After a cancer diagnosis and treatment, you may feel more vulnerable than usual to viruses approaching the winter months, particularly if your immune system has not quite recovered from the impact of treatment. In this blog, we’ll look at some of the nutrients and foods that your immune system needs in order to do its job of protecting you.
Your immune system is miraculously complicated, consisting of many different types of cells which each have their own role. When the environment in your body is optimal, the immune system is equipped to decide which immune cells it needs to produce, where they need to go, and to recognise when they have completed their job and can “stand down”. However, various factors can derail this complex system!
For example, if there is chronic inflammation then signals can be produced which result in immune cells being created that are not the most appropriate for the particular situation. Yet again, following an anti-inflammatory diet is important as a foundational immune support.
There are also certain nutrients that the immune system needs to work well. Let’s look at some of these and consider which foods they are found in.
Nutrients
Vitamin C reduces inflammation and is an antioxidant. The process of having an infection results in high amounts of oxidative stress, and dietary antioxidants are needed to prevent damage to immune cells and to regulate their actions. Vitamin C regulates the activity of various immune cells and the production of antibodies. Contrary to popular belief however, studies on the effects of supplemental doses of vitamin C on colds have been inconsistent. A 2013 Cochrane review(1) found that taking vitamin C does not reduce the chances of getting a cold in most people, although it does in people taking part in endurance sports. Taking vitamin C when you have a cold may reduce the duration and the severity of symptoms. Note that it is generally not safe or appropriate to take supplemental doses of any antioxidant, including vitamin C, when you are having a chemotherapy drug which works by generating oxidative stress. Food sources of vitamin C are safe and important, however. You will all know that vitamin C is found in citrus fruit, but other good sources include berries, peppers, parsley and green leafy vegetables.
Vitamin E is another antioxidant vitamin. It has been found to increase the activity of natural killer cells, to improve the function of T cells and to increase resistance to bacterial infections. Good food sources include avocados, egg yolks, nuts and seeds, spinach, butternut squash and olive oil.
Zinc is a mineral that is needed for immune cells to develop normally. It can prevent viruses from replicating, and is needed for the immune system to be able to respond to opportunistic infections effectively. Food sources include seafood (especially oysters), beef, pumpkin seeds, cashew nuts and fresh root ginger.
Selenium, another mineral, is involved in recycling vitamins C and E so that they can continue to provide their antioxidant benefits in the body. Selenium deficiency has been associated with an increased ability of viruses to cause serious harm(2), (3). Selenium is found in Brazil nuts (limiting to 2-3 per day is recommended to avoid selenium toxicity), seafood, organ meats, meat and poultry. The content of selenium in grains and other plant foods is very dependent on the soil in which they were grown.
Vitamin A is involved in antiviral signalling, and supports immunity within the gut. It can be obtained from animal sources as preformed vitamin A (liver, egg yolks, butter) or from plant sources as beta-carotene, which the body converts to vitamin A (squashes, sweet potatoes, kale, carrots).
Vitamin D is needed for more than just bone health! Vitamin D regulates multiple genes that control immune signalling, and it downregulates inflammation. Vitamin D deficiency increases the risk of upper respiratory tract infections, and the risk of a COVID-19 infection becoming severe(4). Evidence suggests that for immune support, we need higher blood levels of vitamin D than we do for musculoskeletal health(5). As you know, the best source of vitamin D is safe sun exposure. This is not possible in the UK in the winter! Good food sources of vitamin D include oily fish, egg yolks and mushrooms that have been exposed to UV light. However, it would be difficult to correct a vitamin D deficiency using food alone; the best thing to do is to test your vitamin D levels (you can do this at home via https://vitamindtest.org.uk/ ) and to take a supplement if necessary.
Polyphenols and Polysaccharides
In addition to making sure that you eat plenty of food sources of the vitamins listed above, there are other compounds in particular foods that are known to support a healthy immune system. Here are some that you might want to consider eating or drinking more of during the winter.
You might have heard of plant compounds called polyphenols in the context of gut health, but did you know that they are important for immunity too? Polyphenols directly support immune cells and can kill pathogens. They are found in high concentration in herbs, spices, tea and berries.
Epigallocatechin gallate (EGCG) found in green tea activates an antiviral state in the body. White, black and green tea all have antiviral effects.
Garlic is well known for having antiviral properties. Viruses do not have their own cells; they rely on getting into your cells and using your cellular machinery in order to replicate. Garlic is powerful because it prevents viruses from entering your cells, and it also inhibits viral replication. Why not add more cloves of garlic to a recipe than it calls for to increase your antiviral protection?
A compound called carvacrol in thyme and oregano is antiviral, antibacterial and antifungal. Thyme has a long history of traditional use in respiratory issues, since it helps with bringing up phlegm and with calming coughs. You can make a thyme infusion by adding a few sprigs of thyme to a teapot or tea infuser ball, and steeping in hot water for at least 5 minutes. If it’s not to your taste, you can add some lemon use and a little bit of honey.
Quercetin is found in apples and onions (particularly red varieties), cranberries, cacao and capers. This is another polyphenol that stops viruses from entering our cells and replicating. It also works in synergy with zinc, helping zinc to get into your cells to carry out its antiviral activity. Onion skins can contain almost 50 times more quercetin than the flesh. If you really want to increase the quercetin in your diet, you can save your onion skins and put them in a herb bag which you can add to stews and soups while cooking. Just remember to remove the bag before serving!
Polysaccharides are another group of compounds which can support the activity of immune cells. One of the best known sources is mushrooms, all of which contain beta glucans which support the immune system.
Probiotics and Fermented Foods
There is good evidence that multiple strains of Lactobacillus probiotic bacteria can reduce the risk of having an upper respiratory tract infection, can reduce the duration of the infection and can also reduce the need to take antibiotics(6).
A 2021 systematic review and meta-analysis found that consuming fermented dairy products reduced the risk of upper respiratory tract infection by 19%(7). It is likely that other fermented foods, such as sauerkraut or kimchi, would be protective as well.
Lifestyle factors
Your lifestyle choices can impact your immune function just as much as your nutrient intake can. The following factors can suppress immunity by impacting the numbers and/or activity of immune calls:
Insufficient sleep
Alcohol
Emotional stress
Smoking
Sedentary behaviour
Being underweight
By contrast, you can support the activity of your immune cells by laughing regularly (try watching your favourite comedy rather than the news) and spending time in nature. The Japanese art of shinrin-yoku, or forest bathing, has been found to increase the number and activity of natural killer cells, as well as having benefits for metabolic and mental health(8).
Wishing you a healthy winter season!
References
(1) Hemila, H. and Chalker, E. (2013). ‘Vitamin C for preventing and treating the common cold’, The Cochrane Database of Systematic Reviews, 2013(1), CD000980. Available at https://pmc.ncbi.nlm.nih.gov/articles/PMC8078152/
(2) Jain, V.K. and Priyadarsini, K.I. (2024). ‘Selenium compounds as promising antiviral agents’, New Journal of Chemistry, 48, pp6534-6552. Available at https://pubs.rsc.org/en/content/articlelanding/2024/nj/d3nj05180c
(3) Khurana, A., Allawadhi, P., Singh, V. et al. (2023). ‘Antimicrobial and anti-viral effects of selenium nanoparticles and selenoprotein based strategies: COVID-19 and beyond’, Journal of Drug Delivery Science and Technology, 86, 104663. Available at https://pmc.ncbi.nlm.nih.gov/articles/PMC10249347/
(4) Ben-Eltriki, M., Hopefl, R., Wright, J.M. et al. (2022). ‘Association between Vitamin D Status and Risk of Developing Severe COVID-19 Infection: A Meta-Analysis of Observational Studies’, Journal of the American Nutrition Association, 41(7), pp679-689. Available at https://pmc.ncbi.nlm.nih.gov/articles/PMC8425440/
(5) Wimalawansa, S.J. (2023). ‘Infections and Autoimmunity-The Immune System and Vitamin D: A Systematic Review’, Nutrients, 15(17), 3842. Available at https://pmc.ncbi.nlm.nih.gov/articles/PMC10490553/#sec1-nutrients-15-03842
(6) Zhao, Y., Dong, B.R and Hao, Q. (2022). ‘Probiotics for preventing acute upper respiratory tract infections’, The Cochrane Database of Systematic Reviews, 8(8), CD006895. Available at https://pmc.ncbi.nlm.nih.gov/articles/PMC9400717/
(7) Rashidi, K., Razi, B., Darand, M. et al. (2021). ‘Effect of probiotic fermented dairy products on incidence of respiratory tract infections: a systematic review and meta-analysis of randomized clinical trials’, Nutrition Journal, 20(1), 61. Available at https://pmc.ncbi.nlm.nih.gov/articles/PMC8240278/
(8) Li, Q. (2022). ‘Effects of forest environment (Shinrin-yoku/Forest bathing) on health promotion and disease prevention -the Establishment of "Forest Medicine"’, Environmental Health and Preventive Medicine, 27: 43. Available at https://pmc.ncbi.nlm.nih.gov/articles/PMC9665958/
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