Immune Boosting Foods by Nutrition Intern Kristin Cowin

Immune Boosting Foods

Written by Kristin Cowin, BSN

In light of the recent outbreak of the Coronavirus, I thought it would be an appropriate time to talk about the important role that whole foods play in keeping us healthy. As a quick and dirty way to make sure to get the max amount of health benefits from the diet, it is beneficial to practice eating each color of the rainbow. Each whole food offers an array of nutrients that help our bodies maintain health. Today I am highlighting foods that are packed full of evidence-based nutrients that help support and enhance the immune system. The key nutrients highlighted in this article are Vitamins A, C, and E.

First, I want to address some important information about the common cold and the flu. The common cold, the most common infectious disease, is a viral infection that is relatively mild and limited to the areas of the nasal passage and the back of the throat. This infection can be caused by more than 100 different viruses, the most common of them being the rhinoviruses and coronaviruses.1 These two types of viruses are responsible for 50 to 70% of all colds. The average adult acquires 2 to 4 colds a year and children get an average of 6 to 10 depending on their age and their exposure.1 Over 50% of upper respiratory tract infections can be cause by the rhinovirus. The coronavirus accounts for 10-20% of infections, the influenza viruses causing 10-15%, and 5% by the adenovirus.1 The flu is an upper respiratory infection most often caused by flu virus types A and B. The virus has the ability to mutate rapidly making it difficult to prevent the spread of the illness.1 It is also possible for a person to be infected with a combination of viruses at the same time. For more information about the COVID-19 in particular, please check the World Health Organization at and the Oregon Health Authority at

Though it is extremely tempting to take over-the-counter medications, there are some potential drawbacks. Nasal and sinus decongestants dry nasal and sinus secretions which is the desired result, however, nasal and sinus passages that are too dry can increase the risk of further infection. Also, prolonged use of these drugs, more the five consecutive days, and then discontinued can cause a “rebound” effect of worsened symptoms due to mucosal dependence on the drug.1 The use of these medications is not recommended for people with cardiovascular disease, hypertension, diabetes, and thyroid symptoms, and can make urinating difficult.1 it is also important to recognize that the viruses cannot survive in high temperatures, highlighting the importance of a fever as your body’s natural way to fight off the infection.

Now for the fun part, my favorite part, let’s talk about food! Like I mentioned before, there are some key nutrients that help our body’s fight off illnesses. In my son’s words, Let’s ACE the Flu!

Vitamin A

Also known as “the anti-infective vitamin” for its many important roles in the immune system. Vitamin as is tightly associated with skin and eye health. what most people do not realize is that skin included any surface of the body that is exposed to the outside world, including the linings of the nose, mouth, throat, airways, digestive tract, and the urinary tract. These areas are especially important when thinking about immunity because they are going to function as our frontline defenders against infections.4 Vitamin A is a family, the Carotenoid family, of many different inactive and active forms that all specialize in different regions of the body. The most well-known form is Retinoic acid and is found in the mucus membranes mentioned above and is associated with the Lymph nodes of the body. The lymph nodes are like the military base camps for the immune system, they are located near areas of high risk for infection.

When picking foods that are high in Vitamin A, using the color of the food as a guide is a quick and easy way. yellow-to-red colored foods are going to contain carotenoids (Vitamin A), along with some green vegetables because yellow-to-red colors are masked by green, which contains chlorophyll.4

Vitamin C

The most well-known for its immune boosting activity. Also known as L-ascorbic acid, is found to shorten the duration of the common cold but has not actually been proven to reduce the risk of getting sick. What makes this vitamin so special is its ability to protect the body from damage from harmful free radicals that are produced naturally in the body from metabolic processes and exposure to pollutants from outside of the body. Free radicals are compounds that are unstable and highly reactive. If left in their unstable form, they can cause a chain reaction in our cells that can lead to a malfunctioning, cell death, tissue damage, and even damage to the DNA. Vitamin C helps to stabilize the free radicals and stops their disastrous chain reactions in the body. Vitamin E has similar actions in the body, and vitamin C plays a role in regenerating vitamin E after is stabilizes free radicals. Vitamin C also plays a role in enhancing the body’s natural immune response to infections and tissue damage by stimulating the immune cells such as White Blood Cells, neutrophils, lymphocytes, and phagocytes, while at the same time, protecting these immune cells from damage from free radicals that they, themselves, produce during their immune responses.2

When picking foods that are high in vitamin C is always safe to assume that orange, yellow, and red-ish/pink foods are going to be a rich source. However, there is always the surprising source of green foods that can be high in vitamin C.

When it comes to cooking, vitamin C is a very delicate compound; it is sensitive to heat and is water soluble. Steaming and blanching are the gentlest methods over boiling and roasting, but all are going to decrease the amount of this vitamin in the food. Microwaving has actually been shown to be another gentle cooking method on vitamin C because of its shorter cooking times.3

Vitamin E

Is a powerful Antioxidant that goes around the body scavenging damaging free radicals, mitigating age-related weakening of the immune system. As we age, our immune system get less and less nimble increasing our risk for infection and weakening our body’s immune response to those infections.5 Vitamin E is found to enhance the body’s cellular immune responses to infections while cleaning up free radicals. As mentioned in the Vitamin C section, Vitamin C works to regenerate Vitamin E after it has scavenged a free radical. Like Vitamin A, Vitamin E is a family of compounds called Tocopherols that have varying degrees of activity in the body and research is still uncovering the actions and locations of all the Tocopherols.


1.  Mario R, Julie J. Colds and influenza: a review of diagnosis and conventional, botanical, and nutritional considerations. Alternative Medicine Review. 2007;12(1). Accessed March 13, 2

2.   Higdon, Ph.D. J. Vitamin C. Linus Pauling Institute. Published 2020. Accessed March 16, 2020.

  • Higdon, Ph.D. J. Vitamin A. Linus Pauling Institute. Published 2020. Accessed March 16, 2020.
  • Higdon, Ph.D. J. Vitamin E. Linus Pauling Institute. Published 2015. Accessed March 20, 2020.


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