Blog 2: A Naturopathic Approach to Colds and Flus: Immune Support Beyond the Basics

It is within our power to improve or even to optimize our immune systems.  Aside from the advice to wash hands, there are so many other things that we can do to either prevent us from getting sick or lessen the severity or duration of the illness if we do become unwell.  Below is a summary of what I recommend to my patients and my family and what I do myself.   This is not written as a universal cure-all.  Not everything will apply to everyone.  It’s best to seek the advice of a Naturopathic Doctor, herbalist, nutritionist, or other qualified health professional who has had in-depth training in nutrition, nutraceuticals, herbal medicine, hydrotherapy, etc. to individualize a treatment plan for you. 

Let’s assume that you’re already on top of the basics of immune support.  You’re eating well, sleeping like a baby for at least 7 hours a night (ideally 8-9 hours), staying well hydrated, connecting with community, taking a brisk walk, or doing some other gentle form of exercise every day, getting some Vitamin D, and not smoking.   Now, you want to up-your-game to have an even better chance of warding off a nasty virus.  Let’s start by clarifying the language that we use to discuss the immune system.

Immune support, Immunomodulators, Immune stimulants, Antivirals, Antibacterials: What does it all mean?

There are things that we can do to “support” the immune system like “adaptogenic” herbs, which help us to “adapt” to stress and are immunomodulating (which means that they bring an under-active immune system up and an overactive immune system down).  Amazing, huh?  And, these things simply grow out of the ground.  It almost feels too good to be true, which may be in part why people are reluctant to use them.  I’m not here to convince you to try herbal medicine, but if you need any help understanding just how real their effect is on the human body there is a stunning body of evidence.  There are several great studies sprinkled throughout this post, but here is one to get you started:  Modulation of dendritic cell immune functions by plant components (see study here).   If herbs just aren’t for you, keep reading; there are several other tools in the Naturopathic tool kit. 

Next, we have “immune stimulants.”  These are all about revving your immune system up.  Many of these are so good at doing their jobs that I recommend that patients with autoimmunity take caution or work with a Naturopath or Herbalist if taking them. They make the immune system more active without having the dimmer switch that immunomodulators have.  Then, we have “antivirals” which work more specifically by attacking the virus itself.  And, finally, we have antibacterials, which kill bacteria.  Why would antibacterials be important during a viral infection discussion?  Because, very regularly, upper respiratory tract illnesses start as viral, but after days to weeks of stagnant mucus trapped inside inflamed lungs and sinus passages, bacteria start having a field day too.  What started as viral leads to the perfect breeding ground for something bacterial to grow and take hold. This is why when you ask a doctor for antibiotics for a cold or flu, we are compelled to say no, as antibiotics don’t work on viruses and have the potential to create super-bugs from over-prescribing.  But when you call back three weeks later to say that you’re too fatigued to get out of bed and you’ve started coughing up rust-colored phlegm, we give antibiotics (and we might send you straight to hospital for fear of pneumonia).  The bacteria have more than likely capitalized on their opportunity, created by the virus, to breed. So, any discussion about virus prevention should consider bacterial prevention as well.

Start a prevention protocol before you develop symptoms

When it comes to colds and flus, if you are like most people, you probably wait until you feel pretty poorly before you start to rifle through the medicine cabinet for treatment.  Often, this is too late to have much of a chance of modifying the course of the illness by more than a few days. Luckily, the naturopathic medicine cabinet can start treating you before you get hit with a virus and can carry on if you do succumb to one.  Following the practices below will either 1) strengthen your first line of defenses enough to prevent you from getting sick at all, or 2) bolster your immune army to help shut-down any virus that does get through, thus lessening the severity of the illness and/or lessening the duration of the illness.  The old “an ounce of prevention is worth a pound of cure” adage couldn’t be more apt than when it comes to colds and flus.  Please note that strengthening your immune system does not make you invincible.  Please continue to exercise caution, and seek medical attention if you become very unwell.

Here are my top prevention tips:

Add a few supplements to help you to take care of the basics of good health.  See my first post in this series for detailed help with the basics: A Naturopathic Approach to Colds and Flus: The Basics of Prevention.

  • Get your micronutrient gaps covered by taking a daily multi-vitamin.  Look for one with methylated B vitamins for better absorption and in case you are in the 25-40% of the population with the MTHFR gene mutation, which means you can’t convert folic acid into folate (the only form the body can actually utilize). Many people report being reluctant to take multi-vitamins because they don’t know which brands to trust.  I’ve got a post coming explaining the ins-and-outs of selecting quality supplements, or you can buy products through my store that I’ve already vetted.  I only provide the best-quality, independently-tested, doctor-grade supplements available.  Unfortunately, there are companies out there using cheap ingredients and fillers, not abiding by quality standards, and investing in marketing above all else, so we have to be discerning shoppers. Multi-vitamins are crucial to help bridge any micro-nutrient gaps, but they often aren’t enough to reverse a deficiency or even to provide the basics when the system is under stress or fighting an infection.  Working with a Naturopathic Doctor or nutritionist can help you to identify where you need extra support.
  • Take probiotics as a first step in supporting your intestinal health. This topic is so important that it’s got its own series of posts coming soon.  Let’s not forget that approximately 70% of the immune cells of the body are made in the gut.  Look for a probiotic product with at least 10 billion CFUs (colony forming units) and 7-10 strains (the more diversity, the better) and/or try adding some fermented food to your day.
  • Take fish oil which allows the cell walls of the body to be more fluid thus increasing signaling and transport.  If the phone lines are down and the roads are closed, nobody can do their jobs properly.  Including the immune system.  Fish oil is also very anti-inflammatory.

Take larger doses than a multivitamin can offer of a few key vitamins and minerals:

  • Vitamin D and K2. Vitamin D has been touted as a wonder vitamin for several years, and the research is compelling when it comes to bone health, immune support, mental health, and a host of disease processes.  Here is a study that shows that “low vitamin D levels are associated with an increased incidence of upper respiratory tract infections.” (Bartley, 2010)  This could be due, in part, to the fact that, by increasing “defensins” (peptides that kill viruses soon after they land on mucous membranes like the mouth and throat), “Vitamin D has direct anti-viral effects.” (Beard, 2011)  In my first post in the “A Naturopathic Approach to Colds and Flus” series, The Basics of Immune Support, I discuss Vitamin D and sun exposure.  Sunshine is a good starting place to lift levels, but it is often insufficient considering that even those of us who actively try to get outside everyday are typically covered in clothing or sunblock.  And, the darker your skin, the more melanin to block UVB rays (which is excellent from a skin health perspective, but not great for Vitamin D production.)  It’s also hard to eat enough fatty fish and eggs to raise Vitamin D levels.  This is where supplementation comes in to play.   A combo product with K2 helps the calcium (which is absorbed as a result of the Vitamin D) to go to the correct place (i.e. bones and teeth rather than blood vessels and kidneys).  As of the start of the pandemic and coming off of a long grey winter, I personally am doing a month of 10,000 IUs/day, which should raise my Vitamin D levels by about 10 points, then I plan to back down to a 4,000 IUs/day maintenance dose and repeat as necessary.  Many people are grossly insufficient in Vitamin D (especially at the end of winter) and can take several months of 10,000 IUs/day to get into the optimal range (60-90 nmol/L).  In an ideal world, I would check a vitamin D3 (or 25-hydroxy Vitamin D) level on all of my patients to assess their baseline before beginning treatment with it, as it is a vitamin that has the potential to become toxic (by raising  calcium levels).  Yet, the chance of toxicity only really becomes a concern at high doses for a prolonged period without any monitoring by a doctor,  and the benefit to the immune system is so huge that I’d recommend that during cold and flu season everyone (except those with a known excess of Vitamin D or calcium) start taking at least 2,000 IUs/day of vitamin D3.  If you have a known Vitamin D deficiency or insufficiency, I’d work to get that level up as quickly as I could (which will mean more than the standard recommendation of 2,000 IUs/day).  There are several different dosing strategies.   Some doctors give a starting dose of 100,000 IUs to get extremely low levels up quickly.  Others do 50,000 IUs every few weeks.  In this 2016 study, researchers concluded that   “Vitamin D3 therapy (50,000-100,000 IU/week) was safe and effective when given for 12 months…in patients with vitamin D deficiency. Serum vitamin D rarely exceeded 100 ng/mL, never reached toxic levels, and there were no significant changes in serum calcium or eGFR.”  You’ll need to work with your doctors to get prescriptions for mega-doses and to have your Vitamin D and calcium levels monitored.  Other doctors share my strategy by recommending 10,000 IUs daily for a specific amount of time and then reducing to maintenance doses.  If you don’t know your levels or if you know that you are already in the sufficiency range, then a more modest dose of 2,000 to 4,000 IU/day would be appropriate.  Even these lower doses will increase your Vitamin D status and have powerful effects on your immune system. These are fat-soluble vitamins, so they are best absorbed when taken with a meal containing some fat. Personally, I’ve just retested my levels, so I know that my vitamin D levels are already in the middle of the sufficiency range, but I also know that I have a gene mutation or SNP (single nucleotide polymorphism) in the VDR (Vitamin D receptor) gene.  Without going into great detail here, this means, in essence, that I need to load my system with more vitamin D than someone without this mutation in order for my body to register the Vitamin D.
  • Vitamin C.  Okay, everybody seems to know that vitamin C does a body and an immune system good, but there is a lot of confusion out there about what type of Vitamin C and how much of it to take.  Is ascorbic acid, buffered ascorbate, esterified/Ester-C, food-based Vitamin C, or liposomal Vitamin C better?  Well, the confusion is understandable. There are pros and cons to each type. If you need help figuring out where to start with Vitamin C or why it’s so fantastic, please sign up for my newsletter to get my upcoming post: Vitamin C in All its Glory.   If you already have some Vitamin C that works for your body,  I’d suggest that during cold and flu season you work yourself up to a 2,000 mg-4,000 mg (aka 2-4 gram) dose as a preventative step and to be ready to try upping the dose if you develop any cold or flu symptoms.  Take it in 4-5 divided doses throughout the day to reduce the chance of it causing loose stool. And, listen to your body.  If you develop diarrhea, back down to the last dose that didn’t cause loose stool.
  • Zinc.  It serves a mighty double-punch because it 1) helps slow viral replication within a cell and 2) directly supports our white blood cells (the soldiers of the immune system). Most multivitamins have about 15 mg already. I generally ask patients to double that (take an additional 15 mg) during cold and flu season and at least quintuple that (take at least 75 mg in divided doses, ideally in two to three hour intervals throughout the day) at first signs of infection. A 2017 meta-analysis, showed a 33% reduction in duration of illness from colds with zinc doses greater than 75mg.  (Hemila, 2017)  Another meta-analysis of four randomized controlled trials of zinc supplementation on the incidence of pneumonia in children in developing countries showed that the zinc-supplemented groups had a 41% (95% CI: 17–59%) reduction in the incidence of pneumonia. (Group, 1999) There are three main issues to consider with zinc:
  •  1) it will more than likely cause nausea if taken on an empty stomach,       
  • 2) greater than 50 mg of zinc for more than a few weeks can block the body’s absorption of copper, so don’t stay on the virus-fighting dose (>75 mg) for more than two weeks at a time,
  • 3) to be most effective in fighting a virus once it has infected the body, zinc needs help to get into the cell in order to fight the virus there.  Sign-up for my newsletter to get my next blog in the series, entitled “A Naturopathic Approach to Colds and Flus: Treatment Strategies”, for specifics on how to get zinc into the cells. 
  • Vitamin A– Vitamin A is a very potent anti-viral and immunomodulator, so it is also a must in most prevention or treatment protocols for flus.   Vitamin A deficiency is also associated with changes in the lining of the lungs “that disrupt the normal lung physiology predisposing to severe tissue dysfunction and respiratory diseases” (Timoneda, 2018).  In high doses, it can get toxic, so it is to be taken in moderation and under the care of a qualified practitioner.  Most multivitamins already have between 5,000 and 15,000 IUs of Vitamin A, so that should be calculated into your daily dose.  Doses higher than 15,000 IUs/day of Vitamin A (as a retinol rather than a beta-carotene) should be avoided in pregnancy and hepatitis. During cold and flu season, I typically recommend that most of my patients add about 10,000 IUs/day in addition to that which is found in their multivitamin.  Your hair and nails may enjoy the extra A as well.
  • Magnesium– Magnesium is used in nearly every metabolic pathway in our bodies.  Without it in abundance, we can get glitches that lead to big and small issues.  We burn through lots of it when we are under any type of stress, including fighting an infection.  It can also lower blood pressure and help to create a sense of calm. Excessive doses can cause loose stool, so this is another nutrient to be taken to bowel tolerance.  I typically start with 150mg of a bisglycinate form twice/day.
  • N-Acetyl Cysteine (NAC)– NAC has an affinity for the lung, so you can think of it as a lung tonic or protector.  It does this in a few ways.  Gram doses of NAC are mucolytic, which means it helps to liquify a thick, tenacious mucus.  This can be game-changing in a chest infection because it helps the body to expectorate the mucus (cough it up and out) leaving less chance for a secondary bacterial infection to develop.  It’s also anti-inflammatory.  In a severe cold or flu, you’ll get inflammation and damage in the alveolar cells of the lung. Gas (oxygen and carbon dioxide) exchange takes place within these alveolar cells of the lungs.  If they get damaged (inflammation) or gummed up (mucus), the exchange of gases doesn’t work as well, so we experience trouble breathing.  NAC is also a precursor to glutathione (the master antioxidant in the body), so we are actually getting triple duty out of this supplement. This is typically taken orally. Generally, 600 mg two to three times/day is a recommended dose, which your Naturopath may increase if you become unwell.  In cases turning severe or as a preventative measure in patients with COPD, chronic bronchitis, or other known lung pathology, I’d have a patient nebulize NAC. Please seek the advice of your Naturopathic doctor.
  • At this point, you may be thinking.  “What? More? I can’t take twenty pills a day.”  I get it. I am laying out several options because there are shortages of lots of the immune boosting super stars and because different people have different needs.  If, for example, you are a generally healthy person who doesn’t catch every virus going and you know that your Vitamin D level is already in the optimal range, then you might just choose to take extra care with the basics like good sleep and low sugar and add zinc and an immunomodulating tincture to your regime.  If, on the other hand, you suffer with chronic bronchitis and get taken down several times a year with upper respiratory infections, then you’ll want to up your game even more with things like Echinacea, Vitamin A, NAC, etc.  Again, talking to an experienced practitioner of preventative medicine can help you to make good decisions. If you are feeling overwhelmed by finding quality version of some or all of these products, see my Immune Support Protocol in my online store.

Take immune-supportive or “adaptogenic” herbs and/or medicinal mushrooms (which both have an immunomodulating effect—meaning they help to raise a depressed immune system and lower an over-active one.)  Many of my patients take adaptogenic herbs year-round.  I suggest them to nearly everyone during cold and flu season.

  •  Immune modulating and tonic herbs. The best is a tincture that has been formulated specifically for your constitution and existing state of health by a Naturopathic Doctor or Herbalist.  Typical blends that I’m doing now include: Eleutherococcus, Schisandra, Holy Basil, Rhodiola, Withania (Ashwaganda), Shatavari, Melissa (Lemon Balm, which is a lovely option because it is also anti-viral, but is not right for you if you have an underactive thyroid), glycyrrhiza (licorice, only to be taken for a few weeks at a time and not to be taken if there are any issues with hypertension or potassium levels or during pregnancy), and Ginger. Or try a pre-made adrenal tonic product to get a nice blend of immunomodulators. I love Gaia Herbs’s “HPA Axis Daytime Maintenance.”
  • Mushrooms: Cordyceps, Maitake, Reishi, Shitake, Snow Fungus, Split Gills Fungus, Turkey Tail Mushroom. MediHerb’s “Mushroom Forte” blend is a powerful support aid, as is Thorne’s Myco-Immune.

Take immune-stimulating herbs to a) get you ready for a fight and b) start knocking down any existing low-grade infections that are draining your immune system’s resources.  As the saying goes, the best defense is a good offense. These herbs are so stimulating to the immune system that I recommend them with a caution to patients with autoimmune disease. [A word about autoimmunity and immunostimulants: Prescribing caution in taking immune stimulants is not to say that they are not helpful in autoimmunity.  They can be game-changers, as chronic infections can be one of the pieces of the autoimmunity puzzle. (Blum, 2013) It’s just that these herbs can ignite a battle with the bugs causing a flare of symptoms, thus turning people off to these herbs.  The body is wise.  A flare is often a signal that we have pushed too hard too fast, but not necessarily that we should stop altogether.  Any given system can only handle so much at any given time.  Some people can take higher doses of these herbs and have no reaction while others even at low doses feel, for example, achy and tired, or worse, for a period of time while their bodies are killing off existing infections. This is known as a Herxheimer reaction. This is not a time to grin-and-bare it, as too fast a die-off reaction from chronic infections can overwhelm your detox pathways and lead to setbacks in healing. Working directly with a knowledgeable practitioner can help you to find the right balance.] 

During a typical cold and flu season, I have some patients take these immune-stimulating herbs continually while others take them for a few weeks and then pause for a week and repeat.  It’s times like these that it’s helpful to have someone with some clinical insight in order to help you to decide how to use these herbs.  They are some of the most helpful items in the toolkit, but often need fine-tuning:

  • Echinacea. This is arguably the strongest of the immune-stimulating herbs. It is best used as a preventative or a nip-it-in-the-bud therapy throughout cold and flu season and at a higher dose for the first two to four days of actively fighting an infection, in the hopes of helping the immune system to shut it down.  Beyond the first few days of a viral illness, it is traditionally stopped, as the immune system is at that point being stimulated enough (or sometimes too much) by the virus itself. This overstimulation of the immune system by an infection can very rarely lead to what is called a “cytokine storm” and is a feature of severe influenza infections and of the virus that has locked-down the world.  (Sorry, I can’t name it directly or this post may get censored. By the way, everything in this post is relevant to that virus as well.) So, what’s all the fuss with immune stimulants and cytokine storms? In plain language, the body mounts such an attack on a virus using cytokines as it’s instruments of destruction  [think: the soldiers in the war] that the body itself is caught in the crossfire…similar to autoimmunity but with a rapid onset and to a very extreme extent. Extreme enough to result in ARDS (Acute Respiratory Distress Syndrome) leading to death.  Echinacea is really good at helping to get those soldiers armed and moving out, but there is a question as to whether it also helps the body to call those troops off and clean up some of the mess they created (as immunomodulators do). In this 2017 study published in the journal Virus Research, researchers reported that Echinacea purpurea not only doesn’t contribute to a cytokine storm but that part of its benefit is through its “inhibition of inflammation super-stimulation (cytokine storms)” (Vimalananthan S, 2017). This, plus other mounting evidence plus clinical experience, has led many practitioners to give it freely.  With a bit more evidence, I may soon change my tune, but as of now, I’m sticking with my training to use it cautiously in acute illnesses.  I’m still reluctant to take the gamble and possibly (inadvertently) contribute to a cytokine storm.  So, my strategy is this: recommend Echinacea prophylactically while there is a pandemic (and during most flu seasons).  If a patient of mine does succumb to a virus, I’ll keep the Echinacea up at higher doses for the first two to four days of infection (in the hopes that we squash the virus before it takes hold and really starts doing damage).  If my patient is then either stable or improving, I will recommend that they keep taking it until they are completely restored to health, but, if they start to worsen, I will stop Echinacea so as not to worsen a cytokine storm.  Even though it would be the virus causing the vast majority of the cytokines at that point, I can’t in good conscience recommend a treatment that might tip the scales for the worse outcome for my patients.  I will still recommend Echinacea in prevention and early in the disease process because I believe it to be one of the most helpful treatments that the world has in preventing viral infections from progressing to the point of a cytokine storm.  It is generally taken as follows:
  • For prevention, 5mL (1 teaspoon) of tincture of a 1:2 preparation daily. 
    • In times of imminent threat, doubling or tripling the daily dose (split throughout the day) is often recommended. 
    • At first sign of cold/flu, 5 mL of tincture every two waking hours for 1 to 2 days then decrease dose or stop altogether if worsening. 
  • Clinical pearl: a high-quality Echinacea product when held in your mouth for a few seconds will make your tongue temporarily numb and tingly.
  • Astragulus– a much loved immune herb.  As an immunostimulatory, it is second only to Echinacea.  It is an excellent immune tonic for people who are in a chronic state of impaired immunity or those that seem to catch every cold and flu coming down the pike and often feel run-down.  It is also anti-viral.  I suggest the same usage strategy outlined for Echinacea with this herb.  That is, taken as prevention and early in the disease process, but then stopped if symptoms worsen.  It is generally taken as 5mL twice/day as a preventative therapy and then increased to four to six times/day at first sign of infection.
  • Sambucus (Elderberry)– What’s not to love about this?  It tastes great, bolsters the immune system, has direct anti-viral effects, and is anti-inflammatory.  I’m sold.  In a placebo-controlled, double-blind Influenza B study, researchers reported what herbalist have seen clinically for hundreds of years, “A complete cure was achieved within 2 to 3 days in nearly 90% of the SAM-treated [standardized elderberry extract, Sambucol®] group and within at least 6 days in the placebo group (p < 0.001). No satisfactory medication to cure influenza type A and B is available. Considering the efficacy of the extract in vitro on all strains of influenza virus tested, the clinical results, its low cost, and absence of side-effects, this preparation could offer a possibility for safe treatment for influenza A and B.” (Zakay-Rones Z, 1995)  The only caveat to treatment with Elderberry, as with all herbal medicine, is that you need to make sure that you are getting a quality product, in this instance one full of flavonoids, for it to be effective.  Look for a reliable source that is doing a standardized extract. Many argue that Elderberry does not contribute to a cytokine storm, but I’d suggest exercising the same caution as outlined for Echinacea and Astragulus.  As for dosage, 5mL (one teaspoon) per day is typically given preventatively.  At first sign of infection, 5 mL three to four times per day is typically recommended for the first 1-4 days and decreased as a patient improves.

Start using broad-spectrum antimicrobials (which address viral, bacterial, parasitic, and fungal infections) BEFORE you get hit with an influenza virus to 1) kill off existing low-grade bugs that are draining your system, and 2) have antimicrobials on board and ready to start killing any cold or flu viruses that you might pick up.  The earlier you start treating an infection the better you fare.   As for getting existing infections in check using antimicrobials, this approach is similar to that outlined above regarding immune stimulants, but instead of stimulating the immune system to kill the bugs, we are using antimicrobials to kill them directly.  We all cope with varying degrees of infections that our immune systems keep in check.  In order to unencumber the immune system so that it can focus more of its attention on any new viruses that may attack it, we can actively fight these infections now with some broad-spectrum antimicrobials.  Some good options include:

  • Oil of Oregano.
  • Artemisia/Artemisinin.
  • Hydrastis (Golden Seal).
  • Mahonia (Oregon grape).
  • For a full list of specifically antiviral herbs, which we will use extensively at the first sign of a cold or flu, please see my upcoming post entitled: A Naturopathic Approach to Colds and Flus: Treatment Strategies.  

Start utilizing some form of hydrotherapy.  The use of hot and cold water has a very powerful effect on stimulating the immune system, moving stagnant lymphatics, and improving circulation to the vital organs.  As a preventative measure, try starting to incorporate alternating hot and cold shower cycles into your life.  It looks like this:

  •  3 minutes of hot (as hot as you can stand, but not hot enough to burn your skin). Diabetics or anyone with nerve damage which could effect your ability to tell if you are burning your skin should avoid very hot temps,
  • 30 seconds of cold (as cold as you can stand, you might have to build up slowly to the very cold temps). 
  • Repeat three times ending on cold.

This is an excellent practice to incorporate into your daily immune boosting lifestyle.  To get a deeper understanding of hydrotherapy, please sign up for my newsletter to get alerted when my upcoming Hydrotherapy: The Hot and Cold of It post is ready.

Immune Support and Children

When it comes to children and immune support, they are just little human beings with the same metabolic pathways that also need support during times of illness, but they need less of it.  All immune support listed in this post is appropriate for children if given in appropriate doses.  Clark’s rule is a handy tool that lets you convert adult to pediatric doses based on a body-weight adjustment.  Clark’s rule: [Weight (in pounds) / 150 lbs] X Adult Dose = Pediatric Dose.  [To convert kg (kilograms) to lbs (pounds), simply multiply by 2.2.]

In Conclusion

Overall, the name of the game is to optimize your overall health and that of your immune system in order to make you less susceptible to being taken down by an infection.  Using the tools outlined above and those in my first post of the series, entitled A Naturopathic Approach to Colds and Flus: The Basics of Prevention I hope to help you to do just that.  Be prepared, and, if you do become unwell, act fast. The sooner you squash a bug the less damage that it can do and the easier and quicker the recovery.  For more education on this topic, read the third post in this series: A Naturopathic Approach to Colds and Flus: Treatment Strategies.  Be well.


Blum, S. (2013). The Immune System Recovery Plan. New York: Scribner.

Group, T. Z. (1999). Prevention of diarrhea and pneumonia by zinc supplementation in children in developing countries: pooled analysis of randomized controlled trials. Journal of Pediatrics, 689-697.

Hemila, H. (2017). Zinc lozenges and the common cold: a meta-analysis comparing zinc acetate and zinc gluconate, and the role of zinc dosage. Journal of the Royal Society of Medicine Open.

Timoneda, R.-F. Z. (2018). Vitamin A Deficiency and the Lung. Nutrients, 10 (9).

Vimalananthan S, S. R. (2017). Prevention of influenza virus induced bacterial superinfection by standardized Echinacea purpurea, via regulation of surface receptor expression in human bronchial epithelial cells. Virus Research.

Zakay-Rones Z, V. N. (1995). 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. The Journal of Alternative and Complementary Medicine, Volume 1, Issue 4.