Winter Blues: What is SAD and How Can Vitamin D Help?

Winter Blues: What is SAD and How Can Vitamin D Help?

  • Healthy Eating

  • By Mathieu Millette, Ph. D., Mcb. A.

    As the days grow shorter, do you find yourself feeling, well, not like yourself? 

    Maybe your energy levels are lower than usual, your sleep schedule is irregular, or you've noticed changes in your appetite. Perhaps you’ve felt the weight of the world sitting a bit heavier on your shoulders. All of these feelings can be frustrating, especially if you’re unsure of their cause. 

    Don’t worry—you’re not alone. 

    You may be one of the millions of people around the world experiencing seasonal affective disorder, better known as SAD. There are myriad ways to relieve this common condition’s symptoms, including incorporating more Vitamin D into your daily routine. 

    Below, you’ll learn more about what causes SAD, and how you can start taking steps to increase your energy levels and feel like yourself again.


    What Causes Seasonal Affective Disorder? 

    SAD is a recurring major depression with a seasonal pattern. 

    In layman’s terms? This means individuals diagnosed with SAD typically experience sad moods and low energy levels every year as the days get shorter and sunlight decreases. And in some cases, the impact of this seasonal depression may have long-lasting effects that extend beyond the winter months. 

    While the specific cause remains unknown, experts agree on two factors that may contribute to SAD:

  • Lowered serotonin levels. Serotonin is a neurotransmitter—a chemical present in the brain—that works to regulate, among other things, a person’s mood. Your serotonin levels may decrease from reduced sunlight exposure, contributing to SAD.¹

  • Increased melatonin levels. Melatonin is a hormone produced by the body that regulates the sleep cycle; the hormone responds to darkness by inducing sleepiness. Those experiencing SAD may be producing more melatonin, thus feeling more sluggish than usual. 

  • When these two factors collide, the effects can be detrimental. After all:

    Low serotonin + high melatonin = disrupted circadian rhythm.

    Why a Consistent Circadian Rhythm is Important

    The body’s circadian rhythm—think of it as your internal clock—responds to the light and dark hours that correspond with each season. Some studies have shown that people diagnosed with SAD have an internal clock that has been knocked off its axis.

    The human body is an expert in self-regulation, but sometimes it needs a little outside support. In this case, your body needs to go see a clocksmith—or your friendly neighborhood health professional. 

    Do I Have SAD?

    Approximately five percent of the U.S. population experiences SAD every year, with most people affected during the winter months. It’s important to note, this is not some recently discovered disorder. Researchers have found that descriptions of seasonal depression date back to as early as 400 BC. People have been feeling out of sorts during cold, dark winters for centuries. 

    Those who have been diagnosed with SAD often feel inexplicably down, and have trouble enjoying everyday activities—say, afternoon walks—they usually love.

    Common symptoms of SAD may include:

    • Sadness
    • Irritability 
    • Lethargy
    • Social anxiety 
    • Weight gain
    • Weight loss
    • Insomnia
    • Oversleeping
    • Anxiety

    Like other disorders, SAD may be more prevalent in certain groups² (Note: even if you are not in one of these groups you can still experience SAD). These groups are at an increased risk: 

    • People between the ages of 18-30
    • Women, who are four times more likely to experience SAD than men
    • Those living farthest from the equator in northern latitudes 
    • People with a family history of SAD or depression
    • People already experiencing major depression or bipolar mood disorder 
    • Nurses and health professionals who do “shift work”

    Your doctor may conduct a physical exam, lab tests, and a psychological evaluation to diagnose SAD. Once you've received a diagnosis, you'll be ready to start addressing SAD with a fresh new toolkit of resources for treatment. 

    How Do I Relieve the SAD Symptoms?

    Dr. Norman Rosenthal first identified SAD as a treatable clinical condition in the 1980s.⁵

    That means you don’t have to “power through” the dark cold months each year. There are ways to alleviate the negative feelings and physical side effects brought on by SAD. 

    Remember: Taking proper care of your mental health is just as important as tending to your physical well-being, especially if you think you are experiencing SAD. Learning how to stay healthy in winter months can start with addressing SAD symptoms and establishing a self care routine. This can look like everything from bubble baths to a daily check-in with yourself mentally and emotionally. 

    Here, check out a few suggested ways to relieve SAD symptoms:

    #1 Light Therapy (Phototherapy)

    Turn your face toward light therapy and the shadows will fall behind you. 

    Bright light therapy, also known as phototherapy, mimics natural sunlight. Those experiencing SAD may use light boxes—also referred to as SAD lamps, therapy lamps, and bright light boxes—to help the brain create more adequate levels of serotonin and less melatonin, thus recalibrating their off-kilter internal clock. 

    How do I get started?

    First, chat with your doctor. They will advise you on how and when to use your box properly — different people will have different needs.  Before purchasing your first light box, consider the following:

    • A light box is most effective when you are sitting or working near it (about 16-24 inches from your face) with the light entering your eyes indirectly. 
    • Time and consistency are critical. Try to use your therapy lamp the same time daily (recommended usage is about 20-30 minutes)
    • Recommended boxes will emit 10,000 lux and should filter out most or all UV light. 
    • Not all light boxes relieve the symptoms of SAD. Some light boxes treat skin pigmentation irregularities and emit UV light instead of filtering it. 

    Doing your research and chatting with your doctor are important first steps to relieving the symptoms of SAD. Think of it as your self-care homework. 

    Once you’ve determined which light box is right for you, consider creating a daily regimen that includes phototherapy and increasing your Vitamin D status. The two approaches will help you double down on upping your serotonin levels and elevating your mood when combined.

    It's worth noting, experts do not recommend the use of light boxes for absorbing Vitamin D for two reasons: 

    1. Safe and effective light box models should filter out most UV light, a key component in producing Vitamin D. 
    1. If you have a light box that does use UV light, the exposure could increase your risk for skin cancer.  


    #2 Vitamin D

    How can taking Vitamin D help with SAD?

    In addition to regulating the body’s calcium and phosphate levels, Vitamin D is also responsible for mood and behavior. 

    Some studies have shown that individuals diagnosed with SAD may have lower Vitamin D levels, resulting from not ingesting or synthesizing enough of the vitamin. Just as light boxes increase your serotonin levels to help elevate your mood, increasing your Vitamin D status may also help brighten your spirit. 

    How can I increase my Vitamin D levels?

    Because sunlight exposure accounts for “over 90% of the vitamin D requirement for most individuals,” in summer-when the sunlight is strong enough to help our body synthesize the vitamin- it makes sense that during the shorter, darker winter months, our bodies are absorbing less Vitamin D. 

    Individuals experiencing SAD can increase their Vitamin D level by:

    • Eating certain foods. Some of the best sources of Vitamin D include mushrooms, egg yolks, and fatty fish like salmon.
    • Taking Vitamin D for SAD in the form of supplements. Check with your doctor before considering supplementation. Health professionals can test your Vitamin D levels and recommend what your daily usage should be depending on the deficiency. 
    • Try Light Therapy. If you can’t get outside during the winter months, try buying a light therapy lamp. While these lamps will not give your daily dose of vitamin D, they have been helpful in easing SAD symptoms when used supplementally with other products.
    • Taking probiotics. When your gut health is compromised, you may not be able to properly absorb Vitamin D, as the GI tract has been shown to play an active role in the vitamin’s absorption. You can strengthen your gut health by taking a probiotic, like Bio-K+®, which supports the good bacteria found in the intestinal tract.  

    Before moving forward with any of these approaches, be sure to check with your doctor first to determine which method(s) are best for you. 

    #3 Self Care   

    The best way to start relieving the depressive symptoms of SAD is to use all the tools in your toolbox. Luckily, many resources are right at your fingertips. 

    So you've decided to incorporate light therapy and Vitamin D supplementation into your daily regimen? Wonderful. These additional measures may also be a boon to elevate your mood and increase your energy levels. 

    • Psychotherapy/Counseling. The benefits of talk therapy cannot be overstated. Psychotherapy is an excellent way to assess the "why" of your feelings, especially if you think you are experiencing seasonal affective disorder. Working with a trained therapist can help you:
      • Identify negative thoughts and work towards reframing them
      • Learn to manage stress
      • Learn healthy coping mechanisms
    • Take care of yourself. Be gentle and patient with your mind and body — symptom relief may not happen overnight! Simple self-care acts can include practicing at-home yoga, downloading a guided meditation app on your phone, and reaching out to friends and loved ones to catch up. 
    • Brighten up your home. Bring the sunshine in. Light your favorite candles, open up the blinds, and visit your local nursery to find a few potted plants that will instantly freshen up your environment. 

    The Sun’s Still Shining 

    If you think you may be experiencing SAD, remember: you are not alone. For centuries people have felt low moods and decreased energy levels due to a variety of factors. With the help of phototherapy, an increase in your daily Vitamin D intake, and practicing self care, you can relieve the depressive symptoms of this common condition and start getting your sunshine back. 

    If you’re looking for that extra boost to support your gut health or want to know how to increase energy levels, you’re in the right place. At Bio-K+ we offer a line of probiotic products that promotes digestive health, which may help you better absorb Vitamin D. 



    1.  (2017). Seasonal affective disorder (SAD). Mayo Clinic. Retrieved from: 

    2. Melrose S. (2015). Seasonal Affective Disorder: An Overview of Assessment and Treatment Approaches. Depression research and treatment, 2015, 178564.

    3. Kurlansik, S. L., & Ibay, A. D. (2012). Seasonal affective disorder. American family physician, 86(11), 1037–1041.

    4. Neumeister A., Stastny J., Praschak-Rieder N., Willeit M., Kasper S. (1999) Light Treatment in Depression(SAD, s-SAD & non-SAD). In: Holick M.F., Jung E.G. (eds) Biologic Effects of Light 1998. Springer, Boston, MA.

    5.  (2017). Light therapy. Mayo Clinic. Retrieved from: 

    6.  Shiffer EJ. (2020).  Vitamin D and depression: How Vitamin D may affect your mood. Insider

    7. Penckofer, S., Kouba, J., Byrn, M., & Estwing Ferrans, C. (2010). Vitamin D and depression: where is all the sunshine?. Issues in mental health nursing, 31(6), 385–393.

    8. Maurya, V. K., & Aggarwal, M. (2017). Factors influencing the absorption of vitamin D in GIT: an overview. Journal of food science and technology, 54(12), 3753–3765. Factors influencing the absorption of vitamin D in GIT: an overview | Journal of Food Science and Technology (

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    Mathieu Millette Mcb. A.
    About the author
    Graduated with honors from INRS-Armand-Frappier Institute, Dr Mathieu Millette is an authority on probiotics for the last 20 years.
    View all articles by Mathieu Millette
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