Understanding Seasonal Affective Disorder (SAD)

Seasonal affective disorder (SAD) is a form of depression that is active during a particular season of the year. Though clinical depression and SAD have varying longevity of symptoms, they are not an entirely separate mental disorders—SAD just displays a different pattern.1 In fact,
one cannot be diagnosed with SAD without fitting the full criteria for depression.1


Symptoms of major depressive disorder (MDD) include loneliness, hopelessness, and worthlessness; low energy; loss of interest in activities; sleep disturbances, changes in appetite and/or weight; sluggishness; agitation; difficulty concentrating; and/or frequent thoughts of death and/or suicide.1 If these symptoms arise during specific months and reoccur around the same time of year for at least two years, it qualifies as SAD.1 Around five percent of adults in the United States experience SAD for about 40 percent of the year.2 The symptoms primarily linked to winter SAD are low energy levels, hypersomnia (excessive drowsiness and sleepiness3), overeating, weight gain, and/ or isolation.1 Summer SAD symptoms seem to cover the other end of the spectrum, with poor appetite, insomnia, agitation, restlessness, anxiety, and/or episodes of violent behavior.1 Some might experience
a mild form of SAD—popularly referred to as the “winter blues”2—and still be able to perform daily tasks. Others might be severely impacted by SAD and become incapable

of functioning until the spring months.1
Just as the symptoms of SAD can manifest differently in different people, the biological factors that are associated with SAD can vary from person to person.


A lack of sunlight hindering the transportation and activity of serotonin (a neurotransmitter responsible for mood, behavior, digestion, appetite, memory, and feelings of “happiness”) is believed to be
the reason why winter SAD is so prevalent. Serotonin transporter proteins increase with less sunlight, causing the quick reabsorption of serotonin before it releases the nerve impulse that transfers chemical signals upon which the body acts.1 The fluctuation of serotonin causes chemical imbalances in the brain. Sunlight naturally keeps serotonin transporter protein levels low, so during the summer, serotonin activity can improve.1 Chemical imbalances and lack of serotonin activity linked to depressive symptoms are not qualified to a time of year, but studies have reported a five-percent increase in serotonin transporter protein levels in individuals with winter SAD and one-percent level increase in people with summer SAD. 1

Vitamin D is known to play a part in serotonin activity as well. Since vitamin
D is produced when ultraviolet rays from
the sun touch skin, decreased exposure to sunlight might lead to vitamin D insufficiency and deficiency, affecting the production of serotonin.4 A vitamin D deficiency is often found in depressive mental disorders.1

Darker days can also lead to the overproduction of melatonin, which causes those with winter SAD to feel sluggish and sleepy for a majority of the season. Both serotonin and melatonin affect the body’s circadian rhythm, known as our “internal clock.”1 Usually, the body’s internal clock can sense the day/night and light/dark shifts
and adjust chemical activity accordingly. The shifts can be disrupted by the earlier arrival of darkness during the winter months, and the bodies of people with SAD have a difficult time adjusting chemical activity.5


Even with these environmental and biological components, researchers have
yet to determine an exact cause of SAD.1 Investigators have, however, discovered factors that might put individuals more at risk to develop SAD. A family history of depression has been correlated to increased risk.5 Geographical location can affect risk as well. The prevalence of SAD increases the farther people live from the equator. For example, one percent of people who live in Florida have SAD, while nine percent of the people who live in Alaska experience it.1 Female sex and younger age are considered risk factors for SAD as well. Female individuals are four times more likely to be diagnosed with SAD 5
than male individuals. And SAD is reported to occur more often in young children and teens, compared to adults.5


There are four main treatment options1 for people with SAD that can either be practiced all at once or singularly, depending on an individual’s needs and treatment plan.


People with SAD can take medication that prevents the early reabsorption of serotonin, which increasing its activity. Selective serotonin reuptake inhibitors (SSRIs), such as fluoxetine (Prozac®),have been shown to be effective in SAD.1 With any medication, it’s important to be aware of any potential side effects and make note of any you experience and share this information with your doctor so that together with your doctor you can find the best treatment for you. The adverse effects of some medications might steer people with SAD in another direction. If medication is not a desired course of action, or the side effects become too much, there are other treatment options are available.

Light therapy.

Light therapy, or bright light therapy (BLT), is another treatment option that has been shown to be effective in SAD. Using this therapy, the patient sits in front of a lightbox for 20 to 60 minutes every morning from Fall to Spring.5 The lightbox filters out ultraviolet rays and casts 10,000 lux of cool-white fluorescent, aiming to mimic the composition of sunlight.1,5 The adverse effects are generally milder than medication, and may include eye strain, headaches, irritability, and difficulty sleeping. As with medication, treatment with BLT should

be monitored by a qualified healthcare  professional. Photosensitizing medications  should not be used in conjunction with the  1 lightbox. If people with SAD are taking these medications or have sensitivity to light, for example, they can absorb “sunshine” via supplement.

Vitamin D supplements.

Vitamin D supplements can assist in creating serotonin, and taking them before it gets dark each day might improve and even prevent SAD symptoms.4 Though there is no evidence suggesting vitamin D supplements are not effective if taken alone, the body can synthesize vitamin D more efficiently when a person is exposed to ultraviolet rays, though risks of ultraviolet light exposure in general may outweigh the benefits of increasing vitamin D synthesis.4 Adverse reactions are rare but could happen with doses more than 50,000/IU a day.1
This can cause a buildup of calcium in the blood, which could lead to nausea, vomiting, weakness, and frequent urination.4 A healthcare provider can suggest the dosage that is right for you.

Cognitive behavioral therapy (CBT).

CBT is a form of psychotherapy that has been shown to be effective in SAD treatment by helping the individual identify and replace negative thoughts with positive ones.1,5 CBT encourages the practice of behavioral action, a technique in which
the individual engages in activities he or
she finds enjoyable or derives a feeling of satisfaction or achievement. Six weeks of CBT (two 90-minute sessions per week)
can be as effective as 30 minutes of BLT every morning.1 CBT programs might also incorporate diet modification, meditation, yoga, physical activity, and planning trips during the winter to sunnier locations.


1. Melrose S. Seasonal Affective Disorder: An Overview of Assessment and Treatment Approaches. Depress Res Treat. 2015;2015:178564.

2. The American Psychiatric Association. Seasonal Affective Disorder (SAD). https://www.psychiatry. org/patients-families/depression/seasonal-affective- disorder. Accessed January 27, 2020

3. National Institute of Neurological Disorders and Stroke. Hypersomnia Information Page. https:// www.ninds.nih.gov/Disorders/All-Disorders/ Hypersomnia-Information-Page. Accessed January 27, 2020.

4. National Institute of Health: Office of Dietary Supplements. Vitamin D. https://ods.od.nih.gov/ factsheets/VitaminD-HealthProfessional/. Published March 2, 2018.

5. National Institute of Mental Health. Seasonal Affective Disorder. https://www.nimh.nih.gov/ health/topics/seasonal-affective-disorder/index. shtml. Accessed January 27, 2020. NHR

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