Kat Barefield, MS, RD, CPT

Are there certain vitamins, minerals, or other supplements that everyone should consider to support optimal health and build a strong immune system? This article will answer that question and cover more, including:

  • unproven methods for treating and preventing the coronavirus
  • factors that weaken the immune system
  • the key micronutrients involved in the immune system
  • which micronutrients most people fall short of
  • why vitamin D is likely to be low in most people
  • which micronutrients may be beneficial in higher than current recommended amounts

If anything on this list piques your interest, continue reading.

The Truth About Supporting Your Immune System

I wish I could tell you to take a product or supplement that would immediately boost your immune system and provide protection against the coronavirus and other illness.

Unfortunately, that’s not how it works. Accomplishing a fitness related goal such as losing body fat and keeping it off, building muscle tissue, or improving strength requires consistency over time. The same applies to building a strong immune system.

With the current Covid-19 pandemic, people are avidly seeking a way to hack their immune system to somehow protect them from this novel virus. Opportunists have attempted to peddle unproven methods to the public and at least 90 companies were sent warning letters by the Federal Trade Commission (FTC) and Food and Drug administration (FDA).[1]  Letters were also sent to over 100 multilevel marketers allegedly making claims and selling unapproved products related to coronavirus.1

Some of the unproven remedies include:

  • essential oils
  • colloidal silver
  • teas
  • CBD
  • detoxes
  • herbs
  • acupuncture

Factors that Weaken the Immune System

So, what can you do for your immune system? In addition to avoiding unproven remedies that are wasteful and potentially harmful, modifying behaviors that weaken the immune system is something you can act on now even while under quarantine.

As depicted in the graphic below, some of these behaviors include drinking excessive alcohol, eating high calorie, highly processed foods devoid of micronutrients, being sedentary, cigarette smoking and sleep deprivation.[2]



To frame it in a more positive light, you can strengthen your immune system by doing these behaviors:

  • Limit alcohol intake to 1 drink per day for women and 2 per day for men
  • Incorporate relaxation techniques such as deep breathing, mediation, walks in nature, listening and/or dancing to your favorite songs
  • Developing a creative hobby like gardening, painting, or sewing
  • Include a variety of fresh fruits and veggies that you enjoy
  • Prioritize good sleep hygiene such as avoiding screens an hour before bedtime
  • Increase the daily number of steps you take by moving more throughout the day
  • Better yet, rescue a dog and walk it daily
  • Exercise regularly doing activities you enjoy

As the image above demonstrates, suboptimal nutritional status contributes to a compromised immune system and increases the risk of infection.

By improving your nutritional status your body will be better equipped to respond optimally when exposed to viruses, bacteria, or other infections. Let’s take a closer look at how to do this.

The Role of Micronutrients in Immune Function

Our immune system is a complex, multilayered combination of physical and chemical protection against invaders such as bacteria and viruses. Our skin, stomach acid, digestive enzymes, gut bacteria, and mucus membranes provide the first barrier to entry of infectious invaders while white blood cells that engulf and deactivate pathogens provide a second layer of protection. 

We also have a third layer of immunity which gives us the ability to make antibodies when exposed to a pathogen that not only destroy the pathogen but also provide protection from future infection. All these processes require nutrients, and the key ones involved include:

  • Vitamins A, C, D, E, B6, B9 (folate/folic acid), B12
  • Minerals zinc, iron, copper, selenium
  • Omega-3 fish oils EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid)

Some of the immune cells create free radicals, or reactive oxygen species which destroy invaders. Vitamins C and E and minerals iron, zinc, copper, and selenium provide protection for the immune cells, so they’re not damaged in the process. Because of this, they are sometimes referred to as antioxidants.

Vitamins A, D, B6, B9, B12 and the minerals iron and zinc are needed when white blood cell production  is ramped up to fight a foreign body like a novel virus or bacteria.

Inflammation is another response to infection and is needed to isolate the area so white blood cells and antibodies can be delivered to initiate healing a repair. Vitamin D, EPA and DHA play an important in ensuring inflammation isn’t prolonged or excessive, which can delay healing or cause additional damage. You want to make sure you have optimal amounts of these micronutrients all the time to build and maintain a strong immune system. Unfortunately, most people don’t.



The body requires optimal levels of micronutrients for effective immune function, with different requirements throughout every stage of life.2


Data Shows Americans are Lacking in Key Nutrients

Data shows that Americans are falling significantly short of several micronutrients including those that support the immune system - vitamin A, C, D, E, iron and the omega-3 fish oils, EPA and DHA.[4] I discuss this in more depth here.

If you’re a vegan or vegetarian, you’re more likely to have low intakes of vitamin B12, zinc, omega-3 fish oils, vitamin D and iodine. If you’re following a specific diet which restricts food groups or reduces calorie intake, you’re probably missing some micronutrients.

There are two things you can do to fix this. First and foremost, eat a micronutrient rich diet with a variety of colorful, minimally processed foods from all major food groups. Below is a chart which you may find helpful.

Selected Micronutrients Involved in the Immune System

Older adults and those consuming a vegan diet should get B12 from supplements or fortified food

The ultimate balancing act is eating the right portions of all these different foods to achieve and maintain a healthy body weight. Since most eating patterns fall short of recommended amounts for several of the micronutrients, a multivitamin and mineral formula with the common under consumed nutrients that is suitable for your age and life stage is a smart strategy for filling in gaps “just in case” and for ensuring you’re getting what you need consistently. Check out this article for more info on this.

What I don’t recommend is mega-dosing on single vitamins and minerals unless you have a medical need to do so and you’re under the care of a doctor or dietitian. By mega-dosing I mean taking vitamins, minerals or other nutrients in amounts that exceed the tolerable upper limit, which is the amount you can consume with little to no likelihood of adverse effects. Once you exceed the upper limit, you’re putting yourself at risk of toxicity, particularly with the fat-soluble vitamins which are stored in the body. If you’re taking any medications, you definitely want to check in with your doctor prior to taking any supplements.

Research indicates some nutrients may be beneficial when taken in higher amounts than the recommended dietary allowances (RDA) but lower than the upper limit. More details below.

Supplements Everyone Should Consider to Support Your Immune System

Vitamin D

Like the ~30 micronutrients that are essential for human health, vitamin D plays a critical role in numerous functions in the body including normal growth and development, bone health, immunity, and muscle metabolism. Here’s more on vitamin D’s role:

  • Maintenance of blood levels of calcium
  • Absorption of calcium in the GI tract
  • Normal bone mineralization
  • Prevents rickets in kids
  • Prevents osteomalacia in adults
  • Protects older individuals from developing osteoporosis
  • Reduces inflammation
  • Modulates the immune system via receptors on various white blood cells including macrophages and T cells
  • Supplementation reduces incidence of respiratory infections[5]

Vitamin D is unlike the other vitamins and minerals because 1) it has hormone like functions and 2) it can be made in the body when skin is exposed to the sun (UVB radiation). There are a limited number of natural vitamin D food sources including fatty fish, cod liver, and mushrooms exposed to UV light. Vitamin D is also in fortified foods – milk, cheese, and milk alternatives.

Here’s the back story on Vitamin D fortification: as the U.S. workforce transitioned from agricultural to industrial, people began working indoors, and vitamin D deficiency became common. As a result, the normal growth and development of kids became impaired, resulting in rickets. This ultimately led to vitamin D being added to the food supply through fortification of milk and dairy products. Nonetheless, deficiency and insufficiency of this key nutrient sill occurs on a global scale with approximately 70-90% of Americans failing to meet requirements.[6]

Certain groups are at greater risk for deficiency including:

  • Older adults due to poor absorption in the gut, poor conversion, and limited time spent in the sun
  • Obese individuals whose higher body fat levels can store the vitamin and prevent it from reaching receptors throughout the body
  • Those who live in northern latitudes where there is insufficient UV light
  • Dark skinned individuals who have more skin pigmentation (melanin) which blocks UV light

The most reliable way to determine whether you’re getting enough vitamin D is to get your blood levels tested. Here’s where things get tricky. Different organizations have their cutoff recommendations for vitamin D blood levels (technically serum levels of 25-hydroxyvitamin D).

The Institute of Medicine deems blood levels of vitamin D adequate at 20 ng/mL whereas the Endocrine Society recommends higher levels (30-40 ng/mL) to confer greater health outcomes. This which would require adults to supplement at least 800-1,000 IUs daily. More may be needed for at-risk individuals as described above.

A comprehensive review of the research on vitamin D’s immunologic effects on health and disease concluded the following:[7]


The bottom line is that there is no downside to increasing our intake of vitamin D to maintain serum 25(OH)D at at least 30 ng/mL (75 nmol/L), and preferably at 40–60 ng/mL (100–150 nmol/L) to achieve optimal overall health benefits of vitamin D.


The daily recommendation (RDA) is 600 IU/day if you’re between 18 and 70 years old and 800 IUs if you’re older than 70. These amounts would likely be too low to achieve optimal levels as noted above.

You may be wondering how much is too much. The tolerable upper limit for Vitamin D is 4,000 IU/day for those not at risk for deficiency and 10,000 IU/day for those at risk for deficiency.[8]

The practical takeaway is that 1) if you’re not getting regular sun exposure directly to your skin (15-30 minutes daily while avoiding sunburn) and 2) you’re not consuming food sources that meet daily requirements, or 3) you’re in one or more of the groups that are at risk for deficiency,  vitamin D supplementation below the tolerable upper limit should be considered to raise your blood levels to ~30 ng/mL. Dosages above 4,000 IUs/day should be done only with medical guidance.

Vitamin D, Respiratory Tract Infections and Covid-19

Vitamin D supplements for the treatment and prevention of coronavirus have not been tested. So far, there’s observational data which shows an association between low levels of vitamin D and greater infection rates and severity of Covid-19.[9],[10]  The pandemic may result in people spending more time indoors, thus limiting sunlight exposure and reducing vitamin D levels. 

There are randomized, double blind, placebo-controlled trials on vitamin D supplements and the prevention of respiratory tract infections. One systematic review and meta-analysis of nearly 11,000 people revealed that vitamin D supplements resulted in significantly fewer participants having at least one respiratory tract infection.5  The most deficient individuals received the greatest protection and daily or weekly intake of vitamin was found to be effective compared to bolus dosing.  Furthermore, taking vitamin D supplements was found to be safe, with serious adverse events being rare and of equal occurrence between those taking supplements and those taking a placebo.

These findings are similar to those of the Linus Pauling Institute at Oregon State University as depicted in the table below.[11] Keep in mind, these findings are not specific to the coronavirus.


Omega 3 Fish Oils

The fats that are present in oily fish, EPA and DHA, play a vital role in brain health, heart health, eye health, and immunity. Here are some examples of their functions:

  • Structural components of cell membranes
  • DHA is highly concentrated in the brain and eyes
  • They are used to form other compounds called eicosanoids which help regulate the immune system
  • They have anti-inflammatory effects and may be beneficial in the immune response.[12],[13]

EPA and DHA can be made in the body from the essential fat, alpha linoleic acid (ALA) which is present in chia seeds, walnuts, flaxseed oil, and canola oil but the conversion is poor. Hence, to raise levels in the body, one must consume them from supplements or dietary sources such as herring, salmon, sardines, and oysters.

Interestingly, an RDA has not been established for EPA and DHA. The American Heart Association (AHA) recommends at least two servings (8 ounces) of oily fish per week for generally healthy people and four servings of oily fish per week or 1 gram of EPA and DHA from supplements for those with coronary heart disease. Higher amounts are recommended (2-4 grams of EPA and DHA from supplements) to lower triglycerides at the direction of a physician.

The table below contains recommendations for EPA and DHA intakes from various organizations.

American Heart Association

·       Two servings (8 ounces) of oily fish per week

International Olympic Committee[14]

·       2,000 mg of EPA + DHA from oily fish or supplements for high- performance athletes to support recovery

Linus Pauling Institute, Oregon State University

·       Oily fish twice per week + walnuts, flaxseeds, flaxseed or canola oil

·       2 grams of EPA + DHA supplements several times a week if not consuming fatty fish

World Health Organization

·       200-250 mg of EPA + DHA per day for general health

·       2 grams per day for prevention of heart disease

European Food and Safety Authority

·       250 mg of EPA + DHA per day

International Society for the Study of Fatty Acids and Lipids

·       500 mg of EPA + DHA per day minimum for cardiovascular health


Regardless of ethnicity, intakes of oily fish rich in omega-3’s are substantially lower than all the recommended intakes above, as shown in the graph below.[15] All ethnic groups consume less than 4 servings of oily fish a month, which is less than half of what’s recommended.  

Taking this data into account, it is no surprise that adults in the U.S. are falling short of omega-3 recommendations, with an average intake of EPA and DHA of 100 mg/day.15

Given the role omega-3 fish oils play in supporting the immune system and reducing inflammation, consuming two servings of oily fish weekly would help increase EPA and DHA amounts in the body.


Those who are not eating adequate amounts of fish can increase their intake of the omega-3 fats, EPA and DHA using a fish oil supplement. Vegans and vegetarians can increase intakes with algal or krill oil supplements.


Vitamin C

Vitamin C, or ascorbic acid, is arguably the most popular supplement used to support the immune system. Vitamin C is not only needed to form collagen in our skin, but it also helps immune cells with its antioxidant activity.

The strongest evidence for vitamin C is in 1) reducing the duration of the common cold and 2) reducing the occurrence of a common cold in athletes when taken regularly as a preventative aid as opposed to what many people do, which is take high doses after they get sick.

Although the RDA is 75 mg for women and 95 mg for men, routine supplementation with at least 400 mg/day for generally healthy people may help reduce the length and/or severity of symptoms for the common cold.[16]

Athletes training for endurance events or intense combat training may benefit from taking 250-2,000 mg/day.[17]



Consistency is key to getting results, whether that’s losing weight, building muscle, or developing a strong immune system. A wise approach would be to reduce or eliminate behaviors that weaken the immune system while optimizing your nutritional status to strengthen the immune system. This can be done by 1) consuming a wide variety of minimally processed foods from all food groups to maximize intake of vitamins, minerals, and other micronutrients like omega-3 fats, flavonoids and polyphenols and 2) complementing your food intake by supplementing with nutrients you’re falling short of.

If you’re not consuming fatty fish at least twice a week to get the immune supporting nutrients EPA and DHA, a fish oil supplement is something to consider.  Vitamin D is involved in hundreds of metabolic processes throughout the body and supplementation has been shown to be protective of respiratory tract infections in clinical trials.  Data consistently shows that most Americans do not have optimal blood levels of at least 30 ng/mL, so this supplement is another one worth considering, particularly if you have dark skin, you stay indoors, you’re overweight or obese or you’re older.

Finally, recall that micronutrients work synergistically throughout the body and in each layer of the immune system, so be sure to take a daily multivitamin and mineral formula to make up for any gaps in your diet.


A panel of 14 international nutrition experts concluded that multivitamin and mineral supplements can broadly improve micronutrient intakes and achieving the recommended dietary allowances for micronutrients is the goal for long-term health. [18]



[1] Federal Trade Commission, Coronavirus Warning Letters to Companies. https://www.ftc.gov/coronavirus/enforcement/warning-letters. Accessed July 14, 2020.

[2] Maggini, S, Pierre, A. Calder, PC. Immune function and micronutrient requirements change over the life

course. Nutrients 2018, 10, 1531. PMID: 30336639

[3] Gombart AF, Pierre A, Maggini S. A Review of Micronutrients and the Immune System-Working in Harmony to Reduce the Risk of Infection. Nutrients. 2020;12(1):236. Published 2020 Jan 16. doi:10.3390/nu12010236. PMID 31963293

[4] Dietary Guidelines for Americans 2015-2020. 8th ed. Washington, DC: U.S. Department of Health and Human Services; U.S. Department of Agriculture, 2015.

[5]Martineau AR, Jolliffe DA, Hooper RL, et al. Vitamin D supplementation to prevent acute respiratory tract infections: systematic review and meta-analysis of individual participant data. BMJ. 2017;356:i6583. Published 2017 Feb 15. doi:10.1136/bmj.i6583. PMID: 28202713

[6] Palacios, C.; Gonzalez, L. Is vitamin D deficiency a major global public health problem? J. Steroid Biochem.

Mol. Biol. 2014, 144PA, 138–145. PMID: 24239505

[7] Charoenngam, N.; Holick, M.F. Immunologic Effects of Vitamin D on Human Health and Disease. Nutrients 2020, 12, 2097.

[8] Holick MF, Binkley NC, Bischoff-Ferrari HA, et al. Evaluation, treatment, and prevention of vitamin D deficiency: an Endocrine Society clinical practice guideline [published correction appears in J Clin Endocrinol Metab. 2011 Dec;96(12):3908]. J Clin Endocrinol Metab. 2011;96(7):1911-1930. doi:10.1210/jc.2011-0385. PMID: 21646368

[9] Alipio, Mark, Vitamin D Supplementation Could Possibly Improve Clinical Outcomes of Patients Infected with Coronavirus-2019 (COVID-19) (April 9, 2020). Available at SSRN: https://ssrn.com/abstract=3571484 or http://dx.doi.org/10.2139/ssrn.3571484

[10] Laird E, Rhodes J, Kenny RA. Vitamin D and Inflammation: Potential Implications for Severity of Covid-19. Ir Med J. 2020;113(5):81. Published 2020 May 7. PMID: 32603576

[11] Linus Pauling Institute, Micronutrient Information Center’s Immunity in Brief. https://lpi.oregonstate.edu/mic/health-disease/immunity. Accessed July 11, 2020.

[12] Calder PC. n-3 fatty acids, inflammation and immunity: new mechanisms to explain old actions. Proc Nutr Soc. 2013;72(3):326-336. doi:10.1017/S0029665113001031 PMID: 23668691

[13] Tan A, Sullenbarger B, Prakash R, McDaniel JC. Supplementation with eicosapentaenoic acid and docosahexaenoic acid reduces high levels of circulating proinflammatory cytokines in aging adults: A randomized, controlled study. Prostaglandins Leukot Essent Fatty Acids. 2018;132:23-29. doi:10.1016/j.plefa.2018.03.010. PMID: 29735019

[14] Maughan RJ, Burke LM, Dvorak J, et al. IOC consensus statement: dietary supplements and the high-performance athlete. Br J Sports Med. 2018;52(7):439-455. doi:10.1136/bjsports-2018-09902 PMID: 29540367

[15] Cave C, Hein N, Smith LM, et al. Omega-3 Long-Chain Polyunsaturated Fatty Acids Intake by Ethnicity, Income, and Education Level in the United States: NHANES 2003-2014. Nutrients. 2020;12(7):E2045. Published 2020 Jul 9. doi:10.3390/nu12072045. PMID: 32660046

[16] Hemilä H, Chalker E. Vitamin C for preventing and treating the common cold. Cochrane Database Syst Rev. 2013;(1):CD000980. Published 2013 Jan 31. doi:10.1002/14651858.CD000980.pub4. PMID: 23440782

[17] Hemilä  H, Chalker  E. Vitamin C for preventing and treating the common cold. Cochrane Database of Systematic Reviews 2013, Issue 1. Art. No.: CD000980. DOI: 10.1002/14651858.CD000980.pub4.

[18] Blumberg JB, Cena H, Barr SI, et al. The Use of Multivitamin/Multimineral Supplements: A Modified Delphi Consensus Panel Report. Clin Ther. 2018;40(4):640-657. doi:10.1016/j.clinthera.2018.02.014. PMID: 29573851

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