Shedding Light on Seasonal Depression

Winter has its benefits: tasty treats, holidays, cheaper gas, and gnarlier waves for surfing. Unfortunately, it has its drawbacks, too: diet difficulty, weather under 70 degrees, a need for wetsuits, and seasonal affective disorder. The American Psychiatric Association classifies Seasonal Affective Disorder(cleverly abbreviated SAD) as a subtype of Major Depressive Disorder that fluctuates throughout the year ^[1]. The vast majority of sufferers (5% of the population) experience increased depressive symptoms in the winter, though 0.1% of people have increased summer symptoms ^{[1, 2]}. It affects women more than men and usually presents in young adulthood ^[2]. Researchers suggest that genetics may play a role, and the likelihood of SAD increases the further from the equator you live ^{[1, 2, 3]}.

Much like a lousy surf season, SAD has detrimental effects on mood, cognitive function (things like attention, memory, learning, and problem-solving), and physical health ^[2]. Seasonal affective disorder shares symptoms with other forms of major depression, including ^{[1, 4]}

• Sad or depressed mood
• Loss of interest in things you previously liked
• Feeling worthless or guilty
• Decreased cognitive function
• Oversleeping
• Fatigue
• Fidgeting or physical slowing
• Appetite changes, especially a craving for carbs
• Physical aches and pains without other causes
• Thinking about death and/or suicide

These are serious symptoms, and if left unmanaged, they can lead to impacts on daily life, increase social isolation, exacerbate other mental health disorders, and lead to problems with school, work, and relationships ^[2]. Additionally, much like a post-surf-injury period, SAD can increase the risks of obesity, heart disease, and substance abuse ^[2].

Much like surf forecasting, the exact science behind seasonal affective disorder is unclear. There are two major theories. The photoperiod hypothesis proposes that less light in the winter increases melatonin production and gets hormones all out of whack ^[2]. Observations of higher SAD rates at greater distances from the equator (and longer winter nights) support this theory. The phase shift hypothesis proposes that during winter, our circadian system (internal clock) misaligns with our sleep cycle, throwing hormones, etc., off ^{[2, 3]}. Seasonal affective disorder has both sunlight and hormonal aspects, as sufferers show hormone changes more than average people ^[2]. One highly implicated hormone is serotonin. Serotonin is affected by vitamin D levels, which has led many to use vitamin D as a treatment for SAD. However, basic researchers have found that cellular mechanisms of serotonin production and clearance may actually be affected by sunlight, implying that vitamin D alone may not be enough ^{[4, 5]}.

Treating seasonal affective disorder is challenging, in large part due to a scarcity of randomized, controlled clinical trials. In fact, as of the writing of this article, only 18 U.S. clinical trials have been reported to clinicaltrials.gov, and none are currently enrolling ^[6]. Available treatments fall into three categories: light therapy, antidepressants, and talk therapy ^[1]. Light therapy is exactly what it sounds like: bright lights shining on you for 20+ minutes a day, usually in the morning. Going outside for extra time may also help (but don’t forget sunscreen!) ^[1]. A doctor may prescribe an antidepressant, such as Selective Serotonin Reuptake Inhibitors (SSRIs), which can help regulate the amount of serotonin in the brain ^[1]. Talk therapy, especially cognitive behavior therapy, may also provide relief ^[1]. Vitamin D supplementation does not have sufficient data to show efficacy, and in fact, the few randomized, controlled clinical trials for seasonal affective disorder failed to show that supplemental vitamin D was superior to placebo in reducing symptoms ^{[7, 8, 9, 10]}. More clinical trials are needed to seek new, data-driven solutions to seasonal affective disorder. If only there were also a clinical trial seeking solutions to flat ocean waves.

Staff Writer / Editor Benton Lowey-Ball, BS, BFA

References:

^[1] American Psychiatric Association. (2013). Diagnostic and statistical manual of mental disorders (5th ed.).

^[2] Munir, S., Gunturu, S., & Abbas, M. (20 April, 2024). Seasonal Affective Disorder. StatPearls [Internet]. https://www.ncbi.nlm.nih.gov/books/NBK568745/

^[3] Dang, T., Russel, W. A., Saad, T., Dhawka, L., Ay, A., & Ingram, K. K. (2023). Risk for Seasonal Affective Disorder (SAD) Linked to Circadian Clock Gene Variants. Biology, 12(12), 1532. https://www.mdpi.com/2079-7737/12/12/1532

^[4] National Institute of Mental Health. (2023). Seasonal Affective Disorder (NIH Publication No. 23-MH-8138). U.S. Department of Health and Human Services, National Institutes of Health. https://www.nimh.nih.gov/health/publications/seasonal-affective-disorder

^[5] Willeit, M., Sitte, H. H., Thierry, N., Michalek, K., Praschak-Rieder, N., Zill, P., ... & Singer, E. A. (2008). Enhanced serotonin transporter function during depression in seasonal affective disorder. Neuropsychopharmacology, 33(7), 1503-1513. https://www.nature.com/articles/1301560

^[6] National Library of Medicine. (n.d.). Search for: seasonal affective disorder, in United States. ClinicalTrials.gov [Website] https://clinicaltrials.gov/search?locStr=United%20States&country=United%20States&cond=Seasonal%20Affective%20Disorder

^[7] Dumville, J. C., Miles, J. N. V., Porthouse, J., Cockayne, S., Saxon, L., & King, C. (2006). Can vitamin D supplementation prevent winter-time blues? A randomised trial among older women. Journal of Nutrition Health and Aging, 10(2), 151. https://pubmed.ncbi.nlm.nih.gov/16554952/

^[8] Frandsen, T. B., Pareek, M., Hansen, J. P., & Nielsen, C. T. (2014). Vitamin D supplementation for treatment of seasonal affective symptoms in healthcare professionals: a double-blind randomised placebo-controlled trial. BMC research notes, 7, 1-8. https://pmc.ncbi.nlm.nih.gov/articles/PMC4141118/

^[9] Harris, S., & Dawson-Hughes, B. (1993). Seasonal mood changes in 250 normal women. Psychiatry research, 49(1), 77-87. https://pubmed.ncbi.nlm.nih.gov/8140183/