Embracing the Sunshine Vitamin: Vitamin D and Its Role in Preventing Colds and Flu

by Dr. Nick Zyrowski December 03, 2023

As we enter the holiday season, the weather cools and the sunshine disappears. We find ourselves outside less, sitting more, and eating a little too much comfort food. And with all of these negative changes comes another unwelcome guest - cold and flu season.

In the quest for immune system resilience, Vitamin D emerges as a superhero, often outshining its more commonly recognized counterpart, Vitamin C. Referred to as the sunshine vitamin, Vitamin D plays a crucial role in bolstering the immune system, especially during bouts of cold or flu. If you find yourself frequently under the weather and puzzled about the reasons, read on to discover how Vitamin D can be a game-changer, enhancing your immunity and fortifying your defenses against viral infections.

Understanding Vitamin D: More Than Just a Vitamin

Contrary to its classification, Vitamin D is not a traditional vitamin but a prohormone synthesized in response to the interplay between cholesterol, the skin, and sunlight exposure. Beyond its role in bone health and calcium absorption, Vitamin D has been extensively studied for its contributions to heart health and overall immunity. While expert opinions on the optimal Vitamin D intake may vary, consensus agrees that relying on food alone is insufficient, necessitating additional measures to meet recommended levels. [8]

Vitamin D's Immune-Boosting Effect, Especially in Deficiency Supplementing with Vitamin D has shown to reduce the risk of viral infections, such as colds and flu, by a notable 10 percent. Remarkably, individuals deficient in Vitamin D experience an even greater protective effect, slashing their risk by a substantial 50 percent! [11] The immune system's cell surfaces harbor receptors for Vitamin D, enabling it to bind and initiate a cascade of responses. By reducing inflammatory cytokines and enhancing the production of infection-fighting proteins, Vitamin D acts as a natural defense mechanism against pathogens.

Vitamin D and the Immune System's First Line of Defense

Vitamin D takes center stage in fortifying the innate branch of the immune system, the body's initial defense against infections. A robust innate immune response is crucial for warding off illnesses or minimizing their duration. Research indicates that low Vitamin D levels result in a slower response from immune cells, impairing the effectiveness of the innate immune system.

Even if illness strikes, promptly elevating Vitamin D levels can expedite recovery. Each 4 ng/mL increase in Vitamin D concentrations correlates with a seven percent decrease in the likelihood of contracting the flu. Notably, flu season coincides with reduced sun exposure, contributing to lower natural Vitamin D production.

Vitamin D and the Flu Risk: A Deficiency Link

Cold and flu viruses, with symptoms ranging from congestion to body aches, pose a significant health threat. Those at higher risk, including the elderly, young children, and individuals with chronic disorders, can benefit from maintaining optimal Vitamin D levels. Unlike flu vaccines that may vary in effectiveness, Vitamin D consistently supports the immune system.

While flu vaccines are common, they only address a few strains based on the best guesses by experts of which strains will predominate. Sometimes experts guess wrong, rendering the flu vaccine less effective during those seasons. What doesn’t change, however, is the immune system’s reliance on vitamin D levels, making it a more secure way to boost immunity and avoid the flu. One study even drew a direct link between vitamin D levels and flu risk: Those with the lowest serum concentrations had the highest chances of getting viral infections. [15]

Given that a considerable portion of the population falls below the recommended daily allowance for Vitamin D, supplementation becomes crucial.

Food Sources and Supplements

While sunlight is a natural source of Vitamin D, it can also be obtained through certain foods such as:

Fatty Fish:

  • Salmon
  • Mackerel
  • Sardines
  • Tuna

Fortified Dairy Products:

  • Milk
  • Yogurt
  • Cheese

Egg Yolks

Beef Liver

Cod Liver Oil

As mentioned above, achieving sufficient levels solely through diet can be challenging. In many cases, supplements are a practical and effective way to ensure optimal Vitamin D levels, especially during winter months or for those with limited sun exposure.

Supplementing with Vitamin D: Guidelines for Optimal Levels

For individuals lacking regular sun exposure, particularly during the colder months, supplementation becomes essential. Vitamin D3, considered the natural form, is the most effective at raising serum concentrations. Dosage recommendations, varying based on health conditions and absorption factors, range from 400 IU to 10,000 IU.

The Vitamin D Council recommends adults take between 5,000 and 10,000 IU daily, adjusted by body weight. Children should consume 1,000 IU daily per 25 pounds of body weight. Consultation with a doctor for personalized dosage advice is prudent.

Another important note to keep in mind is quality. Many vitamins and supplements found in the grocery store or local drug store are loaded with seed oils, preservatives, and other fillers. Finding a quality Vitamin D3 supplement is very important. This is the D3 + K2 that we recommend.

Cautionary Notes: Avoiding Vitamin D Overload

Given its fat-soluble nature, Vitamin D accumulation in the body can reach toxic levels with excessive supplementation. Blood level checks before supplementation are advisable. We recommend optimal blood range levels of Vitamin D to be 60 - 100 ng/mL. You may find much lower levels on various websites, but we believe in helping your body to be at optimal performance, not just average.

In Conclusion: Elevating Health with Vitamin D

Vitamin D emerges as a critical player in immune support, influencing response times to viral threats, sickness duration, and overall immunity. Although limited in food sources, Vitamin D optimization through a combination of diet, supplements, and sun exposure in warmer months contributes to holistic well-being. As we navigate the intricate landscape of immune health, let Vitamin D be your guiding light toward a resilient and fortified system.


1.Klibanski, A., et al., Osteoporosis prevention, diagnosis, and therapy. Jama-Journal of the American Medical Association, 2001. 285(6): p. 785-795.

2.Holick, M.F., Vitamin D: importance in the prevention of cancers, type 1 diabetes, heart disease, and osteoporosis. American Journal of Clinical Nutrition, 2004. 79(3): p. 362-371.

3.Dawson-Hughes, B., et al., Estimates of optimal vitamin D status. Osteoporosis International, 2005. 16(7): p. 713-716.

4.Bischoff-Ferrari, H.A., et al., Estimation of optimal serum concentrations of 25-hydroxyvitamin D for multiple health outcomes. American Journal of Clinical Nutrition, 2006. 84(1): p. 18-28.

5.Holick, M.F., High prevalence of vitamin D inadequacy and implications for health. Mayo Clinic Proceedings, 2006. 81(3): p. 353-373.

6.Jackson, R.D., et al., Calcium plus vitamin D supplementation and the risk of fractures. New England Journal of Medicine, 2006. 354(7): p. 669-683.

7.Holick, M.F., Vitamin D deficiency. New England Journal of Medicine, 2007. 357(3): p. 266-281.

8.Holick, M.F. and T.C. Chen, Vitamin D deficiency: a worldwide problem with health consequences. American Journal of Clinical Nutrition, 2008. 87(4): p. 1080S-1086S.

9.Ross, A.C., et al., The 2011 Report on Dietary Reference Intakes for Calcium and Vitamin D from the Institute of Medicine: What Clinicians Need to Know. Journal of Clinical Endocrinology & Metabolism, 2011. 96(1): p. 53-58.

10.Gillespie, L.D., et al., Interventions for preventing falls in older people living in the community. Cochrane Database of Systematic Reviews, 2012(9): p. 408.

11.Martineau, A.R., et al., Vitamin D supplementation to prevent acute respiratory tract infections: systematic review and meta-analysis of individual participant data. BMJ, 2017. 356: p. i6583.

12.Molinari, N.A., et al., The annual impact of seasonal influenza in the US: measuring disease burden and costs. Vaccine, 2007. 25(27): p. 5086-96.

13.Shrestha, S.S., et al., Estimating the burden of 2009 pandemic influenza A (H1N1) in the United States (April 2009-April 2010). Clin Infect Dis, 2011. 52 Suppl 1: p. S75-82.

14.Gruber-Bzura, B.M., Vitamin D and Influenza-Prevention or Therapy? International journal of molecular sciences, 2018. 19(8): p. 2419.

15.Laaksi, I., et al., An association of serum vitamin D concentrations < 40 nmol/L with acute respiratory tract infection in young Finnish men. Am J Clin Nutr, 2007. 86(3): p. 714-7.

16.Cannell, J.J., et al., On the epidemiology of influenza. Virol J, 2008. 5: p. 29.

17.Berry, D.J., et al., Vitamin D status has a linear association with seasonal infections and lung function in British adults. Br J Nutr, 2011. 106(9): p. 1433-40.

18.Nair, R. and A. Maseeh, Vitamin D: The “sunshine” vitamin. Journal of pharmacology & pharmacotherapeutics, 2012. 3(2): p. 118-126.

19.Heaney, R.P., Vitamin D in health and disease. Clin J Am Soc Nephrol, 2008. 3(5): p. 1535-41.

20.Korkor, A.B. and C. Bretzmann, Effect of fish oil on vitamin D absorption. Am J Kidney Dis, 2009. 53(2): p. 356.

21.Holick, M.F., et al., Evaluation, treatment, and prevention of vitamin D deficiency: an Endocrine Society clinical practice guideline. J Clin Endocrinol Metab, 2011. 96(7): p. 1911-30.

Dr. Nick Zyrowski
Dr. Nick Zyrowski

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