The Dangers of Low-Grade Inflammation
The quiet fire.
On low-grade inflammation, the symptoms it explains, and why "your bloods are normal" is often the wrong answer.
For a long time the word I used was fine. Not well — I was never consistently well — but fine. Functional, managing, broadly okay. The kind of fine that gets you through appointments where the doctor says your bloods look good and you nod and go home and continue being fine.
What I didn't have a word for was the specific texture of not-quite-right that sat underneath the fine. The stiffness that was always there on waking, that I'd attributed to the mattress, and then to how I slept, and then just to being in my late twenties. The brain fog that came and went but mostly stayed — the sense of thinking through gauze. The fatigue that didn't respond to sleep in the expected way. The persistent, slightly elevated sense of the body managing something, without ever resolving it.
I saw several doctors over several years. I got tests done. I was told my CRP was normal, my thyroid was normal, my full blood count was normal. I was told to exercise more, to stress less, that it might be related to my cycle. None of these things were wrong. None of them were the whole picture.
The framework I eventually found — not in a clinic but in research papers, because of course — was low-grade inflammation. Chronic, systemic, subclinical. Below the threshold that conventional medicine calls concerning. Running quietly enough to be easy to miss, pervasive enough to affect almost every system in the body, and so normalised in the population it screens against that "your levels are normal" had become a sentence that meant very little.
This post is what I found. It is also what I wish had been offered to me earlier, by a system that had all the tools and simply never joined the dots.
First: what inflammation is actually for
Inflammation is not the enemy. Before we talk about what happens when it goes wrong, it's worth being precise about what it does when it goes right — because the demonisation of inflammation in wellness culture has produced a generation of people treating their immune system's most essential mechanism as a problem to be eliminated.
Acute inflammation is the body's first and most powerful repair response. When tissue is damaged, infected, or threatened, the immune system generates a localised cascade: blood flow increases, immune cells flood the area, pro-inflammatory cytokines signal the extent of the damage, and the work of clearing, repairing, and rebuilding begins. It is painful. It is swollen. It is visible. And it resolves — within days to weeks, the inflammation is contained, the repair is done, and the system returns to baseline.
This is the version of inflammation that medicine is well-equipped to handle. It has a clear trigger, a measurable course, and an endpoint.
What low-grade inflammation looks like is something different entirely.
The fire that doesn't announce itself
Low-grade chronic inflammation — sometimes called metainflammation, or sterile inflammation — is characterised by a persistent, low-level activation of the innate immune system without a specific pathogen trigger and without resolution.¹ The same cytokines — IL-6, TNF-alpha, IL-1beta — that operate at high concentrations in acute illness circulate here at two to four times their baseline levels. Consistently. Without the body ever receiving the signal that the emergency is over.
This is what makes it so easy to miss. There is no fever. No localised pain. No obvious swelling. Just a persistent background hum of immune activation that, over months and years, begins affecting every organ system it touches.
The research on what this low-level chronic activation actually does has been building for several decades. What it shows is that metainflammation is not a side issue. It is a central mechanism behind some of the most prevalent chronic conditions of modern life: cardiovascular disease, insulin resistance and type 2 diabetes, depression, cognitive decline, autoimmune disease, and accelerated biological ageing. The inflammatory signature precedes these diagnoses — often by years — and is frequently running at levels that routine clinical testing classifies as normal.
What it does to the brain
This is the piece I find most important, and the piece that is most underrepresented in clinical conversations about inflammation.
Pro-inflammatory cytokines cross the blood-brain barrier. IL-6 and TNF-alpha have specific transport mechanisms that allow them to signal directly to brain tissue — and once there, they activate microglial cells, the brain's resident immune cells, producing a state of neuroinflammation. Dantzer and colleagues published what has become a foundational review of this pathway in Nature Reviews Neuroscience: the cytokine-to-brain signalling cascade produces what they termed "sickness behaviour" — fatigue, social withdrawal, anhedonia, cognitive impairment, disrupted sleep, and low mood.³
In the context of acute infection, sickness behaviour is adaptive. It enforces rest, directs energy toward immune function, and pulls resources away from energetically expensive social and cognitive activity while the body recovers. In the context of low-grade chronic inflammation, it runs continuously. The fatigue, fog, and low mood that many women attribute to stress, burnout, or the demands of their thirties and forties are, in a significant proportion of cases, a direct output of a cytokine-driven brain state that nobody has investigated.
This is not a soft claim. The bidirectional relationship between depression and inflammatory markers is now among the best-evidenced findings in biological psychiatry. CRP and IL-6 are consistently elevated in depressive episodes. Anti-inflammatory interventions — including dietary changes, exercise, and in clinical trials, anti-cytokine medications — produce measurable improvements in mood. The brain is downstream of the immune system in ways that medicine has historically refused to take seriously.
What it does to hormones
The endocrine system is not insulated from inflammatory signalling. It is exquisitely sensitive to it.
Inflammatory cytokines — particularly IL-6 and TNF-alpha — interfere with the hypothalamic-pituitary axis at multiple levels. They suppress GnRH pulsatility, reducing LH release and therefore progesterone production in the luteal phase. They amplify HPA axis reactivity, producing higher and more sustained cortisol responses to stress. They impair thyroid hormone conversion — specifically the conversion of T4 to the active T3 form — at the cellular level. And they promote insulin resistance through direct interference with insulin receptor signalling in both muscle and adipose tissue.⁴
What this means in practice: a woman with chronically elevated low-grade inflammatory markers will often show a hormonal picture that is difficult to interpret without accounting for the inflammatory background. Luteal phase insufficiency, blunted cortisol awakening response, subclinical hypothyroidism with normal TSH, insulin resistance without meeting diagnostic threshold for prediabetes — these are all common presentations of a hormonal system operating in an inflammatory environment. Treating the hormones without addressing the inflammation is like trying to fix a ventilation system in a building that's on fire. The problem isn't the ventilation.
The biomarkers you probably haven't had tested
This is where the clinical gap becomes most specific.
CRP — C-reactive protein — is the most commonly ordered inflammatory marker in primary care. Research by Ridker and colleagues established its predictive value for cardiovascular events decades ago, in findings that were strong enough to shift clinical guidelines.² What those guidelines have been slower to incorporate is the significance of low-level CRP elevation — specifically, the range between 1 and 10 mg/L that is routinely classified as "normal" in clinical practice but that population research consistently associates with elevated metabolic, cardiovascular, and neurological risk.
IL-6 is almost never tested in standard primary care, despite being one of the most biologically active pro-inflammatory cytokines and a direct driver of many of the downstream effects described above. Homocysteine — an amino acid that reflects methylation status and is associated with cardiovascular and neurological risk — is rarely part of a standard panel. Fibrinogen is ordered mainly in specific clinical contexts.
The result: the most clinically informative inflammatory picture is rarely assembled, because the tests that would assemble it are not part of standard screening. The gap is not scientific. The evidence for all of these markers is extensive. The gap is structural.
What drives it — and how the drivers compound
Low-grade inflammation does not have a single cause. It has a constellation of drivers that interact, amplify each other, and collectively determine the inflammatory load the body is carrying at any given time.⁵
Sleep deprivation is one of the fastest triggers — even partial restriction elevates IL-6 and TNF-alpha measurably within days. Chronic psychological stress activates the HPA axis and the innate immune system simultaneously, in ways that perpetuate each other. Ultra-processed food patterns drive intestinal permeability and endotoxaemia — the leaking of bacterial components into systemic circulation, where they trigger immune activation. Visceral adipose tissue is itself an endocrine organ that secretes pro-inflammatory adipokines. Sedentary behaviour removes one of the most potent anti-inflammatory inputs available: skeletal muscle contraction, which releases anti-inflammatory myokines including IL-10 and IL-1ra. Environmental toxin exposure activates the innate immune system through TLR pathways.
The compounding is the important part. No single driver produces a large effect in isolation. But three or four running simultaneously push the system toward a chronic activation state that is qualitatively different from any individual contribution. The drivers create a background that makes resolution progressively harder — which is why low-grade inflammation tends to be self-perpetuating once established.
The clinical gap — and who it costs most
Low-grade inflammation is poorly integrated into conventional primary care. CRP is not part of a standard blood panel in most countries. When it is ordered, ranges that classify 1–10 mg/L as "normal" include levels that population research associates with significantly elevated cardiovascular, metabolic, and cognitive risk. IL-6 is rarely tested at all. Homocysteine — with its strong associations with cardiovascular and neurological outcomes — is not standard screening. The full inflammatory picture that the research considers clinically meaningful is almost never assembled in routine care.
Women bear a disproportionate part of this cost. The symptom presentation of chronic low-grade inflammation — fatigue, cognitive fog, joint stiffness, mood changes, hormonal irregularity, sleep disruption — maps almost exactly onto the constellation of complaints that conventional medicine has historically attributed to stress, anxiety, the cycle, or the vague category of "women's things." The framework that would connect those symptoms to a measurable physiological state is available. It is not offered.
This is not a gap in the evidence. The evidence is decades deep and consistently replicated. It is a gap in translation — between what research shows and what gets communicated to the people who need it, in the appointments that should be where that communication happens.
What to actually do with this
- Get the markers tested — and know what the numbers actually mean. CRP, IL-6 if possible, homocysteine, and fasting insulin give you the most informative inflammatory snapshot available from standard blood testing. If your CRP is anywhere above 1 mg/L, that is worth understanding in context — not dismissing as normal. The research-optimal target for CRP is below 1 mg/L, not below 10. If your practitioner doesn't know why that matters, bring the Ridker paper.
- Treat sleep as the first anti-inflammatory intervention. Sleep is not a lifestyle preference. It is the primary mechanism by which the body resolves inflammatory signalling, clears metabolic waste from the brain, and resets immune activation. Consistent sleep restriction — even modest amounts — elevates IL-6 and TNF-alpha reliably. No supplement, dietary pattern, or anti-inflammatory protocol produces effects that are remotely comparable to the impact of adequate, regular, restorative sleep. If you are building an anti-inflammatory strategy, sleep is not the last item on the list.
- Movement as medicine — specifically the myokine argument. Skeletal muscle contraction during sustained aerobic exercise releases anti-inflammatory myokines — IL-10, IL-1ra, irisin — that directly counter the pro-inflammatory cytokine milieu. This is not a general "exercise is good for you" statement. It is a specific anti-inflammatory mechanism that is dose-dependent and well-evidenced. Thirty to forty-five minutes of moderate aerobic exercise three to five times per week produces measurable reductions in CRP and IL-6 within weeks. The mechanism is specific and the effect is real.
- The dietary pattern matters more than individual foods. The research on diet and inflammation consistently shows that overall dietary pattern — specifically the ratio of minimally processed whole foods to ultra-processed foods — predicts inflammatory marker levels better than any single ingredient. The Mediterranean dietary pattern remains the most replicated anti-inflammatory dietary intervention in the literature. Practically: this means prioritising diversity of vegetables, quality omega-3 fat sources, legumes, and whole grains, and reducing ultra-processed food frequency — not eliminating individual foods or optimising single nutrients.
- Investigate the gut. Intestinal permeability — the leaking of bacterial endotoxins (LPS) into systemic circulation — is one of the most consistent upstream drivers of chronic low-grade inflammation and one of the least investigated in standard care. Symptoms of gut dysbiosis (irregular bowels, bloating, food sensitivities, skin changes) alongside an elevated inflammatory picture warrant specific investigation. Fermented foods, prebiotic fibre diversity, and reduction in ultra-processed food are the most evidence-backed starting points.
- Address the hormonal picture in the context of inflammation — not in isolation. If you have a hormonal presentation that doesn't respond predictably to interventions — progesterone support that doesn't shift luteal symptoms, thyroid treatment that doesn't fully resolve fatigue, insulin management that remains frustratingly unstable — consider the inflammatory background. Cytokines interfere with hormone receptor sensitivity and hormone metabolism at the cellular level. Treating the hormones in an uninflamed system and treating them in a chronically inflamed system are not the same clinical situation. The inflammation has to be part of the conversation.
I still take my temperature before I get out of bed. I still track my cycle and my sleep and the other data points that give me a read on what my body is doing. But the thing that changed most was not any single intervention. It was having a framework.
Inflammation is not the enemy. The body's capacity to generate it is one of the most elegant and important biological mechanisms we have. What is worth paying attention to is when it shifts from a response to a state — from acute and purposeful to chronic and diffuse, from fire fighting a specific threat to fire that doesn't know when to stop.
My stiffness is better. My fog has names and addresses. The persistent sense of managing something has become, most of the time, something more specific: something I am actively working on, with actual tools, instead of something I am quietly enduring and telling doctors is fine.
The bloods are still normal, by the way. That hasn't changed. What changed is what I understand normal to mean.
– Nina- Hotamisligil, G.S. (2006). Inflammation and metabolic disorders. Nature, 444(7121), 860–867. doi:10.1038/nature05485
- Ridker, P.M., Cushman, M., Stampfer, M.J., Tracy, R.P., & Hennekens, C.H. (1997). Inflammation, aspirin, and the risk of cardiovascular disease in apparently healthy men. New England Journal of Medicine, 336(14), 973–979. doi:10.1056/NEJM199704033361401
- Dantzer, R., O'Connor, J.C., Freund, G.G., Johnson, R.W., & Kelley, K.W. (2008). From inflammation to sickness and depression: when the immune system subjugates the brain. Nature Reviews Neuroscience, 9(1), 46–56. doi:10.1038/nrn2297
- Ershler, W.B., & Keller, E.T. (2000). Age-associated increased interleukin-6 gene expression, late-life diseases, and frailty. Annual Review of Medicine, 51, 245–270. doi:10.1146/annurev.med.51.1.245
- Minihane, A.M., Vinoy, S., Russell, W.R., Baka, A., Roche, H.M., Tuohy, K.M., & Calder, P.C. (2015). Low-grade inflammation, diet composition and health: current research evidence and its translation. British Journal of Nutrition, 114(7), 999–1012. doi:10.1017/S0007114515002093