Seasonal Affective Disorder

You know that sad lazy feeling you get on a cloudy rainy day? All you want to do is stay in bed and binge watch Netflix, take a nap (or 2) and make something rich and delicious for dinner. Unless of course you live in Hawaii and have no idea how to relate to the rainy-day blues. Now take that feeling and amplify it by about 210 and you’ll begin to comprehend the feelings behind Seasonal Affective Disorder. It’s not characterized by a sad day here or there, rather it is a DSM-V mental health diagnosis, characterized by recurrent depressions that occur annually at the same time each year. During these depressions, patients typically complain of fatigue, over eating, weight gain and oversleeping.

What causes Seasonal Affective Disorder?

Serotonin, a mono-amine neurotransmitter, has a large role in the symptoms of depression and subsequently, seasonal affective disorder (SAD). It’s primarily stored in the enteric nervous system located in the gastrointestinal tract but also the central nervous system in the brain. Postmortem studies in normal humans have demonstrated marked seasonal fluctuation in serotonin concentration with the highest levels in autumn, and the lowest in winter (1). Similarly, levels of serotonin metabolites (5-HIAA) in cerebral fluid are the highest in summer and lowest in winter and spring (1). Tryptophan, an essential amino acid, is a precursor for the production of serotonin. Rapid depletion of tryptophan can provide insight to possible treatment for SAD as it influences plasma serotonin levels (1).

Lam et al conducted an experiment to explore the effects of rapid tryptophan depletion on depression symptoms in people diagnosed with SAD. Tryptophan circulates in the blood bound to the protein albumin. It competes with other amino acids for absorption across the blood brain barrier. The presence of a large AA mixture with out tryptophan will lower serum tryptophan in the brain by preventing it from entering the brain, making less available for the production of serotonin (2). Tryptophan levels can be rapidly depleted by up to 80% within 3-5 hours by administering an oral tryptophan free mixture containing large amounts of other amino acids (1).

12 participants we given large doses of amino acid to create a significant plasma decrease while refraining from exposure to light during the hours of 9-5pm. These participants had previously been receiving light therapy for treatment for their SAD. Results showed that 80% of participants experienced significant depressive and anxiety symptoms, as rated on the Hamilton Depression Rating Scale score, after depletion of serum tryptophan and a reverse in the antidepressant effects of their light therapy suggesting tryptophan plays a role in managing SAD (1).

How can we increase the absorption of tryptophan?

Unlike protein and neutral amino acids, Carbohydrates can play a role in enhancing serum tryptophan. Although a carbohydrate meal itself lacks tryptophan, a carbohydrate rich meal causes insulin secretion. Insulin, delivering glucose to the muscles and the brain, decreases plasma levels of large neutral amino acids that would ordinarily compete with tryptophan for transport across the blood-brain barrier thus allowing more to be absorbed. This large uptake of tryptophan by the brain, may increase serotonin production and potentially alleviate some of the symptoms of SAD (2). Resulting brain changes in serotonin provide a plausible mechanism whereby diet could affect behavior.

People who suffer from SAD, or anyone bored on a winter Saturday for that matter, typically tend to crave and eat carbohydrate rich food. Think homemade macaroni and cheese and chocolate chip cookies. Carbohydrate craving and consumption might not only be a symptom of the disorder but an attempt to treat it. One of the most popular biochemical hypotheses explores the theory that a carbohydrate rich meal stimulates the influx of tryptophan to the brain and serotonin production.

Danilenko, K.V., et al conducted a study examining this phenomenon by comparing a carbohydrate rich or protein rich diet’s influence depression in SAD. 16 SAD subjects were compared to 16 without the diagnosis. All subjects were provided a carbohydrate rich lunch and a protein rich lunch with 1 day in between, with 105 grams each, respectively. Depression scores were obtained with a series of mood questionnaires and revealed that the carbohydrate rich meal appeared to decrease tension, depression, and anger scores where as the protein rich meal had the adverse effect in many cases. The ratio of tryptophan to other large neutral amino acids increased following the carbohydrate rich meal and decreased after the protein rich meal. There were multiple significant interactions between meal and sequence that point to differences in psychological responses to meals. Carbohydrates affected the SAD patients more so than the “normal” patients, reporting an activating affect of the carbohydrates on their positive mood leading to the conclusion that “the ingestion of high carbohydrate meals may be a mechanism used by affected individual to regulate their own brain serotonin levels.” (2) That’s certainly not to suggest replacing Prozac with M&M’s, but it does provide insight into the eating habits of someone experiencing SAD; allowing you to tailor your intervention with a better understanding of their experience and behavior.

One of the common denominators of SAD lies within geographical location. People are more likely to suffer from SAD if they live far north or far south from the equator. What does geographical location have to do with SAD? Sunlight, the primary source of Vitamin D. Some epidemiological studies suggest low levels of vitamin D may contribute to depression. Vitamin D has receptors distributed in the brain areas associated with emotional processing and affective disorders and regulates serotonin syntheses through transcriptional activation of the tryptophan hydroxylase 2 gene (3). Although Vitamin D is found in mushrooms, egg yolks, and fortified milk its primary source is sunlight. Individuals in a range of climates often become Vitamin D deficient and don’t gain sufficiency for months. It’s possible seasonal changes in Vitamin D levels may account for seasonal depressive symptoms. Kerr et al examined this phenomenon by exploring the relationship between serum vitamin D levels and depressive symptoms in 185 undergraduate college age women living in the pacific north west over a 4-week period. Consistent with their hypothesis, there was a significant correlation between diminished Vitamin D levels and depressive symptoms. At each of the 5 observation points in the experiment, 34-42% of participants reported clinically significant depressive symptoms with rates of vitamin d deficiently at a consistent rate of 31%. Mean depressive symptoms were reported more in women with lower Vitamin D levels and were lowest in the fall than any other term (4). It would be great to suggest a beach vacation as a dietary intervention for SAD treatment, but a less expensive option may be Vitamin D supplements in the amount of 500-1000IU as affective (and affordable) way to ensure you’re getting enough “sunshine” during the months when the sun sets before you step out of your office door. While you’re at the pharmacy, it might be worthwhile to pick up a DHA supplement as well. Either that or grab a nice salmon filet; as seafood is the greatest source of this omega-3 fatty acid. DHA is the brains building block. This omega-3 fatty acid provides structure to neurons and is an anchor point for neurotransmitter receptors. The densities of dopamine and serotonin receptors are dependent on DHA levels and influence the hippocampus and hypothalamus; responsible for hormone production. 1-3gm a day may help assist with seasonal affective disorder (4).

Some facilities are using these dietary interventions currently as treatment for patients with SAD. Study in Europe conducted a postal and web-based survey to 100 institutions treating more than 3100 SAD patients shared their recommended treatments for SAD. The primary interventions are light therapy however 47% of the institutions treating SAD recommended dietary changes as an intervention for alleviating SAD and of all the option, 71% of patients were treated as such. Intervention included: Mediterranean diet with an emphasis on DHA, more fiber and less meat; supplementing with Vitamin D, reducing heavy evening meals, limiting alcohol, and supplementing with B12 and Iron (5).

There are those who can’t wait for winter, and then there are those who can’t wait for winter to be over. Whether you fall into either category, the winter blues are no joke. If you or anyone you work with seems to be eating a lot more macaroni and cheese than normal and losing their stamina to make it to the gym, or even to get up and brush their hair; you have some insight to what might be going on. Fortunately, there are some dietary interventions that may assist you or your clients getting through the winter season that doesn’t mandate they buy a condo in key west. A balance of healthy carbohydrate sources like fruits, vegetables, whole grains (ok fine and an occasional brownie), Vitamin D, some nice wild caught fish (or capsule form if fish isn’t your thing) and of course non-judgmental unconditional support for those days were sweatpants are the only clothes that matter.


  1. Lam, R.W., 1996. Effects of Rapid Tryptophan Depletion in Patients With Seasonal Affective Disorder in Remission After Light Therapy. Archives of General Psychiatry 53, 41
  2. Danilenko, K.V., Plisov, I.L., Hébert, M., Kräuchi, K., Wirz‐Justice, A., 2008. Influence of Timed Nutrient Diet on Depression and Light Sensitivity in Seasonal Affective Disorder. Chronobiology International 25, 51–64
  3. Kerr, D.C., Zava, D.T., Piper, W.T., Saturn, S.R., Frei, B., Gombart, A.F., 2015. Associations between vitamin D levels and depressive symptoms in healthy young adult women. Psychiatry Research 227, 46–51
  4. Mahan, L.K., Escott-Stump, S., Krause, M.V., 2008. Krauses food & nutrition therapy. W.B. Saunders, Philadelphia
  5. Nussbaumer-Streit, B., Winkler, D., Spies, M., Kasper, S., Pjrek, E., 2017. Prevention of seasonal affective disorder in daily clinical practice: results of a survey in German-speaking countries. BMC Psychiatry 17.

Originally written for Nutritional Coaching Institute Seasonal Affective Disorder | Nutritional Coaching Institute (