1. Your gut bacteria help train your immune system - FACT
It might sound like a strange partnership, but your gut microbiome plays a vital role in training and supporting your immune system.
From birth, gut microbes help your immune system mature and learn how to respond to antigens appropriately. We know this from studies on germ-free mice (those without a microbiome), which develop immune system defects compared with normal mice with a microbiome.
Day to day, the gut and immune system stay in close contact. Immune cells line the gut, constantly monitoring what passes through — recognising friendly, harmless bacteria and distinguishing them from harmful microbes. When gut bacteria break down dietary fibre, they produce a beneficial compound called butyrate, which helps immune cells regulate themselves and avoid overreacting.
TL;DR: Your gut bacteria train your immune system to recognise friend from foe. Looking after your gut microbiome with a healthy, high fibre diet is another way you can support your immune health.
2. Going out with wet hair in the cold will give you a cold - FICTION
Did you ever leave the house with wet hair in winter and worry you’d pay for it with a cold? You can relax — being cold or wet doesn’t actually increase your risk of catching one.
Colds are caused by viruses, not being cold per se. They tend to spread more easily in winter because they replicate better in cooler conditions. We also spend more time indoors and in close contact with others during the colder months, which makes it easier for infections to pass from person to person.
TL;DR: Cold weather or wet hair won’t make you sick — viruses do. Winter just gives them a better chance to spread.
3. The harder you exercise, the stronger your immune system becomes - FICTION
We know that being active over the lifespan lowers the risk of many chronic diseases, including cancer, heart disease, type 2 diabetes, and viral infections. But what actually happens to your immune system when you exercise?
Research shows a single bout of exercise of up to 60 minutes temporarily increases the number of immune cells in the blood. Over time when repeated, it’s thought that these transient increases in immune cells might have positive anti-inflammatory effects. Longer term, maintaining an active lifestyle offsets some of the natural decline in immune function caused by aging.
So does this mean pushing harder in workouts makes your immune system stronger? Actually, it seems not. Studies of athletes undergoing heavy training, like marathon runners, show that biomarkers of immune function are suppressed for several hours to a couple of days after intense endurance exercise.
Some scientists think this could explain why colds and coughs often appear after big training loads and competitions. Overtraining (intense exercise without enough rest) is also linked with reduced immune function), partly driven by chronically raised cortisol levels.
TL;DR: Regular, moderate exercise supports immune health throughout life. Aim for around 150 minutes a week (about 30 minutes a day) of moderate-intensity activity that gets you warm and breathing harder. If you’re training intensely, sufficient rest days, good sleep, and the right nutrition are important to balance out the increased stress on your immune system.
4. A strong immune system means you’ll never get sick - FICTION
We all know someone who claims they never get sick — or someone who seems to bounce back from illness faster than everyone else. So does that mean they’ve got an unusually strong immune system?
Not exactly. The idea of a “strong” immune system is actually a bit misleading. What we actually want is a balanced immune system. An immune system that is too strong or turned up too much may start attacking healthy tissues — something we see in autoimmune conditions.
Just like your gut microbiome, your immune system is unique to you. The genes that control it vary between individuals, which helps explain why people respond differently to illnesses and vaccinations.
If we both catch the same virus and I recover faster, it doesn’t mean my immune system is better than yours - just different. Immune diversity is natural. You can be more prone to one condition, while being more resistant to another.
TL;DR: Immune systems naturally vary from person to person, and help to explain why differences in immune response. Lifestyle factors can support your personal immune system to function optimally, but it won’t overcome genetic differences in immune function.
5. Stress affects your mood - not your immune system - FICTION
Stress is an inevitable part of being human. It’s a natural response to threat — or, in today’s world, to work, relationships, financial pressures and well - everyday challenges! Some stress is normal and even helpful, motivating us to adapt and respond to challenges. But when stress is persistent and starts to affect our functioning, it can harm both mental and physical health, including the immune system.
When we’re stressed, the body releases hormones like cortisol as part of the “fight or flight” response, which prepares us for action. Research shows that cortisol can dampen immune function and affect our ability to fight off infections.
Short periods of stress aren’t a problem, but chronic stress does have a negative impact on immune health. So, taking steps to manage stress is an important part of looking after your immune health.
TL;DR: Everyday stress is normal, but persistently high levels of stress can dampen your immune response. Explore ways to unwind and manage stress with these tips from GP Dr Sarah Jarvis.
6. Taking vitamin supplements is important for a healthy immune system - FACT (IN PART!)
It’s true that many vitamins and minerals are important for normal immune function - including vitamin A, vitamin C, vitamin D, vitamin E, selenium, and zinc. Having deficiencies in these nutrients has been linked with increased susceptibility to infections.
So if you’re not getting enough of these nutrients in your diet for one reason or another (perhaps because of limiting your diet due a medical condition) then a vitamin supplement can be helpful. But most of us should be able to get enough of these nutrients from a healthy balanced diet containing plenty of fruits and vegetables, fibre rich foods, lean proteins and healthy fats.
The main exception is vitamin D. Our main source of vitamin D is sunlight on our skin. During the autumn and winter months, levels can drop because the sun’s rays aren’t strong enough for us to make vitamin D. Recent research backs this too, with data from the UK showing that ~ 1 in 5 adults have low vitamin D levels.
So, adults and children over four are advised to take a daily supplement containing 10 micrograms of vitamin D from October through April.
TL;DR: Most people can meet their immune-supporting nutrient needs through a healthy diet, unless their diet is restricted. Vitamin D is the main exception — everyone should supplement through the cold months in the UK.
Discover more tips to help support your gut-immune connection.
Sources
The compelling link between physical activity and the body's defense system. Pub Med.(2018). Link.
National Diet and Nutrition Survey 2019 to 2023: report. (2025). Link.
