By Savanna Ledford

Does falling back an hour cause you to experience seasonal depression? You can thank Congress for that. Daylight savings time has been observed by most people in the United States since 1918 with the hopes that it will save energy consumption and improve the economy (Figure 1)². However, many have expressed concerns towards adopting daylight savings time due to its effect on seasonal depression.

Seasonal depression, also known as seasonal affective disorder (SAD), is a type of mood disorder that occurs during a specific time of the year². Most people impacted by SAD experience it during the fall and/or winter months, with symptoms lasting for about 40% of the year³. In fact, about 5% of adults in the United States experience SAD, 75% of which are women^3,4. A study conducted in the United States showed that a mild version of SAD, known as the “winter blues”, affects about 10-20% of adults⁴. While SAD is more common in younger populations and women, you are at higher risk if you have a mood disorder, family history of mental health conditions, or live in high latitudes or cloudy regions⁴. Although researchers are not exactly sure what causes seasonal depression, there are five theories that explain how a lack of sunlight may cause the condition in those who are more prone to SAD⁴:

(1) biological clock change

(2) brain chemical imbalance

(3) vitamin D deficiency

(4) melatonin boost

(5) negative thoughts

First, the biological clock (circadian rhythm) theory, also known as the phase-shift hypothesis⁵ (Figure 2A), suggests limited exposure to light in the fall/winter months can cause difficulty in regulating mood, sleep, and hormones resulting in SAD symptoms⁵. These symptoms can include but are not limited to anxiety, sadness, irritability, extreme fatigue, inability to concentrate, and increased sleep⁴.

Second, the brain chemical imbalance theory focuses on the low serotonin activity in the brain. A lack of sunlight in the winter can cause serotonin levels to drop, leading to mood changes⁴. The serotonin hypothesis indicates that individuals with SAD have a greater binding potential at the pre-synaptic serotonin transporter⁵. Greater binding results in a greater uptake of serotonin into the presynaptic neuron (as indicated in Figure 2B)⁵. A greater uptake in serotonin decreases the available serotonin in the synaptic cleft which is associated with the outcome of depression symptoms⁵.

Third, serotonin is affected by vitamin D. Vitamin D helps boost serotonin levels in the brain⁴. Sunlight promotes vitamin D synthesis in the body, thus a lack of sunlight exposure during the winter may cause vitamin D deficits. Vitamin D deficits can then lead to low serotonin levels which impact mood⁴.

The fourth theory regards melatonin boost, which is what causes someone to feel more sluggish in the winter months⁴. Melatonin is synthesized in the pineal gland and is stimulated by β-adrenergic activity⁵. The synthesis of melatonin is inhibited when one is exposed to light⁴. Therefore, a lack of sunlight may cause an overstimulation of melatonin production, causing one to feel sleepier than usual⁴.

The fifth theory posits that those who experience anxiety, stress, and negative thoughts are prone to SAD⁴. This theory needs more research since scientists are unsure whether negative thoughts are the cause, or rather, an effect of SAD⁴. Since symptoms of SAD include feelings of hopelessness or worthlessness, investigators are interested in understanding if associated negative feelings cause SAD symptoms⁴. As we approach the long, northeast winter, it may feel at times that we will never see the sun again, putting us at risk for experiencing SAD symptoms due to the theories discussed. However, thanks to light therapy, we can now feel our best even on those gray, dreary days.

Bright light therapy (BLT) has been recognized as the first-line therapeutic modality for those with SAD⁶. Research into the utilization of BLT started in 1984 when a study showed that when exposing SAD patients to bright white light (increasing their daily light exposure), they experienced a reduction in symptoms⁷. Two meta-analyses that consisted of eight randomized, blinded, and controlled studies showed the efficacy of BLT⁶. Patients with SAD underwent BLT for four weeks and results showed that 50% of patients had a reduction in their symptoms⁶. It is hypothesized that BLT increases synaptic serotonin by reducing serotonin receptor binding which increases available serotonin, leading to an elevation in mood and the reduction of SAD symptoms⁹. In relation to melatonin, BLT inhibits β-adrenergic activity within the pineal gland, which plays a role in the inhibition of melatonin synthesis⁹.

The current strategy for optimizing BLT benefits is to undergo BLT in the morning⁸. Additionally, the light source should be a fluorescent light box with a diffusion screen and an intensity of 10,000 lux for 30 minutes⁸. Patients should position the box at a 30-degree angle from the line of gaze and at 12-24 inches away (Figure 3).

Now, before you run to Amazon or any store to purchase a light as seen in Figure 3, you should contact your medical provider first to ensure that what you are experiencing is SAD¹¹. Patients using BLT have experienced side effects like headaches and nausea¹¹, so it is important to work with your doctor. Additionally, keep in mind that the use of a light box device is not FDA-approved nor regulated¹¹. If you and your doctor believe BLT is right for you, your doctor can help you make sure to buy a light box appropriate for SAD treatment¹¹.

Besides BLT, there are other natural ways to reduce SAD symptoms, like increasing your dietary intake of vitamin D¹², as low levels of vitamin D have been found in patients with SAD¹². Keep in mind, the recommended dietary allowance for an adult is 600 international units (IU)¹³. Further research is still needed to explore if vitamin D supplements relieve SAD symptoms¹², so it is again important to talk with a doctor before taking any vitamin supplement. Certain foods that can provide dietary vitamin D include salmon, egg yolks, and fortified foods¹⁴. Knowing the association of sunlight exposure with SAD symptoms exists, one can understand why scientists have expressed concerns towards adopting daylight savings time. Decreasing energy consumption and improving the economy are two important elements but, that should not cost citizens their health and well-being.

TL:DR

Seasonal affective disorder (SAD) affects 5% of adults in the United States and can last up to 40% of the year. Bright light therapy (BLT) reduces SAD symptoms and is considered among the first-line of treatment for patients.

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References

1. Robinson, R. & Vick, A. (2019). The Congress Project: The Standard Time Act of 1918. Retrieved from https://www.thecongressproject.com/standard-time-act-of-1918.
2. Healthline (2021). Daylight Saving Time: Falling Back Can Increase Seasonal Depression. Retrieved from https://www.healthline.com/health-news/daylight-saving-time-and-seasonal-depression.
3. American Psychiatric Association (2021). Seasonal Affective Disorder (SAD). Retrieved from https://www.psychiatry.org/patients-families/depression/seasonal-affective-disorder.
4. Cleveland Clinic (2021). Seasonal Depression. Retrieved from https://my.clevelandclinic.org/health/diseases/9293-seasonal-depression.
5. Leersnyder et al. (2003).β₁-adrenergic antagonists and melatonin reset the clock and restore sleep in a circadian disorder. Retrieved from https://jmg.bmj.com/content/40/1/74.citation-tools.
6. Campbell et al. (2019). Bright Light Therapy: Seasonal Affective Disorder and Beyond. Retrieved from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6746555/.
7. Rosenthal et al. (1984). Seasonal affective disorder. A description of the syndrome and preliminary findings with light therapy. Retrieved from https://pubmed.ncbi.nlm.nih.gov/6581756/.
8. Pail et al. (2011). Bright-light therapy in the treatment of mood disorders. Retrieved from https://www.karger.com/Article/Abstract/328950.
9. Oldham, M. & Ciraulo, D (2017). Bright light therapy for depression: A review of its effects on chronobiology and the autonomic nervous system. Retrieved from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5403163/.
10. Healthline (2021). 5 Best SAD LAMPS for Seasonal Affective Disorder and How to Use Them. Retrieved from https://www.healthline.com/health/sad-lamp.
11. Miller, M (2012). Seasonal affective disorder: bring on the light. Retrieved from https://www.health.harvard.edu/blog/seasonal-affective-disorder-bring-on-the-light-201212215663.
12. NCCIH (2021). Seasonal Affective Disorder. Retrieved from https://www.nccih.nih.gov/health/seasonal-affective-disorder.
13. Flo (2021). Too Much Vitamin D: Is it Possible?. Retrieved from https://flo.health/menstrual-cycle/health/symptoms-and-diseases/too-much-vitamin-d.
14. NHS (2021). Vitamin D. Retrieved from https://www.nhs.uk/conditions/vitamins-and-minerals/vitamin-d/.