Bounce Back Better: The Science of Immune Resilience
Why some immune systems recover from stress, poor sleep, and inflammation while others stay stuck, and what you can do about it
WHAT IS IMMUNE RESILIENCE?
Most of us think of the immune system as the part of us that fights off colds, flu and other infections. That is an important part of its job, but it is far from the whole story.
Over the years in clinic, I've come to see it as one of the body's great communicators. Immune cells are in constant conversation with the gut, the brain, our hormones and our metabolism. So when the immune system is under strain, we often feel it in places we might not expect: flagging energy, broken sleep, a foggy head, or simply taking longer to get back on our feet after a busy spell. When I talk about immune resilience, I mean your body's ability to respond appropriately to whatever life throws at it. That includes infections, but also the constant, subtler pressures of modern living, without tipping into exhaustion, inflammation, allergy or burnout.
A TWO-WAY STREET
The relationship runs in both directions. Your immune system shapes your sleep, energy, mood and focus. In turn, your sleep, food, stress levels and daily rhythms shape how well your immune system works.
If we keep pushing on without the right foundations in place, the immune system can become dysregulated in one of two ways:
It under-responds, so you pick up more infections or take longer to recover.
It over-responds, reacting to harmless triggers such as foods or pollen, or losing its tolerance of the body's own tissues, which is what happens in autoimmune conditions.
This is why I'm wary of the idea of "boosting" immunity. An immune system that is permanently switched on is not a healthy one, and for anyone living with an autoimmune condition, stimulation is the last thing it needs. True resilience is about balance.
A BIOLOGICAL MISMATCH
Our immune systems evolved in a world of natural light and dark, whole foods, daily movement and face-to-face connection. Modern life tends to offer the opposite: bright screens late at night, processed convenience food, long hours sitting down and much of our social life conducted online.
On top of that, we are exposed to things our ancestors never encountered, from air pollution to the endocrine-disrupting chemicals found in some plastics, pesticides, household cleaners and personal care products.
The result is a mismatch. The immune system is repeatedly asked to respond to inputs it was never designed to handle, and it can end up in a low-level but continuous state of alert. Immune cells never quite get the chance to stand down. Over time, that background activation can contribute to chronic, low-grade inflammation, fatigue and a feeling of being permanently on edge.
WHAT REDUCED RESILIENCE CAN LOOK LIKE
At first the signs are subtle, and easy to dismiss as "just getting older" or "just life":
Catching more colds than you used to, or taking longer to recover from them.
New sensitivities, such as foods you once tolerated now causing problems.
Skin flares, such as eczema, rosacea or rashes.
Histamine-type reactions, such as facial flushing or itchy skin.
Tiredness that has become your "new normal": the afternoon slump, waking groggy after a full night's sleep, or persistent brain fog.
Any one of these may seem like a minor annoyance. Together, they can be an early warning that the immune system has lost some of its flexibility and is working harder than it should. Many of these symptoms overlap with the hormonal changes of midlife, which is one reason it is so useful to look at the whole picture rather than each symptom on its own.
This matters for the long term too. Chronic, low-grade inflammation is associated with many of the conditions we most want to avoid in later life, including heart disease and dementia.
WHAT WE ARE AIMING FOR
A resilient immune system:
Responds quickly and effectively, but only to genuine threats.
Calms down again once the threat has passed.
Doesn't overreact to harmless triggers such as food or pollen.
Maintains tolerance, recognising the body's own tissues as "self".
COVID illustrated this vividly. People who became seriously unwell were often those whose immune response was poorly regulated, either failing to respond effectively or overreacting in a so-called cytokine storm. The goal is not a "strong" immune system that is always switched on, but one that is intelligent, balanced and adaptable.
FOUR DRAINS, FOUR FOUNDATIONS
Adaptability doesn't happen by itself. If the system is constantly being drained, those drains need attention first. In clinic, I see four come up again and again:
Poor sleep
Blood sugar swings
Living permanently in "go mode"
An unhappy gut
The body doesn't distinguish neatly between these stressors. Each one adds to the same load, and as that load builds, adaptability falls.
The encouraging part is that the same four areas, turned around, become the foundations of immune resilience: restorative sleep, steady blood sugar, a well-supported gut and deliberate recovery.
FOUNDATION 1: RESTORATIVE SLEEP AND A STEADY BODY CLOCK
Sleep is your overnight repair shop, restoring the brain, body and immune system. It has been preserved through evolution in almost every animal studied, and we spend roughly a third of our lives asleep. Evolution doesn't hold on to things that aren't essential.
Sleep is also part of a bigger system: your circadian rhythm, or body clock. Immune cells follow this rhythm too. When you sleep, when you eat and how much daylight you see all send signals that set the tone for the day.
Two hormones work in opposite cycles here. Melatonin rises as light fades, telling the body it is night. Cortisol peaks in the morning to help you wake, then gradually tapers through the day. When late-night screens or bright lights suppress melatonin, that rhythm is blurred, and you can wake feeling groggy even after enough hours in bed.
With the clocks having just gone back, this is a particularly good moment to reset:
Keep consistent sleep and wake times, including at weekends.
Get outside within an hour of waking, even for five to ten minutes. Morning daylight is one of the strongest signals to your body clock, so try to see the sky before you see your phone.
Dim the lights in the evening and reduce screen use for at least an hour before bed, ideally two.
Finish eating two to three hours before bed where you can.
Build a calming wind-down routine. Slow breathing, a warm Epsom salt bath, magnesium-rich foods or a magnesium supplement can all help.
FOUNDATION 2: STEADY BLOOD SUGAR
This is one of the most common drains I see, and most people don't realise it is happening.
After a high-carbohydrate meal or sugary snack, blood glucose can rise sharply, prompting a large release of insulin to bring it down. It can then fall quickly. The body treats that sudden drop as a potential threat and releases cortisol to push glucose back up. Repeated many times a day, this rollercoaster can drive fatigue, cravings, anxiety and, over time, immune imbalance.
Persistently high blood sugar and insulin also encourage fat to be stored around the abdominal organs. This visceral fat is metabolically active and releases inflammatory signals, even in people who look slim. High glucose also forms compounds called advanced glycation end products, or AGEs, which add to inflammation, and it can affect the integrity of the gut lining.
Some simple ways to steady things:
Start the day with a balanced breakfast built around protein, healthy fats and fibre. Eggs, Greek yoghurt with nuts and seeds, or leftovers from last night's dinner all work well.
Ask "where's my protein, fat and fibre?" at every meal.
Don't eat carbohydrates on their own. Pair fruit with a handful of nuts, or rice with fish and plenty of vegetables.
Start meals with vegetables or a salad, and leave the bread basket until later.
Take a 10 to 15-minute walk after meals. Working muscles take up glucose, which helps blunt the rise.
Have caffeine with or after food rather than on an empty stomach.
Avoid constant grazing. Leaving time between meals gives insulin levels a chance to come down.
I'll be looking at blood sugar and insulin resistance in much more depth in my next newsletter, so if this section resonates, watch this space.
FOUNDATION 3: A WELL-SUPPORTED GUT
The gut is essentially a long tube running through the body, and everything inside it is, technically, still the outside world. A large proportion of the immune system is stationed along the gut lining, acting like border control: deciding what is safe to let in and what needs to be dealt with. This is where the immune system learns to respond appropriately.
The trillions of microbes in the gut are often described as an immune army, but I think of them more as personal trainers. They don't do the fighting themselves; they train and condition immune cells so they respond in a balanced way.
The gut and brain are also in constant conversation through the vagus nerve, a kind of hotline that helps tell the immune system when to gear up and when to stand down.
Problems arise when the gut lining becomes more permeable, sometimes described as a "leaky gut". Normally the cells of the lining are packed tightly together. If that barrier loosens, food particles, microbial fragments and toxins can pass through when they shouldn't, and the immune system reacts. This can contribute to food sensitivities, skin problems, low-grade inflammation and, in some people, autoimmune reactions.
Helpfully, beneficial bacteria ferment the fibre we eat into short-chain fatty acids. One of the most important, butyrate, fuels the cells lining the gut, strengthens the barrier and helps train a balanced immune response.
I think of this as the gut–immune triad, three systems that work together:
The gut lining, which we need to protect.
The microbiome, which we need to feed.
The vagus nerve, which we need to tone.
Step 1: Reduce what irritates. Alcohol, smoking, ultra-processed foods, unnecessary antibiotics and frequent use of anti-inflammatory painkillers such as ibuprofen can all affect the gut lining or microbiome. A big night out followed by a couple of ibuprofen for the hangover is a particularly unkind combination. (Please don't stop any prescribed medication without speaking to your GP.)
Step 2: Add what nourishes.
Fibre, fibre, fibre, from a wide variety of plants, to feed the bacteria that make butyrate.
Fermented foods such as live yoghurt, kefir, sauerkraut, kimchi and miso, if well tolerated.
Resistant starch from cooked-then-cooled potatoes or rice, and slightly green bananas.
Polyphenols from berries, green tea, extra virgin olive oil and dark chocolate, which act as food for beneficial microbes.
Omega-3 fats from oily fish, flaxseed and walnuts, to help regulate inflammation.
Zinc from seeds, shellfish and meat, which supports the tight junctions between gut cells as well as immune function.
Where gut repair needs more targeted support, I sometimes use nutrients such as L-glutamine, butyrate and zinc carnosine in clinic, tailored to the individual.
Step 3: Tone the vagus nerve. Slow breathing with long exhales, humming or singing, yoga, time in nature and brief cold-water exposure, such as splashing your face with cool water, can all improve vagal tone. (If you have a heart condition, check with your GP before trying cold showers or cold-water swimming.)
FOUNDATION 4: BUILD RECOVERY INTO EVERY DAY
Modern life keeps many of us stuck in "go mode", and it isn't only workload that does it. Unstable blood sugar, poor sleep, an unresolved infection, even gum disease, can all send the same "stay alert" signal.
The body copes well with short bursts of challenge. When the burden becomes chronic, it is overloaded. We can't remove every stressor, but we can build more recovery into the day. Recovery isn't a treat you earn after a hard day; it is part of how the body is designed to work.
Some easy recovery moments:
4–2–6 breathing. Breathe in for four, hold for two and breathe out slowly for six. One or two minutes can help shift you out of fight-or-flight.
Two-minute resets. After a call or a task, sit back, roll your shoulders and take a few slow breaths before the next thing.
Micro-breaks. Stand, stretch or walk to refill your water roughly every hour.
Look into the distance. Every hour or so, gaze out of a window for 20 to 30 seconds to rest your eyes and signal safety to your nervous system.
Pair calm with habits. Take three slow breaths each time you refill your water, or keep your phone away for the first five minutes of every meal.
Fuel calm focus. Stay hydrated, eat magnesium-rich foods such as leafy greens, nuts and seeds, and enjoy green tea, which contains L-theanine, an amino acid associated with calm alertness.
A handful of these, practised consistently, can help retrain the nervous system to move more easily between effort and rest. That flexibility is at the heart of immune resilience.
BRINGING IT TOGETHER
Immune resilience isn't about avoiding every bug or "boosting" your defences. It is about a body that is adaptable, well regulated, able to recover and aligned with its natural rhythms.
You don't need to tackle all four foundations at once. Choose the one that feels most relevant to you this month and start there.
We are all different, and sometimes it helps to look beneath the surface. In clinic, functional testing such as vitamin D and inflammation markers, comprehensive stool analysis, micronutrient testing and DUTCH hormone testing can show where your system might be struggling, so we can stop guessing and personalise the plan. If you'd like to explore this, you can book via my contact page.
ACADEMIC REFERENCES:
Dantzer R, Cohen S, Russo SJ, Dinan TG. Resilience and immunity. Brain, Behavior, and Immunity 2018;74:28–42.
Morey JN, Boggero IA, Scott AB, Segerstrom SC. Current directions in stress and human immune function. Current Opinion in Psychology 2015;5:13–17.
Bae YS, Shin EC, Bae YS, Van Eden W. Editorial: Stress and immunity. Frontiers in Immunology 2019;10:245.
Alotiby A. Immunology of stress: a review article. Journal of Clinical Medicine 2024;13(21):6394.
Yang SN, Hsieh CC, Kuo HF, Lee MS, Huang MY, Kuo CH, Hung CH. The effects of environmental toxins on allergic inflammation. Allergy, Asthma & Immunology Research 2014;6(6):478–484.
Janeway CA Jr et al. Immunobiology, 5th edition. Self-tolerance and its loss. Garland Science, 2001.
Hou K et al. Microbiota in health and disease. Signal Transduction and Targeted Therapy 2022;7:135.
Bjarnason I et al. Mechanisms of damage to the gastrointestinal tract from nonsteroidal anti-inflammatory drugs. Gastroenterology 2018;154(3):500–514.
Tracey KJ. The inflammatory reflex. Nature 2002;420(6917):853–859.