What it means
C-reactive protein is made by the liver in response to interleukin-6, the master inflammatory cytokine. The "high-sensitivity" assay measures it precisely at the low levels (0.1–10 mg/L) that reflect chronic, low-grade inflammation rather than infection. It is the standard clinical proxy for inflammaging.
Conventional cut-offs: under 1 mg/L low risk, 1–3 average, over 3 high. Values above 10 usually mean an acute infection or injury and should be repeated after two weeks.
Why it matters for longevity
Chronic inflammation drives atherosclerosis, insulin resistance, sarcopenia and the senescent-cell burden. hs-CRP is the one marker on a routine panel that reports on all of them at once, and it responds within weeks to the levers that matter: body fat, sleep, training and diet.
What the evidence says
In the Women's Health Study (Ridker 2000, 28,000 women) hs-CRP predicted cardiovascular events as strongly as LDL cholesterol and independently of it. The JUPITER trial (2008) showed that people with normal LDL but hs-CRP above 2 mg/L had their cardiovascular events cut 44% by a statin. The CANTOS trial (2017) showed that lowering inflammation directly with an IL-1β antibody reduced heart attacks without touching cholesterol — proof that inflammation itself is causal.
In ageing cohorts, higher hs-CRP and IL-6 predict frailty, muscle loss and mortality. Weight loss of 5–10% typically lowers hs-CRP by 20–30%; regular exercise, Mediterranean-pattern diet and correcting sleep apnoea each lower it in trials.
How to measure or use it
- A standard blood test; no fasting needed. Take the average of two readings two weeks apart, and ignore any reading taken within two weeks of an infection, injury or hard race.
- Target under 1 mg/L; under 0.5 is common in lean, fit adults.
- If persistently above 3 with nothing obvious, look for a cause — sleep apnoea, gum disease, visceral fat, an autoimmune process — rather than reaching for an anti-inflammatory supplement.
Related
- Inflammation and immunity — the full article
- Biomarkers of ageing — hs-CRP in the core panel
- The immune and inflammation protocol — how it is used in a plan
Frequently asked questions
What is a normal hs-CRP?
Under 1 mg/L is low risk; 1–3 average; above 3 high. Readings above 10 usually reflect acute infection and should be repeated.
What raises hs-CRP?
Visceral fat, poor sleep, infection, injury, hard training in the previous 48 hours, gum disease, smoking and autoimmune conditions.
How quickly does it change?
Within weeks of a change in body fat, sleep or training load. Retest at 8–12 weeks after a lifestyle change.
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