The Slow Burn Behind Most Chronic Disease
One process sits behind many separate names.
“The good physician treats the disease; the great physician treats the patient who has the disease.”
— William Osler
Heart disease, type 2 diabetes, several cancers and some forms of dementia are filed as separate conditions, treated by different specialists and researched in different departments. Across the past three decades a thread has been found running through many of them, and the thread is immune activity that never quite switched off. That observation has been genuinely productive, and it has also been enthusiastically oversold, which makes it worth separating what the evidence actually supports from the confident structure that has been built on top of it.
The distinction that matters throughout is between association and cause. Finding raised inflammatory markers in people who later develop a disease establishes that the two travel together. It does not establish which one is driving. Inflammation might be causing the damage, or reflecting damage already underway, or both at once in a loop that feeds itself. Untangling that requires a different kind of study, and for one condition that study has actually been done. For the rest, the honest answer is that the question remains open.
The Thread Running Through Separate Names
Atherosclerosis is the clearest illustration and the one that changed the field. Arteries do not simply silt up with fat the way a pipe accumulates limescale. Immune cells enter the artery wall, take up modified cholesterol particles, and become the foam cells that form the core of a plaque. Further immune activity then determines whether that plaque stays stable or ruptures, and rupture is what causes most heart attacks. What was once described as a plumbing problem is now understood as substantially an inflammatory one.
Similar threads appear elsewhere. Inflammatory signalling interferes with how cells respond to insulin, which links it to type 2 diabetes. Chronic inflammation at a specific site, as in some persistent infections and inflammatory bowel conditions, raises cancer risk at that site. Immune cells in the brain behave differently in neurodegenerative disease. The pattern is real and it recurs. What it does not licence is the leap to a single unified cause, because each of those conditions also carries genetics, metabolism and exposure history alongside it. Every one of them would still exist in a world where nothing was ever inflamed.
Where the Heart Evidence Went Further
For cardiovascular disease, researchers ran the experiment that association studies cannot run. A large trial gave people who had already had a heart attack a drug that blocks one specific inflammatory signal and does nothing whatever to cholesterol. Cardiovascular events fell. That result matters because it isolated the variable: nothing about the lipids changed, and the outcome moved anyway. Inflammation was not merely accompanying the disease in those patients. It was contributing to it, which is a considerably stronger claim than anything observational work can deliver.
The same trial carries the caution that usually gets omitted when the finding is quoted. Suppressing part of the immune system raised the rate of fatal infection, which is exactly what an honest reading would predict. The drug is expensive, injected, and was never a general purpose intervention for anybody. Later trials of colchicine, a much older and cheaper anti-inflammatory, have shown benefit in similar patients. Both belong to specialist cardiology practice for people with established disease, not to anybody wondering whether their lunch was inflammatory.
Where the Evidence Is Much Weaker
Beyond the heart, confidence drops sharply, and popular coverage rarely reflects that drop. Depression is the most discussed example. Raised inflammatory markers are found more often in people with depression, some inflammatory conditions raise depression risk, and treatments that lower inflammation have shown effects in certain subgroups. That is genuinely interesting work. It is not the same as showing that depression is an inflammatory disease, and the subgroup findings have proved difficult to replicate with any consistency across different populations.
Dementia is similar. Immune cells in the brain are clearly involved in the disease process, but whether their activity starts the damage or responds to it remains unsettled. With cancer, chronic inflammation at a specific site is an established risk factor, while a modest whole-body elevation is a much weaker and far less specific signal. Reverse causation haunts all of it, because illness that has begun but has not yet been diagnosed raises inflammatory markers on its own, sometimes years before anybody notices anything.
What This Does and Does Not License
The reasonable conclusion is narrower than the one usually drawn. Persistent low-grade inflammation is a real biological phenomenon, it is involved in several major diseases, and it is influenced by how people live. That is worth knowing and it changed medicine. It does not follow that inflammation is the root cause of modern illness, that any single food meaningfully alters disease risk, or that a marker measured once tells you where you are heading. The step from an interesting mechanism to a personal prescription is where the overreach lives. The mechanism is genuine, and most of what has been built on top of it is not.
It also does not follow that anybody should be self-treating. The interventions with actual trial evidence behind them are prescription drugs, used in specialist settings, for people with diagnosed disease, and they carry real risks. What is available to everybody else is the familiar list: not smoking, moving regularly, sleeping enough, eating a pattern rather than a product, and treating what is treatable. That advice was already justified without any of this, which is either a disappointment or a reassurance depending on what was hoped for.
💡 Key Takeaway
Immune activity that never switches off is genuinely involved in heart disease, diabetes and other conditions, and for cardiovascular disease a trial showed it contributes causally. Elsewhere the evidence is mostly association, and illness itself raises the markers, which makes direction hard to establish. None of this licenses self-treatment. The interventions with real trial evidence are specialist drugs with real risks.