Inflammation Explained: Acute Inflammation vs Chronic Low Grade Inflammation

Few words in health writing are used as loosely as inflammation. It is blamed for almost everything, promised to be reduced by almost every product, and measured by a single blood test that most people have never heard of. Behind the noise lies one of the most important developments in modern medicine: the recognition that a persistent, low level activation of the immune system contributes to many of the chronic diseases that dominate health today. To use that insight well, practitioners need to understand how acute and chronic inflammation differ, what drives the chronic form, and what the evidence says about reducing it.

Acute inflammation: a defence that ends

Acute inflammation is the body’s immediate response to injury or infection. Its classical signs, described since antiquity, are redness, heat, swelling, pain and loss of function. They reflect a coordinated sequence: blood vessels dilate and become more permeable; immune cells, led by neutrophils, migrate to the site; signalling molecules such as cytokines and prostaglandins amplify the response; the threat is contained and cleared.

Just as important is what happens next. Inflammation does not simply fade. Its resolution is an active process, orchestrated by specialised lipid mediators and by immune cells that switch from pro inflammatory to repair functions, clearing debris and restoring tissue. When resolution works, the response is brief and proportionate. When it fails, inflammation can persist.

Chronic low grade inflammation: a different phenomenon

Chronic low grade inflammation is not simply acute inflammation that has gone on too long. It is a distinct state: a sustained, modest elevation of inflammatory signalling, usually without the classical signs, often detectable only through blood markers or at the tissue level. It has been described by several names reflecting its settings, including metaflammation, for inflammation arising from metabolic excess, and inflammaging, for the gradual rise in inflammatory tone with age.

How we know it matters

For years, the link between inflammation and chronic disease rested on associations: people with higher levels of inflammatory markers such as C reactive protein had higher rates of cardiovascular disease, diabetes and other conditions. Associations alone cannot show cause.

The CANTOS trial changed that. Patients with a previous heart attack and raised high sensitivity C reactive protein were randomised to canakinumab, an antibody that blocks the inflammatory cytokine interleukin 1 beta, or placebo. Canakinumab reduced recurrent cardiovascular events without lowering cholesterol, providing strong evidence that inflammation itself contributes to atherosclerotic disease. It also increased the risk of fatal infections, a reminder that the immune system cannot be suppressed without cost. The drug was not adopted for this purpose, but the principle was established.

What drives chronic inflammation

For practitioners, the most important question is not whether a patient has inflammation but why. The common drivers are well characterised.

Visceral adiposity

Fat stored around the abdominal organs is metabolically active. Expanding fat tissue attracts immune cells and releases inflammatory signals and free fatty acids, which impair insulin signalling in liver and muscle. This link between metabolic excess and inflammation lies at the centre of the relationship between obesity, insulin resistance and type 2 diabetes.

Physical inactivity

Contracting muscle releases signalling molecules with anti inflammatory effects, and regular exercise reduces visceral fat. Inactivity removes both benefits.

Smoking

Tobacco smoke is a potent and persistent inflammatory stimulus, affecting the lungs, blood vessels and systemic markers.

Diet

Dietary patterns rich in vegetables, fruit, legumes, whole grains, nuts and olive oil are associated with lower inflammatory markers, and trials of Mediterranean style diets have shown modest reductions. Patterns high in ultra processed foods, refined carbohydrates and certain fats are associated with higher markers, partly through their effects on weight and glucose.

Poor sleep

Short and disrupted sleep raises inflammatory markers in experimental studies, and sleep disorders such as obstructive sleep apnoea are associated with systemic inflammation.

Chronic psychological stress

Persistent stress alters the regulation of inflammatory responses, in part by changing how immune cells respond to cortisol.

Other sources

Periodontal disease, chronic infections, autoimmune disease, environmental exposures such as air pollution, and gut barrier dysfunction can all contribute. Ageing itself is associated with a gradual rise in inflammatory tone.

Measuring inflammation

High sensitivity C reactive protein is the most widely used marker of low grade systemic inflammation. Guidance from American cardiovascular and public health bodies has categorised values below 1 milligram per litre as lower cardiovascular risk, 1 to 3 as average and above 3 as higher, while noting that values above 10 usually indicate an acute process and should be repeated after it resolves. hsCRP varies within individuals and rises with any infection or injury, so a single value should be interpreted cautiously and ideally confirmed.

Other markers have their own roles. The erythrocyte sedimentation rate is useful in some inflammatory diseases but less specific. Ferritin rises with inflammation, which complicates the assessment of iron stores. White cell counts may be modestly raised. Specialised cytokine measurements are research tools rather than routine clinical tests.

Markers are not a substitute for the history. In most patients, the drivers of chronic inflammation are identifiable from lifestyle, weight distribution, sleep, stress and medical history, and markers mainly help confirm the picture and track change.

Reducing inflammation: what works

Because chronic low grade inflammation is driven by identifiable factors, the most effective approach is to address those factors.

• Weight reduction, particularly loss of visceral fat, lowers inflammatory markers in proportion to the loss.
• Regular physical activity reduces markers over time, independently of weight change to some degree.
• Dietary pattern changes towards a Mediterranean style diet produce modest reductions.
• Smoking cessation reduces inflammatory markers over months to years.
• Improving sleep, and treating sleep apnoea where present, addresses an important driver.
• Stress reduction through psychological approaches and social support may help, although effects on markers are less consistent.
• Treating specific sources such as periodontal disease or chronic infection.

Supplements marketed as anti inflammatory deserve careful evaluation. Omega 3 fatty acids have modest effects on some markers and established benefits in specific contexts, such as very high triglycerides. Curcumin has shown effects in some small trials, with variable absorption and occasional safety concerns. None is a substitute for addressing the drivers, and none has been shown to replicate the effects of comprehensive lifestyle change.

An illustrative case

A 52 year old office manager has an hsCRP of 4.2 milligrams per litre on 2 occasions a month apart, with no infection. She has central weight gain, sleeps 6 hours with loud snoring, walks little and has gum disease her dentist has mentioned. Her physician considers the hsCRP alongside her other cardiovascular risk factors. The functional assessment identifies 4 likely drivers: visceral adiposity, possible sleep apnoea, inactivity and periodontal disease. The plan includes a sleep study through her doctor, dental treatment, a structured walking programme and dietary change towards a Mediterranean pattern. 6 months later her hsCRP has fallen to 1.8, her waist circumference is smaller and her sleep apnoea is being treated. No anti inflammatory product was needed.

Keeping perspective

Inflammation is not an enemy to be eliminated. It is a vital defence, and suppressing it indiscriminately carries real risks, as CANTOS showed. The goal in chronic disease is to remove the persistent stimuli that keep it switched on, allowing the body’s own resolution mechanisms to work. Framed that way, inflammation becomes less a mysterious force and more a signal, pointing the practitioner towards the modifiable drivers that matter most.