Do you keep catching colds even though you’re forever loading up on vitamin C? Here’s why your gut is making you susceptible to illness even though you eat a healthy diet.

We’re in the thick of cold and flu season. Everyone seems to be sick right now – even those of us who eat our weight in vitamin C-rich fruits and take regular zinc tablets (which may do less for colds than we hoped). But while chugging a load of orange juice and supplements may be more psychosomatic than scientific when it comes to warding off bugs, what we consume may indeed make a difference to how prone we are to picking up infections.

Why? Because it turns out that a whopping 80% of our immune system is located in the gut. Yep, just when we thought the gut couldn’t influence any more of our lives (it’s already where the majority of our serotonin is produced), it now transpires that our ability to fight off colds and work through illnesses quickly is determined by our microbiomes too.

So, what exactly is the gut’s role in our immunity, and how might we harness our gut health to make us less liable to pick up the office bug? 

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What role does gut health play in immunity?

That 80% figure is based on the surface area of the gut versus that of the skin, respiratory system and reproductive systems, explains nutritional therapist Marjolein Dutry van Haeften.

“The gut functions as a big part of the immune system for various reasons. Firstly, it is a literal barrier to the outside world. The entire lining of the gut (from the mouth all the way down the intestinal tract) is lined with a mucosal layer that functions to protect us from viruses, bacteria, fungi.”

And then you have the microbiome – the collection of bacteria, viruses and fungi that “lives in harmony with us when well balanced”, van Haeften tells Stylist. “Essentially, the immune system is primed to identify invaders which shouldn’t be there (not all of which cause disease). Our microbiome and body work together to recognise disease-causing agents and set them apart from harmless foreign material.” 

Gut health and autoimmune disease

The inability to tell the difference between harmless foreign objects and disease-causing pathogens is what causes us to become hyper-reactive.

So, does that mean that the gut plays a big role in autoimmune disease? After all, many autoimmune conditions and allergies are caused by the body attacking things it shouldn’t. Van Haeften says that the gut is “very relevant” to autoimmune disease – particularly when it comes to functional medicine.

She explains that within functional medicine, autoimmune disease tends to be caused by three main factors:

1. Genetic susceptibility to the condition (“But genetic susceptibility alone does not mean you will definitely develop an autoimmune condition.”)
2. The health of the gut wall has been compromised (this can be “either the gut wall or the mucosal layer of the gut wall”).
3. The presence of a trigger that has primed the immune system to start identifying the self (aka your own tissue) as foreign tissue. (“A clear example of this is in coeliac disease where gluten is a trigger to the immune system identifying cells in the small intestine as tissue to target,” van Haeften explains. 

How to improve gut health for better immunity

At this stage, you’re probably wondering whether you need to eat more fibre or saurkraut to avoid catching a cold. But van Haeften explains that it’s not so simple: “When it comes to nutrients that support gut health, we also need to be able to absorb them well – so if the gut wall is compromised, it is likely that absorption of nutrients from food is impacted as well. Bit of a vicious cycle.”

Eat foods that will nourish the mucosal membranes

That means loading up on 30 plants a day or chugging your weight in vitamin C might not have the desired effect. It’s more important, van Haeften says, to choose foods that can nourish and support the epithelial cells in the gut and encourage the health of the mucosal membranes in the body. Such as bone broth, lion’s mane mushrooms and marshmallow root tea.

But the more commonly championed immunity nutrients like vitamin D, zinc and vitamin A are still also really important to support the mucosal lining of the gut, too. Chickpeas and lentils are rich in zinc, while oily fish like salmon and tuna contain plenty of vitamin D. For vitamin A, load up on orange and yellow veg such as carrots, squash and peppers.

“Foods which are prebiotic and probiotic are also important to support the diversity and health of the gut microbiome, contributing to a healthy gut environment and healthy immune response.” So that’s your yoghurt, kimchi and miso.  

Rest up and prioritise stress-relief

If you’re the kind of person who picks up a cold the moment you see someone else sneeze, you might now be wondering if your diet or gut wall are to blame. And while the gut might be struggling, it’s probably the wrong way around to immediately start chastising yourself for not eating enough sour foods.

Van Haeften says that your first port of call if you’re susceptible to illness is to examine if there’s anything you can do to prioritise taking more rest. “Often, stress on the body is playing a role,” she says. To protect the gut, it’s as important to support your stress response as it is to examine your food intake. “If we aren’t getting enough restful downtime and good quality sleep, this has an impact on our gut,” she explains.

Get your vitamin levels tested

Once you’ve done that, it’s time to look at your nutrition. “Often when clients are low in key minerals and vitamins, there is an issue with absorption. This means that you can be eating an incredibly diverse and health-promoting range of foods, but you simply aren’t breaking down and absorbing the foods effectively.”

To do that, it’s worth asking your GP for a blood test. That can check your vitamin D, iron, B12 and other vitamin levels.  

Stay hydrated

Drinking plenty of water has also been shown to have a positive effect on the lining of the intestines as well as the balance of good bacteria in the gut. 

Think about taking collagen

Van Haeften previously recommended thinking long-term about what you can do to improve your gut wall health. “That’s where things like collagen may come in. But the thing with collagen is that it’s really abundant in the body, and your body is going to prioritise it where it needs it first. So, it might need it to go to joints or it may need to go to other connective tissues.”

It’s worth flagging that often you don’t end up absorbing collagen because it gets broken down into amino acids, which your body then does what it wants with. In theory, it can be beneficial to gut health, but you don’t really have any control over how the body uses it.

Images: Getty

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