Thank you! Your submission has been received!
Oops! Something went wrong while submitting the form.
Subscribe to the Magazine for free
Subscribe for free to keep reading! If you are already subscribed, enter your email address to log back in.
Thanks for subscribing!
Oops! Something went wrong while submitting the form.
Are you a healthcare practitioner?
Thanks for subscribing!
Oops! Something went wrong while submitting the form.

Winter Blues: Addressing Seasonal Affective Disorder with Functional Medicine

Medically reviewed by 
Winter Blues: Addressing Seasonal Affective Disorder with Functional Medicine

Feeling the winter blues? You're not alone. At least 20% of Americans experience mood changes, ranging from feeling down to full-blown depression, at some point during the year. Winter blues refers to seasonal changes in mood and affect during the winter, as days get shorter, darker, and colder. It is a mild form of seasonal affective disorder, a type of depression triggered by a change in seasons. Wherever you fall on the spectrum of seasonal depression, treatment can help get you back to feeling your normal self. This article will explore the functional medicine approach to understanding and managing seasonal affective disorder during the winter.


What is Seasonal Affective Disorder (SAD)?

Seasonal affective disorder (SAD) is a type of depression that occurs at specific times of the year, most commonly in the fall and winter months when there is less natural sunlight. Symptoms of seasonal affective disorder, including persistent low mood, lack of energy, difficulty concentrating, changes in sleep patterns and appetite, and a tendency to withdraw from social activities, will begin in the fall and resolve during the spring and summer months. Less often, SAD can affect people during the spring and summer.

Unlike other forms of depression, SAD is characterized by a seasonal pattern, with symptoms recurring during the same time each year. Different types of depression, like major depressive disorder (MDD) or persistent depressive disorder (PDD), do not have a specific seasonal pattern. The exact cause of SAD remains unknown; however, theories suggest the reduction in sunlight during the winter season leads to disruptions in circadian rhythm, a drop in serotonin levels, and elevations in melatonin levels. Combined, these changes alter sleep patterns and mood, contributing to winter-onset depressive symptoms. (6

The Functional Medicine Approach to SAD

Differentiating SAD from other types of depression is the first step in the functional medicine approach to SAD. Understanding the seasonal component of depression allows practitioners to better understand the leading mechanisms contributing to a patient's sadness. From there, they can tailor their recommendations for testing and treatment options to focus on the leading causes of SAD versus other forms of depression. For example, understanding that lack of sunlight likely causes winter-onset SAD, a functional medicine provider will create a holistic treatment protocol for SAD by optimizing vitamin D, melatonin, and serotonin levels while prescribing light therapy during the winter. This differs from an approach directed toward MDD, which, for example, may instead focus on optimizing thyroid hormones and dopamine levels.

In short, the functional medicine approach to SAD (and any type of depression, really) seeks to identify the underlying causes of symptoms rather than just treating symptoms. In doing so, this strays away from the one-size-fits-all approach of prescribing an antidepressant to treat depression and, instead, embraces a personalized strategy for medicine. 

Functional Medicine Lab Testing for SAD

To diagnose SAD, a patient must meet the following DSM-5 diagnostic criteria:

  • Depression begins and ends during a specific season, with complete remission during other times of the year
  • The individual demonstrates at least two depressive episodes in the previous two years
  • Seasonal episodes substantially outnumber nonseasonal episodes 

While laboratory tests cannot diagnose SAD directly, lab testing does play a valuable role in identifying contributing factors and developing comprehensive SAD treatment plans. Below are some top labs to consider ordering for individuals experiencing SAD.


Serotonin is a monoamine neurotransmitter derived from the amino acid L-tryptophan. Often called the body's natural "feel good" chemical, serotonin acts as both a neurotransmitter and neuromodulator to contribute to feelings of well-being. Low levels of serotonin are linked to low mood and changes in sleep and appetite patterns – typical SAD symptoms. (17)

Serotonin levels in the brain are partially regulated by Serotonin Transporter (SERT), which transports serotonin back into neurons, reducing circulating levels. Diminished sunlight corresponds to higher SERT levels and lower serotonin activity. In one study, people with SAD had 5% more SERT than those unaffected. (21)

Neurotransmitters, including serotonin, can be measured in urine with a test like the Neurotransmitters panel by ZRT Laboratory. In addition to directly measuring serotonin to assess if it is within an optimal range, this panel also measures serotonin's precursor (tryptophan) and downstream metabolite (5-HIAA) to better understand how the body synthesizes and breaks it down. 

Vitamin D

Vitamin D is a fat-soluble vitamin naturally made by the body when the skin is exposed to sunlight. People are often exposed to less sunlight in the winter, increasing the risk of vitamin D deficiency. Vitamin D deficiency has been associated with an increased risk of depression. One mechanism through which vitamin D influences mood is its impact on serotonin levels. Vitamin D receptors are present in areas of the brain involved in serotonin synthesis and regulation. Vitamin D activates tryptophan hydroxylase 2 (TPH2), which catalyzes the first step in serotonin synthesis – the conversion of tryptophan to 5-hydroxytryptophan (5-HTP). Vitamin D deficiency may lead to alterations in serotonin production and function, potentially contributing to depressive symptoms.

Vitamin D status is assessed by serum 25-hydroxyvitamin D (25-OH vitamin D) levels. Vitamin D by Ayumetrix is a bloodspot version of this test. While vitamin D levels greater than 30 ng/mL are considered sufficient, functional medicine doctors generally agree that an optimal vitamin D level is at least 50 ng/mL. (35)


Melatonin, the body's sleep hormone, is produced by the brain's pineal gland in response to darkness. During winter's dark days, melatonin production increases, leading to daytime sleepiness and lethargy. The circadian signal indicating a seasonal change in day length is found to be timed differently in people with SAD, making it more challenging to adjust to seasonal variations. This disrupted circadian rhythm may contribute to the characteristic SAD symptoms, such as disturbances in sleep patterns and energy levels. The Melatonin Profile by Doctor's Data measures melatonin levels throughout the day to provide a snapshot of the sleep-wake cycle. (21)

Because melatonin naturally has an inverse relationship to cortisol, our "get up and go" hormone, doctors often will measure the two together, such as with the Sleep and Stress Panel by Ayumetrix, to explore the nuanced interplay between circadian rhythm dysregulation, sleep disturbances, and stress response in individuals with SAD.


Nutritional Strategies for Managing SAD

A 2020 systematic review concluded that patients with SAD display unique diet preferences and eating behaviors. While the review does not establish whether these habits are a cause or an effect of seasonal depression, it underscores the importance of screening for certain dietary choices in patients with SAD. Patients with SAD were more likely to adhere to vegetarianism, exhibit patterns of alcohol dependence, emotionally eat, and overeat. 

Considering depressive disorders as a whole, research shows that diets high in ultra-processed foods and added sugars increase the risk for depression. In contrast, anti-inflammatory diets, such as the Mediterranean diet, are associated with as much as a 73% risk reduction. Understanding this, it makes sense to recommend an anti-inflammatory diet – emphasizing fruits, vegetables, whole grains, lean proteins, and healthy fats while limiting processed meats, simple carbohydrates, sweets, saturated/trans fats, and alcohol – to patients wanting to prevent and treat SAD. 

Endogenous serotonin synthesis is dependent on various nutrients, including tryptophan, vitamin D, omega-3 fatty acids, magnesium, zinc, iron, and vitamins B6, B9 (folate), and C. Incorporating foods into the diet that are rich in these nutrients can support optimal serotonin levels. (13)

Sources: (5, 10-12, 20, 33, 34, 36, 37)

Lifestyle Modifications and Natural Therapies

Light therapy, also called bright light therapy (BLT) or phototherapy, shows promise in treating SAD. Light boxes emit full spectrum light similar to sunlight, supporting natural vitamin D, serotonin, and circadian rhythms. Studies have shown BLT has moderate-to-large positive clinical effects in treating SAD symptoms, notably daytime sleepiness and excessive hunger. Standard recommendations call for sitting 16-24 inches from a lightbox with an intensity of 10,000 lux for 30-60 minutes daily. BLT can induce remission when used as a standalone treatment; nevertheless, it is frequently recommended alongside prescription antidepressants because clinical trials have demonstrated that the combination is superior to relying on either intervention as monotherapy. (2, 21)

Sleep hygiene is often encouraged in patients participating in trials studying light therapy. Phase-delayed circadian rhythms relative to sleep, which can cause insomnia, are characteristic of SAD. Excessive light during the two hours before bedtime interferes with circadian rhythms. Therefore, forming sleep hygiene habits that foster a healthy sleep-wake cycle is important to SAD treatment. This includes avoiding light exposure in the late evening, especially blue light emitted from electronic screens. Other basic sleep hygiene rules include keeping a regular sleep schedule (i.e., going to bed and waking up at the same time every day), avoiding caffeine and alcohol in the afternoons and evenings, and creating a calming bedroom environment conducive to sleep. 

Aerobic and resistance exercise is generally recommended as part of standard treatment for mild-to-moderate depressive disorders for its mental and physical health benefits. One eight-week trial compared the efficacy of aerobic exercise to relaxation training in patients with SAD; researchers concluded participating in one hour of aerobic exercise 2-3 times weekly produced a greater improvement in SAD symptoms than relaxation training for one hour weekly. 

The Role of Supplements in Treating SAD

A 2018 systematic review of herbal medicine for anxiety and depression concluded that herbal remedies can alleviate symptoms of mild-to-moderate depression, some being just as effective as standard pharmaceuticals. Using evidence-based dietary supplements and herbal remedies for SAD can reduce the need for medication and the risk of common side effects associated with antidepressant medications. 

Vitamin D

Vitamin D is the most researched dietary supplement specific to SAD. Vitamin D levels inversely correlate with clinical depression. Vitamin D deficiency typically results from too little outdoor exposure to sunshine (common in the winter) or insufficient dietary intake. Vitamin D supplementation results in significant improvements in depressive symptoms. Trials have found favorable outcomes with dosing schedules that vary from 800 IU daily to a single mega-dose of 100,000 IU. Vitamin D can cause toxicity, so it is essential to consult with a healthcare provider to discuss a dosing strategy that is both safe and effective. (21)


Lavender has a calming effect on the nervous system by inhibiting excitatory neurotransmitters and potentiating inhibitory ones. Clinical trials that have investigated the effects of lavender in aromatherapy and oral forms on depression have found it to have significant antidepressant effects. Much of the data suggests it is comparable or superior in efficacy to selective serotonin receptor inhibitors (SSRIs). It can be safely used as monotherapy or with pharmaceutical antidepressants to treat mild-to-moderate depression. (1


Research indicates that saffron, derived from the Crocus sativus flower, is clinically efficacious in treating mild-to-moderate depression in doses of 30 mg administered 1-3 times daily. Saffron's active compounds, crocin and safranal, contribute to its mood-enhancing effects by enhancing the effects of serotonin and dopamine. (7)

Addressing Environmental and Emotional Factors

Up to 73% of the population in northern latitude locations has serum vitamin D levels less than 20 ng/mL (clinical deficiency). During the winter, the skin cannot synthesize sufficient vitamin D at latitudes above 37 degrees north. This is an important geographical factor to consider when optimizing vitamin D levels in patients with SAD. A patient in Seattle, for example, will be more likely to require vitamin D supplementation and light therapy to maintain optimal vitamin D status than a patient living in San Diego.

Cognitive behavioral therapy (CBT) is another very effective modality to implement with patients with SAD. CBT is one of the most evidence-based psychological interventions for the treatment of psychiatric and mood disorders, including depression. It uses various strategies to change thinking and behavioral patterns. Many studies support the notion that CBT is effective as a standalone treatment for depression and enhances treatment outcomes when paired with pharmacotherapy. (15)

Integrating Conventional and Functional Medicine Approaches

Functional medicine can seamlessly integrate with conventional treatments for SAD to create a more holistic and personalized approach to patient care. By incorporating principles of functional medicine, healthcare providers aim to identify and address the underlying factors contributing to SAD, creating a personalized approach to medicine that tailors treatments to the individual's unique health profile and needs. The synergy of complementary and conventional modalities, such as psychotherapy or BLT with pharmacotherapy, yields improved health outcomes.


A Functional Medicine Approach to Seasonal Affective Disorder

The holistic management of seasonal affective disorder through the principles of functional medicine offers a comprehensive and personalized approach to addressing the root causes of seasonal depression. By integrating conventional treatments with functional medicine tactics that target the root causes of mood imbalances, individuals can benefit from a well-rounded strategy that combats the winter blues and fosters happiness throughout the year.

The information provided is not intended to be a substitute for professional medical advice. Always consult with your doctor or other qualified healthcare provider before taking any dietary supplement or making any changes to your diet or exercise routine.
Learn More
No items found.

Lab Tests in This Article


  1. Appleton, J. (2014, February 19). Lavender Oil for Anxiety and Depression. Natural Medicine Journal.
  2. Avery, D. (2022). Seasonal affective disorder: Treatment. UpToDate.
  3. Blake, K. (2023, May 22). Anti Inflammatory Diet 101: What to Eat and Avoid Plus Specialty Labs To Monitor Results. Rupa Health.
  4. Cloyd, J. (2023, February 2). Top Lab Test to Run on Your Iron Deficiency Anemia Patients. Rupa Health.
  5. Cloyd, J. (2023, March 1). A Functional Medicine Protocol for Seasonal Depression. Rupa Health.
  6. Cloyd, J. (2023, August 9). A Root Cause Medicine Protocol for Patients With Depression: Comprehensive Lab Testing, Therapeutic Diet, and Supplements. Rupa Health.
  7. Cloyd, J. (2023, August 25). A Root Cause Medicine Protocol For Patients With Insomnia: Testing, Therapeutic Diet, and Supportive Supplements. Rupa Health.
  8. Cloyd, J. (2023, October 17). The Role of Nutrition in Managing Depression: Foods that Boost Mood. Rupa Health.
  9. Cloyd, J. (2023, November 16). The Role of Amino Acids in Mood Regulation: A Functional Medicine Perspective. Rupa Health.
  10. Cloyd, J. (2023, December 4). Omega-3 Fatty Acids in Cardiovascular Health: A Functional Medicine Guide. Rupa Health.
  11. Cloyd, J. (2023, December 6). Winter Wellness: Optimizing Vitamin D Levels in the Colder Months. Rupa Health.
  12. Diorio, B. (2022, September 6). How To Increase Your Serotonin Levels Naturally. Rupa Health.
  13. Firoozeei, T. S., Feizi, A., Rezaeizadeh, H., et al. (2021). The Antidepressant Effects of Lavender (Lavandula angustifolia Mill.): A Systematic Review and Meta-Analysis of Randomized Controlled Clinical Trials. Complementary Therapies in Medicine, 59, 102679.
  14. Gautam, M., Tripathi, A., Deshmukh, D., et al. (2020). Cognitive Behavioral Therapy for Depression. Indian Journal of Psychiatry, 62(8), 223–229.
  15. Gloth, F. M., Alam, W., & Hollis, B. (1999). Vitamin D vs broad spectrum phototherapy in the treatment of seasonal affective disorder. The Journal of Nutrition, Health & Aging, 3(1), 5–7.
  16. Gupta, A., Sharma, P. K., Garg, V. K., et al. (2013). Role of serotonin in seasonal affective disorder. European Review for Medical and Pharmacological Sciences, 17(1), 49–55.
  17. Henry, K. (2023, February 21). An Integrative Medicine Approach to Depression. Rupa Health.
  18. Kennel, K. A., Drake, M. T., & Hurley, D. L. (2010). Vitamin D Deficiency in Adults: When to Test and How to Treat. Mayo Clinic Proceedings, 85(8), 752–758.
  19. Magnesium Fact Sheet for Health Professionals. Office of Dietary Supplements; National Institutes of Health.
  20. Melrose, S. (2015). Seasonal Affective Disorder: An Overview of Assessment and Treatment Approaches. Depression Research and Treatment, 2015, 1–6.
  21. Menon, V., Kar, S., Suthar, N., et al. (2020). Vitamin D and depression: A critical appraisal of the evidence and future directions. Indian Journal of Psychological Medicine, 42(1), 11.
  22. Michael, D. R. (2020). Seasonal Affective Disorder (SAD) Differential Diagnoses. Medscape.
  23. Neibling, K. (2023, March 20). Health Problems Linked to Vitamin D Deficiency. Rupa Health.
  24. Partonen, T., Leppamaki, S., Hurme, J., et al. (1998). Randomized trial of physical exercise alone or combined with bright light on mood and health-related quality of life. Psychological Medicine, 28(6), 1359–1364.
  25. Patrick, R. P., & Ames, B. N. (2015). Vitamin D and the omega-3 fatty acids control serotonin synthesis and action, part 2: relevance for ADHD, bipolar disorder, schizophrenia, and impulsive behavior. The FASEB Journal, 29(6), 2207–2222.
  26. Saeed, S. A., Cunningham, K., & Bloch, R. M. (2019). Depression and Anxiety Disorders: Benefits of Exercise, Yoga, and Meditation. American Family Physician, 99(10), 620–627.
  27. Seasonal Depression (Seasonal Affective Disorder). (2022, April 10). Cleveland Clinic.
  28. Serotonin. (2022, March 18). Cleveland Clinic.
  29. Siddiqui, M. J., Saleh, M. S. M., Binti Basharuddin, S. N. B., et al. (2018). Saffron (Crocus sativus L.): As an antidepressant. Journal of Pharmacy and Bioallied Sciences, 10(4), 173.
  30. Spedding, S. (2014). Vitamin D and Depression: A Systematic Review and Meta-Analysis Comparing Studies with and without Biological Flaws. Nutrients, 6(4), 1501–1518.
  31. Sweetnich, J. (2023, April 5). Health Benefits of Zinc. Rupa Health.
  32. Sweetnich, J. (2023, April 24). How To Make Sure Your Patients Are Getting Enough Vitamin B6 In Their Diet: Testing, RDA's, and Supplementation 101. Rupa Health.
  33. Sweetnich, J. (2023, May 4). Getting to Know Vitamin D: From Testing to Supplementing and Meeting your RDA's. Rupa Health.
  34. Sweetnich, J. (2023, May 8). Understanding the Importance of Folate Testing and Proper Supplementation for Optimal Health. Rupa Health.
  35. Sweetnich, J. (2023, May 9). How to Make Sure Your Patients Are Getting Enough Vitamin C in Their Diet: Understanding Testing, RDAs, and The Benefits of Supplementation. Rupa Health.
  36. Terman, M., Terman, J. S., & Ross, D. C. (1998). A Controlled Trial of Timed Bright Light and Negative Air Ionization for Treatment of Winter Depression. Archives of General Psychiatry, 55(10), 875.
  37. Vitamin D. (2020, May 21). Fullscript.
  38. What Is Cognitive Behavioral Therapy? (2017). American Psychological Association.
  39. Yang, Y., Zhang, S., Zhang, X., et al. (2020). The Role of Diet, Eating Behavior, and Nutrition Intervention in Seasonal Affective Disorder: A Systematic Review. Frontiers in Psychology, 11.
  40. Yeung, K. S., Hernandez, M., Mao, J. J., et al. (2018). Herbal medicine for depression and anxiety: A systematic review with assessment of potential psycho-oncologic relevance. Phytotherapy Research, 32(5), 865–891.
  41. Yoshimura, H. (2023, October 11). An Integrative Medicine Approach to Circadian Rhythm Disorders. Rupa Health.
Subscribe to the Magazine for free. to keep reading!
Subscribe for free to keep reading, If you are already subscribed, enter your email address to log back in.
Thanks for subscribing!
Oops! Something went wrong while submitting the form.
Are you a healthcare practitioner?
Thanks for subscribing!
Oops! Something went wrong while submitting the form.