How to Reduce your Risk of COVID-19

It’s hard to believe that I published my first blog on COVID-19 almost exactly 6 months ago. In the intervening time, we’ve learned a lot and I’ve updated the information extensively, espcecially focusing on advice about how to keep from being exposed. Let me know what you think!

General Health Advice

This hasn’t changed. There is a lot you can do to keep your immune system strong.  My patients are familiar with my four pillars of health.  Eat a healthy diet with as many vegetables and as little added sugar and alcohol as possible.  Get enough sleep; sleep deprivation dramatically weakens your immune system.[1],[2]  While regular moderate exercise is immune-enhancing, intensive exercise can reduce immunity[3] so this may not be the year to train for a marathon.  Manage stress. Stress affects your immune system.  While it’s hard during a pandemic to not feel stressed, do what you can to stay positive.  Meditation, prayer, breathing exercises will reduce your cortisol and bring a calmer state of mind.  You may want to limit the time you spend reading the news or scrolling on social media, and spend down time reading, doing puzzles, or watching funny movies.  As the weather gets colder, make sure you are still connecting with family and friends, through phone or video links or in person outside.

Avoiding Exposure

We often talk about sneezing or coughing as transmitting particles the farthest but breathing and speaking in an enclosed space can transmit aerosolized particles very effectively.  These particles can remain suspended in the air for (depending on which experiment you look at ) between up to 14 minutes[4] or 3 hours.[5]  Exposure is more likely when the space is small, ventilation is poor, people are breathing heavily (like when they are singing or exercising). The risk goes up with the longer you are in a space, which makes sense. [6]  The more breaths you take, the more risk that one of them will have virus in it. And there does seem to be a dose-related risk of getting sick.[7]  So going shopping for 20 minutes in a store where people are required to wear masks is a very different level of risk than going to a restaurant or bar, and certainly different than going to a church or gym.

In other words, just because you are 6 feet away from people, it doesn’t guarantee that you won’t breathe in the virus. You heard that right—I have just busted the myth that all you have to do is stay 6 feet away from everyone else. 

Surprisingly, airplanes do not appear to be higher risk than other spaces.  The ventilation system requirements for airplanes meet the levels recommended by the Centers for Disease Control and Prevention for use with covid-19 patients in airborne infection isolation rooms.  So you may be exposed to infection by the person sitting right next to you but there is less likelihood that everyone on an airplane will be exposed. This risk goes down if everyone is wearing masks.[8] (And we’ll talk a lot about masks in a minute.)

So how far apart is far enough?  Particles can travel up to 10 meters (that’s about 10 yards for you non-metric people).[9]  And they can remain suspended in the air for up to 3 hours as I said before.[10]

Now, things are different when we’re talking about the open air. Because nature is like a big air exchange device, being around people 6 feet apart makes it much less likely that you will be exposed to the virus. 

Furthermore, sunlight inactivates the virus, at least according to laboratory evidence and what we know about sunlight and other viruses.[11] So at least for our 20 minutes of summer here in Minnesota, we’re good.

Okay, let’s talk about masks.  Masks do appear to reduce transmission of this infection.[12],[13]  Rates of transmission are reduced more when an infected person wears a mask than when an uninfected person does.  Given the fact that a high proportion of infected people are asymptomatic or pre-symptomatic,[14] it is critical for everyone to wear a mask even if they feel well.  The combination of both wearing a mask is most protective.  My favorite research study proving this was done on hamsters and I couldn’t wait to see pictures of the hamsters with cute little masks on—but it turns out they just put masks on the sides of the cages of the infected or uninfected hamsters, or both to show there was a benefit.[15]  

If you  want to look at what happens when different percentages of the population wear masks, go to  And for a simulation of different levels of mask wearing, check out

In fact, evidence from research suggests that it is masks and not physical distancing or the so-called “lockdown” that is most likely to lead us out of the pandemic as well as the economic collapse we are seeing due to businesses being shut.[16]

Wait a minute—all of a sudden we went from, “masks are unnecessary and should be reserved for healthcare workers” to “everyone needs to wear a mask.” From my reading of the literature, it’s not like we suddenly discovered that masks were beneficial, but we finally started listening to the people who had been saying that masks were beneficial all along. The initial rejection of masks was related, I think, to the lack of masks for health care personnel, and wanting to save masks for them. 

Which brings us to the question:  Which masks are best?  We’ve all been going gaga over N95 masks all of a sudden.  (Keep in mind that the N95 masks sold in hardware stores with a valve allow your exhalations to be released and are therefore ineffective for preventing infection.)  One meta-analysis did not find a difference between surgical masks and N95 masks.  This may be related to the level of exposure involved; if there is heavy exposure such as during an intubation, it may make a difference but not if there is more casual contact. [17]  Some doctors feel like face shields should also be worn in public.[18]  But you can’t wear a shield without a mask as the particles will just waft underneath it.

One study showed that even cloth masks are effective especially when they consist of multiple layers and difference materials, so the electrical charges help trap particles.[19]

Here is a link to the differences between mask types:

It is important to wear masks covering your nose and mouth. Wearing it with your nose poking out will defeat the purpose of enclosing your respiratory particles.  It is important also to make sure you have a tight fit around the sides to reduce the number of particles that are pushed out the sides.  If your glasses are fogged every time you breathe out, it means the fit is not as tight as it needs to be.  Having said that, though, any reduction in particles is better than nothing, so even a bandanna is better than a naked face. 

But even if fit isn’t perfect, it will filter out some particles.  Since the severity of illness may depend on the dose you get, you are likely to get a milder form of the illness even if you don’t avoid getting sick.[20]

What about getting infected through things like doorknobs, elevator buttons, mail or groceries?  It is true that SARS COV-2, the virus that causes COVID-19, can last on surfaces for up to 3 days.[21]  However, there have been no documented case of transmission by inanimate objects.[22]  This doesn’t mean you shouldn’t wash your hands and not touch your face.  It’s just much more likely that you would inhale particles in the air than get enough particles on your hands to make yourself sick. 

Supplements to Boost Immunity

A number of supplements have evidence of reducing the risk of infection as well as the severity of COVID-19 if you do get sick. Herbs in particular are amazing defenses against any type of infection. They contain not just antibacterial and antiviral properties but many are immune-enhancing and anti-inflammatory, and are synergistic with each other and antibiotics.[23],[24]  

You do not have to take all of the supplements below.  You may already be on some of them.  I would definitely take vitamin D, vitamin C and zinc, all of which are quite inexpensive and safe.

In terms of supplements, my favorite is vitamin D.  We think of vitamin D as enhancing bone strength (which it does) but its effects on the immune system are significant, particularly for viral infections.[25],[26],[27]  Checking your vitamin D level and keeping it at least above 50 ng/ml is an easy step you can take to boost immunity.  The daily allowance recommended  by the Institute of Medicine for vitamin D is 400 international units (IU) for children up to age 12 months, 600 IU for ages 1 to 70 years, and 800 IU for people over 70 years.This is woefully inadequate and not supported by the evidence.[28]  The Endocrine Society recommends somewhat higher levels. 1500–2000 IU/day for adults, though they found that obese adults required 2–3 times more vitamin D to sustain a blood level of at least 30 ng/ml.   In my experience, even this higher dose is inadequate.  Researchers who have actually measured vitamin D levels have found that even 2000 IU a day does not maintain levels in even the normal range, let alone in the optimal range.[29]   In my professional experience, most people need at least 5000 IU a day during the winter to maintain these levels. If you can’t get your level checked, this is a pretty safe dose.  In fact, much higher doses than that have been found to be safe.[30]  The only contraindication for high dose vitamin D is sarcoidosis.

Zinc is essential for approximately 2000 enzymatic actions in the human body and its role in immune function is well-known.[31]  Zinc deficiency is not uncommon and particularly affects the elderly, vegans/vegetarians, and individuals with chronic disease such as inflammatory bowel disease.[32]  There is evidence that zinc supplementation may reduce viral infections.[33],[34] I recommend taking 15-30 mg. a day, and balancing it with copper 2 mg. to avoid a copper deficiency. Check any multivitamins, mineral or other combination supplements to make sure you don’t go above about 40 mg. a day. 

Despite its reputation, the evidence for vitamin C for prevention of the common cold and other viruses is weaker. However, there is a trend toward protection in studies where participants were intentionally exposed to cold viruses and the duration of the infection seems to be shorter.[35]  This seems particularly true if you are already taking vitamin C and increase the dose when you get sick.[36]  Given its safety and low cost, taking at least 1000 mg. and probably more like 2000-3000 mg. a day for prevention can’t hurt.  The only real risk is of looser stools which can be eliminated with lowering the dose. 

Quercetin is a bioflavonoid antioxidant found in colorful fruit and vegetables. It is also antiviral.  Start with 250 mg. twice a day and go up to 1000 mg. twice a day.  It does not have any known side effects.  It is not well-absorbed from the digestive tract. the form most bioavailable is quercetin chalcone (more expensive but you may be able to use half the dose of other forms) followed by dihydrate, glycosides, aglycone, and finally rutinoside.  There is some evidence that taking it with other bioflavonoids such as resveratrol, genistein, or green tea catechins to increase the potency.  Speaking of green tea, EGCG, a component of green tea, has been found to prevent influenza in healthcare workers and appears to target SARS COV-2 in particular.[37],[38]  While supplements are available (take 225 mg. a day), you can also just drink up to 4 cups of green tea a day.

The most effective immune boosters in the plant world are mushrooms. They have been used for millennia in Chinese medicine[39] and in Eastern European traditional remedies.  Much of the research so far has shown activity in the test tube,[40],[41],[42] but there is evidence of effectiveness in humans as well. [43]  Each mushroom species has differing properties and they may be synergistic.[44]  Your best bet may be to take a combination product such as those sold by  Fungi Perfecti ( or Mushroom Wisdom (  These supplements are more expensive than the preceding recommendations, so if you are relatively low risk for serious illness, you may want to balance cost against protection. 

Our understanding of our gut microbiome’s role in infection is evolving.  There is evidence that live and even killed probiotics can strengthen the response to viral infections.[45],[46],[47] Probiotics are an easy, safe and inexpensive intervention.  I recommend a multi-strain product with at least 20 billion CFU’s purchased from a reputable source such as a food co-op or Whole Foods. 

There is evidence for the effectiveness of elderberry in particular against other strains of coronavirus.[48],[49],[50],[51]  A preventive adult dose is a tablespoon of elderberry syrup or once capsule once a day. Reputable brands include Sambucol liquid or black elderberry capsules by Nature’s Way.  You can also make a tea or just eat elderberries.

Curcumin is an extract from the spice turmeric, a brightly colored orange root used extensively in Indian cooking.  It is anti-inflammatory and may target SARS COV-2 in particular.[52]

We think of melatonin as a sleep aid, but its effects on immune function are quite well-accepted. There has been research recently on using it specifically for COVID-19.[53],[54] Recommended doses are higher than might be used to help with sleep—I would recommend starting with 5 mg.  The most likely side effect is vivid dreams, which usually goes away within a few nights.  

N-acetylcysteine (NAC) modulates cellular defense and repair mechanisms and has been shown to reduce influenza-like illness in one placebo-controlled trial.[55]  Take 600 mg. twice a day. 

Resveratrol is a component of many herbs, most notably Japanese knotweed.  It is antiviral and shows evidence against MERS-COV, another coronavirus.[56]  The dose is 100-150 mg. a day. 


In summary, we have learned more about how COVID-19 is transmitted over the past few months, but there is still no magic bullet for ending the pandemic.  Vaccines are not around the corner.  It is up to us over the coming months to keep ourselves and our communities safe. I hope that this article helps you do this.  Be well!

[1] Besedovsky L et al. The Sleep-Immune Crosstalk in Health and Disease. Physiol Rev 2019; 99:1325-1380.  Full text available at

[2] Prather AA et al.  Behaviorally assessed sleep and susceptibility to the common cold. Sleep 2015; 38:1353-1359.

[3] Simpson RJ et al. Exercise and the regulation of immune functions. Prog Mol Biol Transl Sci 2015; 135:355-380.

[4] Stadnytskyi V, Bax CE, Bax A, Anfinrud P. The airborne lifetime of small speech droplets and their potential importance in SARS-CoV-2 transmission [published online ahead of print, 2020 May 13]. Proc Natl Acad Sci U S A. 2020;202006874.

[5] van Doremalen N, Bushmaker T, Morris DH, et al. Aerosol and Surface Stability of SARS-CoV-2 as Compared with SARS-CoV-1. N Engl J Med. 2020;382(16):1564‐1567.

[6]  Accessed 5/25/20.

[7] “The virus load is important,” said Eugene Chudnovsky, a physicist at Lehman College and the City University of New York’s Graduate Center. “A single virus will not make anyone sick; it will be immediately destroyed by the immune system. The belief is that one needs a few hundred to a few thousand of SARS-CoV-2 viruses to overwhelm the immune response.” In Accessed May 25, 2020.

[8] Accessed 5/25/20.

[9] Setti L, Passarini F, De Gennaro G, et al. Airborne Transmission Route of COVID-19: Why 2 Meters/6 Feet of Inter-Personal Distance Could Not Be Enough. Int J Environ Res Public Health. 2020;17(8):2932. Published 2020 Apr 23.

[10] van Doremalen N, Bushmaker T, Morris DH, et al. Aerosol and Surface Stability of SARS-CoV-2 as Compared with SARS-CoV-1. N Engl J Med. 2020;382(16):1564‐1567.

[11] Ratnesar-Shumate S, Williams G, Green B, et al. Simulated Sunlight Rapidly Inactivates SARS-CoV-2 on Surfaces [published online ahead of print, 2020 May 20]. J Infect Dis. 2020;jiaa274.

[12] Accessed 8/5/20

[13] Cheng VC, Wong SC, Chuang VW, et al. The role of community-wide wearing of face mask for control of coronavirus disease 2019 (COVID-19) epidemic due to SARS-CoV-2 [published online ahead of print, 2020 Apr 23]. J Infect. 2020;S0163-4453(20)30235-8.

[14] Accessed 8/5/20.

[15] Hamster study. Accessed May 25, 2020. 

[16]  Goodman B. Aerosol Scientist: COVID-19 Is Likely Airborne. WebMD. Accessed May 28, 2020.

[17] Bartoszko JJ, Farooqi MAM, Alhazzani W, Loeb M. Medical masks vs N95 respirators for preventing COVID-19 in healthcare workers: A systematic review and meta-analysis of randomized trials [published online ahead of print, 2020 Apr 4]. Influenza Other Respir Viruses. 2020;10.1111/irv.12745.


[19] Konda A, Prakash A, Moss GA, Schmoldt M, Grant GD, Guha S. Aerosol Filtration Efficiency of Common Fabrics Used in Respiratory Cloth Masks. ACS Nano. 2020;14(5):6339‐6347.

[20]  Goodman B. Aerosol Scientist: COVID-19 Is Likely Airborne. WebMD.  Accessed May 28, 2020.

[21] van Doremalen N, Bushmaker T, Morris DH, et al. Aerosol and Surface Stability of SARS-CoV-2 as Compared with SARS-CoV-1. N Engl J Med. 2020;382(16):1564-1567.

[22] Dietz L, Horve PF, Coil DA, Fretz M, Eisen JA, Van Den Wymelenberg K. 2019 Novel Coronavirus (COVID-19) Pandemic: Built Environment Considerations To Reduce Transmission [published correction appears in mSystems. 2020 May 5;5(3):]. mSystems. 2020;5(2):e00245-20.

[23] Aiyegoro OA and Okoh AI.  Use of bioactive plant products in combination with standard antibiotics: implications in antimicrobial chemotherapy.  J Medicinal Plants Res 2009; 3:1147-1152.

[24] For a well-researched and comprehensive review of herbs see Buhner SH. Herbal Antibiotics: Natural Alternatives for Treating Drug-Resistant Bacteria, Second Edition. North Adams, MA 2012. Storey Publishing.

[25] Martineau AR et al.  Vitamin D supplementation to prevent acute respiratory tract infections: systematic review and meta-analysis of individual participant data. BMJ  2017;  356: i6583.

[26] Beard J et al. Vitamin D and the anti-viral state. J Clin Virol 2011; 50:194-200.

[27] Edlich RF et al.  Pandemic preparedness for swine flu influenza in the United States. J Env Pathol, Toxicol and Oncol 2009; 28:261-264 (editorial).

[28] Vieth R and Holick MF. Chapter 57B- The IOM-Endocrine Society controversy on recommended vitamin D targets: In support of the Endocrine Society Position. Vitamin D 4th Edition Volume 1: Biochemistry, Physiology and Diagnostics.   pages 1091-1107. Academic Press, 2018.

[29] Sadat-Ali M et al. Maintenance Dose of Vitamin D: How Much Is Enough? J Bone Metab  2018; 24:161-164.

[30] Kimball SM et al. Safety of vitamin D3 in adults with multiple sclerosis. Am J Clin Nutr 2007; 86:645-651.

[31] Shankar AH, Prasad AS. Zinc and immune function: the biological basis of altered resistance to infection. Am J Clin Nutr. 1998;68(2):447s–63s.

[32] Siva S et al. Zinc deficiency is associated with poor clinical outcomes in patients with inflammatory bowel disease. Inflamm Bowel Dis. 2017;23(1):152–7.

[33] Allan GM and Arroll B. Prevention and treatment of the common cold: making sense of the evidence. CMAJ 2014; 186: 190–199.

[34] Read SA et al. The role of zinc in antiviral immunity. Advances in Nutrition, 2019; 10: 696–710.

[35] Allan GM and Arroll B. Prevention and treatment of the common cold: making sense of the evidence. CMAJ 2014; 186: 190–199.

[36] Ran L, Zhao W, Wang J, et al. Extra Dose of Vitamin C Based on a Daily Supplementation Shortens the Common Cold: A Meta-Analysis of 9 Randomized Controlled Trials. Biomed Res Int. 2018;2018:1837634.

[37] Matsumoto K, Yamada H, Takuma N, Niino H, Sagesaka YM. Effects of green tea catechins and theanine on preventing influenza infection among healthcare workers: a randomized controlled trial. BMC Complement Altern Med. 2011;11:15. 

[38] Lee HE, Yang G, Park YB, et al. Epigallocatechin-3-gallate prevents acute gout by suppressing NLRP3 inflammasome activation and mitochondrial DNA synthesis. Molecules. 2019;24(11):E2138. 

[39] Aung SK: The Clinical Use of Mushrooms from a Traditional Chinese Medical Perspective. 2005, 7(3):375–376.

[40] Eguchi N et al. In-vitro anti-influenza virus activity of agaricus brasiliensis KA21. Biocontrol Sci 2017; 222:171-174.

[41] Ellan K.  Anti-viral activity of culinary and medicinal mushroom extracts against dengue virus serotype2: An in-vitro study. BMC Complement Altern Med 2019; 19:260.

[42] Benson, K.F. et al. The mycelium of the Trametes versicolor (Turkey tail) mushroom and its fermented substrate each show potent and complementary immune activating properties in vitro. BMC Complement Altern Med 19, 342 (2019).

[43] Nishihira J et al. Maitake mushrooms (Grifola frondosa) enhances antibody production in response to influenza vaccination in healthy adult volunteers concurrent with alleviation of common cold symptoms. Functional Foods in Health and Disease 2017; 7: 462-482.

[44] Wang L and Hou Y. Determination of trace elements in anti-influenza virus mushrooms. Biol Trace Elem Res  2011; 143:1799-1807.

[45] Allan GM and Arroll B. Prevention and treatment of the common cold: making sense of the evidence. CMAJ 2014; 186: 190–199.

[46] Hao Q et al. Probiotics for preventing acute upper respiratory tract infections. Cochrane Database Syst Rev. 2011 Sep 7; (9):CD006895.

[47] Kanauchi O et al.  Probiotics and paraprobiotics in viral infection: Clinical application and effects on the innate and acquired immune systems.  Curr Pharm Des 2018; 24:710-717.

[48] Chen C et al.  Sambucus nigra extracts inhibit infectious bronchitis virus at an early point during replication. BMC Vet Res. 2014; 10: 24. 

[49] Zakay-Rones Z et al. Inhibition of Several Strains of Influenza Virus in Vitro and Reduction of Symptoms by an Elderberry Extract (Sambucus Nigra L.) During an Outbreak of Influenza B Panama. J Alt Complement Med 1995 1:361-369.

[50] Weng JR et al. Antiviral activity of Sambucus FormosanaNakai ethanol extract and related phenolic acid constituents against human coronavirus NL63. Virus Res. 2019;273:197767.

[51] Zakay-Rones Z et al. Randomized Study of the Efficacy and Safety of Oral Elderberry Extract in the Treatment of Influenza A and B Virus Infections. J Int Med Res 2004; 32:132-140.                  

[52] Sun Y, Liu W, Zhang H, et al. Curcumin prevents osteoarthritis by inhibiting the activation of inflammasome NLRP3. J Interferon Cytokine Res. 2017;37(10):449-455. 

[53] Zhou Y, Hou Y, Shen J, Huang Y, Martin W, Cheng F. Network-based drug repurposing for novel coronavirus 2019-nCoV/SARS-CoV-2. Cell Discov. 2020;6:14. 

[54] Zhang R, Wang X, Ni L, et al. COVID-19: melatonin as a potential adjuvant treatment. Life Sci. Published online March 23, 2020.

[55] McCarty MF, DiNicolantonio JJ. Nutraceuticals have potential for boosting the type 1 interferon response to RNA viruses including influenza and coronavirus. Prog Cardiovasc Dis. Published online February 12, 2020. 

[56] Lin SC, Ho CT, Chuo WH, Li S, Wang TT, Lin CC. Effective inhibition of MERS-CoV infection by resveratrol. BMC Infect Dis. 2017;17(1):144.