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Avoiding getting sick: Research-backed ways to prevent Covid, colds, and flu

Key takeaways:
~Everyone is exposed to viruses that cause respiratory illness, but not everyone develops symptoms.
~ There are research-backed ways to both prevent colds and respiratory illnesses and reduce symptoms when you do get sick.
~ Genetics affects whether you are likely to get sick from certain viruses.

Staying Well During Virus Season

No one enjoys getting sick—time off work, feeling terrible, and being confined to the couch with a box of tissues — it stinks!

I remember when my kids were little and they got sick. A trip to the doctor would inevitably result in the doctor saying, “It’s just a virus”. Nothing to be done, viruses can’t be treated or prevented, and your child will feel better in a few days.

This mindset that there is nothing to be done about viruses continued, at least for me, until recently. My thoughts were that everyone catches a cold or “the crud” every year or two, usually in December or January.

But I was wrong. It turns out that there is a lot you can do to help your immune system and not get sick for a week or two.

Viruses are all around us, and we’re not going to avoid exposure to them. But getting sick – having symptoms for days or weeks – seems to be something that can be greatly reduced.

Context: Viruses are everywhere, including your nose.

A 2015 study looked at how many respiratory viruses were found in Utah families.

For an entire year, researchers swabbed noses and asked about symptoms weekly in 26 households (108 people). The results showed that 783 viral episodes were detected, with less than half of the viral episodes causing any symptoms. Viruses were detected in a quarter of the weekly samples, and almost everyone had a rhinovirus detection at some point during the year.

The most common viruses causing symptoms were coronaviruses, human metapneumovirus, and influenza A. Bocavirus and rhinovirus detections were usually asymptomatic. Households with many young children had more viral infections.

The study concluded that adolescents and adults had an average of 5 viral respiratory illnesses per year, but that most were asymptomatic. Children under the age of 5 were much more likely to have respiratory symptoms. (Anyone who has worked with children and wiped their noses all winter knows this.)

Not everyone is equally susceptible to every virus. Some people have genetic factors that bolster their defenses against certain viral infections. Check out the full article on susceptibility to viral illnesses to see where your superpowers lie.

Prevention and Treatment Strategies for Flu, Cold, and Common Cold:

Let me be clear up front: I’m not saying that any of the following are miracle pills that will prevent all illness for everyone. Instead, I want everyone to take away from this article the research-backed ideas for preventing the common respiratory illnesses that circulate every year. You may still get sick, but knowing what works and being prepared can help lessen the symptoms and duration.

Disclaimer: This is all for informational purposes. If you are sick or have medical questions, please consult to your doctor.

Covid and SARS-CoV-2:

Nobody wants covid (or long covid), so let’s talk about some of the safe, inexpensive, and easy things you can do to reduce your risk.

In a large population study (4.5 million people), researchers investigated which current medications or supplements were associated with reduced severity and reduced risk of Covid. One of the strongest associations was CoQ10 supplementation, which reduced the risk of hospitalization by 85% in Covid patients.[ref] (Full CoQ10 article)

SARS-CoV-2 is an enveloped virus, and the membrane around the viral DNA is susceptible to disruption. For SARS-CoV-2, both Listerine and a povidone-iodine solution can kill it. Gargling with either for 30 seconds can inactivate the virus in the throat.[ref] Other studies showed that chlorhexidine mouthwash was not effective.[ref]

Nasal rinsing:
Nasal saline (salt) irrigation is another proven method for reducing respiratory infections, including Covid. There are at least 33 studies now on the reduction of viral load and transmission of SARS-CoV-2 using nasal saline irrigation or gargling[ref]

A meta-analysis of 10 studies on povidone-iodine gargling and/or nasal rinsing. When combining the data, the studies show an average reduction in Covid severity of 71% when used early and a 45% reduced risk of getting Covid when used as a prevention.[ref]

Is it safe to use iodine nasal rinse or gargle every day?  A study in JAMA on Covid patients who gargled with a 1% iodine solution 4 times a day found that some of the iodine was absorbed and caused TSH (thyroid) levels to rise for a couple of days. However, once the patients stopped gargling with iodine 4 times a day, the TSH levels returned to normal.[ref]

Several clinical trials early on showed that quercetin was likely effective in reducing the duration of covid.[ref][ref] A meta-analysis of data from 10 randomized clinical trials shows that quercetin (typical doses 500 mg) reduced symptoms, duration, and hospitalization by about 40-60%.[ref][ref] (More on quercetin)

Melatonin is produced in high levels at night, but it is more than just a sleep hormone. Melatonin is also important in the way your immune system works by modulating the immune response. Clinical trials of melatonin have shown that it reduces symptom progression, days of illness, and death[ref][ref][ref]  Melatonin was one of the first ‘drugs’ that computer models showed in March of 2020 that would target SARS-CoV-2.[ref]

Blocking blue light from screens and LED lights for two hours before bedtime can increase your overnight melatonin production. Taking low-dose, time-released melatonin can also boost your levels.   (More on melatonin and immune response)

While zinc is important for fighting off all types of infections, it can specifically inhibit the replication of the Covid virus. Several clinical trials have found that zinc, usually in conjunction with other nutriceuticals such as quercetin or resveratrol, is effective in reducing viral load and decreasing days of symptoms.[ref] (More on zinc and genetics)

Vitamin D:
While the headlines talk a lot about vitamin D, the research really points to not being deficient. Adding lots of vitamin D once you’re sick hasn’t been shown to have much effect.[ref] So if you have low levels, either get sun exposure or take vitamin D before respiratory illness season.

N-acetylcysteine (NAC):
A meta-analysis that pooled data from ~20,000 participants found that NAC supplementation reduced mortality in covid by 40%.[ref] Other studies show that NAC (600 mg/2x/day) may work to prevent covid symptoms and infection.[ref]

Common Cold and Respiratory Tract Infections:

The common cold is a general term applied to symptoms of several different respiratory viruses, including coronaviruses, rhinoviruses, adenoviruses, RSV (respiratory syncytial virus), and bocaviruses.[ref] Many of the Covid coronavirus prevention strategies likely work for common colds as well.

Get enough sleep:
Getting less than 6 hours of sleep per night increases the risk of catching a cold by 4-fold.[ref] This means that getting to bed on time is really important during cold and flu season.

Melatonin as a general antioxidant and immune function regulator is effective against many viral respiratory illnesses including the viruses that cause the common cold.[ref][ref][ref] Animal studies show that it prevents lung damage in RSV and prevents staph infections.[ref][ref]

There are tons of studies on daily gargling to prevent respiratory illnesses. For example, a study of Japanese children found that gargling with either green tea or plain water reduced the risk of respiratory illness by 30-40%.[ref]

Another study found that gargling with salt water reduced the duration of colds by a couple of days. Moreover, gargling also reduces transmission, so you won’t be sharing the cold with everyone in your household.[ref]

Vitamin C:
Studies on vitamin C for reducing the risk of the common cold show mixed results – depending on the study group and the amount of vitamin C taken. One recent study on Korean army personnel found that 6g of vitamin C per day reduced the risk of colds by 80%. [ref] A meta-analysis of studies in kids under the age of 6 found that vitamin C didn’t prevent colds but it did reduce the duration of the cold.[ref]

Vitamin D:
A prospective, randomized, double-blind, placebo-controlled trial (the gold standard) found that daily vitamin D supplementation for 16 weeks reduced the duration and severity of respiratory infections in adults aged 45-74.[ref]

Multiple randomized controlled trials in children show that honey works better for a cough than placebo, diphenhydramine, or dextromethorphan.[ref][ref][ref]


Influenza: Beating the flu

First, keep in mind that genetics plays a role in whether you are likely to get certain variants of the flu virus. We all have different variants in immune system genes that give us protection from some viruses and susceptibility to others. You can read about flu genes here.

Gargling and nasal rinse:
Researchers found that iodine throat spray or iodine gargle (both containing 0.23% iodine) would kill the avian flu virus within 10 seconds of application.

Gargling and hand washing:
A large study showed that just teaching kids about hand washing and gargling reduced influenza infections by 20-30%.[ref]

Hesperidin has been shown in several cell studies to inhibit the replication of influenza A. However, there aren’t any clinical trials of hesperidin for the flu.[ref]

Black elderberry:
The anthocyanin in black elderberry extract has been shown to inhibit neuraminidase in cell testing.[ref][ref]

An important co-factor in immune response pathways, zinc deficiency can increase the risk of severity in respiratory viruses, including the flu.[ref]

A natural flavonoid and popular supplement, quercetin has been shown in several studies to inhibit the replication of influenza.[ref][ref]

A component of the spice turmeric, curcumin has been shown in multiple studies to have antiviral activity against influenza viruses.[ref][ref]

Vitamin C:
A small study in healthy adults showed that 1,000 mg of vitamin C taken every hour for six hours at the onset of symptoms reduced symptoms by 85%. After the first six hours, participants took 1,000 mg three times a day.[ref]

N-acetylcysteine (NAC):
NAC provides the cysteine precursor that the body needs in order to make glutathione. NAC also acts as a mucolytic, thinning out thick lung mucous. An Italian study found that 600 mg/2x/day for 6 months significantly reduced the number of influenza-like illnesses in older adults. [ref]


Wrapping this up:

Research shows that there are a number of things you can do to prevent viral respiratory infections or reduce the duration of symptoms.

There is a lot of overlap in what works for different viral infections. The easiest and most effective preventive measure for all of these viruses is gargling. Gargle with iodine or Listerine to kill the virus if you have symptoms or exposure. However, simply gargling daily with water or green tea seems to help prevent all types of respiratory illnesses.

Melatonin helps you to fight off viruses overnight. Prioritizing your sleep schedule, sleeping in the dark, and taking supplemental melatonin if needed are all relatively simple. Think about how many times you’ve gotten sick when traveling across time zones — or after a night out partying. Just sticking to a solid sleep, wake, and eating schedule helps your circadian rhythm and immune response.

N-acetylcysteine (NAC) has some fairly good studies on it for a variety of respiratory infections, and it may be something to consider as a preventative for people who are older or who regularly catch respiratory infections. Of course, talk to your doctor if you’re on any medications before starting a supplement.[ref]

The key is to be prepared. The last thing you want to do when you wake up with a cold is to run to the store or even try to think about what you need. Have a go-to supply ready if you start feeling a sore throat.  If you don’t normally use mouthwash, get a little bottle of Listerine — or an iodine-based mouthwash. If you’re planning on making your own 0.2 – 1% iodine solution, figure out how to dilute your iodine ahead of time. Don’t try to do the math with a head cold.

Have a ‘cold box’ ready for that first tickle of a sore throat. Whether it’s quercetin, NAC, melatonin, gargle/nasal rinse, zinc, elderberry, honey, or vitamin C – the key is to have it on hand and actually take it when you first think you’re getting sick. Take care of yourself, get plenty of sleep, and avoid stressors.



About the Author:
Debbie Moon is the founder of Genetic Lifehacks. Fascinated by the connections between genes, diet, and health, her goal is to help you understand how to apply genetics to your diet and lifestyle decisions. Debbie has a BS in engineering from Colorado School of Mines and an MSc in biological sciences from Clemson University. Debbie combines an engineering mindset with a biological systems approach to help you understand how genetic differences impact your optimal health.