The immune system is functioning at all times, working hard to protect us, heal and repair us, it's even our main cancer surveillance system. But we probably don't think about it day-to-day. It’s only when the cold and flu season sets in that we thank our immune system as we scramble for vitamin C supplements. Or at unprecedented times like now, amidst the global SARS-CoV-2 pandemic. With the worry and anxiety that grips our world against this silent enemy, caring for our immune systems has firmly been given immunity a seat at the conversation table of most households around the globe. It’s no wonder then, in times of such uncertainty, we want a sense of agency over our health.
Abundance of nutritional supplements, old wives remedies and fortified foods all with the promise of ‘boosting’ your immune system and, by doing so, to stave off colds and flu are everywhere. But is there any scientific truth in these claims? Google search results of ‘immune boosting’ reveal the majority of products/articles are rooted in false claims and misleading info which could result in you not only parting with money with the hope of becoming invincible to germs (1). True, many supplements do have studies to support that they help the immune system to do its job. But how robust is the evidence? How applicable is it to humans? Do they interact with any medications you may have to take? And is there any risk? You get the picture.
There is no scientific way to boost your immunity. And perhaps you should not want to. The symptoms and damage that come with COVID19 are in part a result of our immune system overshooting. But can diet be helpful in strengthening our immunity and keeping us well? Before we dive into the details, let’s be clear: there is no such thing as an immunity diet, per se. Ultimately, we want a balanced immune system, and this requires a balanced diet. Your immune system is immensely, mind-bogglingly intricate and complex, perhaps second only in its complexity after your brain. The huge constellation of immune cells not only have their own unique functions but an equally unique nutritional demand. In such a multifaceted system, nutrition can only ever be part of the whole immunity health equation. Eating for immunity should equate to eating for your longevity, not just a short term fix during the panic of a global pandemic. Your immune system ages, weakening as you get older (and this starts surprisingly early in our 20s). Because even after the threat of this virus has passed – sooner or later another one is going to come along, and none of us is getting any younger. Fortunately, we are discovering plenty of things you can do to turn back the immunological age clock and stay healthy throughout your lifespan.
THE MICROS: VITAMINS AND MINERALS
The immune system requires all the essential micronutrients (vitamins and minerals) to function properly. There are several that are highlighted as particularly important for infection protection: vitamins A, C, D, and E, folate, vitamins B6 and B12, beta carotene, iron, riboflavin, selenium, coenzyme Q10 and zinc (2). Deficiencies in any of these can impair your immunity and increase risk for infection. Adding the deficient nutrient back into the diet restores the immune function and resistance to infection. If you are healthy and have no deficiencies, benefits of supplementation are limited. Taking more isn't necessarily going to make your immune system work better than it already does at baseline. Mega-dosing of supplements is never a good idea because many contain active ingredients that may exert negative effects. Consuming large doses of fat-soluble vitamins can lead to toxic levels. Some supplements interact with medications.
A food first approach is your best bet to get all essential micronutrients and comes with a few added benefits too (see below). The exception being vitamin D. Current advice from Public Health England is that adults and children over the age of one should consider taking a daily supplement containing 10mcg of vitamin D during autumn and winter in the UK. Maintaining your vitamin D status reduces the risk of respiratory tract infections (3, 4, 5). It's also important to bear in mind that different life stages and lifestyle choices may require supplementation.
When we are fighting an infection the cells and molecules of our immune system become increasingly active. This results in a significant increase in the demand of the immune system for nutrients to provide a ready source of energy as they go to battle fighting off those trespassing germs. Not to mention resolving the collateral, healing and repairing after the germ is gone. Vitamin C is a key example of this, with our immune system using more when we are sick (6). Taking vitamin C supplements may provide a small reduction in the length and severity of a cold, particularly for those with busy or stressful lives, or who do a lot of sport (7). Often touted as immune boosting, zinc certainly does play an important role in immunity, helping both our immune cells to do their job in the fight against an infection as well as helping our cells resist infection with viruses that cause the common cold 8, 9). This means there may be a small benefit from taking zinc supplements upon onset of symptoms. But there are risks related to prolonged zinc supplementation. Too much zinc may throw out other nutrients like copper and can cause gut distress.
FIBRE, FLORA AND PHYTONUTRIENTS
There is possibly no better way to nourish your immunity than through good gut health. We are superorganisms. Home to some 38 trillion microbes (our microbiota, or flora). These ‘good’ germs living in our gut are our main immunity educators with whom we form a lifelong health alliance. By now, it’s a familiar fact (and yes, it’s true) indeed almost 70 per cent of the entire immune system resides in the gut. The strength of our immunity is in part beholden to the health of our gut flora so we have to feed those gut bugs well (10). Much of the immune education takes place in early childhood (before age 5), but there is still work we can all do.
When your microbes chow down on fibre, they produce a veritable banquet of metabolic trash by-products known as ‘postbiotics’ (11). Consider it your own personalised health pharmacy. These beneficial by-products change the personalities of our immune cells for the better, sparking signals that dial down inflammation, reducing all the unpleasant symptoms we experience when sick and switching on our peacekeeping immune function to repair inflammatory damage.
The tricky thing about fibre is that it’s not a monolith, but many different types intrinsic to plant-based foods. Plus fibre in the UK, fibre has a bit of an image problem. A good rule of thumb is to ensure you are not only getting enough fibre but quality and diversity too is to aim for over 30 different plant foods per week. A carb-fibre ratio (at least 1g fibre to every 10g total carbohydrate) can guide you as you look at food labels: simply divide the total carbohydrate in grams by fibre (in grams) (12). Fibre found in fruit and veg, nuts and seeds, legumes and whole grains. Resistant starches – so called because they are resistant to digestion in your gut, but not for your gut bugs include cooked and cooled white potatoes, oats, lentils and rice. Some specific fibres such as beta-glucans from oats or mushrooms are known to have direct antimicrobial and anti-inflammatory activity. Take care to increase dietary fibre slowly to give your gut time to adjust. Avoiding unnecessary antibiotics can help too. A handful of small studies have shown certain probiotics may be helpful, but the current evidence is limited with no immune system-specific recommendations (13, 14).
While micronutrients are essential for health, phytonutrients are very beneficial. Phytonutrients are biologically active chemical compounds found in plants. They act as a natural pesticide, helping to protect plants from predators. So it’s no surprise that regular consumption helps to prevent us from getting sick too. Currently, phytonutrients are referred to as non-nutritive, meaning we don’t have a specific recommended daily intake or reference amount deemed necessary for health – partly because they are not as essential to survival as vitamins and minerals. But there are many ways in which eating a variety of phytonutrients provides us with extra ‘immune-nourishing’ benefits, not only protecting us from infection but warding off long-term chronic disease. There are over 25,000 different phytonutrients recorded across many foods – not only fruits and veggies, but also beans and pulses, tea, coffee, red wine, cacao, herbs, spices, and olive oil (15). Their immune-nourishing effects cannot be explained by selecting just one or two like curcumin in turmeric or polyphenols from blueberries. Think about them working synchronously and collectively producing their maximum health effects when consumed consistently (16).
THE MACROS & ENERGY BALANCE
Now you are aware that vitamin deficiencies are bad for immunity and that taking more than you need wont make your immune system work better than it does at baseline. What might not be so obvious though, is that cells of the immune system utilise all the macros: carbohydrates, proteins and fats. These provide fuel for energy and the building blocks to their many signalling molecules and antibodies. Immunometabolism – that is, how metabolism of these macronutrients is integrated with the fate and function of our immune cells – is a swiftly growing area of research (17). Scientists have long recognised that metabolic problems are linked to issues with our immune defences. This means that too much or too little of one or another macronutrient can have quite a profound knock-on impact on immunity. Inadequate protein consumption is a well established immune impairing factor (18). To date, there are very few studies examining the impact of carb and protein content of meals with different macronutrient composition on immunity. But we are starting to get a few clues.
The immune system also suffers in both conditions of under- and overnutrition: too much food can be bad as can too little (19). If you are stuck at home during COVID19 lockdown, be mindful that it’s all too easy to overeat ultra processed food that are high in calories and low in nutritional quality. These are often the foods that really hit the bliss point making them easy to overconsume. On the flip side, it's probably not the best time to jump on the fasting bandwagon which could risk us under consuming enough calories. This is known to negatively impact our infection protection.
The World Health Organization recommends that people eat no more than 5 grams of salt a day to avoid high blood pressure, which can cause strokes and heart disease. In the UK, people eat 8 grams on average. Eating too much salt may also impair our immunity including the ability to fight infections. When we eat lots of salt, hormones are released to make the body excrete more salt. These include glucocorticoids that have the side effect of suppressing the immune system throughout the body (20). Oversalting also tips the delicate immune system balance away from proper regulation which can impair our ability to minimise collateral damage from fighting an infection with inflammation (21).
While moderate alcohol consumption may have some health benefits, higher amounts can lead to severe problems. In many healthful dietary patterns, such as the Mediterranean, wine is consumed in low quantities with meals. However our immunity could indirectly be negatively affected through alcohol’s influence on sleep, which may be poorer in quality and quantity. In terms of gut health, alcohol can cause serious problems too (22). People who drink excessive alcohol tend to be at an increased risk for infectious diseases, take longer to recover from illnesses and have more complications (23, 24). Heavy alcohol intake can also affect organs that regulate immunity, such as the liver and bone marrow (23).
FLAVOUR, FUN AND EVERYTHING ELSE
Just as the nutritional quality of our food is important for immunity, so are our emotions around food. Reclaim the joys of your dinner table and give your meals some thoughtful presentation, which studies show leads to a more enjoyable meal (25). Take time for proper chewing and digestion that may avert digestive upset from quickly gulping down food as we might all have been guilty of pre-lockdown in our fast-paced lives. We might have limited cupboard staples right now but doesn’t mean meals need to be bland. Try a new recipe or challenge yourself with different flavour combinations to bring your food to life.
Loneliness and social connection matter as much for our immunity as our mental health (26). Our connections to the ones we love might feel broken right now, but it's an opportunity to connect more broadly to our neighbours, local communities as well as globally through technology while we are confined to our homes. Cultivating opportunities for those endorphins and feel-good hormones through daily movement, stress management and quality sleep also have a much needed nourishing effect on our immunity. Finally, perhaps most importantly, there is no way to become invincible to all germs. We are all immunologically unique and that’s by design. Even if you are doing everything ‘right’ etc you can’t eliminate risk completely.
This post was written by, Dr Jenna Macciochi who is based in Brighton, she is an immunologist and lecturer at the university of Sussex and author of Immunity. Her work has a specific focus on the role of diet and lifestyle in inflammation and immunity. Jenna is also a qualified fitness instructor and mother to 5 year old twins. You can find her on Instagram @dr_jenna_macciochi
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