Preparing for Cold and Flu Season

As if protecting your health in the year 2020 hasn’t been tough enough, cold and flu season is rapidly approaching. While it is possible to catch a cold or flu virus at any time of the year, cases tend to rise rapidly in October, peak around December, and continue to be seen frequently until around May [1]. Unfortunately, there are still no true “cures” for colds or flu, so our best offense is a good defense. Fortunately, there are lots of things we can do to help protect ourselves from getting really sick this flu season. When possible, we can physically protect ourselves from exposure. When we do come into contact with a virus, a strong immune system can fight off invaders before they cause damage and symptoms. 

Here we have provided some valuable information about building and maintaining a healthy immune system so you may have a preparedness plan in place before the onset of flu season.

Avoiding Exposure

All the practice we’ve had social distancing is going to benefit our bodies during cold and flu season. Some viruses can travel through the air and some survive for long periods of time on surfaces. So, maintain as much distance as you can between your body and anyone who may be sick, spend your time in well-ventilated places when possible, and try not to touch surfaces touched often by strangers (think public door handles, water fountains, and countertops). If you do touch something in public, be sure to wash your hands well with soap before touching your mouth, nose, eyes, or any other orifice on your body. Any place your skin opens is a fast-track highway for viruses to get where they need to go to cause illness. This is why wearing a mask is smart; not only do they create a barrier between your nose and mouth and the surrounding environment, they also provide a barrier for viruses leaving someone else’s body through breath, spittle, or mucus from a sneeze.

Strengthening the Immune System

Because the virions of a virus are too small to see, we have to assume they are everywhere and act accordingly. Your body has 2 lines of defense against pathogens: the innate immune system and the adaptive immune system. Each of them can be strengthened with good nutrition and healthy lifestyle choices. 

Innate Immune System

The innate immune system is a nonspecific defense system and protects against any intruder. First, the skin, hair (eyelashes, nose hair, etc.), and mucous membranes provide a physical barrier against anything that tries to enter orifices. Chemical defenses like stomach acid and enzymes in tears, saliva, and on the skin are enough to break down some invaders. Then there are non-specific inflammatory cell types that are sent to the site of infection to trap and break down possible pathogens before they can multiply inside the body. Inflammation is also an innate immune response, and the associated heat and swelling are caused by a widening of blood vessels to bring more immune cells to the site of infection. This is why, rather than constantly turning to anti-inflammatories, we try to promote balanced, natural inflammatory responses in the body through proper nutrition: in certain cases, inflammation is a good thing.

Adaptive Immune System

The body’s second line of defense is called the adaptive immune system. It is secondary to the innate because it takes much longer to respond. As its name suggests, the “adaptive” immune system changes in response to exposure by developing specific antibodies. When a new pathogen enters the system, only the innate system can work to kill it, but if that same pathogen enters the body again in the future, it is immediately recognized as an unwelcome intruder due to the antibodies built in response to the first exposure. Antibodies are like a big red flag attached to the pathogen that signals “all hands on deck” to get rid of it fast. Vaccines work by introducing the body to a small dose or a dead version of a particular pathogen so that the body can build antibodies against it without having to fight a true, more dangerous infection.

Gut Health and the Immune System

The gut is an important barrier between the circulation and anything ingested. Therefore, the types of microorganisms living in the gut can have an effect on whether pathogens can invade via intestinal absorption to multiply in the body. “Probiotics” are yeasts or bacterial species that benefit the human host when their populations dominate the available adhesion sites in the gastrointestinal tract. Beneficial strains of probiotics have both direct and indirect immunomodulatory properties. Probiotics can increase the activity of macrophages and natural killer cells, they can modulate the secretion of antibodies or peptide cell signals called cytokines, they enhance the gut epithelial barrier, support healthy levels of mucus secretion, and contribute to the competitive exclusion of other, pathogenic bacteria [2].

When the health of your gut is compromised, not only can unwanted pathogens move into the bloodstream more freely, but your body may also have trouble digesting and absorbing the micronutrients (vitamins and minerals) needed to properly fight back. Restoring health to the gut is a first step in supporting your immune system and overall health. Taking a daily probiotic supplement can help restore balance to the microbiome. Eating plenty of prebiotic fiber feeds the beneficial microbial species and can optimize the transit time of digested material for maximized nutrient absorption.

Nutrition for Immunity

Antioxidants are a great start for optimizing your health as we enter cold and flu season. Antioxidants not only clear out the free radicals that cause oxidative damage to cells, but they can also help rebuild and repair the damage that has been previously caused. If your cells aren’t busy fighting oxidative stress, they will be better prepared to fend off viral invasion. You can get a diverse and plentiful dose of antioxidants by eating a rainbow of brightly colored fruits and vegetables. For example, berries (blueberries, raspberries, goji berries) are a highly concentrated source of antioxidants, dark green veggies like spinach and kale, tomatoes, eggplant, pumpkin, and mangoes all contain complementary types of antioxidants that fight and repair oxidative damage in different ways. 

Vitamin A is a fat-soluble antioxidant vitamin. In terms of the innate immune system, it contributes to the integrity of mucosal membranes, especially in the eyes, respiratory tract, and gut [3]. It is also associated with the activity of macrophages, T cells, lymphocytes, and natural killer cells, as well as a healthy inflammatory response during infection [3]. Vitamin A is also integral to the adaptive immune system, as antibody-mediated immunity is strongly impaired in cases of vitamin A deficiency [3]. As such, those with healthy vitamin A levels at the time of vaccination often show better antibody production in response to a vaccine [3]. This nutrient is one to be watchful when supplementing because chronically taking too much vitamin A can be difficult for the liver to process. 

B Vitamins. Clinical studies have demonstrated that vitamin B-6 deficiency impairs lymphocyte maturation and growth, antibody production, and T cell activity [3]. Folate (vitamin B-9) deficiency has been shown to negatively impact immunity and reduce resistance to infections by reducing the number of circulating T lymphocytes produced in response to a pathogen [3]. B-12 is required for folate metabolism, and so can cause a secondary folate deficiency if levels are low. B-12 is also a modulatory agent for cellular immunity and contributes to lymphocyte production and natural killer cell activity [3]. B vitamins are water-soluble, which means your body will flush out excess dietary B vitamins it does not need. High doses of B vitamins are safe and often needed to effectively increase circulating levels and correct problems created by insufficiencies [4]. 

Vitamin C is a particularly powerful antioxidant and cold fighter. As an essential micronutrient, you must get vitamin C from your diet or supplements to prevent disease, and a fairly high dose can be especially helpful come cold and flu season. It has been shown to reduce the risk of catching a cold, shorten the duration, and reduce the severity of a cold if you do catch one [5]. Vitamin C is also a required cofactor for the movement of neutrophils (white blood cells/part of the innate immune system) to an infection site, and for the engulfment and breakdown of pathogens [6]. It also participates in pathways that protect tissue from excessive damage by supporting the breakdown and removal of spent immune cells once they have finished their job [6]. The more invaders present, the more vitamin C your body needs to fight them.

Vitamin D is another micronutrient that has been extensively studied for its cold-fighting properties [7]. While vitamin D is not technically essential if you are getting proper sun exposure, today’s typical mostly-indoor lifestyles and sun protection measures mean that many people are making insufficient amounts of this important vitamin. Vitamin D supplements cannot prevent the common cold, but they have been shown to reduce the risk of more serious acute respiratory tract infections [7]. While the underlying mechanisms of this effect are not completely understood, studies have shown that vitamin D stimulates the innate immune system to produce antimicrobial peptides, and induces autophagy (clearing out damaged cells) in response to both bacterial and viral infections [7]. Almost all cells in the immune system (except B cells) have vitamin D receptors, providing evidence that vitamin D is an important mediator of immune response [3]. Vitamin D intake may be especially important in a year where the most worrisome viral threat is closely linked with respiratory infection.

Immune systems tend to degrade overall as we age. Vitamin E, specifically, has been studied extensively in the context of the immune system. It has been demonstrated to have an overall positive effect on the immune system of the elderly through multiple mechanisms [3]. Vitamin E is another strong, fat-soluble antioxidant, meaning its antioxidant activities take place in lipid-based structures such as cell membranes and fat storage compartments. Lipid peroxidation by free radicals is known to be immunosuppressive, and vitamin E can fight and reverse some of this damage, contributing to the strength of the immune system [3]. Supplementation with vitamin E has also been associated with increases in lymphocyte proliferation, and both the production and activity of killer cells and macrophages [3].

Trace Elements

Zinccontaining supplements have gained in popularity over the last couple of decades as more evidence accumulates on its power as an immune booster. It has a complex role in the immune system as it has both direct effects on innate and adaptive immune functions and acts as a cofactor for more than 300 enzymes [8]. Zinc is essential for DNA synthesis and cell proliferation, so any new immune cells created in response to infection are dependent on zinc. Zinc is involved in antioxidant defense in the cytosol (the inner cellular space) and helps to maintain skin and mucosal membrane integrity [3]. Unbound zinc ions have even demonstrated a direct antiviral effect on rhinovirus replication (cause of the common cold) [3]. Zinc supplementation increases cellular components of innate immunity, antibody responses, and the numbers of cytotoxic cells [3]. 

Selenium is another essential mineral that has an influence on both the innate and adaptive immune systems. Selenium participates in glutathione (GSH) antioxidant activity and is especially important for cellular protection from inflammatory events [3]. Selenium deficiency decreases immunoglobulin and negatively impacts cell-mediated immunity, but can be rescued with supplementation [3].


Metabolic Maintenance offers many of the above-mentioned nutrients as either standalone supplements or in multivitamin/mineral formulas. Taking a daily multivitamin/mineral such as Basic Maintenance®️ or FemOneTM helps to fill any nutritional gaps in your diet that may be compromising the efficacy of your immune system. Metabolic Maintenance also offers BioMaintenanceTM products, a high-quality, shelf-stable probiotic blend and a prebiotic fiber supplement to nurture your gut health and optimize your nutrient absorption.

If you are worried about increased pathogenic exposure (air travel, returning to in-person work or school etc.), Acute Immune Boost may be a smart choice. Acute Immune Boost provides generous doses of vitamins A, C, D, and zinc, alongside N-Acetyl-L-Cysteine (NAC) and research-supported herbal extracts of Sambucus (elderberry) and Andrographis.  N-Acetyl-L-Cysteine (NAC) has a protective effect over the strength of the immune system, especially in the aging population, and may aid in shortening the duration of respiratory tract/bronchial infections [9,10]. When colds lead to excess mucus formation, NAC may help to thin mucus for easier expectoration. Elderberry has been scientifically linked to a significant reduction in the duration and severity of colds and flu-like symptoms [11]. There may also be preventative benefits to taking elderberry. One study noted a significant reduction in both the severity and duration in colds in those who supplemented with elderberry before and during air travel, compared to a placebo group [11]. Elderberries also contain a variety of nutrients ranging from various vitamins (A, B1, B2, B6, B9, C, and E), trace elements (such as Cu, Zn, and Fe), minerals (such as K, Ca, and Mg), and antioxidant phytochemicals (such as carotenoids, phytosterols, and polyphenols). Andrographis has traditionally been used in Chinese herbal medicine and ayurvedic medicine as an antipyretic (fever reducer) and for relief from the severity and duration of common colds, coughs, and sore throats [12]. Studies have shown that Andrographis also expresses direct antiviral activities [12]. For additional information on nutrients that may support the immune response, consult with your healthcare practitioner, and visit the Institute for Functional Medicine resources.


In a world that glorifies being busy, sometimes rest and good sleep feels like a guilty pleasure. But sleep is not a luxury, it is a basic necessity, especially for your immune system. Cytokines, the molecules that target infection and inflammation in an appropriate immune response, are both made and released during sleep [13]. Chronic sleep loss even makes the flu vaccine less effective by reducing your body’s ability to respond [13]. Aiming for eight hours of sleep each night will not only help keep your immune system in optimal shape, but it can also help protect you from health issues such as heart disease, diabetes, and obesity [13]. If you have trouble going to sleep or staying asleep, supplements containing melatonin (a naturally-produced sleep hormone) may help prepare your brain for rest and allow you to wake up in the morning without grogginess. Magnesium and GABA are two other nutrients that may help your brain and body settle and calm after a busy day. Check out Metabolic Maintenance’s R.E.M. MaintenanceTM sleep support supplement if your sleep patterns are standing between you and a stronger immune system.


Daily exercise is great for keeping your body trim and strong, but it also benefits your mental health and your immune response, lowering your risk of illness and chronic inflammation [14].

When you exercise, it increases blood and lymph flow, circulating immune cells around the body at a higher rate. This means specialized immune cells such as natural killer cells and T cells are more likely to quickly find and kill any invading pathogens. A 45-minute brisk walk, for example, has been shown to cause an increase in immune cells floating around the body for up to three hours afterward [14]. Repeating this activity every day only strengthens the benefits.

The risk of upper respiratory tract infection, specifically, is lower in physically fit and active adults [14]. A 2011 study showed that those who did aerobic exercise five or more days of the week experienced 40% fewer viral upper respiratory tract infections during the 12-week study [15].

With many gyms and group classes closed due to social distance restrictions, it may be tempting to take a break from your exercise routine. Remember that a brisk walk is free and can be done without driving to a gym. But you don’t even have to leave the house to exercise! There are many forms of exercise instruction available for free online. Some can be done in spaces as small as a yoga mat footprint and many require no equipment at all. 


  1. CDC. “The Flu Season”. Centers for Disease Control and Prevention, National Center for Immunization and Respiratory Diseases (NCIRD). Accessed September 11, 2020.
  2. La Fata, Giorgio, Peter Weber, and M. Hasan Mohajeri. “Probiotics and the gut immune system: indirect regulation.” Probiotics and antimicrobial proteins 10.1 (2018): 11-21.
  3. Maggini, Silvia, et al. “Selected vitamins and trace elements support immune function by strengthening epithelial barriers and cellular and humoral immune responses.” British Journal of Nutrition 98.S1 (2007): S29-S35.
  4. Ford, Talitha C., et al. “The effect of a high-dose vitamin b multivitamin supplement on the relationship between brain metabolism and blood biomarkers of oxidative stress: a randomized control trial.” Nutrients 10.12 (2018): 1860.
  5. Hemilä, Harri, and Elizabeth Chalker. “Vitamin C for preventing and treating the common cold.” Cochrane database of systematic reviews 1 (2013).
  6. Carr, Anitra C., and Silvia Maggini. “Vitamin C and immune function.” Nutrients 9.11 (2017): 1211.
  7. Martineau, Adrian R., et al. “Vitamin D supplementation to prevent acute respiratory tract infections: systematic review and meta-analysis of individual participant data.” bmj 356 (2017).
  8. Rink, Lothar. “Zinc and the immune system.” Proceedings of the Nutrition Society 59.4 (2000): 541-552.
  9. National Center for Biotechnology Information. PubChem Compound Database; CID=445354, (accessed Oct. 19, 2018).
  10. Tiralongo, Evelin, Shirley S. Wee, and Rodney A. Lea. “Elderberry supplementation reduces cold duration and symptoms in air-travellers: A randomized, double-blind placebo-controlled clinical trial.” Nutrients 8.4 (2016): 182.
  11. Krawitz, Christian, et al. “Inhibitory activity of a standardized elderberry liquid extract against clinically-relevant human respiratory bacterial pathogens and influenza A and B viruses.” BMC complementary and alternative medicine 11.1 (2011): 16.
  12. Hu, Xiao-Yang, et al. “Andrographis paniculata (Chuān Xīn Lián) for symptomatic relief of acute respiratory tract infections in adults and children: A systematic review and meta-analysis.” PloS one 12.8 (2017): e0181780.
  13. National Sleep Foundation. “How Sleep Affects Your Immunity.” July 28, 2020.
  14. Nieman, David C., and Laurel M. Wentz. “The compelling link between physical activity and the body’s defense system.” Journal of sport and health science 8.3 (2019): 201-217.
  15. Nieman, David C., et al. “Upper respiratory tract infection is reduced in physically fit and active adults.” British Journal of Sports Medicine 45.12 (2011): 987-992.