The common cold is the leading cause of doctor visits in the U.S. 1 There are several factors that increase your risk for a cold, including: 2
• Season — A majority of colds occur during fall and winter months, 3 and research reveals there is more than one reason for this. For starters, cold weather drives people indoors where exposure to those who are already ill increases. Cold temperatures also weaken the first line of immune defense in your nose. 4
Research 5 reveals the immune system responds slower at cold temperatures than at body temperature, and the rhinovirus — known to replicate faster at lower temperatures — typically invades your body through the nose, where the air tends to be cooler than body temperature. Dry winter air may also dry your mucous membranes, making the symptoms of a cold worse.
• Age — The immune system in children younger than 6 is still developing and they have not yet developed resistance to many viruses, which is why children tend to have far more colds than adults.
• Weakened immune system — Poor diet, lack of sleep, stress, food allergies, overtraining and concurrent or chronic illness are factors that can weaken your immune system.
• Smoking — Compared to nonsmokers, smokers are more prone to colds and have a greater risk of developing subsequent infections. 6
• Exposure — A cold passes through direct physical contact with one of nearly 200 viruses that can trigger symptoms. 7 Someone who has a cold can pass it to you by touching your hand, sneezing near your face, or through contact with their body where the cold virus has been sprayed after a cough or sneeze. Hence, being in close proximity and contact with others, such as at school, day care or on an airplane, increases your risk for contracting a cold.
Once inside your body, the virus attaches itself to the lining of your throat or nose, triggering your body's immune system to send white blood cells. If you've built antibodies to this virus in the past, the fight doesn't last long.
However, if the virus is new, your body sends reinforcements to fight, inflaming your nose and throat. With so much of your body's resources aimed at fighting the cold, you're left feeling tired and miserable. The good news is there are simple ways to strengthen your immune function to ward off both the common cold and influenza.
Four nutrients known to offer powerful protection during cold and flu season are vitamins C and D, zinc and beta glucans. These can also be used acutely if you feel like you're coming down with a cold or flu. Getting plenty of prebiotic fiber and sleep are also important.
Vitamins C Offers Powerful Protection Against Cold and Flu
Research 8 , 9 , 10 supports the use of vitamin C during a common cold to reduce the duration of symptoms. Typically, the higher the dose you take the better the results during a cold. However, there are limitations when taking oral vitamin C, as it can cause loose bowels.
You can get higher doses when using intravenous vitamin C or liposomal vitamin C. Personally, I use 3 to 4 grams of liposomal vitamin C every hour in the rare occasion when I get sick, with great results. 11
As a general rule, I don't recommend high doses of vitamin C unless it's in liposomal form. I also don't recommend long-term or chronic high-dose vitamin C supplementation as this may cause nutritional imbalances.
For example, taking large doses of vitamin C (ascorbic acid) on a regular basis lowers your level of copper, so if you are already deficient in copper and take high doses of vitamin C, you can actually compromise your immune system.
So, whereas temporarily taking megadoses of liposomal vitamin C to combat a case of the cold or flu will be helpful, for year-round support, get your vitamin C from food instead.
Kiwi fruits , for example, are exceptionally high in vitamin C. Research 12 published in the British Journal of Nutrition found that a kiwifruit-packed diet reduced the duration and severity of upper respiratory tract infections symptoms in older individuals. Other foods high in vitamin C include: citrus fruits, red bell peppers , broccoli, Brussels sprouts , butternut squash, papaya and sweet potatoes .
High-Dose Vitamin C for Viral Infections
According to Dr. Albert Szent-Gyorgyi, a biochemist who was the first to isolate vitamin C and who received a Nobel Prize for his work with the vitamin, "health" occurs when there is an ample flow and interchange of electrons in your cells. Impaired or poor electron flow and interchange equals "disease," and when the flow and interchange ceases entirely, your cells die. Oxidation, caused by free radicals in your body, involves the loss of electrons.
Antioxidants counter the disease process caused by oxidation (loss of electrons) by supplying electrons. Vitamin C is a major antioxidant, and perhaps the most important electron donor to maintain optimal electron flow in your cells. As reported by Orthomolecular Medicine News Service (a nonprofit and noncommercial informational resource): 13
"High dose vitamin C is a remarkably safe and effective treatment for viral infections. In high doses, vitamin C neutralizes free radicals, helps kill viruses, and strengthens your body's immune system. Taking supplemental vitamin C routinely helps prevent viral infections."
For severe types of influenza, such as swine flu, very high dosages of intravenous vitamin C are recommended, typically between 200,000 to 300,000 milligrams or more. 14 For this, you would need to see a physician. Vitamin C, at saturation, can even replace antiviral drugs in many cases.
Vitamin D Deficiency May Be an Underlying Cause of Cold and Flu
Low vitamin D also increases your risk of contracting a cold or flu. 15 Vitamin D — produced in your skin in response to sun exposure — is a steroid hormone with powerful antimicrobial activity, capable of fighting bacteria, viruses and fungi. The evidence is clear that the lower your vitamin D level, the higher your risk of developing a cold or the flu. 16
Dr. John Cannell, founder of the Vitamin D Council, was one of the first to introduce the idea that vitamin D deficiency may actually be an underlying cause of influenza. His hypothesis 17 was initially published in the journal Epidemiology and Infection in 2006. 18
His hypothesis was subsequently followed up and supported by studies published in the Virology Journal in 2008 19 and the Archives of Internal Medicine in 2009. 20 Since then, a number of other studies have come to similar conclusions. Most recently, a scientific review 21 , 22 of 25 randomized controlled trials confirmed that vitamin D supplementation boosts immunity and cuts rates of cold and flu.
Like Cannell before them, the researchers believe vitamin D offers protection by increasing antimicrobial peptides in your lungs, and that "[t]his may be one reason why colds and flus are most common in the winter, when sunlight exposure (and therefore the body's natural vitamin D production) is at its lowest …" 23
According to this international research team, one person would be spared from influenza for every 33 people taking a vitamin D supplement, whereas 40 people have to receive the flu vaccine in order to prevent one case of the flu. Among those with severe vitamin D deficiency at baseline, 1 in 4 people taking a vitamin D supplement would be protected from the flu.
For optimal protection, get tested at least twice a year and aim for a level between 60 and 80 nanograms per milliliter (ng/mL) year-round. While sensible sun exposure is your best source of vitamin D, many cannot get enough sun during winter months, which may make oral supplementation a necessity. Your best source is sensible sun exposure.
If this is not an option where you live, using an oral vitamin D3 supplement is advisable. In this case, keep in mind you may also need take additional calcium and vitamin K2 (MK7 form) to protect your arteries, and magnesium to activate vitamin D.
Cold or Flu Symptoms? Try This Crash Treatment
If you are coming down with cold or flu-like symptoms and have not been taking vitamin D on a regular basis, you can take 50,000 international units (IUs) a day for three days to treat the acute infection. (Cannell believes the dose could even be as high as 1,000 IUs per pound of body weight for three days.)
That said, there's still the possibility that vitamin D won't work, even in these mega-doses, if you've never been exposed to the antigens before. (Ultimately, your best bet is to maintain a vitamin D level between 60 and 80 ng/mL year-round.) Alternatively, take 3 to 4 grams of liposomal vitamin C every hour until you feel better.
Low Zinc Also Raises Your Risk of Viral Infections
A third nutrient deficiency associated with increased risk for cold and flu is zinc. Zinc may also reduce the duration and severity of your cold if taken at the first signs of infection. Your body has no way to store zinc, so it depends on a daily supply through diet. For a list of foods rich in zinc, see "Zinc — One of the Best Supplements to Fight Cold and Flu."
Zinc is a constituent of at least 3,000 different proteins in your body and a component of more than 200 different enzymes. In fact, zinc is involved in more enzymatic reactions in your body than any other mineral.
Zinc increases your production of white blood cells and helps them fight infection more effectively. It also helps your immune system release more antibodies. If your body has inadequate zinc stores, you will experience increased susceptibility to a variety of infectious agents, as your white blood cells simply can't function without zinc.
Zinc affects multiple aspects of your immune system, including neutrophils, natural killer (NK) cells, phagocytosis, cytokine production and even gene regulation within your lymphocytes.
Zinc Lozenges May Cut Duration of a Cold
As with other nutrients, your best bet is to make sure you're getting enough zinc in your diet year-round. However, if a cold strikes, you could use zinc lozenges. A meta-analysis 24 of seven randomized trials published in 2017 concluded people taking zinc lozenges shortened the duration of their colds by 33 percent on average.
Zinc acetate may be slightly better than zinc gluconate, although the difference was not considered significant. A third form is zinc citrate. It's advantageous to take a supplement with a variety of forms, if possible. Zinc sulfate is one of the inorganic forms of zinc and can cause stomach irritation, so I don't recommend using this form. According to this study:
"Five trials used zinc doses of 80 to 92 mg/day, common cold duration was reduced by 33 percent, and two trials used zinc doses of 192 to 207 mg/day and found an effect of 35 percent. The difference between the high-dose and low-dose zinc trials was not significant …"
Beta-Glucans Protect Against Flu by Boosting Natural Killer Cells
Beta-glucan is a polysaccharide known for its immune-boosting and cancer-fighting activities. Mushrooms such as shiitake , maitake and oyster mushrooms are a good source. 25 Importantly, beta-glucans enhance NK cell activity and function, 26 and recent research 27 , 28 shows that if you have enough NK cells in your system, you will not contract influenza.
As reported by Live Science, 29 a specific gene called KLRD1 "could serve as a proxy for a person's levels of natural killer cells." KLRD1 is a receptor gene found on the surface of NK cells, and the level of KLRD1 found in a person's blood prior to exposure to the influenza virus was able to predict whether that individual would contract the flu with 86 percent accuracy.
According to senior study author Purvesh Khatri, associate professor of medicine and biomedical data science at Stanford University School of Medicine, KLRD1 is "the first biomarker that shows susceptibility to influenza, across multiple strains." 30 As reported by Eurekalert: 31
"[O]n the whole, those whose immune cells consisted of 10 to 13 percent natural killers [NK cells] did not succumb to the flu, whereas those whose natural killer cells fell short of 10 percent wound up ill.
It's a fine line, Khatri said, but the distinction between the groups is quite clear: Everyone who had 10 percent or more natural killer cells stood strong against the infection and showed no symptoms. Khatri said his findings could help health professionals understand who's at the highest risk for flu infection."
Beta-Glucans — Powerful Cold and Flu Prevention
A number of studies have confirmed beta-glucans offer powerful protection against cold and flu, including the following.
- A 2013 study 32 found that taking 900 mg of beta-glucans in the form of brewer's yeast for 16 weeks reduced the rate of cold infections by 25 percent, and eased symptoms in those who got ill by 15 percent
- Marathon runners who took 250 mg of brewer's yeast for 28 days following a marathon were 37 percent less likely to contract a cold or flu compared to those taking a placebo 33
- People who took 250 mg of a beta-glucan product called Wellmune WGP per day for 90 days reported 43 fewer days with symptoms of upper respiratory tract infection compared to those taking a placebo 34
- A 2015 animal study 35 found feeding mice beta-glucans for two weeks "significantly reduced the effects of influenza infection in total mortality." According to the authors, "these effects are caused by stimulation of both cellular and humoral immune reaction resulting in lower viral load"
Get Your Z's
The importance of sleep also should not be underrated. Studies show that not getting enough sleep (which for most adults is around eight hours per night) will quickly decrease your immune function, leaving your system wide-open for environmental influences, including cold and flu viruses.
Missing as little as just one hour of sleep per night increases the expression of genes associated with inflammation, immune excitability, diabetes, cancer and stress. 36
An interesting animal study 37 published in 2012 found that the circadian clocks of mice control an essential immune system gene that helps their bodies sense and ward off bacteria and viruses. When the level of that particular gene, called toll-like receptor 9 (TLR9), was at its highest, the mice were better able to withstand infections. As noted by lead author Dr. Erol Fikrig from Yale University School of Medicine:
"These findings not only unveil a novel, direct molecular link between circadian rhythms and the immune system, but also open a new paradigm in the biology of the overall immune response with important implications for the prevention and treatment of disease."
Optimizing Your Immune Function Can Keep You Healthy This Winter
As you can see, there are simple ways to dramatically reduce your risk of cold and flu this winter. Ideally, optimize your vitamin D level and make sure you're getting enough zinc and vitamin C in your diet on a daily basis. This will lay the groundwork for healthy immune function.
To further boost your immune function in preparation for cold and flu season, you may want to consider a beta-glucan supplement. And, should a cold or flu strike, you may significantly cut its duration and severity using either high-dose vitamin C or D (or a combination of both, short-term) and/or zinc lozenges. Fiber, a source of prebiotics, and sleep are also important factors, both for the prevention of cold and flu, and during the treatment of these infections.
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