Dietitian, Dr Carrie Ruxton
The global pandemic has shone a light – as never before – on how each of us manages our health and immunity. While we don’t yet know enough about the Covid-19 virus and how it operates, there is growing evidence from researchers and medics that our own health and lifestyles create a particular risk profile, with type 2 diabetes, inflammation, obesity and poor immune function all putting us at greater risk of worse health outcomes if exposed to the virus.
Professor Tim Spector, of King’s College London, said recently: “Obesity and poor diet is emerging as one of the biggest risks factors for a severe response to Covid-19 infection that can no longer be ignored.” And Professor Philip Calder and colleagues writing in the journal, Nutrients, commented: “There is a need for additional strategies to support the immune system, in order to reduce the impact of respiratory and other infections.”
This e-news from the Health and Food Supplements Information Service (www.hsis.org) shines a spotlight on the latest news around immunity and asks: How can good nutrition optimise our immune health?
What is immunity?
Our immunity is unique to each person and involves both innate and adaptive immune systems that combine to fight off infections and foreign bodies. It isn’t like a simple dial that can be turned up or down but is a highly complex system involving the gut, skin, bone marrow, tonsils, spleen and mucous membranes.
Innate immunity is the ‘quick response’ baseline protection we have from birth that includes our skin, gut environment, and types of immune cells including phagocytes and natural killer cells. Adaptive immunity is slowly learnt in response to new bacteria or viruses and relies on the actions of T lymphocytes and B lymphocytes which target and destroy bacteria or virus-infected cells in our bodies. It is the adaptive system that generates an immune memory to enable our bodies to recognise specific viruses and bacteria the next time they attack.
Dr Carrie Ruxton, a dietitian at the Health and Food Supplements Information Service, says: “One issue with the popular concept of ‘boosting’ immunity is that we actually don’t want this to happen. Like many other body systems, such as blood glucose levels or brain oxygen levels, our immune response works across a tight optimal range. Too low and our sluggish system will not successfully attack and contain pathogens, but too high and we are at risk of developing so-called autoimmune conditions where the body’s overreactive immune response starts to attack normal healthy tissue. Examples of these conditions include type 1 diabetes, multiple sclerosis, rheumatoid arthritis and psoriasis.”
While we cannot ‘boost’ immunity, we can ensure that our own personal immunity is functioning optimally. Nutrition is a big part of this, with a healthy balanced diet working hand in hand with appropriate supplementation.
The Global Centre for Nutrition and Health highlights the role that micronutrients have in supporting aspects of immune function, saying: “Poor nutrition, due to either insufficient dietary intake of key nutrients or a poor overall diet quality, can compromise immune function and increase overall infection risk. Micronutrients, commonly known as vitamins and minerals, are required in small quantities but are critical for health and pivotal in strengthening the immune system.”
The key nutrients are:
Vitamin A – plays a role in the regulation of the innate immune response through natural killer cells, macrophages and neutrophils, as well as cell-mediated immunity through the growth and differentiation of B cells. Cell-mediated simply means an immune response that doesn’t involve an antigen. Food sources include dairy foods, broccoli, kale and eggs.
Vitamin C – influences the production of interferon, a protein made by immune cells which can inhibit virus replication, including the influenza A virus. Vitamin C also has anti-inflammatory and anti-oxidant effects which are important in limiting damage by free radicals released during rapid immune response. Studies show that vitamin C represses the viral lytic cycle (the stage at which a virus bursts out of the host cell to infect other cells). Food sources include citrus fruits and juices, peppers, berries and spinach.
Vitamin D – one of the most important nutrients for the immune system. Many immune cells have vitamin D receptors and vitamin D has been shown to increase the killing capacity of immune cells (e.g. macrophages), control the production of inflammatory cytokines, and help immune cells lock onto antigens (proteins on the surface of bacteria and viruses). Studies have reported associations between poor vitamin D status (blood levels) and susceptibility to acute respiratory tract infections. Meta-analyses (super studies) have reported that vitamin D supplementation prevents acute respiratory infections., Dietary sources are limited – mainly oily fish and eggs – so UK health experts recommend that everyone consider a daily supplement of 10 micrograms.
Vitamin E – working with vitamin C, vitamin E acts as a powerful anti-oxidant that helps protect body cells by strengthening their cell walls. Vitamin E also supports T cell function by improving the cells’ membrane defenses and reducing inflammation. Studies show that vitamin E has clinical relevance as it affects host susceptibility to infectious diseases, such as respiratory infections, and allergic diseases, such as asthma. Food sources include vegetable oils, nuts and seeds.
Zinc – plays a role in innate immunity, adaptive immunity and the production of cytokines – proteins that are produced across the immune system to attack invading microorganisms. In the initial immune response, zinc supplies in the blood are drained to supplement immune cells. When people are low in zinc, the immune response is the first to suffer and there is a greater risk of oxidative stress (free radical attack) and inflammation. Food sources include seafood, pork and beans.
Omega-3 fatty acids – the most important are DHA and EPA, found in oily fish and fish oil supplements. These support immune function by acting directly to resolve inflammation and promote healing once bacteria and viruses have been neutralised. Commenting in the journal, Nutrients, Professor Calder and colleagues explained: “Nutritional deficiencies in these essential fatty acids can result in delayed or suboptimal resolution of inflammation. This could be very important in the context of severe COVID-19 which manifests as uncontrolled inflammation, the so-called cytokine storm linked with acute respiratory distress syndrome (ARDS).” Natural dietary sources are limited to oily fish and seafood, so supplements made from fish oil or algae (vegan) are important alternatives if you don’t eat fish regularly.
The new review paper, published in Nutrients, strongly recommends nutrition strategies to help support immune function, concluding that: “Optimal nutrient intake, including supplementing above the [recommended daily amount, RDA] for certain immune-supporting vitamins, promotes optimal immune function, helps to control the impact of infections, and could help limit the emergence of novel, more virulent strains of pathogenic viruses.”
In summary, Dr Carrie Ruxton comments: “Ensuring that we have the right balance of vitamins, minerals and essential fatty acids in our diets, is an important step in providing personal protection to our immune systems. We can’t control our environment – including the bacteria, viruses and yeast that could potentially cause infection – but we can do everything possible to get our immune systems ready to respond. As the evidence shows, certain nutrients can help, and a daily multivitamin and multimineral supplement, plus a fish oil supplement if you don’t regularly eat oily fish, is worth considering and is good, common sense.”
 Official advice has recently changed due to the COVID-19 pandemic and now asks everyone to consider a year-round vitamin D supplement instead of at specific times of the year.