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Vitamin D and Seasonal Affective Disorder Symptoms

New study examines vitamin D effect on seasonal affective disorder symptoms.

It's wintertime once again. For many of us who live far from the equator, late autumn and winter are welcome seasons—building snowmen, skiing, and sledding are all popular snowy pastimes. However, for some of us, the change in seasons can bring about a severe mood disturbance or "wintertime blues" known as seasonal affective disorder (SAD). A new Danish study examines vitamin D supplementation as a possible benefit for SAD symptoms.

What Is SAD?

Seasonal affective disorder is similar to typical depression. However, unlike people with depression, people with SAD usually don't have thoughts of hurting themselves (suicidal ideation) or feelings of worthlessness. Instead, people with SAD display the following symptoms:

  • Sleepiness
  • Craving carbohydrates
  • Difficulty with concentration
  • Depressed mood
  • Anxiety
  • Irritability
  • Weight gain
  • Lethargy
  • Decreased libido
  • Hyperphagia (increased consumption of food)
Leonid Tit ©
Source: Leonid Tit ©

Symptoms of SAD recur every winter and dissipate in spring or early summer. During winter, there is less sunlight and people are outdoors less. SAD is more prevalent in women than men, and this condition affects between 1 and 10 percent of people living in high latitudes.

Light therapy or exposure to artificial ultraviolet light improves symptoms in about 50 to 80 percent of people affected by SAD. Such light can be delivered in several ways: lightboxes, dawn simulators situated bedside, or light-emitting caps or visors. The antidepressant fluoxetine (Prozac) has also been used in combination with light therapy, and there may be a synergistic effect when both therapies are administered together. Finally, talk therapy may also be of benefit.

Despite limited research into the subject, we're unsure how sunlight improves the symptoms of SAD. At first, researchers hypothesized that light therapy helped with melatonin metabolism; however, subsequent investigation failed to support this hypothesis. Now, some researchers have targeted an increase in vitamin D as the mechanism for improved mood in people with SAD. Of note, vitamin D is produced in our skin after exposure to sunlight, and there are plenty of vitamin D receptors in the brain.

Vitamin D and SAD

To date, clinical studies examining whether vitamin D supplementation helps people with SAD have demonstrated mixed results. In a recent Danish study published in 2014 in BMC Research Notes, researchers set out to examine whether vitamin D supplementation would improve symptoms of SAD in indoor healthcare workers who had experienced such symptoms in the past.

In the study, healthcare workers from two hospitals were solicited by e-mail, flyers, and posters in order to participate in the study. Participants were screened using a Danish version of the SAD questionnaire (they weren't clinically diagnosed with SAD per se). The trial was randomized and blinded and lasted 12 weeks. The experimental group received daily vitamin D supplementation, and the control group received placebo.

The primary outcome of the study involved results from the "Structured Interview Guide for the Hamilton Depression Rating Scale, Seasonal Affective Disorders" (SIGH-SAD). Various secondary outcomes were measured including the World Health Organization-Five Well-being Index (WHO-5), 25(OH)D (a measure vitamin D levels in the blood), weight, waist circumference, blood pressure and absenteeism from work.

Unfortunately, researchers found that vitamin D supplementation had an insignificant effect on both primary and secondary outcomes. In other words, the researchers found that vitamin D supplementation didn't help with SAD symptoms. Of note, and as conceded by the researchers, there were some serious limitations with the study. Most notably, the study was underpowered with a mere 34 people completing the study. Additionally, researchers weren't able to examine vitamin D supplementation in people who had low levels of vitamin D in their blood or low 25(OH)D.

This Danish study along with all the research done so far reinforces how little we know about SAD. In particular, we don't know how light therapy works to improve symptoms of SAD. On a related note, more research needs to be done on the use of antidepressants to treat SAD, too.


Research article titled "Vitamin D Supplementation for treatment of seasonal affective symptoms in healthcare professionals: a double-blinded randomised placebo-controlled trial" by TB Frandsen and colleagues published in BMC Research Notes in 2014. Accessed from PubMed on 12/28/2014.

Iserson KV. Chapter 35. Psychiatry. In: Iserson KV. eds. Improvised Medicine: Providing Care in Extreme Environments. New York, NY: McGraw-Hill; 2012. Accessed 1/2/2015.

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