How to boost your immune system for cold and flu season?

Summer is definitely over and not only the cool down reminds us that autumn has arrived. This time of the year brings colorful landscapes but also morning fog, rainy, windy and variable weather. More frequent temperature changes during the day could also cause health problems, such as colds or other infectious respiratory diseases. A balanced and nutritionally rich diet, enough quality sleep and regular physical activity are essential for supporting the immune system. But if we want to support our body in case of cold, cough or flu, it’s also good to focus on immune booster nutrients. We will introduce the most suitable supplements that may help you fight against infections or colds in this article.

What will you learn from this article?

1. What Is Our Immune System Made Of?
2. Lifestyle Factors That Weaken Immunity
3. How Lifestyle Supports Immunity
4. Vitamin C
5. Vitamin D
6. Zinc
7. Beta-glucans
8. Other Important Nutrients for Immunity
9. Key Takeaways

What Is Our Immune System Made Of?

The immune system protects the body against invading microorganisms such as bacteria, viruses or fungi. It is made up of two parts that work together.

Innate immunity is the body's oldest and fastest line of defence, present from birth. It includes phagocytes that engulf pathogens, opsonins that mark pathogens for destruction, and natural killer cells, together with the physical and chemical barrier provided by the skin and mucous membranes. It reacts within hours, but it does not distinguish between different types of pathogens.

Adaptive immunity develops throughout life and reacts more slowly, usually within 3 to 5 days, but it is highly specific to individual pathogens. Its main actors are B-lymphocytes, which produce antibodies (immunoglobulins), and T-lymphocytes, which support antibody production and release signalling molecules called cytokines. Adaptive immunity also "remembers" pathogens it has already met, so the next response to the same pathogen is faster.

Factors such as the method of birth, how long a baby was breastfed, and the environment in early childhood also play a role in shaping immune defences for the rest of life.

Lifestyle Factors That Weaken Immunity

A number of everyday factors can gradually weaken the immune system:

• a diet low in nutrients, or high in simple sugars, ultra-processed foods and artificial additives
• overuse of antibiotics and other medicines
• excess body weight
• lack of physical activity
• a polluted environment and smoking
• excessive hygiene and cleaning at home
• long-term elevated cortisol linked to chronic stress

A weakened immune system often shows up as frequent colds, irritability, slow-healing wounds, digestive problems, or skin rashes. These are usually the body's first signals that its defences are out of balance, and it is worth responding to them with changes in diet and lifestyle.

How Lifestyle Supports Immunity

Gut health: an estimated 80% of the immune system is located in the gut. The intestinal lining acts as a barrier that lets nutrients through while keeping out harmful substances. A diet high in ultra-processed food and chronic stress can damage this barrier and trigger inflammation, which in turn can let harmful molecules through more easily.

Regular movement and exercise: physical activity helps lower stress hormone levels and chronic inflammation in the body, and some research suggests it also supports the production of antibodies and white blood cells.

Melatonin and sleep: this hormone regulates the sleep-wake cycle and also supports immune function. Its production depends on darkness and is disrupted by blue light in the evening; levels typically peak between 10 p.m. and 6 a.m., which is one reason quality sleep matters for immunity.

Vitamin C

Vitamin C is probably one of the most popular supplements used during periods of increased physical or mental stress. It plays an important role in the immune system. It supports the functions of innate and acquired immunity cells and is also highly concentrated in the skin - our first barrier that prevents the entry of pathogens into our body. White blood cells (leukocytes), involved in the functioning of the immune system, also protect their cellular structure by accumulating a higher amount of vitamin C, which provides them a protection against oxidative damage. Vitamin C is one of the most important antioxidants that help us fight free radicals. An excessive amount of free radicals (generated both endogenously during normal cellular metabolism as well as those from the external environment) contributes to oxidative stress. Oxidative stress negatively affects immunity and a disturbed immune system is more susceptible to various viral or bacterial infections. On the other hand, an already ongoing infection reduces our level of vitamin C because of the increased inflammatory response of the body and higher metabolic demands.

To conclude, vitamin C supplementation can be effective both in the prevention and in the treatment of respiratory infectious diseases. Scientific articles point to the fact that vitamin C supplementation in doses of at least 200 mg per day can reduce the duration and severity of respiratory infections, including the common cold.

Our body cannot produce vitamin C on its own and is therefore dependent on its intake from external sources. Vitamin C is a water soluble vitamin which means that our body does not have a storage capacity for it. That is why we need to ensure its regular and adequate intake. Foods rich in vitamin C include, for example, red pepper, kiwi, rose hips, sea buckthorn, acerola or broccoli and Brussels sprouts. Vitamin C lacks thermostability and is destroyed at higher temperatures. That is why it is better to consume raw foods rich in vitamin C or choose gentle preparation techniques.

You can read more about vitamin C, its functions and health benefits in a seperate article. Another article gives you more tips on how to increase the intake of vitamin C from your diet and advises what are other vitamin C food sources.

Vitamin D

Vitamin D is a fat-soluble vitamin that is crucial for the healthy functioning of the immune system. Most cells in the body contain a vitamin D receptor, which also points to its importance. Vitamin D is involved in the correct cell differentiation, enhances the pathogen-fighting effects of white blood cells and decreases inflammation. Long-term vitamin D deficiency is associated with a higher susceptibility to acute respiratory infections, including flu. The negative effects of vitamin D deficiency were even more emphasized during Covid-19 pandemic. Some studies show that vitamin D reduces the risk of infectious diseases of the respiratory tract. For example, in 2019, 25 randomized studies were assessed and data from almost 11,000 participants were examined. The evaluation of these studies confirmed that vitamin D supplementation helps protect against the development of acute respiratory diseases.

In the summer, vitamin D is obtained naturally by skin exposure to the sun. However, vitamin D synthesis from sunlight also contains limiting factors such as the time of sun exposure or the wavelengths of ultraviolet radiation. In winter, vitamin D can be obtained from certain foods such as fatty fish or some mushrooms*. Unfortunately, the majority of people consume these vitamin D food sources only occasionally. That is why we often suffer vitamin D deficiency during winter and it is definitely desirable to focus more on its supplementation.

*Mushrooms contain vitamin D only under certain conditions. Vitamin D content in mushrooms always depends on a number of factors like climatic conditions, level of UV radiation, type and color of the mushroom, etc. Wild mushrooms growing with access to natural sunlight have the highest vitamin D content. If someone wants to consume mushrooms as a significant source of vitamin D2, it would be needed to dry them in the sun (ideally during August or the first week of September) or irradiate them with a special UVB lamp. However, specific mushrooms that are grown for increasing vitamin D content are to be found on the market. The controlled process uses UV radiation under precisely defined conditions and vitamin D content in these mushrooms is around 7 µg/100 g of a fresh mushroom.

It would be ideal to measure in the laboratory the level of vitamin D or 25-hydroxyvitamin D prior to determining the optimal supplementation dosage. 1000-2000 IU D3 per day is recommended as a maintenance dose. When supplementing vitamin D3, don't forget to use the synergistically acting vitamin K2.

You can read more information on how to choose a quality source of vitamin D and what are the differences between animal and plant sources in a seperate article.

Zinc

Zinc is another nutrient that is essential for healthy functioning of our immune system. We need it for proper immune cell development & communication and it plays an important role in regulating inflammatory response. Zinc can help our body fight bacteria and viruses and increase resistance to pathogens. It is also an important immunomodulator and significantly affects a balanced immune system. The essential endogenous antioxidant SOD (superoxide dismutase) that represents our body’s first line antioxidant defense also needs zinc for its proper functioning.

Some studies report that zinc deficiency affects around 2 billion people globally and is relatively common in older adults. Zinc deficiency symptoms can include higher susceptibility to infectious diseases, poor wound healing, white spots on the nails or poor hair quality. Decreased appetite and taste & smell loss represent other zinc deficiency signs.

Zinc deficiency affects the functioning of the immune system and leads to an increased risk of developing infectious diseases. Numerous studies reveal that zinc supplements may protect against respiratory infections including the common cold. It’s important to bear in mind that excessive long-term zinc supplementation may interfere with copper absorption. That is why our supplement contains zinc in combination with copper to maintain the balance of these two minerals in the body.

The richest source of zinc are oysters and other seafood. Zinc can also be found in meat, especially beef. Pumpkin seeds represent a good plant zinc source.

You can read more about zinc in our previous article “Zinc and immune system”.

Zinc chelated 15 mg + copper

Beta-glucans

Beta-glucans are natural polysaccharides found mainly in mushrooms, yeast, seaweed and cereals such as oats and barley. They are known as important immunomodulators, which means that they have the ability to modulate the immune system in the human body. In nature, beta-glucans occur in various configurations. It was found that beta-glucans with a basic chain of glucose molecules connected by a 1,3 bond and with a glucose side chain at position 1.6 have higher immune-enhancing effects.

The positive properties of beta-glucans primarily include immunity support as well as increase of the body's resistance to physical and mental stress. The beta-glucan’s effect on infectious respiratory tract diseases, such as colds and flu, was the subject of investigation. As shown in a 2013 double-blind, placebo-controlled, randomized study, (1.3)-(1.6) beta-glucan supplementation reduced symptoms of the common cold by 25% compared to placebo. The results of the study revealed that beta-glucans supplements increase the body's defense system and protects against infections.

If we want to support our immunity during the period of various infectious diseases and colds, it is certainly a good choice to include sources of beta-glucans in our diet. Mushrooms (for example, oyster and shiitake mushrooms) or oatmeal represent good dietary beta-glucan sources.

Other Important Nutrients for Immunity

Besides vitamin C, vitamin D, zinc and beta-glucans, several other nutrients contribute to the normal function of the immune system:

• Copper contributes to the normal function of the immune system, and alongside zinc it is part of the antioxidant enzyme superoxide dismutase (SOD).
• Iron contributes to the normal function of the immune system and to normal cognitive function.
• Selenium contributes to the normal function of the immune system and helps protect cells from oxidative stress.
• Magnesium contributes to normal psychological function and to the normal functioning of the nervous system, both of which also affect how well the body copes with stress.
• Vitamin B6 and vitamin B12 contribute to the normal function of the immune system.
• Vitamin E contributes to the protection of cells from oxidative stress.
• Vitamin A contributes to the normal function of the immune system.

Key Takeaways

Sources:

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Carr AC, Maggini S. Vitamin C and Immune Function. Nutrients. 2017 Nov 3;9(11):1211. doi: 10.3390/nu9111211. https://pmc.ncbi.nlm.nih.gov/articles/PMC5707683/

Martineau AR, Jolliffe DA, Greenberg L, et al. Vitamin D supplementation to prevent acute respiratory infections: individual participant data meta-analysis. Health Technol Assess. 2019 Jan;23(2):1-44. doi: 10.3310/hta23020. https://pmc.ncbi.nlm.nih.gov/articles/PMC6369419/

Wessels I, Maywald M, Rink L. Zinc as a Gatekeeper of Immune Function. Nutrients. 2017 Nov 25;9(12):1286. doi: 10.3390/nu9121286. https://pmc.ncbi.nlm.nih.gov/articles/PMC5748737/

Prasad AS. Zinc: role in immunity, oxidative stress and chronic inflammation. Curr Opin Clin Nutr Metab Care. 2009 Nov;12(6):646-52. doi: 10.1097/MCO.0b013e3283312956. https://pubmed.ncbi.nlm.nih.gov/19710611/

Auinger A, Riede L, Bothe G, Busch R, Gruenwald J. Yeast (1,3)-(1,6)-beta-glucan helps to maintain the body's defence against pathogens: a double-blind, randomized, placebo-controlled, multicentric study in healthy subjects. Eur J Nutr. 2013 Dec;52(8):1913-8. doi: 10.1007/s00394-013-0492-z. https://pmc.ncbi.nlm.nih.gov/articles/PMC3832763/

https://hygiena.szu.cz/pdfs/hyg/2016/04/11.pdf