Updated: Nov 12, 2020
With COVID-19 dominating headlines across the globe and governments urging the public to keep themselves safe from the virus, it is unsurprising that the role of nutrition in relation to immunity has been a topic of interest. Headlines have reported that overweight and obese individuals are at greater risk of suffering long term effects from the virus (1) which has prompted the UK government to encourage us as individuals to take responsibility for our health and our weight, in order to reduce the burden on the NHS. The intersection of nutrition and COVID-19 has been examined, with several people/organisations pushing the narrative that we can ‘boost’ our immune system via our nutritional intake. This is naïve at best, and fear mongering and predatory at worst. While nutrition is an important aspect of health and immunity, it can not prevent COVID-19 and to suggest such is unethical.
What is Immunity?
Immunity is a complex and sophisticated system designed to protect our bodies from harmful pathogens (such as viruses, bacteria, fungi and parasites) which are constantly present in the environment around us. There are many different cells, tissues and organs that are required to work in harmony in order to deploy a suitable attack on these pathogens. These processes require tight regulation to switch the immune response on and off appropriately so we can effectively remove the harmful cells while protecting our own healthy cells. As you can imagine, these processes involve a range of factors which must be controlled in a balanced and harmonious way, only one of which is nutrition.
The immune system can be broadly categorised into two branches: innate immunity and adaptive immunity. We are all born with an innate immune system that acts as the first line of defence and produces a rapid but generalised response to any invading pathogens. This system is comprised of physical and chemical barriers such as our skin and mucus membranes (lining our respiratory and gastrointestinal tracts), as well as a host of white blood cells, natural killer cells and compounds that signal and regulate cells and reactions within the body. Inflammation is an example of a normal immune response (2). This is a carefully controlled process which aims to kill the pathogens by increasing temperature and blood flow, to allow immune cells to find and target the threat in order to remove it. Inflammation signals to our body that something is wrong and allows us to respond and is usually ‘switched off’ after the threat has been removed. However chronic inflammation can occur when the body cannot regulate and switch off this response. Chronic inflammation is linked to many adverse health conditions such as heart disease, diabetes and obesity, however whether it is a cause or a symptom of these health conditions remains unclear (3).
Over the course of our life we develop and fine tune an additional adaptive (also known as acquired) immune response, which is much more specific and efficient at dealing with pathogens. When our body encounters a pathogen for the first time, our body initially identifies it as foreign and then detects specific molecules on its surface. The most common molecule we hear about is an antigen and each antigen requires a specific antibody to eradicate the pathogen. Our body must learn how to make these specific antibodies, however other cells are also involved in adaptive immunity. Our body then is able to amplify the immune response by creating multiple copies of the antibody to quickly eradicate the target, and once it is removed other cells signal to turn off the immune response to preserve our own healthy cells. The body has cleverly adapted to retain a memory of antigens it has encountered before. Therefore, if the body encounters it again it can quickly multiply and make more antibodies to remove it efficiently. This is the reason it is called adaptive immunity, as we learn from each encounter and can launch a more efficient response the second time around (2). This is why people rarely catch the chicken pox twice, our bodies remember the pathogen and can quickly eradicate it before it takes hold and causes any symptoms.
As this system is so complex, there are several factors which can affect and compromise our immune system. For example, as we get older our immune system slows down and we are not as capable of creating the specific antibodies needed for newly encountered pathogens. Medical conditions and medication can also alter our immune response, either by reducing its efficiency or sending it into overdrive which can cause harm to our own healthy cells. Environmental factors such as air pollution, smoking and alcohol can trigger our immune response and lead to chronic inflammation as our body constantly tries to eliminate them. Lifestyle factors such as stress and lack of sleep have widespread effects on the body including lowering our immunity. Excess weight as previously mentioned can lower our immunity, as it is often combined with low grade chronic inflammation which disrupts many chemical balances throughout the body (4). Lastly, we know that poor nutrition can lower our immunity as certain vitamins and minerals are required to produce an immune response. So we can see that while nutrition is important for a healthy immune system, it is only one part of the puzzle.
Nutrition and immunity: the evidence
While many of us like to believe that food is medicine, sadly this is not the case. The links between immunity and nutrition have been well studied however as both are so complex, variable and individualised it is difficult to draw firm conclusions on the relationship between the two. However, the European Food Safety Authority (EFSA) have declared a handful of nutrients with sufficient evidence to support their role in human immune function. These nutrients are copper, iron, zinc, selenium, vitamin A, vitamin B6, vitamin B9 (folate/folic acid), vitamin B12, vitamin C and vitamin D (5). This means that any other nutrients outside of this list should not claim to improve or ‘boost’ immunity. Here I will outline the sources of each approved nutrient and the likelihood of deficiency:
Recommended amounts stated are daily amounts adults should be striving for. Please check the NHS website for any other recommendations (e.g. children). μg stands for micrograms, and may also be written as mcg.
It is important to note that a lot of the research carried out on these nutrients used participants who were already deficient in the nutrient. Therefore, the effects of supplementing healthy persons are not clear, and may provide no benefit. Some studies found supplementing deficient persons helped improve health outcomes (for example less severe symptoms, reduced duration of illness, reduced mortality rates), while some studies found no measurable benefit in terms of immune function. It is important that if we are considering supplementation, we consult a health professional first (especially if we have underlying medical conditions).
There are a few other nutrients which may play a role in maintaining a healthy immune system, however do not have enough evidence to prove their effects. These include protein and omega 3 fatty acids (e.g. oily fish) (6). Another interesting area of research which might have implications for immune function is prebiotics, probiotics and synbiotics (7). These are essentially various types of fibres which interact with the beneficial bacteria in our gut to produce a wide range of molecules which can have wide reaching effects in the human body. Prebiotics include plant-based foods such as bananas, asparagus, leeks, oats and cocoa. Probiotics are typically fermented foods such as yoghurt, kefir, sauerkraut, miso and kimchi. Synbiotics are a combination of the two and can be achieved by combining the foods mentioned previously, or are commonly sold as supplements. This is a relatively new area of research and so may have promising results in the near future. However, it is important to remember these have not been approved by EFSA and therefore can not claim to improve immune function.
Do we need to ‘boost’ our immune system/take supplements?
As we can see from the table, the risk of deficiency is fairly low for the nutrients mentioned. This is based on the assumption that the majority of people are consuming a varied, balanced diet based on the Eatwell Guide. The Eatwell Guide is the UK’s dietary guidelines, and recommends a balance of foods containing all the nutrients we need to live a healthy life, therefore many of us do not need supplements or juices or shakes in order to boost our immune system as we are already receiving these in our diet. Therefore, the most simple advice to keep your immune system healthy is to consume a balanced and varied diet containing foods from all the main food groups, particularly fruit and vegetables as they contain lots of vitamins and minerals. If you don’t eat some of the recommended foods in the table or you can’t eat them for medical, religious or ethical reasons then it may be advisable to ask your doctor if you are at risk of deficiency and consider supplementation with medical guidance.
Eating a balanced diet in theory will help us maintain a healthy weight, which is also important for our health. An adequate and varied diet will also help prevent malnutrition, which is a condition caused by either lack of (or excess) nutrients and calories meaning our body is not receiving the right balance of foods to function properly. This is a concern as when a person is malnourished it can affect their immune function, and malnourished people typically experience poorer outcomes when faced with illness (8). Food insecurity is a growing issue, and many of us have found ourselves buying less (varied) food due to unemployment and rising costs which may put people at risk of malnutrition. Fresh fruit and vegetables can be expensive and spoil quickly, so it might be useful to buy more frozen and tinned products if these are affordable. In these circumstances, supplementation may be a useful strategy to improve nutritional intake. A simple multivitamin containing the nutrients mentioned above can be relatively inexpensive, most supermarkets sell their own brand. However, it is advisable to check the suitability of supplementation with a health professional. It is important to note that nutrition cannot prevent COVID-19, but it may help improve outcomes and recovery.
It is also beneficial to try and maintain a healthy weight, keep active and limit smoking and alcohol. Managing stress and getting a good night’s sleep may also help, although in the current climate that is much easier said than done! Basically, we should try and follow the general health guidance where possible and be mindful of people who are trying to sell you anything that claims to boost your immune system. Your body is extremely clever and can fight infections, however if we can nourish and look after ourselves then we can help it work at its most efficient.
Thanks to Lora Hennity for writing this week's blog, she is a Registered Associate Nutritionist (ANutr). She recently graduated from Ulster University in July 2020 and has been seeking employment to boost her skills and experience. Before university, she trained as a chef. Lora shares "I am a massive foodie and love playing around with ingredients to make my own recipes, and so I planned on combining my passions for food, sustainability and nutrition to create my own business when I graduated. However, the final two years of my degree have cultivated a deep interest in health promotion and health equality. I completed a one-year work placement within the charity sector, working as a Health Promotion Officer as part of my degree. Working with members of the public from various communities across Northern Ireland has allowed me to develop a good understanding of the various barriers people face in relation to receiving optimal nutrition, and has inspired me to pursue an MSc in Global and Public Health. My hope is to cultivate change, to begin lessening health inequalities prevalent in our society and empower people to look after themselves through positive health promoting behaviours and habits."
You can find Lora on social media here:
1. Public Health England. Excess weight can increase risk of serious illness and death from COVID-19. 2020, p 1-67. Available from: https://www.gov.uk/government/publications/excess-weight-and-covid-19-insights-from-new-evidence
2. Chaplin, D.D., 2010. Overview of the immune response. Journal of Allergy and Clinical Immunology, 125(2), pp.S3-S23.
3. Bennett J.M., Reeves G., Billman G.E., Sturmberg J.P. Inflammation-Nature’s Way to Efficiently Respond to All Types of Challenges: Implications for Understanding and Managing “the Epidemic” of Chronic Diseases. Front. Med. 2018;5:316.
4. Milner, J.J. and Beck, M.A., 2012. The impact of obesity on the immune response to infection. Proceedings of the Nutrition Society, 71(2), pp.298-306.
5. EFSA Panel on Dietetic Products, Nutrition and Allergies (NDA), 2016. Guidance on the scientific requirements for health claims related to the immune system, the gastrointestinal tract and defence against pathogenic microorganisms. EFSA Journal, 14(1), p.4369.
6. Grimble, R.F., 2009. Basics in clinical nutrition: Immunonutrition–Nutrients which influence immunity: Effect and mechanism of action. e-SPEN, the European e-Journal of Clinical Nutrition and Metabolism, 1(4), pp.e10-e13.
7. Frei, R., Akdis, M. and O’Mahony, L., 2015. Prebiotics, probiotics, synbiotics, and the immune system: experimental data and clinical evidence. Current opinion in gastroenterology, 31(2), pp.153-158.
8. Handu, D., Moloney, L., Rozga, M. and Cheng, F., 2020. Malnutrition Care during the COVID-19 Pandemic: Considerations for Registered Dietitian Nutritionists Evidence Analysis Center. Journal of the Academy of Nutrition and Dietetics.