Doctor and former professional triathlete Els Visser on why you cannot really boost your immune system, and what genuinely supports it when the marketing noise dies down.
Key Takeaways
In medicine we do not talk about boosting immunity. The goal is an immune system that responds when it needs to and stays balanced the rest of the time.
A more active immune system is not a better one. When that regulation breaks down you get chronic inflammation and autoimmune conditions, not extra protection.
Vitamin C, vitamin D and zinc are recognised as contributing to normal immune function. Once your needs are met, taking more does not add further benefit.
Vitamin D is the exception worth acting on. Sunlight is limited through autumn and winter, so deficiency is common and supplementation may be appropriate.
Sleep, regular activity, a varied fibre-rich diet and managing stress do more for immune function than any single supplement can.
Els is a medical doctor with a PhD and a professional long-distance triathlete, European Champion, and Dutch record holder. Her work centres on longevity—helping individuals optimise their health, performance, and recovery over the long term through the four key pillars of nutrition, movement, sleep and recovery, and mental health. A survivor of a life-changing boat disaster in 2014, she brings a deeply personal perspective on resilience and purpose to everything she does.
During my career as a professional triathlete, my body was exposed to heavy training, international travel and disrupted sleep. Staying healthy wasn't just important, it determined whether I could train and compete. Like many athletes, I wondered whether supplements such as vitamin C or zinc could help protect me. The science, however, tells a more nuanced story: there is no magic solution.
In medicine, we don't actually talk about boosting the immune system. The goal isn't to make your immune system stronger or more active. In fact, an overactive immune system can be harmful and is responsible for autoimmune diseases and chronic inflammation. What we really want is an immune system that functions as it should: capable of responding when needed while remaining balanced the rest of the time.
The encouraging news is that many of the things that genuinely support your immune system are already within your control. Your daily habits how you sleep, eat, exercise, recover and manage stress, have a far greater impact than any single supplement. Because when it comes to immune health, consistency almost always beats quick fixes.⊕
The idea of "boosting" your immune system is everywhere. There are countless products claiming to strengthen immunity, prevent illness or help you recover faster. While these claims sound appealing, they're often an oversimplification of how the immune system actually works.
Unlike building stronger muscles through training, your immune system can't simply be switched into a permanently higher gear. It's an incredibly complex network that depends on careful balance. If it responds too weakly, you're more susceptible to infections. But if it becomes overactive, it can start attacking healthy tissues or create excessive inflammation. Autoimmune diseases such as rheumatoid arthritis, lupus and multiple sclerosis are examples of what can happen when immune regulation is disrupted. Clearly, "more immunity" isn't necessarily better.
Healthcare professionals increasingly prefer the term supporting normal immune function rather than boosting immunity. Research consistently shows that the biggest contributors to healthy immune function aren't found in a single pill or trendy wellness product. Instead, they come from maintaining a healthy lifestyle over months and years. Adequate sleep allows your immune cells to recover and communicate effectively. A balanced diet provides the vitamins, minerals, healthy fats and protein your immune system relies on. Regular physical activity improves immune surveillance, while excessive stress and poor recovery can have the opposite effect.
Nutrition provides the building blocks your immune system needs to function properly. While no single food or nutrient can prevent you from getting sick, a varied, balanced diet helps ensure your immune cells have the resources they need to respond effectively. Rather than focusing on "superfoods," it's more helpful to think about your overall dietary pattern. Consistently eating enough energy, consuming sufficient protein, and including a wide variety of fruits, vegetables, whole grains, legumes, nuts and healthy fats will have a far greater impact than relying on individual supplements. That said, several nutrients have well-established roles in supporting normal immune function.
Vitamin C contributes to the normal function of the immune system and also acts as an antioxidant, helping protect cells from oxidative stress. It supports the function of several immune cells, including neutrophils and lymphocytes, and plays an important role in collagen formation, which helps maintain healthy skin and mucosal barriers, our body's first line of defence against infection.
Obtaining enough vitamin C through food is relatively easy. Citrus fruits, strawberries, kiwi, bell peppers, broccoli and Brussels sprouts are all excellent sources. A common misconception is that taking very high doses of vitamin C will prevent colds altogether. While regular supplementation may slightly reduce the duration of a common cold in some individuals, particularly those exposed to prolonged, intense physical exercise, it doesn't appear to dramatically reduce the risk of catching one in the general population.
When people think about immunity, they often picture white blood cells circulating in the bloodstream. But a large proportion of your immune system is closely connected to your gut. The gastrointestinal tract is constantly exposed to food, bacteria and other foreign substances. To distinguish between harmless and potentially harmful invaders, the body has developed an extensive network of immune tissue known as the gut-associated lymphoid tissue (GALT).
At the same time, trillions of microorganisms collectively known as the gut microbiome live within our intestines. These bacteria help digest certain fibres, produce beneficial compounds and interact continuously with immune cells. Research increasingly suggests that a diverse and healthy gut microbiome plays an important role in supporting immune function.
The strongest evidence to support your gut health still points toward simple dietary habits: eat a wide variety of plant foods, include plenty of dietary fibre from vegetables, fruits, legumes and whole grains. Consume fermented foods regularly such as yoghurt or kefir, and limit highly processed foods where possible. While probiotics may be useful in certain clinical situations, they're not a universal solution, and different strains have different effects. For most healthy individuals, building a healthy microbiome starts with everyday nutrition rather than a supplement.
If I had to choose the three lifestyle habits that consistently have the greatest influence on immune health, they would be sleep, physical activity and stress management. These may not sound as exciting as the latest wellness trend, but they're supported by decades of scientific research.
Sleep is one of the most powerful recovery tools your body has. During sleep, your immune system produces and regulates signalling proteins called cytokines, which help coordinate immune responses. Sleep also supports communication between immune cells and contributes to the formation of long-term immune memory following vaccination or infection.⊕ Even a few nights of insufficient sleep can reduce aspects of immune function and may increase susceptibility to illness. That's why I encourage people to view sleep in exactly the same way they view nutrition or exercise: not as spare time, but as an essential investment in long-term health.
Regular physical activity supports immune health in multiple ways. Moderate exercise improves circulation, allowing immune cells to move more efficiently throughout the body. It also helps reduce chronic inflammation, supports cardiovascular and metabolic health, and contributes to a well-functioning immune system.
The internet is full of claims about immunity, but not all are supported by evidence.
Once your nutritional needs are met, taking increasingly high doses doesn't automatically improve immune function and, in some cases, may even be harmful.
No individual food can compensate for an otherwise poor lifestyle. It's your overall dietary pattern that matters most.
Sometimes, rest is the most productive decision. Listening to your body and allowing adequate recovery often shortens the time needed to return to training safely.
No supplement can compensate for chronic sleep deprivation, poor nutrition, prolonged stress or lack of physical activity.
If you want to support your immune system over the long term, focus on the habits you can repeat consistently. These habits may seem simple, but together they create the environment in which your immune system can function at its best.
As both a doctor and a former professional athlete, I've spent much of my career thinking about performance, recovery and long-term health. One lesson has become increasingly clear: the fundamentals matter. It's tempting to search for a supplement, a shortcut or a product that promises to strengthen your immune system overnight. But the science tells a different story.
Your immune system doesn't need to be constantly stimulated; it needs to be supported. That support comes from the choices you make every day: eating a balanced diet, getting enough sleep, staying physically active, managing stress and allowing your body the time it needs to recover. Many of the same lifestyle habits that support immune function are also associated with healthy ageing, making immune health another reason to invest in the fundamentals.
These habits aren't always the most exciting, but they're the ones with the strongest scientific foundation. And unlike quick fixes, their benefits extend far beyond immunity, they contribute to better overall health, improved resilience and healthy ageing.
Not in the way many advertisements suggest. Your immune system is a highly regulated network that functions best when it's balanced, not simply more active. Rather than trying to "boost" immunity, it's more accurate to focus on supporting normal immune function through healthy lifestyle habits such as adequate sleep, balanced nutrition, regular physical activity and stress management.
Several nutrients contribute to the normal function of the immune system, including vitamin C, vitamin D and zinc. Protein is also essential because antibodies and many immune cells are built from amino acids. The best approach is to obtain these nutrients through a varied, balanced diet, while supplements may be appropriate if dietary intake is inadequate or a deficiency has been identified.
Yes. A large part of the immune system is closely connected to the gastrointestinal tract. A healthy, diverse gut microbiome helps support normal immune function through continuous communication with immune cells. Eating a fibre-rich diet with a wide variety of plant foods is one of the best ways to support gut health.
Your immune system is one of the most sophisticated systems in your body. Rather than being a single organ, it's a network of cells, tissues and organs that work together to protect you against viruses, bacteria, fungi and other harmful invaders. To understand how to support your immune system, it helps to know that it has two main components: the innate immune system and the adaptive immune system.
The innate immune system is your body's first line of defence. It's always active and responds rapidly whenever something potentially harmful enters your body. Your skin, the lining of your respiratory tract, stomach acid and immune cells such as macrophages and neutrophils are all part of this system. They provide immediate protection, but they're relatively non-specific, they respond to many different threats in a similar way.
The adaptive immune system is slower to respond but much more specialised. It learns to recognise specific viruses and bacteria, allowing it to mount a faster and more effective response the next time you're exposed. This is where T-cells, B-cells and antibodies play a central role. Vaccinations work by training this adaptive immune system, helping your body build immune memory without causing the disease itself.
Inflammation is another essential part of your immune response. Although inflammation often has a negative reputation, it's actually a normal and necessary process. When you cut your finger or catch a virus, inflammation helps recruit immune cells to the affected area so healing and recovery can begin. Problems arise when inflammation becomes chronic or excessive. Long-term, low-grade inflammation has been linked to conditions such as cardiovascular disease, type 2 diabetes and several autoimmune disorders. That's one reason why maintaining overall health is so important, not just for preventing illness today, but for supporting healthy ageing over the long term.
An effective immune system therefore isn't the strongest possible immune system. It's one that's well regulated, able to respond appropriately when needed and then return to balance once the threat has passed.
This doesn't mean supplements have no role. Certain nutrients, such as vitamin C, vitamin D and zinc, are recognised for their contribution to the normal function of the immune system.⊕ However, they're most effective when they help correct an inadequate intake or deficiency, rather than being taken in extremely high doses in the hope of preventing illness. The immune system responds best when the body as a whole is well cared for. Rather than chasing quick fixes, focus on creating the conditions that allow your immune system to do exactly what it was designed to do.
Vitamin D is unique because it's produced in the skin when we're exposed to sunlight, although we also obtain smaller amounts from foods such as oily fish, egg yolks and fortified products. Unlike many vitamins, vitamin D acts more like a hormone and influences numerous processes throughout the body, including immune regulation.
Vitamin D contributes to the normal function of the immune system by helping coordinate both innate and adaptive immune responses. Low vitamin D levels have been associated with an increased susceptibility to respiratory infections. The evidence suggests that correcting a vitamin D deficiency is beneficial, whereas additional supplementation offers little benefit once vitamin D levels are sufficient. In many countries, particularly during autumn and winter, vitamin D deficiency is relatively common because sunlight exposure is limited. Supplementation may therefore be appropriate.⊕
Zinc is an essential trace mineral involved in hundreds of biological processes, including immune cell development, communication and wound healing. Even mild zinc deficiency can impair normal immune function, making adequate intake important throughout life. Good dietary sources include meat, shellfish, dairy products, beans, lentils, nuts and seeds. The goal is to meet your body's requirements, not greatly exceed them. Excessive zinc supplementation can interfere with the absorption of other minerals, such as copper, and may lead to unwanted side effects.
One nutrient that's often overlooked in conversations about immunity is protein. Proteins provide the amino acids needed to build antibodies, immune signalling molecules and many of the cells involved in your immune response. Without adequate protein, your body simply can't maintain these processes as efficiently. This is particularly relevant for older adults, people recovering from illness, and athletes during periods of heavy training.
An effective immune response also requires energy. When the body is under-fuelled, sleep-deprived or recovering from prolonged physical stress, it has to prioritise how its resources are used. That's one reason why adequate energy intake, together with sufficient protein and recovery, is so important for maintaining normal immune function.
Like many aspects of health, exercise follows a "dose-response" relationship: enough is beneficial, but more is not always better. Very high training loads, particularly when combined with inadequate recovery, poor sleep or insufficient nutrition, can temporarily increase susceptibility to infections. This is especially relevant for endurance athletes during periods of heavy training or competition. Professional endurance sport taught me that recovery is just as important as training itself. Training adaptations occur during recovery, not during the workout itself, and maintaining immune health often depends on recognising when the body needs rest rather than additional stress.
For most people, the takeaway is simple: regular movement is one of the most powerful tools to support long-term health. Whether it's walking, cycling, swimming, strength training or another form of exercise, consistency matters far more than intensity.
Short-term stress is a normal part of life and can even enhance certain aspects of immune function. Chronic stress is different. When stress persists for weeks or months, elevated levels of stress hormones such as cortisol may interfere with normal immune regulation. Chronic stress is also associated with poorer sleep, unhealthy eating habits and reduced physical activity, creating a cycle that further impacts overall health.
Managing stress doesn't necessarily mean eliminating it, something that's rarely realistic. Instead, it's about building recovery into daily life. That might include spending time outdoors, exercising regularly, maintaining social connections, practising mindfulness, or simply protecting enough time for rest.
For most healthy people, high-dose vitamin supplements do not prevent common colds. Some evidence suggests regular vitamin C supplementation may slightly shorten the duration of a cold in certain groups, such as endurance athletes exposed to prolonged physical stress, but megadoses are generally not recommended. Meeting your nutritional needs consistently is far more important than taking very large doses.
The strongest evidence supports focusing on the basics: getting enough sleep, eating a balanced diet with adequate protein, staying physically active, managing stress, maintaining a healthy gut microbiome, avoiding smoking, limiting excessive alcohol consumption and allowing your body sufficient time to recover after illness or periods of heavy physical or mental stress.
