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Defend against cold and flu season with vitamin D

Last Modified: October 04, 2019

Family Medicine

vitamin D

This post was written by Angela LaSalle, MD, PPG – Integrative Medicine.

Fall and winter are notorious for cooler temperatures, minimal sunshine and more time indoors. With these seasonal factors, a vitamin D deficiency could also be looming, and ultimately impact and your overall immune health. Angela LaSalle, MD, PPG - Integrative Medicine, shares the signs and symptoms of vitamin D deficiency and offers guidance for proper intake.    

Boosting the immune system is one of the top reasons why many Americans take vitamins and supplements. But with so many products available, what supplement might give us the best protection at the lowest cost during cold and flu season? The answer: Vitamin D3.


A 2009 study of 19,000 adults and adolescents, published in the Archives of Internal Medicine, showed that individuals with low vitamin D levels (less than 10) were 40% more likely to get a respiratory infection. Whereas, people with levels greater than 30 faired the best, perhaps due to the immune-boosting benefits of vitamin D.

The study also showed that individuals who already had lung issues like asthma or emphysema were at an increased risk of a respiratory infection, especially if their vitamin D levels were low. Those patients with a combination of low vitamin D and asthma were five times more likely to suffer a bout with a cold or the flu, and those with Chronic Obstructive Pulmonary Disease (COPD) were at twice the risk.


Because vitamin D plays such a vital role in your overall immune health, it’s important to understand how it works in your body. While the exact mechanisms of how vitamin D boosts the immune system is not fully known, it has been shown to increase the levels of a protein group called Cathelicidins, or antimicrobial peptides. These proteins are made by macrophages, a type of white blood cells and a key group of immune cells, that fight bacterial and viral infections in the body.

Identifying a deficiency

So, how do you know if you might be deficient in vitamin D? It can present in many ways, but the condition is often associated with risk factors including:

  • frequent infections   
  • eczema
  • asthma
  • allergies   
  • tooth decay   
  • hair loss   
  • muscle or bone pain  
  • osteoporosis   
  • insomnia      
  • having dark skin, being overweight or older age  
  • having chronic diseases (i.e. high cholesterol, hypertension, diabetes, etc.)

If you are experiencing any of the following symptoms, consult your doctor. He or she can order the appropriate blood work to determine the right treatment and appropriate dosage for supplementation. Remember, it’s important to always have your levels checked before starting yourself or family members on any kind of supplementation. Before flu season hits, think “D” for “Defense” … vitamin D that is.

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