This piece was written by one of our contributors; immunologist and university lecturer – Jenna Macchiochi.
The idea that you can boost your immune system is enticing. Search health websites or walk through the aisles of any health food store and you’ll find no shortage of nutritional supplements, cold remedies and fortified foods that promise to ‘boost’ your immune system and by doing so stave off colds and flu. But the notion of the immune system as some kind of internal force field that can be boosted is rooted in misunderstood science. Because of the way your immune system is designed to work, you definitely wouldn’t want it to be boosted! Nevertheless, I appreciate that the term ‘immune-boosting’ is an unintentional malapropism and that the goal is mainly to avoid succumbing to those seasonal lurgies and to get swiftly back on our feet.
Most research casts doubt on many of the overstated ‘immune-boosting / strengthening / supporting’ marketing claims. However, occasionally these claims do actually have a kernel of tangible truth at their core. The complicating factor is that most studies on immune-boosting supplements tend to look at the effects on people who are already sick or have a pre-existing deficiency. Currently, there is little to zero evidence for a normal healthy person with no nutritional deficiencies that taking supplements will make their immune system work better than it already does at baseline. The potential placebo effect also complicates things: we feel better because we are investing in something marketed to make us feel better, or we temporarily improve other areas of our diet and lifestyle.
A closer look at some ‘immune-boosting’ suspects
Vitamin C will ward off a cold 🍊
While vitamin C does play a key role in the functioning of our immune system, it is also a practically unavoidable component of a normal balanced diet. So, while marketing claims might not be saying anything untrue, implying that if someone with a normal diet supplements with vitamin C then they are less likely to get sick, is plain wrong. However, studies do suggest that supplementing with vitamin C upon the onset of an infection can help reduce symptoms and speed recovery (1). There is just no need to continually supplement.
Zinc cuts the length of the common cold 🕒
Zinc is an essential mineral that’s found in almost every cell and plays a multitude of roles in the body. Zinc deficiency has been shown to impair our defence system (2). Zinc appears to lower the ability of cold viruses to grow on or bind to the lining of your nose, and improve the ability of special immune cells to fight infection (3), suggesting there is a small benefit in supplementing with zinc during the winter months for prevention of infection, particularly if you are at risk of a deficiency (elderly, children or those with underlying health concerns) (4). There is some evidence that starting to supplement with zinc upon onset of symptoms (when our need for extra zinc increases) may help to reduce the severity and duration of an infection (5). Zinc lozenges in particular seem to be effective in the short term, but it’s still debated what the best formulation or dose should be (6). Long-term use – more than 6 weeks – can lead to copper deficiency and an irritated digestive tract.
Echinacea prevents colds and flus 🌿
Long been talked about as an immune booster, the jury is still out on echinacea (7). Despite a large volume of evidence that it might be helpful in treating or preventing colds (including large meta-analyses), there is substantial conflicting evidence (8). Research is mainly complicated by the fact that there are three different species of echinacea and numerous parts of the plant all considered to contain various active ingredients. This means there are over 800 different echinacea products. There is little information or consensus on the best formula to take, what dose or how long it should be taken to be effective. Plus its important to note that it may interact with some medications (9).
Selenium – how important for immunity is it? 🥔
Selenium is an essential micronutrient with antioxidant properties that is involved in many biological processes throughout the body, including immune responses (10). It is not surprising then that getting adequate dietary selenium strongly influences how well we deal with infections. Selenium is found in the soil and naturally appears in produce grown in the soil. It’s quite rare to be deficient in selenium unless you are living in specific geographical regions growing produce in areas that have a known selenium soil deficiency (11). Studies looking at selenium status on immunity have suggested that, in absence of an overt deficiency, more selenium might not always be better and could actually drive unruly inflammatory processes in the body (12).
Infection-fighting Turmeric 🟡
Turmeric is having a moment in the health media but should we get sucked in to the hype? Despite some solid anti-inflammatory and anti-oxidant properties(13) shown to be clinically effective in treating specific illnesses such as forms of arthritis (14). Often the claims get overblown by the media into a catch-all cure for all ailments. Much of the research is on curcumin, one of the active ingredients in turmeric, but there are over 300 compounds in turmeric (15) and curcumin-free turmeric was also clinically effective, so stick to the whole root if you choose to use it (16). Interestingly, raw turmeric seems to be more anti-inflammatory, whereas cooked turmeric appears better for protecting from oxidative damage.
Turmeric is also a good inhibitor to viral entry into our cells. So, adding this spice regularly to meals could be useful in warding off infections. However, bioavailability can be a problem (17). Eaten with a source of fat and a pinch of black pepper it gives remarkable improvements in digestive uptake so make sure you add these when consuming turmeric although you probably wont reach near the therapeutic doses used in scientific studies. In Ayurveda, golden milk (turmeric added to warm milk) is traditionally used to fight sore throats, colds and flu, though bear in mind the evidence is anecdotal rather than clinically proven.
Sweat it out with spicy foods 🌶️
Some people swear by eating spicy foods to heal them by ‘sweating it out’. Capsaicin, the chilli pepper component that produces a burning sensation, can be effective against nasal congestion (18) and lowering inflammation (19), therefore reducing symptoms. It’s also shown clinical utility in pain management (20). There is also something to be said for enjoying a nourishing curry when feeling under the weather and it’s a great way to get a healthy hit of antioxidants, fibre and polyphenols from the veggies and spices.
Elderberry – a traditional immune-booster 🌱
Elderberries are a traditional wintertime plant used for thousands of years as both a medicine and in food. Purported to decrease pain and inflammation with antiviral properties, studies do indeed show that elderberry syrup can specifically shorten the duration of and reduce the symptoms of respiratory infections (21). In fact, when trialled against the anti-influenza drug Tamiflu®, elderberry extract came out as more effective (22). Components in the elderberry also have shown potential to prevent viruses from actually getting into our cells in the first place (23). So far, so good? There is a caveat. While current research does appear to substantiate the preventative claims against infections, the studies are small and mostly funded by companies producing commercial elderberry products. While this may not negate the research and clinical trials, it is a conflict of interest.
Immune super trio: lemon, honey, & ginger 🍋
Used for generations, this trio has stood the test of time but these do not cure a cold and actual evidence for it speeding up your recovery is quite thin, with the exception of honey which was found to be more effective as a cough suppressant for children when tested against dextromethorphan — the active ingredient in most cough medicines. In fact the National Health Service (NHS) in the UK now recommend honey first (24), not antibiotics for treatment of coughs based on guidelines from the National Institute for Health and Care Excellence (NICE) (25). Scientific evidence aside, combined in a hot drink they do soothe and hydrate. To ease the discomfort of feeling unwell, this age-old remedy may be a viable and cheaper alternative to over-the-counter pharmaceuticals, but it’s no miracle worker.
Jewish penicillin 🥣
Although not technically a supplement, chicken soup is actually one of the most effective cold and flu-busting ingredients out there . Shown experimentally to improve cold and flu symptoms through the direct effects of a number of substances such as carnosine on immune cells and lowering the symptoms induced by inflammation (26), it’s also a comforting and nourishing way to consume veggies, herbs and spices while keeping you well hydrated.
Gargling with water alone to wash the throat is commonly performed in certain parts of the world in the belief that it prevents upper respiratory tract infections (URTIs). Its effectiveness was recently explored in a small trial that indicated a 36% decrease in incidence of URTIs among apparently healthy adults by tap water gargling (27) whilst other studies cite that washing out your throat and mouth with salty water is among the most effective nonmedical URTI prevention measures (28).
Garlic – a food and medicine 🧄
Used for centuries as both a food and a medicine, garlic contains compounds that improve the germ-fighting ability of immune cells (29) and hold potential to help prevent infection in the first place (30). However, many of the studies demonstrating this were of poor quality and it’s not clear if you need to continually eat garlic to see the beneficial effects (31). Nevertheless, the way garlic is processed can really change its effects. To optimise, use the ‘hack and hold’ technique –crushing fresh garlic and letting it stand before cooking allows enzymatic conversion of alliin to beneficial allicin, the main active ingredient.
Multivitamins, vitamin drinks and juices 💊
They might sound appealing, particularly if you are feeling unwell and don’t have much of an appetite, but are they really worth it? It’s true that nutrient deficiencies can impair our immune system, but the key word here is deficiency – most of us can meet our RDA nutrient needs with a balanced diet. Adding extra in the form of vitamin-enriched drinks is probably not necessary for most healthy adults and these drinks make it easy to ingest potentially harmful excess amounts.
What about over-the-counter (OTC) medications 🏥
Many of the symptoms of an infection are actually our immune system doing its job. In healthy adults with no other underlying health issues, colds and flus are usually self-limiting. Many over-the-counter (OTC) cold and flu remedies designed to reduce these symptoms are therefore actually preventing the immune system from doing its job. Many treatments for the common cold claim to alleviate nasal symptoms, such as congestion, runny nose, and sneezing. Evidence for the effectiveness of these treatments are limited and of low quality, and clear guidance is lacking (32). Taking decongestants for longer than 5 days for example, can cause a rebound effect and actually worsen congestion. Letting a fever run its course is now considered potentially protective (33). That fever is happening for a reason as higher body temperatures actually enhances the functions of certain immune cells that are involved in clearing infections (34). It also makes microbial replication more inefficient. Blunting with medications such as ibuprofen may therefore interfere with this productive response.
The exceptions to the rule ❌
Ultimately, most of us come down with a couple of colds per year (more if you are at either extreme of the age spectrum). With so many strains of infections circulating, there is always a new one to catch, and most often this will be in the winter months (many cold and flu viruses prefer cooler temperatures). Vitamin D is vital to both the defence and regulating functions of the immune system. Most of our vitamin D comes from sunlight so there is a marked seasonal variation with lower levels during winter, which is speculatively thought to contribute to the increased risk of colds and flu during these months.
It’s also important to take care of your microbiome, which is intimately entwined with our immunity. Your diet is only as good as your microbiome. These microbes manufacture many of our vitamins and active compounds necessary for our wellbeing, and they form a large physical barrier against infection. Evidence is emerging that probiotics may be helpful in preventing upper respiratory tract infections (35) and people who have taken recurrent antibiotics are at increased risk of getting infections due to the effects on their microbiome (36). But despite promising evidence emerging, we still don’t know enough to know which strains and in what amounts. Since we all come with a unique microbiota starting point, aim to care for your good gut bugs through a food first approach by eating a diet rich in plant fibres.
There are a few clinical situations that negatively affect the functioning of the immune response, resulting in a greater than average number of infections that are harder to shift. For example, immunodeficiency diseases or the extremes of age, combinations of relentless stress, poor diet and lifestyle and intense exercise without adequate recovery. In these cases, no amount of immunity boosting will counter the root cause. Plus its important to remember that our immune system is immensely powerful so there may be medical situations where we don’t want to ‘boost’ our immunity, for example in patients on immunosuppressive drugs.
Ultimately, there is no hierarchy of a good or bad immune system – we all get sick sometimes, no matter how healthy we may be (37). This diversity in human immunity is by design and essential to our survival as a species. Immunity is a system, not a single entity, and to function well it requires balance, not boosting. Balance comes from more than just nutrition and supplementation and extends to basic hygiene and washing hands (38), a sensible lifestyle with regular physical activity (39), getting adequate sleep (40) and managing stress (41). By trying to do this most of the time, we stand the best chance of letting our immune system do what it does best.
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