Seasonal Affective Disorder and Sleep Disorders

It’s normal to feel a little blue during the winter, when the days are short and the weather is cold. But some people experience something more extreme – a seasonal form of depression that interferes with their mood, weight, energy levels, and sleep. Recognized by the American Psychiatric Association in the late 1990s, seasonal affective disorder (SAD) affects 4 to 6 percent of people.

Learn more about the symptoms and causes of SAD, how it affects sleep during the winter and summer seasons, and what affected individuals can do to get a better night’s sleep.

What is seasonal affective disorder?

For most, seasonal affective disorder (SAD) happens when the days are short during the winter. 3 percent of Americans have winter-onset SAD, and nearly 7 percent of individuals with depression have worse symptoms during winter.

SAD is more than just the “winter blues. It is a seasonal form of mild to moderate depression tied to the increasing levels of darkness and the sun’s lower position in the sky. During the winter season, individuals with SAD experience lower energy levels and poor mood.

SAD symptoms usually start and end at the same time for affected individuals each year (with the changing of the seasons in late fall or early spring). In what’s known as reverse SAD or summer-onset SAD, one out of ten SAD patients experience it in the summer.

Symptoms of seasonal affective disorder

People with SAD experience the following symptoms of depression for a period lasting roughly 5 months (through the length of the season):

  • Low energy levels
  • Difficulty concentrating
  • Depression, including feelings of hopelessness and suicidal thoughts
  • Loss of interest in formerly enjoyable activities
  • Appetite and weight changes
  • Trouble sleeping, feelings of sluggishness and/or agitation

Some of these symptoms present oppositely depending on whether the individual has winter-onset or summer-onset SAD (meaning the disorder affects them during the winter or summer, respectively):

Symptoms of winter-onset SAD (Winter depression) Symptoms of summer-onset SAD (Summer depression)
Oversleeping (hypersomnia)
Increased cravings for carbohydrate-rich foods
Weight gain
Increased lethargy
Increased moodiness and irritability (difficulty getting along with others)
Increased sensitivity, especially to rejection
Heavy sensation in arms and/or legs
Difficulty falling or staying asleep (insomnia)
Reduced appetite
Weight loss
Increased anxiety

To be diagnosed with SAD, a person must experience these symptoms at a significantly higher rate or intensity during the winter or summer season.

Changing seasons may also affect individuals with bipolar disorder, inducing depression during the fall and winter months and mania during the spring and summer. If an individual has depression as well as SAD, they typically experience worse symptoms during the winter.

Causes of seasonal affective disorder

Your body’s circadian rhythms depend in large part on sunlight. One study found individuals with SAD may be more sensitive to light than others, especially during the winter. When the amount of sunlight decreases during the winter, individuals with SAD experience disruptions to their biological clock that disrupt their body’s serotonin and melatonin production.

Serotonin and melatonin play a key role in regulating your mood and sleep patterns, and they’re both affected by the changes in light that bring on SAD. These hormones share an inverse relationship: happiness hormone serotonin rules the daytime, and as it gets dark, the brain metabolizes it into sleepiness hormone melatonin to help you fall asleep.

Vitamin D contributes to your body’s serotonin production, and we get less vitamin D when there’s less sunlight. Lower vitamin D (and lower serotonin) levels correlate with lower energy levels during the day and increased drowsiness.

When the day is done, the pineal gland in your brain kickstarts melatonin production. But the main way it knows the day is done is through perceiving sunlight during the day. When there’s less sunlight, it doesn’t do its job as well, and the effect is disproportionate for people with SAD.

Individuals with SAD have longer melatonin production during the winter than summer. Because it gets darker earlier, the brain thinks it’s time for bed and begins melatonin production earlier than normal. And because there’s less direct sunlight in the morning during the winter, it keeps melatonin levels higher than they should be, resulting in daytime grogginess.  

Individuals with summer-onset SAD experience the opposite problem. With summer there is more light, so melatonin production is delayed later than normal, especially for those living farthest from the equator.

Risk factors for SAD

Although the seasonal change in sunlight is the main culprit behind SAD, there are certain risk factors that make a person more likely to get SAD.

  • Women are more likely than men to have SAD, although symptoms are more severe in men.
  • There is some tendency for SAD to run in families. Two-thirds of people with mood disorder in their families have SAD.
  • People with depression or bipolar disorder are more likely to experience worsened symptoms during seasons changing.
  • Younger people are more likely to experience winter SAD than older people.
  • Overall, SAD is more common among individuals who live farther from the equator, due to correspondingly extreme differences in levels of sunlight.

In 2012, researchers studied and compared the sleep patterns of individuals in Ghana, located a mere 5 degrees above the equator, with those living in Norway, at 69 degrees above the equator. They wanted to see how the extreme fluctuations in sunlight affected Norwegian sleep patterns, as compared to the Ghanaians who enjoyed fairly steady sunlight. They found Norwegians went to bed and woke earlier in the summer, and experienced higher rates of insomnia, fatigue, and poor mood during the winter. In contrast, there were no seasonal differences for Ghanaians.

Seasonal affective disorder and sleep

SAD causes or exacerbates many sleep problems. Sleep problems are often a first warning sign of depression, so it makes sense that they accompany SAD. A 2016 study of Finnish adults reported the following prevalence of sleep problems among individuals with SAD:

Sleep issue Affected percentage of people with SAD Affected percentage of general population
Insomnia 25% 7.6%
Frequent nightmares 16% 2.4%
Hypnotic usage during last month 26.3% 7.6%
Received depression diagnosis within the last year 30.4% 4.1%
Antidepressant usage during the last month 24.3% 3.6%

People with SAD are more likely to be night owls, and to sleep either for too long or for too short (fewer than 6 hours or more than 9).

The biggest sleep issues for people with SAD are hypersomnia, insomnia, or both. Although, hypersomnia is much more common, affecting as many as 80 percent of people with SAD.  There are good evolutionary explanations for this.  The paucity of food in Winter should drive ancient humans to sleep more and consume fewer calories.

Even when they do sleep, that sleep may not be as restorative as it could be. Brain studies show that when SAD strikes, the efficiency of sleep (percentage of time in bed spent asleep) decreases, and the amount of time spent in deep sleep decreases while the time in REM actually increases.

Speaking of sleep efficiency, people with SAD spend a lot of time in their beds, causing many to mistakenly that they’re getting a lot more sleep than they actually are. This can prevent them from getting properly diagnosed, and cause undue anxiety or concern about why they feel so tired during the day (when they think they’re getting enough sleep).

Can weather affect sleep for people with SAD?

Daily circadian rhythms are closely tied to the sleep-wake cycle, but SAD shows an example of another natural cycle that affects sleep.  You might call these circannual rhythms. In some animals, circannual signals such as temperature and rain patterns can trigger physiological changes.  The light levels and position of the Sun in the sky are among those proximal cues.

In other words, other environmental factors besides light influence sleep. Cooler temperature facilitates sleep, and the outside wintry air may contribute to the hypersomnia associated with winter depression. On the flipside, the heat and humidity associated with summer makes it tougher to cool down and be comfortable enough for sleep – contributing to summer insomnia.

For many individuals with SAD, symptoms naturally go away with the changing of the seasons. However, until that point, there are several things they can do to feel and rest better.


Because the many people with SAD experience insomnia, or share the same kind of thoughts that keep insomniacs up at night, therapies such as cognitive behavioral therapy for insomnia (CBT-I) may be helpful. In CBT-I, the therapist works with the patient to help them recognize thought patterns and behaviors that prevent them from falling asleep, so they can replace those with better thoughts and new habits that facilitate sleep.

Light therapy – exposure to a strong artificial light – works extremely well for this type of depression. Patients sit in front of a light box for 30 to 60 minutes in the morning (those falling asleep too early should use it in the evening instead). The lightbox uses 10,000-lux bright white fluorescent bulbs to simulate the sunlight, but in a safe way without the UV rays. Some of these (known as “dawn simulators”) are meant to simulate dawn and turn on gradually in the morning.

Behavioral changes

Besides light therapy, simply spending more time outdoors can minimize feelings of sleepiness and depression. Exercising outdoors, even when it’s overcast, can energize the body and brighten the mind. Doing so in the morning will help reset the circadian clock.

When indoors, maximize your exposure to natural light as much as possible. Opening the shades and make your living space more sunny.  A study of office workers found that those who worked near windows experienced better sleep, due to their increased exposure to natural light:

natural light and sleep quality

Of course, if you have summer insomnia, you’ll want to limit your exposure to light by investing in blackout curtains, wearing sunglasses during the day, and turning off electronics 1 hour before bed.

If you can afford it, use your SAD as an excuse to go on vacation somewhere with the opposite season (although prepare accordingly for jet lag).

Many with winter-onset SAD experience increased cravings for carbohydrate-rich food. It doesn’t help that the winter season is filled with holidays offering sweet, fatty foods to celebrate. Manage your diet by avoiding sugary junk foods that interfere with sleep, and instead lean into your cravings with the kind of carbohydrate-rich foods that promote sleep, such as oats, yogurt, and bananas.

Supplements and medication

Melatonin supplements are considered a safe way to facilitate sleep and rebalance melatonin levels. A 2006 study found that taking melatonin in the morning or the afternoon helped reset the biological clock for individuals with SAD, depending on whether it was the early sunsets or the late sunrises affecting their symptoms (morning larks did better with morning dose while night owls benefitted from an afternoon dose). Feelings of depression decreased by 34 percent.

Doctors whse patients have SAD often prescribe anti-depressant drugs and SSRIs to increase serotonin levels.  If a person is already on medication, their doctor may recommend increasing the dose during the fall and winter months.

Natural antidepressants include vitamin D supplements and St. John’s Wort tea. Although St. John ‘s Wort is not approved by the FDA, it’s a popular herbal treatment for depression in Europe. Always check with your doctor before taking St. John’s Wort or another supplement as it may interfere with other medication or symptoms.

Additional resources

  • People with SAD can connect with others on forums like the Winter Blues subreddit, or Seasonal Affective Disorder Forums on PsychForums, Mental Health Forum, and DailyStrength.
  • TeensHealth has a resource guide for adolescents experiencing SAD, which breaks down the differences between SAD and major depression, and offers coping strategies.
  • HelpGuide provides an in-depth overview of seasonal affective disorder, including a diagnostic checklist.
  • Learn more about possible causes and risk factors for insomnia and hypersomnia from Tuck, and suggested treatment options for both.