Winter slump? Vitamin D could be the culprit.

Written By Taryn K White

Feeling down or low on energy this winter? You’re not alone.

It’s easy to chalk it up to the cold, gray weather, long days indoors, or the post-holiday slump after a season of travel and packed schedules. But what if there’s more to it than that? Could the lack of sunshine be messing with your energy and mood? 

The answer is yes! Science shows that your vitamin D levels may be the hidden culprit behind the winter blues and fatigue.

In fact, about 50% of the global population is thought to have insufficient vitamin D levels (Di Gessa et al., 2021). Think about your winter routine: shorter days with the sun setting before you leave work, outdoor runs swapped for the treadmill, cozy indoor activities replacing afternoons outside, and layers of clothing shielding your skin from the elements. With so little sun exposure, it’s no wonder your skin is struggling to synthesize the vitamin D that you need to function. Let’s dive into why this matters and how to reclaim your energy and mood this season.

Winter, SAD, vitamin D, fatigue, UV exposure

Why is Vitamin D so important?

Vitamin D serves many important roles in the body, including:

  • Bone/musculoskeletal health

  • Reduction of inflammation

  • Cell growth and muscle function

  • Immune function

  • Glucose metabolism

Vitamin D and Mental Health:

Vitamin D isn’t just important for strong bones and overall physical health—it also plays a big role in mental health. Low levels of vitamin D have been linked to conditions like depression, anxiety, and schizophrenia. For example, a study of over 12,000 people found that lower vitamin D levels were associated with a higher risk of anxiety (Wen et al., 2024). Other studies have shown that older adults with low vitamin D levels are more likely to develop depression (Di Gessa et al., 2021), and one four-year study found that people with a vitamin D deficiency were 75% more likely to experience depression compared to those with healthy levels (Akpınar & Karadağ, 2022). This could be because vitamin D receptors are found in parts of the brain linked to depression, vitamin D helps produce serotonin (the “happy hormone”), and it also has anti-inflammatory benefits that may protect the brain.

Snow, winter, UV exposure, vitamin D

How to increase your vitamin D levels

Vitamin D deficiency can take a toll on both your physical and mental health, but boosting your vitamin D levels—and restoring your energy levels and mood this winter—can be achieved with a few simple steps.

Take advantage of good weather and sunny winter days

About 80% of vitamin D in the body is synthesized in the skin by ultraviolet rays (Akpınar & Karadağ, 2022). Sunlight is critical for your vitamin D levels, and while not every winter day allows for maximum UV exposure for the most efficient vitamin D production, your skin can still synthesize vitamin D on cloudy days. 

  • Get outside as much as possible: Unfortunately, UVB radiation does not penetrate glass, so sun exposure indoors through windows does not produce vitamin D (U.S. Department of Health and Human Services, 2024). However, only about 15 to 20 minutes daily of direct exposure to sunlight outdoors is needed for vitamin D synthesis to occur in the skin (Akpınar & Karadağ, 2022). 

  • Sunlight upon waking: Try eating breakfast or drinking your morning coffee outside first thing in the morning. This helps to regulate your circadian rhythm, allowing you to sleep better and feel more energized.

Ahi tuna, vitamin D foods, wild-caught fish

Eat more vitamin D-rich foods

There are a limited number of foods rich in vitamin D, so make sure that you’re prioritizing those that are to ensure adequate consumption through your diet. The recommended daily dietary intake for vitamin D is 600 IU for most people. However, older adults (>70 years) have increased vitamin D needs due to decreased absorption efficiency and decreased skin synthesis and should consume 800 IU daily.

  • Eat More:

    • Cod liver oil, 1 T, 1,360 IU

    • Trout, 3 oz, 645 IU

    • Wild salmon, 3.5 oz, 900 IU

    • Cod, 3.5 oz, 104 IU

    • Ahi Tuna, 3.5 oz, 404 IU

    • White mushrooms (exposed to UV light), ½ cup, 366 IU 

      *Most mushrooms are grown indoors without UV exposure; however mushrooms that have been treated with UV lamps or exposed to sun (e.g. grown outdoors) have much higher vitamin D content.

    • Atlantic sardines (canned and drained), 2 sardines, 46 IU

    • Eggs, 1 large, 44 IU

    • Tuna (canned in water and drained), 3 oz, 40 IU

  • Opt for wild-caught, oily fish: Farmed salmon has been found to contain approximately 25% of the vitamin D content as wild salmon (Lu et al., 2007), so always look for wild-caught when purchasing fish.

  • Try this Air Fryer Cajun Salmon for a quick 20-minute dinner that’s rich in vitamin D, omega-3 fatty acids, and protein!

  • Gut health is key: Vitamin D from foods you eat is absorbed in the small intestine, and your gut health – including stomach acid and bile production or the strength of your gut lining – strongly influence how much vitamin D you absorb. 

Take a high-quality vitamin D supplement

Getting enough vitamin D during the winter months can be difficult, particularly for individuals who are already deficient. Supplementing with vitamin D may be necessary, but it's crucial to do so properly to support your body's needs.

  • Before starting supplementation, it’s important to understand your baseline levels. Without getting a sense of your starting point, it can be easy to under-supplement if you’re very deficient or, on the contrary, over-supplement if your levels are adequate. Check out the GreenMind Fullscript store to see some of our favorite products, and always start by consulting a nutrition or health professional who can help you decide what supplement and dose is right for you.

  • Take your vitamin D supplement with the largest meal of the day. One study found that those who take vitamin D with the largest meal had improved absorption and a 50% increase in serum levels of vitamin D (Mulligan & Licata, 2010).

  • Opt for vitamin D3 over vitamin D2. A 12-week study found that vitamin D3 was 87% more potent in raising serum concentrations of vitamin D with two-to-three fold greater tissue storage than vitamin D2 (Heaney et al., 2011). 

  • Supplement vitamin K with vitamin D. These two vitamins work synergistically to support bone health and high doses of vitamin D can also increase your demand for vitamin K. Talk to a trusted health professional when supplementing vitamin D to decide if it’s appropriate to also take vitamin K.

Winter doesn’t have to feel like a low season while you wait for spring to bring the sunshine back. By taking proactive steps, you can start feeling more energized and uplifted today—regardless of the ice and snowstorms outside. Incorporate vitamin D-rich foods like wild-caught fish into your weekly meals, soak up the sun for 15-20 minutes whenever possible, and consider a high-quality supplement if you’re not hitting your daily vitamin D needs. These small tweaks in your routine can make a difference, allowing you to take control of your health and enjoy the season to its fullest!




Sources

Akpınar, Ş., & Karadağ, M. G. (2022). Is Vitamin D important in anxiety or depression? What is the truth?. Current Nutrition Reports, 11(4), 675–681. https://doi.org/10.1007/s13668-022-00441-0

Di Gessa, G., Biddulph, J. P., Zaninotto, P., & de Oliveira, C. (2021). Changes in vitamin D levels and depressive symptoms in later life in England. Scientific Reports, 11(1), 7724. https://doi.org/10.1038/s41598-021-87432-3

Heaney, R. P., Recker, R. R., Grote, J., Horst, R. L., & Armas, L. A. (2011). Vitamin D(3) is more potent than vitamin D(2) in humans. The Journal of Clinical Endocrinology and Metabolism, 96(3), E447–E452. https://doi.org/10.1210/jc.2010-2230

Lu, Z., Chen, T. C., Zhang, A., Persons, K. S., Kohn, N., Berkowitz, R., Martinello, S., & Holick, M. F. (2007). An evaluation of the vitamin D3 content in fish: Is the vitamin D content adequate to satisfy the dietary requirement for vitamin D?. The Journal of Steroid Biochemistry and Molecular Biology, 103(3-5), 642–644. https://doi.org/10.1016/j.jsbmb.2006.12.010

Mulligan, G. B., & Licata, A. (2010). Taking vitamin D with the largest meal improves absorption and results in higher serum levels of 25-hydroxyvitamin D. Journal of Bone and Mineral Research: The Official Journal of the American Society for Bone and Mineral Research, 25(4), 928–930. https://doi.org/10.1002/jbmr.67

U.S. Department of Health and Human Services. (2024). Vitamin D Health Professional Fact Sheet. NIH Office of Dietary Supplements. https://ods.od.nih.gov/factsheets/VitaminD-HealthProfessional/

Wen, Z., Bai, L., Wu, S., Chen, J., Jama, H. A., & Sawmadal, J. D. (2024). Association of serum vitamin D with anxiety in US adults: a cross-sectional study. Frontiers in Nutrition, 11, 1371170. https://doi.org/10.3389/fnut.2024.1371170

Taryn K White
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