Vitamin D And Your Immune System

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Vitamin D is one of the most common nutrient deficiencies I see in my practice. Studies show that 40% of Canadians have insufficient vitamin D blood levels in the winter, and 25% have insufficient levels in the summer (1). This widespread deficiency is concerning, because vitamin D plays such an important role in so many areas of our health. Vitamin D helps maintain calcium homeostasis and healthy bone mineral density, and plays a role in prevention of breast and colon cancer, cardiovascular disease in men, and seasonal affective disorder (2,3,4,5,6,7). Vitamin D also has a huge influence on the health of our immune system, and a deficiency of this critical vitamin can increase the risk of autoimmune disease and respiratory tract infections (8,9,10,11,12).

With winter quickly approaching, and with it the onset of the cold and flu season, I recommend vitamin D testing and supplementation for everyone. Studies show that people with sufficient vitamin D levels have fewer upper respiratory infections, and if/when they do get sick, they have a shorter duration of illness and less severe symptoms overall (13,14).

So having sufficient vitamin D levels will not only help to keep you healthy during the cold and flu season, but it also has long term benefits associated with the prevention of chronic disease.

Why is Vitamin D so Commonly Deficient?

1. Few Foods Naturally Contain Vitamin D

Vitamin D is naturally found in very few foods, and these foods are typically lacking in western diets. Foods that have the highest vitamin D levels are fatty fish such as salmon, cod liver oil, and egg yolk. Diary and soy products are also commonly fortified with vitamin D (15).

2. Lack of Sun Exposure (16)

Our primary source of vitamin D is through sun exposure. When sun hits our skin, it triggers a biochemical process that produces vitamin D. However, with our modern lifestyle, we spend most of our hours inside, and when we’re in the sun we often cover up or wear sunscreen. On top of this, as Canadians, we receive fewer direct sunrays then in other parts of the world.

3. Malabsorption

Vitamin D is a fat-soluble vitamin, meaning your body has to be able to absorb dietary fat in order to absorb vitamin D. Chronic digestive conditions such as celiac disease and inflammatory bowel disease impair fat absorption and commonly lead to vitamin D deficiency (17).

How Can I Improve my Vitamin D Levels?

In winter months most Canadians have to supplement with vitamin D in order to maintain healthy blood levels. If you have not had your vitamin D checked, a safe maintenance dose is 1000-2000 IU of vitamin D per day. However, for those with known deficiencies, 1000-2000 IU per day may not be enough to raise vitamin D levels to a satisfactory level; this is why I always recommend vitamin D testing. If deficient, supplementing with 4000-5000 IU of vitamin D per day for 3-6 months will increase your serum vitamin D to a healthy level. In cases of malabsorption due to chronic digestive issues, supplementing with 10,000 IU per day is often needed to replenish levels, along with addressing the underlying gastrointestinal illness (18). In these cases vitamin D blood levels should be closely monitored by your health care provider.

In health and happiness,

Dr. Meghan van Drimmelen | Naturopath Victoria BC


  1. Janz, T. et al. “Vitamin D Blood Levels of Canadians.” Statistics Canada Catalogue no-82-625-X, 2013.

  2. Pazirandeh S. et al. “Overview of Vitamin D.” Up To Date, 2016.

  3. Lin J. et al. “Intakes of calcium and vitamin D and breast cancer risk in women.” Archives of International Medicine, 167(10):1050-1059, 2007.

  4. Gorham E. et al. “Optimal vitamin D status for colorectal cancer prevention: a quantitative meta analysis.” American Journal of Preventative Medicine, 32(3):210-216, 2007.

  5. Giovannucci E. et al. “25-Hydroxyvitamin D and risk of myocardinal infarction in men: a prospective study.” Archives of Internal Medicine, 168(11):1174-1180, 2008.

  6. Kerr DC. et al. “Associations between vitamin D levels and depressive symptoms in healthy young adult women.” Psychiatry Res, 30;227(1):46-51, 2015.

  7. Melrose S. “Seasonal Affective Disorder: An Overview of Assessment and Treatment Approaches.” Depress Res Treat, 178564, 2015.

  8. Rosen Y. et al. “Vitamin D and Autoimmunity.” Scandinavian Journal of Rheumatology, 18:1-9, 2016.

  9. Antico A. et al. “Can supplementation with vitamin D reduce the risk or modify the course of autoimmune disease? A systemic review of the literature.” Autoimmune Review, 12(2):127-36, 2012.

  10. Pelajo CF. et al. “Vitamin D and Autoimmune Rheumatologic Disorders.” Autoimmune Review, 9(7):507-10, 2010.

  11. Zhao G. et al. “Low Concentration of Serum 25-Hydroxyvitamin D Associated with Increased risk of Chronic Bronchitis Among US Adults.” British Journal of Nutrition 107(9):1386-92, 2012.

  12. Ginde AA. et al. “Association Between Serum 25-Hydroxyvitamin D Level and Upper Respiratory Tract Infection in the Third National Health and Nutrition Examination Survey.” Archives of Internal Medicine, 169(4):384-90, 2009.

  13. Bergman P. et al. “Vitamin D Supplementation Improves Well-Being in Patients with Frequent Respiratory Tract Infections: a Post Hoc Analysis of a Randomized, Placebo-Controlled Trial.” BMC Res Notes, 8:498, 2015.

  14. Bergan P. et al. “Vitamin D Supplementation to Patients with Frequent Respiratory Tract Infections: a Post Hoc Analysis of a Randomized and Placebo-Controlled Trial.” BMC Res Notes, 8:391, 2015.

  15. “Food Sources of Vitamin D.” Dieticians of Canada, 2014. [Accessed October 18th, 2016].

  16. Pazirandeh S. et al. “Overview of Vitamin D.” Up To Date, 2016.

  17. Pazirandeh S. et al. “Overview of Vitamin D.” Up To Date, 2016.

  18. Pazirandeh S. et al. “Overview of Vitamin D.” Up To Date, 2016.

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