Nutritional considerations for seasonal affective disorder

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By Kellie Blake, RDN, LD, IFNCP

The changing seasons can be a difficult time for some patients. Even those without a clinical diagnosis of seasonal affective disorder (SAD) may experience negative symptoms with the waning daylight that accompanies fall and winter. Tack on the challenges of the novel coronavirus (COVID-19) and this year we may be seeing an increase in depressive symptoms.

SAD, sometimes called seasonal depression, is a subtype of major depression and is seen in two to three percent of the population. To be diagnosed with SAD, patients must meet the criteria for major depression corresponding with the change of seasons and have full remission of symptoms once the difficult season is over. Patients with SAD experience low energy levels; often overeat, especially carbohydrates, which can lead to weight gain; sleep excessively; and retreat from their usual social activities.

Patients with SAD may also have difficulty concentrating and experience an increase in irritability. Some patients can suffer headaches, gastrointestinal distress, and in severe cases, suicidal thoughts. Women, those living farther from the equator, and those with a history of depression are at greatest risk.

The exact cause of SAD is unknown, but as reported in the European Review for Medical and Pharmacological Sciences, it is believed that dysregulation of the serotonergic system is one key culprit. Serotonin is created from L-tryptophan and acts as a neurotransmitter, neuromodulator, and hormone. In its role as a neurotransmitter, serotonin is involved in mood and emotion regulation, as well as sleep and appetite. As a hormone, serotonin acts to link the gut-brain axis, which is the communication highway connecting emotions and cognition with gastrointestinal tract function.

Serotonin is stored in three main areas, the serotonergic neurons located in the central nervous system and in the nerve fibers servicing the muscular tissue of the esophagus, stomach, and intestines; the enterochromaffin cells (EC) located in the gastrointestinal tract mucosa; and in blood platelets. Any alteration in the creation, metabolism, and/or uptake of serotonin is implicated in mental health conditions like schizophrenia, depression, and compulsive disorders and serotonin levels are known to vary with the change of seasons in healthy individuals.

In addition to the alteration in serotonin, some people with SAD may have an overabundance of melatonin and also tend to have lower vitamin D levels. Bright light therapy is the recommended treatment for SAD, but nutrition-related changes to target gut function and vitamin D can also be formidable interventions.

As reported in a 2016 review in Nutrients, 90 percent of serotonin synthesis occurs in the gastrointestinal (GI) tract EC cells. The gut microbiota communicates with the EC cells via the creation of short chain fatty acids and bile acids and in turn regulate serotonin.

There seems to be an alteration in the gut microbiome of patients with major depression when compared to healthy controls. As reported in Brain, Behavior, and Immunity, those with depressive symptoms have increased levels of potentially harmful bacteria and reduced levels of beneficial bacteria.  Many of my patients with symptoms of depression, whether clinically diagnosed or not, experience gut dysfunction, so my initial focus is often to target gut health. By removing substances known to be harmful to the commensal bacteria and adding their preferred fuel, balance can be restored and symptoms of SAD can be prevented or better controlled.

Of course, the therapeutic meal plan is personalized, but the Modified Mediterranean Diet (Mod/MedDiet) as studied in the SMILES trial is one option to consider. As described in Nutritional Neuroscience, the Mod/MedDiet contains plentiful vegetables, fruits, whole grain cereal, oily fish, legumes, unsalted nuts and seeds, and extra virgin olive oil. It allows for moderate consumption of natural reduced-fat dairy products and lean red meat. The results of the SMILES randomized controlled trial indicated this meal pattern, with the support of a registered dietitian, is one effective option for improving symptoms in those with major depression.  

While the Mod/MedDiet significantly reduces sugar and inflammatory fats, these are two specific areas of focus when I educate patients with depressive symptoms. In a prospective study published in Scientific Reports, increased sugar intake raised the likelihood of mood disorders like depression. One possible mechanism involves the dysregulation of glucose in the brain leading to inflammation, but sugar is also known to negatively affect the gut microbiota. As reported in Nutrients, after treatment with high glucose and high fructose diets, mice showed lower microbial diversity, increased intestinal permeability, and higher levels of inflammatory cytokines.

Inevitably, when I suggest removing sugar, my patients ask about artificial sweeteners. However, artificial sweeteners have been shown to alter the gut microbiota as well. In addition, a variety of studies have shown an increase in glucose intolerance and altered microbial metabolic pathways increasing the risk of metabolic disease. I generally have patients avoid all added sugars, refined carbohydrates, and artificial sweeteners. As occasional sweeteners, I recommend organic honey and pure maple syrup.

In addition to sugar, I discuss the importance of the quality and quantity of fat consumed. People who consume diets high in omega-6 fatty acids are four times more likely to suffer from depression and an imbalanced omega-6 to omega-3 ratio affects emotional regulation and can lead to depression. Inflammation is a key factor, but fat also affects the gut microbiome. Animal studies confirm a change in gut microbiota composition depending on the type of fat consumed whether it be saturated fatty acids (SFAs), monounsaturated fatty acids (MUFAs), or polyunsaturated fatty acids (PUFAs). For example in mice fed a high SFAs diet, there is a decrease in Bacteroidetes and increase in Firmicutes and Proteobacteria, which can lead to dysbiosis.

Furthermore, a high fat diet has been shown to have a negative impact on the intestinal barrier, affect the protective mucus layer, and increase gut inflammation. Patients consuming more MUFAs have significantly lower depression risk, so I encourage a moderate intake of MUFAs primarily from olives and olive oil, avocado and avocado oil, almonds, cashews and their nut butters, but I also recommend a healthy dose of omega-3 fatty acids. Omega-3 fats are essential, so must be provided in the diet and among other functions, they are vital for lowering brain inflammation and protecting neurons. To maintain the optimal omega-6 to omega-3 fat ratio, I encourage my patients to consume high-quality fatty fish at least twice weekly and for those who don’t regularly eat fatty fish, I encourage high-quality omega-3 supplements.  Patients should avoid margarine, shortening, hydrogenated oils, and vegetable oils high in omega-6 fats.

Vitamin D is another important consideration for those suffering from SAD. As daylight wanes and temperatures drop, patients are less likely to have adequate sun exposure. While there are some food sources of vitamin D such as fish, eggs, and mushrooms, these are not adequate to meet the vitamin D needs of even healthy individuals. This combination of limited sun exposure and lack of adequate vitamin D in the diet can create suboptimal vitamin D levels. According to a study published in the journal Depression Research and Treatment, low vitamin D levels are associated with depression and vitamin D is important for serotonin regulation. Vitamin D supplementation has been shown in some studies to improve SAD symptoms.

I test vitamin D levels and supplement based on the individual. I often recommend 10 to 15 minutes of sunscreen-free sun exposure daily during the summer months and have patients add supplements just prior to and during the fall and winter months.

While SAD is multifactorial requiring a personalized approach, targeting gut function and vitamin D can be effective for symptom prevention and management. Patients, of course, will fare better if they can incorporate the recommended nutrition-related changes all throughout the year as opposed to only during the problematic season.

References

Gupta, A., Sharma, P.K., Garg, V.K., Singh, A.K., and Mondal, S.C. (2013) Role of serotonin in seasonal affective disorder. European Review for Medical and Pharmacological Sciences. Retrieved from: https://www.europeanreview.org/article/1251

Jenkins, T.A., Nguyen, J.C., Polglaze, K.E., and Bertrand, P.P. (2016) Influence of Tryptophan and Serotonin on Mood and Cognition with a Possible Role of the Gut-Brain Axis. Nutrients. Retrieved from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4728667/

Jiang, H., Ling, Z., Zhang, Y., Mao, H., Ma, Z., Yin, Y., Wang, W., Tang, W., Tan, Z., Shi, J., Li, L., and Ruan, B. (2015) Altered fecal microbiota composition in patients with major depressive disorder. Brain, Behavior, and Immunity. Retrieved from: https://pubmed.ncbi.nlm.nih.gov/25882912/

Jorde, R., Sneve, M., Figenschall, Y., Svartberg, J., & Waterloo, K. (2008) Effects of vitamin D supplementation and symptoms of depression in overweight and obese subjects: randomized double blind trial. Journal of Internal Medicine. Retrieved from:  https://onlinelibrary.wiley.com/doi/full/10.1111/j.1365-2796.2008.02008.x

Knüppel, A., Shipley, M.J., Llewellyn, C.H., and Brunner, E.J. (2017) Sugar intake from sweet food and beverages, common mental disorder and depression: prospective findings from the Whitehall II study. Scientific Reports. Retrieved from: https://pubmed.ncbi.nlm.nih.gov/28751637/

Martin, A.M., Yabut, J.M., Choo, J.M., Page, A.J., Sun, E.W., Jessup, C.F., Wesselingh, S.L., Khan, W.I., Rogers, G.B., Steinberg, G.R., and Keating, D.J. (2019) The gut microbiome regulates host glucose homeostasis via peripheral serotonin. Proceedings of the National Academy of Sciences of the United States of America.  Retrieved from: https://pubmed.ncbi.nlm.nih.gov/31527237/

Melrose, S. (2015). Seasonal Affective Disorder: An Overview of Assessment and Treatment Approaches. Depress Res Treat. Retrieved from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4673349/

Opie, R., O’Neil, A., Jacka, F., Pizzinga, J., and Itsiopoulos, C. (2018) A modified Mediterranean dietary intervention for adults with major depression: Dietary protocol and feasibility data from the SMILES trial, Nutritional Neuroscience. Retrieved from: https://pubmed.ncbi.nlm.nih.gov/28424045/

Rinninella, E., Cintoni, M., and Raoul, P. (2019). Food Components and Dietary Habits: Keys for a Healthy Gut Microbiota Composition. Nutrients. Retrieved from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6835969/

National Institute of Mental Health. (2020) Seasonal Affective Disorder. National Institutes of Health. Retrieved from:  https://www.nimh.nih.gov/health/topics/seasonal-affective-disorder/index.shtml

Spies, M., James, G.M., and Vraka, C. (2018) Brain monoamine oxidase A in seasonal affective disorder and treatment with bright light therapy. Translational Psychiatry. Retrieved from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6155094/