whole grains, and lean proteins can help boost your energy level,” Wenner says.
  • Exercise regularly. Exercise releases endorphins,” Wenner adds, “which can help reduce stress and improve your mood. Aim for at least 30 minutes of physical activity a day.”
  • Engage in activities you typically find enjoyable. “Sometimes we may not feel as motivated to hang out with friends or participate in a hobby,” Ford says. “But if you can give yourself the push to start, you may find that you are glad that you did.”

Another important thing to remember about SAD, or any other form of depression, is that it’s not your fault. SAD is brought on by many factors out of your control. If the above DIY strategies don’t provide you relief, be sure to consult with a mental health professional. “A therapist can help you develop coping strategies to manage your symptoms,” Wenner says. Your physician or medical professional may determine that medication may also be appropriate; everyone’s situation will be slightly different.