At InsideTracker, we've always been here to provide you with science-based guidance and the essential truths about your blood and genetic biomarkers—and now is no different. We noticed an influx of misinformation spreading about immunity and respiratory infections like COVID-19, and it's times like these when we feel we have a role to fill. Respiratory infections (also called respiratory tract infections) affect the sinuses, throat, airways or lungs, and include a range of illnesses from pneumonia to the common cold. Your immune system is a complicated network of cells, tissues, and organs that work together to protect your body on a daily basis from infections like these.
Research shows that certain supplements may reduce your risk of infection and the severity of your symptoms. In this blog, we clarify and recommend scientifically-proven supplement remedies that may safely support your immune system. As always, consult a medical doctor before taking any nutritional supplements that we recommend. If you have or suspect a medical condition, or are taking any medications, please consult a doctor before acting on any of our recommendations.
Fermented foods and probiotics can have anti-inflammatory and anti-pathogenic effectsYour gut contains a rich community of healthy microbes that compete against invading pathogens, acting as your body’s first defense against infection. They also digest nutrients that you otherwise couldn’t (like fiber and other carbohydrates) in a process called fermentation, which results in byproducts that play many important roles in the body from protecting the colon to improving insulin sensitivity.
Research, especially of late, has found that your microbiome is a key component of a healthy immune system and your body’s ability to fight off viral and bacterial infections. Both probiotic supplements and fermented foods—which are sources of live microbes—can significantly reduce your risk of infection by fighting pathogens in the gut and contributing to anti-inflammatory pathways around the body.
But certain strains contribute stronger anti-infection and anti-inflammation effects than others—Lactobacillus plantarum, Bifidobacterium lactis, Lactobacillus casei, and Lactobacillus rhamnosus (also known as Lactobasciullus GG) are all the best warriors against viral infections, particularly in the upper respiratory tract.[1-4]
Takeaway: First, if you’re considering taking a probiotic supplement, look for one that lists two or more of the above strains. Bottles that acknowledge immunity or inflammation on the label are the ones likely to contain them, but always take the time to look at the ingredient list. Second, your diet is an important tool for nurturing a healthy microbiome. Fermented foods like kefir and kimchi can directly plant healthy microbes in your gut, and foods rich in fiber like beans and cruciferous vegetables help them to thrive once they’ve found their home.
Zinc makes an infection less severe—but common supplements exceed a safe limit of intakeZinc plays an important role in immunity, as it's involved in your body's cell-mediated and humoral immune responses (two types of immunity where a specific immune response is generated for a particular pathogen). Low or deficient levels of zinc, therefore, profoundly affect the number of your immune cells that are available to fight an invader. After examining 13 randomized placebo-controlled studies between zinc and the common cold, researchers found that taking zinc within 24 hours of the first signs of cold could shorten its duration and make the symptoms less severe.
Men and women need 11mg and 8mg of zinc per day, respectively. It's found primarily in red meats and seafood, especially oysters and mollusks. Zinc is also found in plant sources like whole grains and legumes, but in much lower quantities and with lower absorption than that from animal products. Vegetarians and the elderly, therefore, are at particular risk for insufficient zinc intake from diet alone.
While it is important to meet your zinc needs, it's equally as important to not go overboard. The maximum amount of zinc you should take in a day is 40mg— known as the Tolerable Upper Intake Level established by the Food and Nutrition Board. Intakes above 40mg can cause copper deficiency and neurological problems.[6,20] Most supplements and zinc-based cold remedies offer levels above this upper limit, so be diligent about which bottles you choose from the shelf.
Takeaway: If you have trouble meeting your daily zinc needs or if you feel the signs of a cold coming on, take 25mg of zinc per day. Most supplements come as 50mg, so split the dosage in two before taking it. Zinc supplements are best taken on an empty stomach.
Vitamin C's reputation for immune support is justified—but more is worse, not betterWe can’t talk about immunity without addressing vitamin C. Like zinc, vitamin C is an essential micronutrient that we must obtain from our diets. It plays an important role in immunity by acting as an antioxidant, enhancing immune cell function and supporting anti-inflammatory pathways in the body. A vitamin C deficiency can therefore lead to impaired immune function and a higher susceptibility to infections. This review looked at hundreds of studies examining vitamin C’s role in immunity. The researcher concluded that supplementing with vitamin C at around 100-200mg per day may prevent respiratory infections.
A typical Airborne packet or supplement has around 1,000mg of vitamin C! And what’s more, the absorption of vitamin C decreases with increased intake. For example, only 16% is absorbed at high intakes (~1,200mg) but up to 98% is absorbed at low intakes (<20mg). Once you hit 1,000mg, approximately less than 50% of the vitamin C you consume will be absorbed—and the rest will just be excreted in the urine. Therefore, vitamin C is best taken in two to three smaller doses with meals. Toxicity of vitamin C is unusual, but adverse effects may increase if you supplement above the Tolerable Upper Intake Level (2,000mg per day) in the long-term.
Vitamin C is most abundant in fresh, whole foods like pineapple, kiwi, and broccoli. And the lack of fresh produce in the typical U.S. diet (among other reasons) has caused vitamin C deficiency to be one of the leading nutrient deficiencies in the country. As a water soluble vitamin, vitamin C is never stored in the body. We, therefore, must focus on eating vitamin C-rich foods every day to meet our needs.
Takeaway: Adequate intake of vitamin C is imperative for proper immune function. If you’re worried about not reaching sufficient amounts in your diet, take two to three smaller doses (200mg) of the vitamin each day.
Vitamin D supplementation can protect your respiratory tractStudies show that people with optimal vitamin D concentrations are less likely to experience the common cold and other respiratory tract infections than those with low vitamin D. In a systematic review of randomized control trials (the gold standard of tests), vitamin D supplementation appeared to protect individuals from acute respiratory tract infections (aka the common cold). This was especially true for people who started out deficient in vitamin D from the onset. Furthermore, upper respiratory tract infections were found to be inversely associated with serum (blood) levels of vitamin D—that is, as your levels go down, your chance of infection goes up. InsideTracker recommends serum vitamin D levels remain above 32 ng/mL for optimal health.
Takeaway: Optimal vitamin D levels may be protective against respiratory infections. Aim for an intake of 1,000 IU of vitamin D daily.
Ginseng can improve respiratory symptoms in the elderlyGinseng is a root with potent antioxidant effects that contributes to reduced inflammation, supported immunity, and other health benefits. Multiple studies have shown ginseng’s positive effects on the common cold and respiratory tract infections. In a systematic review looking at multitude studies, researchers concluded that ginseng extract reduced the duration of the common cold. The same results were replicated in a double-blind randomized control trial where subjects were given ginseng extract over a period of four months. Of particular relevance, ginseng reduced the risk and duration of respiratory symptoms in an elderly population by 48 and 55%, respectively.
Takeaway: Ginseng could be especially helpful for the elderly. It's most effective when taken within a two-hour window of a meal. Aim for 2,000mg of ginseng extract daily.
Garlic can activate immunity-related genes and lower your likelihood of getting sickGarlic has been used by many different cultures to fight infectious diseases as it has antimicrobial, antifungal and antiviral properties. Modern studies have shown that incorporating garlic into your diet may actually activate immunity genes and reduce the severity and incidence of a cold. In a double-blind randomized control trial, subjects were given a garlic supplement or a placebo over 12 weeks between November and February (peak cold and flu season). The treatment group presented with fewer colds and recovered quicker compared to the placebo group.
In a similar study design, after 45 days of supplementing with garlic, participants presented with significantly improved function of NK and T-cells (both of which are involved in immune function) compared to the placebo group. After 90 days, the garlic group also had fewer cold symptoms, sick days, and incidences of colds compared to the placebo group. Lastly, another study found that adding raw garlic to meals helped to activate genes related to immunity.
Takeaway: Garlic may activate immunity-related genes and reduce the likelihood of getting sick in the first place. Add a raw garlic clove to your meals or supplement with two 500mg doses. Take one pill after breakfast and the other one after dinner.
The research is out on elderberry and echinacea
- Elderberry syrup has recently entered the spotlight as a natural way to support immune system. The flowers and berries of the Sambucus nigra species have been the most studied and used in teas, syrups and gummies. To date, only a handful of small scale studies (about four) have been conducted. While the outcomes were positive—elderberry supplementation can lessen the duration and severity of upper respiratory symptoms—the quantities used differed by study. For example, one had participants take 300mg of elderberry extract while another provided 60mL of elderberry syrup for five straight days. Sambucol, one of the most popular commercially-available elderberry syrups, has 3.8mg of elderberry for one recommended serving (10mL)—and and a whopping 8g of sugar. Even when taken four times a day (as suggested for “intensive use” purposes), this still wouldn't reach clinically-tested levels—plus provides roughly the amount of sugar in two Hershey's bars!
Now a quick word on echinacea. In a meta analysis examining 24 randomized controlled trials, researchers concluded that “echinacea products have not been shown to provide benefits for treating colds.” Furthermore, a study made headlines in 2003 when researchers tested 59 different echinacea supplements available on the market. They found that only 52% met the quantities of echinacea listed on the supplement label and 10% contained no echinacea at all!
Takeaway: Given the lack of studies examining elderberry and the inconclusive results for echinacea, we do not recommend taking either to treat colds or to support immune function at this time.
So, which supplements are proven to support the immune system?In closing, researchers examined the effectiveness of each supplement in combating colds, the flu, upper respiratory infections, and other related symptoms, and the results were unanimous: taken daily, the following supplements were associated with a reduced risk of infection, duration of infection, and severity of symptoms. Each supplement offers unique properties that may support the immune system.
- Vitamin C
- Vitamin D
It's always important to remember that the supplement industry isn't regulated, so the onus is on you as the consumer to choose a reputable product that's backed by science. Hopefully this recap helps you choose wisely and arm yourself against winter's worries and woes, and place you in the best position to protect yourself from contracting and suffering from COVID-19.
Diana Licalzi, MS, RD
- Diana is a Content Strategist and Team Nutritionist at InsideTracker. As a Registered Dietitian and self-proclaimed "biohacker," Diana enjoys researching and testing the latest trends and technology in the field of nutrition and aging. You'll often find Diana completing a 24-hour fast, conducting self experiments, or uncovering strategies to increase longevity. Follow her on Instagram at @dietitian.diana.
 19747410 Consumption of a fermented dairy product containing the probiotic Lactobacillus casei DN-114001 reduces the duration of respiratory infections in the elderly in a randomised controlled trial. https://www.ncbi.nlm.nih.gov/pubmed/19747410
 20803023 Randomised, double-blind and placebo-controlled study using new probiotic lactobacilli for strengthening the body immune defence against viral infections. https://www.ncbi.nlm.nih.gov/pubmed/20803023
 23020819 Effect of Lactobacillus rhamnosus LGG® and Bifidobacterium animalis ssp. lactis BB-12® on health-related quality of life in college students affected by upper respiratory infections. https://www.ncbi.nlm.nih.gov/pubmed/23020819
 25927096 Probiotics for preventing acute upper respiratory tract infections. https://www.ncbi.nlm.nih.gov/pubmed/25927096
 Groff. Advanced Nutrition and Human Metabolism. Australia: Wadsworth/Cengage Learning, 2009. Print.