With so many unknowns surrounding COVID-19, it’s natural for us to flock to possible protective actions and remedies to keep ourselves and our loved ones safe. Journalists and media sources aren’t immune to this tendency, which is why you see an uptick in headlines about actions you can take to reduce your risk for getting coronavirus.
We know wearing a mask and washing your hands can greatly reduce the risk, but what about nutrition-related strategies? If you’ve skimmed the headlines, you might get the impression that the scientific community can offer definitive evidence on the link between COVID-19 and nutrition, however, that’s not exactly the case, and that’s why we wrote this piece.
It’s difficult enough navigating our new normal, let alone needing to sift through scientific publications on top of it. We’ve done the work for you to give you a high level understanding of what some of the major headlines and studies in the news really mean.
Below is a quick guide that examines the state of the science around COVID-19 and nutrition in addition to the well-established connection between micronutrients and general immunity.
Observational studies: the early stages of understanding
Right now, the most available and reliable research regarding micronutrient status and COVID-19 exists within observational studies. Observational studies don’t involve any type of intervention (meaning, nothing is being done to impact the outcome), and are mainly relevant in the early stages of researching a hypothesis. They can show correlations between two aspects that are being studied, but can’t actually determine causation. In the following studies, researchers are observing micronutrient status in correlation with a COVID-19 diagnosis.
The researchers compared the averages of vitamin D status to the number of reported COVID-19 cases in 20 countries. They observed that lower vitamin D levels are associated with a higher number of infections.
Editorial: low population mortality from COVID‐19 in countries south of latitude 35 degrees North supports vitamin D as a factor determining severity
Again to search for a connection between vitamin D and COVID-19, researchers looked to latitudinal coordinates to gauge vitamin D status. It turns out that countries positioned below 35 degrees north of the equator have a relatively low mortality rate compared to their northern counterparts.
A cohort study to evaluate the effect of combination Vitamin D, Magnesium and Vitamin B12 (DMB) on progression to severe outcome in older COVID-19 patients.
Here, scientists looked retrospectively at individual cases of COVID-19 patients older than 50 years old. Looking specifically at vitamin B12, vitamin D, and magnesium, cases were divided into one of two groups: those who received supplementation as part of their treatment, and those who did not. Ultimately, they concluded that fewer individuals who took these nutrients ended up needing intensive care during their treatment.
The study authors performed a population-based, retrospective analysis on real-time health data (cure rate, death rate, etc.) coming out of China at the height of the country’s first outbreak. What’s important to note about China is their population contains groups, who have both the world’s lowest and highest selenium statuses in the world because of the difference in soil compositions across China. The analysis results show a positive association between selenium status and cure rates.
We can see clearly that there’s an association between micronutrition and COVID-19. The “why” and “how” are still out there, so let’s take a look at what other types of research can tell us.
Literature reviews: connecting existing research with a new hypothesis
A literature review is a collection and analysis of previous studies to attempt to conclude a hypothesis, or justify the need for further research. Literature reviews should have inclusion and exclusion criteria, which is basically how the authors determine which studies are valid for their review. For example, if you’re writing a literature review about vitamin D status in the US, you would exclude any studies performed outside of the US from your review.
Several published reviews regarding micronutrient status and COVID-19 discuss mechanisms of action to justify this relationship. Essentially, they attempt to explain the “why” and “how” behind a nutrient’s role in immune response.
Evidence that Vitamin D Supplementation Could Reduce Risk of Influenza and COVID-19 Infections and Deaths
This review clearly explains vitamin D’s many roles in immune response, specifically for influenza. In essence, Vitamin D can essentially reduce pro-inflammatory cytokine production while increasing anti-inflammatory cytokines. You can read more about cytokine storm here.
The authors also note that vitamin D levels tend to decrease with age, consistent with the number of COVID-19 fatalities. The review delves into actual trials which have attempted to justify the theories that relate vitamin D to immune response. In many randomized control trials, researchers weren’t able to support the hypothesis that vitamin D supplementation would reduce disease risk. However, flaws in study designs may explain the discrepancy between proposed mechanisms of action and actual results.
The authors discuss the lack of vitamin D recommendations in many countries and explain that existing guidelines are likely too low, despite recognition that no study has reported adverse effects of supplementation below 10,000 IU per day of vitamin D. Consequently, more clinical trials should be done to determine more specific dosage recommendations.
Nutrients in prevention, treatment, and management of viral infections; special focus on Coronavirus
Here, several micronutrients and their relationship with viral infections are investigated within the scope of COVID-19, specifically considering supplementation, rather than just diet alone. The nutrients examined include omega-3 fatty acids, vitamin A, vitamin D, vitamin E, vitamin B12, zinc, and selenium, among others.
After establishing each nutrient’s mechanism of action in immune response, the authors conclude that while following a well-rounded diet is important to supporting your immune system, “supplementation with proper dietary components may also improve the health-related outcome of patients with COVID-19”. Ultimately, further studies are needed to quantify the significance of supplementation.
So, what can literature reviews tell us about COVID-19 and micronutrition? We can see that vitamin D supplementation plays a role in immunity, especially in more thoroughly-researched respiratory diseases like influenza and pneumonia. Evidence that supplementing with other micronutrients can support a healthy immune system is promising, but these nutrients are far less studied than vitamin D.
Randomized controlled trials: the gold standard
Randomized controlled trials, also known as RCTs, are the gold standard studies for evaluating hypotheses. These trials involve providing some sort of intervention to randomized groups of subjects to evaluate a hypothesis and reduce bias among researchers.
RCTs take time to plan and carry out. No major RCTs involving nutrition interventions and COVID-19 have been published so far.
The coronavirus is novel, but the link between immunity and nutrition is not
Studies on nutrition and COVID-19 will continue to be published for years to come, which will help us better understand how nutrition interventions interact with coronavirus risk and prognosis. In the meantime, let’s quickly review the existing strong link between nutrition and immunity.
In essence, an optimal nutrient status is crucial for a strong immune system. Micronutrients linked to immune health and support include vitamin A, vitamin C, vitamin D, vitamin E, vitamin B6, vitamin B12, copper, Omega-3, selenium, iron, and zinc. The Linus Pauling Institute’s Micronutrient Information Center covers their specific immunity-related functions in great detail.
Before diving deeper, it’s important here to stress that the majority of studies we reviewed for this piece focus on nutrient status measured by blood nutrient levels (rather than looking at nutrient intake through diet recalls or other methods of assessing statuses such as urine, hair, or microbiome analysis).
Blood nutrient status is a critical (and reliable) data point for researching, confirming, or disproving scientific hypotheses. Here are just a few call-outs to get a solid understanding of why not just micronutrients matter, but even more so, why an optimal micronutrient status is critical:
- “Clearly, micronutrients are an integral part of the immune system, and the body needs optimal levels for effective immune function. It is well established that overt micronutrient deficiencies can adversely affect the immune system and predispose individuals to infections. It is likely that marginal deficiencies are also associated with increased risk of infections, although the effect may be less pronounced than those observed with overt deficiencies. The dietary intake of various micronutrients is inadequate worldwide, including industrialized countries, which can increase the risk of infection.” according to the 2020 paper, A Review of Micronutrients and the Immune System–Working in Harmony to Reduce the Risk of Infection.
- “Micronutrient deficiencies are a recognized global public health issue, and poor nutritional status predisposes to certain infections. Immune function may be improved by restoring deficient micronutrients to recommended levels, thereby increasing resistance to infection and supporting faster recovery when infected. Diet alone may be insufficient and tailored micronutrient supplementation based on specific age-related needs necessary.” according to a 2018 review in Nutrients.
- “These molecules [Omega-3 fatty acids], along with others, function together to orchestrate the resolution of inflammation and to support healing, including in the respiratory tract. Notably, nutritional deficiencies in these essential fatty acids can result in delayed or suboptimal resolution of inflammation” as stated in the 2020 review Optimal Nutritional Status for a Well-Functioning Immune System Is an Important Factor to Protect against Viral Infections.
- Vitamin D supplementation can reduce the risk for acute respiratory tract infections, particularly if someone has deficient vitamin D levels according to a 2017 BMJ study. Vitamin D deficiency increases the risk of respiratory infection.
It’s also important to note here that immunity goes far beyond nutrition—it’s about taking a big-picture approach to your health. These actions go beyond the scope of this piece, but check out more from our dietitians here.
What we can conclude (and what we can’t)
True science takes time and patience, and evolves as the knowledge base grows. This is the case with the science of nutrition and COVID-19. New studies are coming out frequently, which is adding to our growing understanding of this novel virus.
As of right now, we cannot definitively say that optimal micronutrient status will reduce COVID-19 risk or improve prognosis if someone gets the virus. However, we can say definitively that optimal nutrient status supports a healthy and functioning immune system as noted above, and that’s the best place we can all begin.
To start, check out these additional blogs the Baze dietitians have written on immunity and nutrition. Additionally, to check your micronutrition status without needing to head to a lab, consider purchasing a Baze Nutrient Test Kit.
- Our Dietitians Take on Your Immunity Questions
- Immunity: It Starts From the Ground Up
- Cold and Flu No More! Your Immune Support Guide
- What Dietitians and Naturopaths Want You to Know About Immunity
- Elderberry: What You Need to Know About This Immune-Supporting Berry
- 7 Immunity Supporting Tips for Busy Super Moms
- Why Vitamin C isn’t what you should be taking to fight the flu
BourBour, F., Mirzaei Dahka, S., Gholamalizadeh, M., Akbari, M. E., Shadnoush, M., Haghighi, M., … Doaei, S. (2020). Nutrients in prevention, treatment, and management of viral infections; special focus on Coronavirus. Archives of Physiology and Biochemistry, 1–10. https://doi.org/10.1080/13813455.2020.1791188
Calder, P. C., Carr, A. C., Gombart, A. F., & Eggersdorfer, M. (2020). Optimal Nutritional Status for a Well-Functioning Immune System Is an Important Factor to Protect against Viral Infections. Nutrients, 12(4), 1181. https://doi.org/10.3390/nu12041181
Gombart, A. F., Pierre, A., & Maggini, S. (2020). A review of micronutrients and the immune system–working in harmony to reduce the risk of infection. Nutrients, 12(1). https://doi.org/10.3390/nu12010236
Grant, W. B., Lahore, H., McDonnell, S. L., Baggerly, C. A., French, C. B., Aliano, J. L., & Bhattoa, H. P. (2020, April 1). Evidence that vitamin d supplementation could reduce risk of influenza and covid-19 infections and deaths. Nutrients. MDPI AG. https://doi.org/10.3390/nu12040988
Ilie, P. C., Stefanescu, S., & Smith, L. (2020). The role of vitamin D in the prevention of coronavirus disease 2019 infection and mortality. Aging Clinical and Experimental Research, 32(7), 1195–1198. https://doi.org/10.1007/s40520-020-01570-8
Jolliffe, D. A., Griffiths, C. J., & Martineau, A. R. (2013, July 1). Vitamin D in the prevention of acute respiratory infection: Systematic review of clinical studies. Journal of Steroid Biochemistry and Molecular Biology. Elsevier Ltd. https://doi.org/10.1016/j.jsbmb.2012.11.017
Maggini, S., Pierre, A., & Calder, P. C. (2018, October 17). Immune function and micronutrient requirements change over the life course. Nutrients. MDPI AG. https://doi.org/10.3390/nu10101531
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 (Online), 356. https://doi.org/10.1136/bmj.i6583
Rhodes, J. M., Subramanian, S., Laird, E., & Kenny, R. A. (2020). Editorial: low population mortality from COVID-19 in countries south of latitude 35 degrees North supports vitamin D as a factor determining severity. Alimentary Pharmacology & Therapeutics, 51(12), 1434–1437. https://doi.org/10.1111/apt.15777
Tan, C. W., Ho, L. P., Kalimuddin, S., Cherng, B. P. Z., Teh, Y. E., Thien, S. Y., … Ng, H. J. (2020). A cohort study to evaluate the effect of combination Vitamin D, Magnesium and Vitamin B12 (DMB) on progression to severe outcome in older COVID-19 patients. MedRxiv, 2020.06.01.20112334. https://doi.org/10.1101/2020.06.01.20112334
Zhang, J., Taylor, E. W., Bennett, K., Saad, R., & Rayman, M. P. (2020). Association between regional selenium status and reported outcome of COVID-19 cases in China. The American Journal of Clinical Nutrition, 111(6), 1297–1299. https://doi.org/10.1093/ajcn/nqaa095