‘Tis the season for respiratory viruses to be on our minds. I’ve been following the science regarding steps that can be taken to lower the risk from these viruses, including COVID.  Here are some recommendations for simple, safe, inexpensive actions you can take to improve your odds of avoiding a serious disease.
 

Building a Disease Resistant Body

A strong immune system helps keep you from contracting infections, and reduces the severity of them.  There are several simple things that make a big difference here.

Vitamin D 

Vitamin D stands out as foundational to building a disease resistant body.  I have read many studies about vitamin D over the last several years that find vitamin D works to both prevent infection and to reduce symptoms if infected.  There isn’t money to be made in vitamin D, so large randomized studies haven’t been funded.  But unusually for health sciences, nearly all the smaller studies seem to agree on the value of the sunshine vitamin.

Vitamin D is inexpensive and tough to overdo, so there is little reason not to try it.  But note, vitamin D works preventively.  You have to take it well before (like 60 days before) you are exposed for it to work.  Once you have an infection, it is too late.

Everyone absorbs vitamin D differently, so get your blood level checked with a test to verify you reach your target.  60 ng/mL seems like a solid, safe target.  Some people will say that 20 ng/mL is “good”, but they are thinking only of avoiding scurvy.  To get the benefits to your immune system the level must be higher, so being told your level is “good” isn’t enough.

Reduce Inflammation

COVID, in particular, seems to do worse in those who already have inflammation.  A better quality diet can help reduce inflammation, and certainly mitigate diabetes.  In fact, it is clear that people with uncontrolled diabetes do worse with COVID, but people with well controlled diabetes taking metformin actually do better than average.  The link between obesity and bad outcomes in COVID is clear, so dropping some pounds, though difficult, can help if you are carrying too much.

Gum Health

Please do not put off your dental care! People with periodontal disease (which involves inflammation of the supporting structures of the teeth) have been shown to do substantially worse with COVID than people with healthy gums.  If you are concerned about exposing yourself at your dentist, know that the transmission from staff to patient in dental offices has been remarkably low.  Even after several years, we have seen very few cases world wide.

Zinc

Zinc is a trace mineral key to maintaining a healthy immune system.  It is present in meat, beans, and nuts. Zinc lozenges have a long history of use to shorten a cold.  Current research shows that zinc can be anti-inflammatory, helping to regulate cytokine production, and reduce metabolic syndrome.  Oral zinc is considered generally safe.  Intranasal zinc can result in anosmia, which is the $20 word for loss of sense of smell.

Keep It Clean

Now that your body is strong, we can help it out by keeping exposure down.

Hand Hygiene

COVID isn’t transmitted by touch, but several other respiratory viruses are.  Washing your hands often when you are in public places and, most importantly, avoiding touching your eyes, nose, and mouth can make a big difference.

Nose Rinsing

Nasal rinsing is new to many people, but it has been used for thousands of years.  It appears to be quite helpful if you are exposed or think you might be catching a bug.  Like with vitamin D, there hasn’t been a single large study.  A number of small studies have very promising results, and no study has negative results. Rinse after exposure to people who might have COVID, and if you feel something “coming on”.  It appears that if you can knock down the virus load in the replication phase, your illness will be less severe.

Note that nasal rinsing works best when used preventively, before you know you are sick. If you begin early in the disease cycle, it is very effective at reducing symptoms. 

Using antimicrobials like xylitol or dilute iodine has shown the best results, but note that using iodine incorrectly could hurt you, so be sure to do it under the supervision of a physician.

Face Masks

Face masking has received a lot of attention based on claims that it slows the spread of COVID.  However, an examination of the science shows that masking does a very poor job of inhibiting transmissions of COVID and other respiratory infections.  This leads to the problem that people using masks have a false sense of security, thinking they are protected when they aren’t.

Cloth masks and surgical masks have been studied the most, and the large majority of studies find no benefit.  Studies that do find benefit are generally either purely theoretical, or based on a specific time and place with results that do not generalize.

Looking at the rate of infection before and after masking mandates in various locations reveals no observable difference in the infection rate trend before and after the mandate.

Some people believe that N95 masks are much better.  N95 effectiveness falls off quickly as they become wet from breath.  Pulling your smushed mask out of your pocket and wearing it longer than recommended makes it less effective than in a medical setting.  But even in healthcare settings, with trained, professional users adhering to the usage instructions, a recent good sized study found no observed difference between N95 and surgical masks in blocking COVID.

Outside of the clinic, when Bavaria required N95 masks for the general public, their rate of COVID infections did not vary from the rest of Germany.  N95s do not appear to give substantially better protection than other masks.
 

Note that the eyes are directly connected to the nasal passages, so that even if masks work to protect the nose and mouth, there is still an open highway for viruses to use.  If you are concerned with blocking the virus with a mask, then you should also use good eye protection, such as swim goggles.

Conclusion

To protect yourself against respiratory viruses, including COVID, ensure your vitamin D is near 60 ng/mL and flush your nose when you might have been exposed.  Those two seem to have the highest impact.  Maintaining good zinc levels and taking care of any inflammatory process in your body, including in your gums, also helps.  These all deserve your attention.  If you choose to mask, understand that the protection is likely not high, and be sure to include eye protection.

Of course, consult with your own physician before undertaking any of these to make sure they are OK for you.

And as always, floss your teeth!
 

Selected References

Here are some studies and resources but there are a great many more, so do a search if you are interested.

Vitamin D

A video that explains vitamin D and some of the research pretty well by John Campbell:
https://www.youtube.com/watch?v=MbUm5FyrHRk

“Pre-infection 25-hydroxyvitamin D3 levels and association with severity of COVID-19 illness“
https://pubmed.ncbi.nlm.nih.gov/35113901/

• Notable quote: “Patients with vitamin D deficiency (<20 ng/mL) were 14 times more likely to have severe or critical disease…”

“Vitamin D status and COVID-19 severity“
https://pubmed.ncbi.nlm.nih.gov/35546959/

“Vitamin D and survival in COVID-19 patients: A quasi-experimental study“
https://pubmed.ncbi.nlm.nih.gov/33065275/

“Association between vitamin D supplementation and COVID-19 infection and mortality“ 
https://www.nature.com/articles/s41598-022-24053-4#Tab3

• Notable quote: “Vitamin D3 was associated with a significant 33% decrease in mortality within 30-days of COVID-19 infection.”

Zinc

“A Case-Control Study for the Effectiveness of Oral Zinc in the Prevention and Mitigation of COVID-19“
https://www.frontiersin.org/articles/10.3389/fmed.2021.756707/full

• Notable quote: “Zinc is a relatively inexpensive mineral nutrient that is an effective prophylactic agent to prevent and mitigate the potentially deadly symptomatic SARS-CoV-2 infection.“

“Zinc supplementation and COVID-19 mortality: a meta-analysis“
https://eurjmedres.biomedcentral.com/articles/10.1186/s40001-022-00694-z

• Notable quote: “Zinc deficiency decreases CD8 + T cell responses and activation of helper T cells.”

Diet and Inflammation

Gary Taubes - The Case Against Sugar
https://www.youtube.com/watch?v=E0QvRreX7Gk

Nina Teicholz - The Big Fat Surprise
https://www.youtube.com/watch?v=hzQAHITIUhg
 

Diabetes

“Protection by metformin against severe Covid-19: An in-depth mechanistic analysis”
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9154087/

• Diabetics often take metformin.

Periodontal Disease

“Association between periodontitis and COVID-19 severity in a tertiary hospital: A retrospective cohort study“
https://pubmed.ncbi.nlm.nih.gov/35915835/

• Notable quote: “Periodontitis patients were three times more likely to have COVID-19 complications”

“Could there be a link between oral hygiene and the severity of SARS-CoV-2 infections?“
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7319209/

• Notable quote: “The reduction or eradication of periodontal disease significantly reduces one's risk of pneumonia.”

“Periodontitis as a Risk of Hospitalization and Death by SARS-CoV-2“
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9472290/

• Notable quote: “patients with periodontitis were significantly more likely to need hospital admission, assisted ventilation or have COVID-19 related pneumonia than the periodontally healthy patients”

“Risk of SARS-CoV-2 transmission following exposure during dental treatment – A national cohort study”
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8388145/

• Notable quote: “The transmission rate of SARS-CoV-2 in dental settings was very low for both patients and DSMs (Dental Staff Member).”

“Porphyromonas gingivalis in Alzheimer’s disease brains: Evidence for disease causation and treatment with small-molecule inhibitors“
https://www.science.org/doi/10.1126/sciadv.aau3333

• Bonus reason to control periodontal disease.

Nasal rinsing

“Nasopharyngeal and oropharyngeal rinses with neutral electrolyzed water prevents COVID-19 in front-line health professionals: A randomized, open-label, controlled trial in a general hospital in Mexico City“
https://pubmed.ncbi.nlm.nih.gov/34987795/

• Notable quote: “The prophylactic protocol was demonstrated as a protective factor, in more than 90%, for developing the disease, and without adverse effects.”

“Rapid initiation of nasal saline irrigation to reduce severity in high-risk COVID+ outpatients“
https://journals.sagepub.com/doi/10.1177/01455613221123737

• Notable quote: “In older outpatients testing positive for SARS-CoV-2 who initiated nasal irrigations rapidly after diagnosis, the risk of hospitalization or death was eight times lower than national rates reported by the CDC.”

“Intranasal Xylitol for the Treatment of COVID-19 in the Outpatient Setting: A Pilot Study“
https://www.cureus.com/articles/100176-intranasal-xylitol-for-the-treatment-of-covid-19-in-the-outpatient-setting-a-pilot-study

• Note that this study has less scientific rigor than others we have listed.

“Potential Role of Xylitol Plus Grapefruit Seed Extract Nasal Spray Solution in COVID-19: Case Series“
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7645297/

For more information about Xylitol: https://xlear.com/xylitol-and-saline/
 

Masks 

“Effectiveness of Adding a Mask Recommendation to Other Public Health Measures to Prevent SARS-CoV-2 Infection in Danish Mask Wearers“
https://www.acpjournals.org/doi/10.7326/M20-6817

• Notable quote: “recommendation to wear a surgical mask when outside the home among others did not reduce, at conventional levels of statistical significance, incident SARS-CoV-2 infection compared with no mask recommendation”

“Nonpharmaceutical Measures for Pandemic Influenza in Nonhealthcare Settings—Personal Protective and Environmental Measures“
https://wwwnc.cdc.gov/eid/article/26/5/19-0994_article

• CDC study showing that masks don’t work for protection or source control.

“Medical Masks Versus N95 Respirators for Preventing COVID-19 Among Health Care Workers : A Randomized Trial”
https://pubmed.ncbi.nlm.nih.gov/36442064/

In their enthusiasm to publish something showing positive effect, many publishers brought out studies early in the pandemic that seemed to show that masks worked.  However, there are big problems with most of these studies, and many have been withdrawn.  When reviewing them, it is important to also understand what critics say about them.  Of course, understanding criticism is always important for any study you wish to rely on, but many of these studies are particularly weak, so special care is indicated.