Chronotherapy For Seasonal Affective Disorder: An Overview

Seasonal affective disorder (SAD) is a type of major depressive or bipolar disorder marked by depressive symptoms that begin and end during a specific time of the year. 

SAD is often referred to as the “winter blues,” as the most common time for depressive episodes is during autumn/winter, followed by complete recovery in spring/summer. 

SAD affects 5% of the U.S. population every year and is usually more common in women than men. 

Because SAD is considered a type of depression that recurs during specific seasons, the mood changes and symptoms of SAD are consistent with depression. 

Despite being seasonally limited, these changes can be overwhelming and negatively impact people’s ability to work, socialize, and perform everyday activities. 

While antidepressant medication and lifestyle changes can treat SAD, other natural alternative treatments can complement medication, such as chronotherapy. 

What is chronotherapy?

Chronotherapy refers to a type of treatment that incorporates a range of strategies to control factors influencing your biological clock and internal biological rhythms. It has been studied as a possible treatment approach for SAD and other mental health disorders. 

Research indicates chronotherapy to be as effective as other similar¹ treatment types. 

What is SAD?

Commonly known as the “winter blues” or “winter depression,” SAD is a subtype of depression that recurs seasonally. 

It accounts for approximately 10% to 20% of returning depression cases², with women being four times more likely³ to experience it than men.

Symptoms of SAD

People with SAD typically have symptoms consistent with depression. Some symptoms that are more common in SAD include:

• Craving for carbs or starchy foods

• Hyperphagia (abnormally increased appetite)

• Hypersomnia (excessive sleepiness/drowsiness)

• Weight gain

• Slowed movements/mental processes

A SAD diagnosis is made if:

• The symptoms occur consecutively during specific seasons (i.e., only during winter or summer) for a minimum of 2 years

• Major depressive episodes experienced during specific seasons outnumber the number of episodes experienced throughout the year.

• The major depressive episode is unrelated to other known triggers that may have happened at the same time.

Risk factors of SAD

Factors that may increase the risk of experiencing SAD include:

• Sex—women are four times more likely to experience SAD than men

• Age—younger people are more likely to develop SAD, as onset typically occurs at 18 to 30 years old.

• Family history—a family history of SAD or other forms of depression can increase the risk of developing the disorder.

• Geography—people living further from the equator are believed to have an increased risk of SAD

Causes of SAD

It is not entirely clear what causes SAD. However, research has indicated that it may be related to reduced sunlight, affecting essential hormones such as serotonin and melatonin.

Serotonin is a brain chemical (neurotransmitter) responsible for regulating mood, emotion, and sleep through binding onto serotonin receptors. 

As daylight reduces during winter/fall months, there is a related reduction in serotonin levels and activity. 

People with SAD may have difficulty regulating serotonin during the winter months. 

One study showed that people with SAD had relatively higher levels of serotonin reuptake transporters (SERT)⁴ in winter than people without SAD. As winter reduces light exposure, SERT activity increases, reducing serotonin activity.

Vitamin D production is also affected when sunlight exposure is reduced, which is believed to be important in serotonin production.

Melatonin is a hormone that regulates the sleep/wake cycle and promotes sleepiness. It is usually produced and secreted at night before your regular bedtime. 

People with SAD may overproduce melatonin⁵, causing fatigue and tiredness. This is likely due to the reduction in sunlight, which may increase melatonin production.

A combination of changes to serotonin and melatonin is believed to disrupt our body’s internal clock (aka circadian rhythms). This can cause our internal cues to become misaligned, increasing the risk of SAD.

The use of chronotherapy in treating SAD

Chronotherapy refers to various treatments to influence our circadian rhythms and help resync our sleep/wake cycles. 

Because SAD may arise due to reduced sunlight, chronotherapeutic treatments are often recommended to treat SAD. Treatments can include any of the chronotherapy types listed below.

Bright light exposure therapy

Bright light exposure therapy (BLT) is a form of chronotherapy that involves daily exposure to bright artificial lights for 30 to 60 minutes during the symptomatic months. 

Exposure to light therapy may replace the reduced sunlight exposure during the winter months.

BLT typically involves sitting in front of a lightbox or wearing a light visor fitted with white fluorescent lights with a light intensity of approximately 10,000 lux. 

It is generally delivered in the morning for 20 to 60 minutes for up to two weeks during affected months. However, this can vary depending on the light intensity used.

Sleep deprivation/wake therapy

Also known as wake therapy, sleep deprivation (SD) therapy is another form of treatment that can affect circadian rhythms and sleep/wake cycles. 

Individuals can be kept awake for approximately 36 hours (total sleep deprivation) or sleep for half the night and stay awake for a prolonged period (partial sleep deprivation).

SD therapy has been used for mood disorders like SAD due to its rapid antidepressant action in depressed patients. A meta-analysis showed that 50% to 60% of depressed patients showed quick improvements⁶ to their mood after sleep deprivation. 

However, these effects were not long-lasting. Many people tend to relapse after one night’s sleep, indicating that it may be better as a short-term treatment.

Sleep phase advancement

Sleep phase advancement is a form of chronotherapeutic treatment that involves rescheduling sleep to an earlier time to compensate for abnormal circadian rhythms in depressed patients. 

This treatment can include BLT or SD therapy to shift bedtime schedules to an earlier time (phase advance) or toward a later time (phase shift) and will vary from person to person.  

The link between chronotherapy and SAD

As SAD has been linked with misalignment of our circadian rhythms and reduced sunlight exposure, chronotherapy has been recognized as an effective treatment for the disorder. Despite this, experts are not entirely sure how chronotherapy works to relieve SAD symptoms.

A review has suggested that chronotherapy works to alter melatonin expression⁷ through BLT. 

When receptors in your eyes (photoreceptors) receive light, signals are sent to the suprachiasmatic nucleus, a structure in the hypothalamus that regulates many circadian rhythm processes. One of its functions includes influencing the pineal gland, which produces melatonin based on cues received from the environment. 

As light suppresses melatonin production, timing chronotherapeutic treatments (i.e., using BLT during the day or the night) would most likely influence when melatonin levels would change.

Home treatments for SAD: What to consider

Although chronotherapeutic treatments sound like a viable home treatment, it is always best to exercise caution and consult your doctor about any concerns.

While most light therapy devices are believed to be suitable for clinical use, it’s always important to consult a healthcare/sleep professional about treatment before starting. This is especially important if you are taking medications that may affect sleep. 

This is also because light therapy is associated with some side effects such as headaches, eye strain, and irritability. To choose the best light therapy, it is important to consider the following factors:

• The intensity of the device

• The wavelength of the device

• Distance from the light source

• Time of application

• Dose

While SD therapy has seen benefits in up to 40% to 60%¹ of patients, it may not be as effective as BLT due to the fairly short-lasting effects, high chance of relapse, and side effects such as sleepiness and manic episodes.

The lowdown

Although the exact mechanisms of SAD are not fully understood, there is evidence that chronotherapy may help relieve symptoms of the disorder.

If you have symptoms related to SAD or are considering chronotherapy as a potential treatment, see your doctor or a trained mental health professional who may be able to refer you to further specialist assistance if needed.

With the right treatments, you can manage seasonal affective disorder adequately.