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Nutrition for Immunity: Spotlight on Vitamin D and Omega 3

By Kelsey Smith | May 19, 2020, 5 p.m. (ET)

It feels like “immunity” and “immune boosting” recommendations are everywhere right now, and with good reason.

Diseases like COVID-19 can be a huge motivator to evaluate your current lifestyle and try to enhance your immunity in any way you can. While there are so many things to learn from our current climate, I hope that one of those is an appreciation of how precious our health is. As a Registered Sport Dietitian at eNRG Performance, I want to help you adopt immune supporting nutrition as a daily practice.

Today, I am spotlighting two critical nutrients in immune supporting nutrition: Vitamin D and Omega-3.

Vitamin D

Vitamin D has garnered much attention in recent years for good reason. You may know its classic role in bone health by aiding the absorption of calcium in the gut. We are also learning that vitamin D plays a critical and complex role in the immune system.

Despite strong evidence of the benefits of vitamin D, deficiency or insufficiency of this vitamin remains extremely common. It is estimated that 28.9% of U.S. adults are vitamin D deficient (<20 ng/dL), and another 41.1% are vitamin D insufficient (<20-30 ng/dL). That’s approximately two thirds of the U.S. population with low levels of vitamin D, which is a staggering figure.

Vitamin D deficiency is becoming more prevalent due to changes in our lifestyle. While we are able to synthesize vitamin D when sunlight hits the skin, many of us have occupations that require us to be indoors for most of the day. Additionally, sunscreen is wonderful to use for skin cancer prevention, but it can block the UV rays needed for vitamin D synthesis.

Athletes with higher levels of skin pigmentation are also at increased risk of developing deficiency because melanin can block some vitamin D synthesis. To combat some of these challenges, focus on consuming good sources of vitamin D daily, including fatty fish, eggs, fortified milks, fortified cereal, and some mushrooms. Vitamin D is fat soluble, meaning that fat is required for it to be properly absorbed, so be sure to have high vitamin D foods with some fat source to enhance absorption. 

We’re still learning a great deal about the role of vitamin D in immunity, but one meta-analysis concluded that vitamin D supplementation reduced risk of acute upper respiratory infections. Serum vitamin D levels have been inversely related to incidence of viral respiratory infections, meaning higher serum vitamin D is linked to lower risk of infection. There is even some emerging research that shows this same relationship with COVID-19. The prevalence and severity of viral respiratory illness is multifactorial, but this literature strengthens the recommendation to check your serum vitamin D levels routinely. Consult with a Registered Sport Dietitian about how to maximize vitamin D through food and decide if vitamin D supplementation is appropriate for you.  


Omega-3 fatty acids are essential fatty acids, meaning that the body cannot make them from other fats. We have to consume foods high in omega-3’s frequently to meet our needs. There are three main types of omega-3 fats: EPA and DHA, which are from fish and algae, and ALA, which is mainly from plants. 

You might have heard of omega-3 fats as being anti-inflammatory and omega-6 fats (mainly from vegetable and seed oils) as being pro-inflammatory. There is a bit of truth to this, however, this is not the complete story. In the last 60 years or so, the standard American diet has shifted from being fairly balanced in omega-3’s and omega-6’s, to being very high in omega-6’s and very low in omega-3’s. When this ratio is so skewed, that’s when inflammatory markers can become elevated and immune function can suffer.

Omega-3 fats have been linked to many healthy outcomes, including reduced cardiovascular disease, improved anxiety and depression symptoms, and improved immune function. In fact, supplementing with omega-3 has been associated with a significant decrease in CRP, IL-6 and TNF-α levels, which are all markers of inflammation. Besides the health benefits, fish oil supplementation has also been shown to reduce exercise induced inflammatory response in elite swimmers. Foods that can enhance immunity and performance are a win-win!

To optimize your omega-3 intake, focus on consuming good sources of omega-3 fats frequently: fatty fish, grass-fed meat, pastured eggs, seaweed, algae, chia seeds, flax seeds, walnuts, and hemp seeds. Also, evaluate your current intake of omega-6 rich foods, which include sunflower, corn, soybean and cottonseed oils. These are found in many packaged/processed products, so aim to minimize these foods. Some athletes might require supplementation to reach optimal omega-3 levels. To really dial in your specific needs, you can take an Omega-3 Index blood test to determine your current omega-3 levels and if dietary changes should be implemented. Consider reaching out to a Registered Sport Dietitian to help maximize your diet and evaluate if omega-3 testing and supplementation is right for you. 

As I close out, I want to take a moment to pause. I don’t know how the words “coronavirus” and “COVID-19” are impacting you right now, but if you are like many Americans, there has probably been some kind of impact to your financial, physical, or mental well-being.

“Immune supporting nutrition” might feel like a luxury at best, or even a little cavalier or insensitive when there are so many people suffering. Please know that our intention is to help you find tangible, affordable ways to support your health and happiness right now, when so much feels outside of our control.

One day, we will all be together again, toeing the start line. Until then, we are wishing you and your loved ones all the best. 

Kelsey Smith is a Registered Sport Dietitian at eNRG Performance ( Based out of Colorado, she works with endurance athletes all over the world and is a specializes in periodizing an athlete’s nutrition plan to support optimal health and performance. Contact her at

The views expressed in this article are the opinion of the author and not necessarily the practices of USA Triathlon. Before starting any new diet or exercise program, you should check with your physician and/or coach.


1. Martineau, A. R., Jolliffe, D. A., Hooper, R. L., Greenberg, L., Aloia, J. F., Bergman, P., … Camargo, C. A. (2017). Vitamin D supplementation to prevent acute respiratory tract infections: systematic review and meta-analysis of individual participant data. Bmj, i6583. doi: 10.1136/bmj.i6583

2. Grant, W. B., Lahore, H., Mcdonnell, S. L., Baggerly, C. A., French, C. B., Aliano, J. L., & Bhattoa, H. P. (2020). Evidence that Vitamin D Supplementation Could Reduce Risk of Influenza and COVID-19 Infections and Deaths. Nutrients, 12(4), 988. doi: 10.3390/nu12040988

3. First Data to be Published on COVID-19 Severity and Vitamin D Levels. (n.d.). Retrieved May 15, 2020, from

4. Li, Kelei & Huang, Tao & Zheng, Ju-Sheng & Wu, Kejian. (2014). Effect of Marine-Derived n-3 Polyunsaturated Fatty Acids on C-Reactive Protein, Interleukin 6 and Tumor Necrosis Factor α: A Meta-Analysis. PloS one. 9. e88103. 10.1371/journal.pone.0088103

5. Andrade, Priscila & Ribeiro, Beatriz & Bozza, Marcelo & Rosa, Luiz & Tavares do Carmo, Maria. (2007). Effects of the fish-oil supplementation on the immune and inflammatory responses in elite swimmers. Prostaglandins, leukotrienes, and essential fatty acids. 77. 139-45. 10.1016/j.plefa.2007.08.010.