Interleukin-6 (IL-6)

Interleukin-6 (IL-6) is a pleiotropic cytokine central to the body's inflammatory response, and chronic low-grade elevation of circulating IL-6 is one of the most consistently replicated blood markers of inflammaging, the persistent, sterile inflammation that accumulates with age. The claim: higher circulating IL-6 independently predicts mortality and age-related disease across multiple large cohorts, largely independent of other inflammatory markers.

A 2025 analysis of 1,009 hospitalized older adults (median age 84) in the ReportAGE cohort, followed over roughly 5,196 person-years with 833 deaths (82.6%), found median IL-6 levels were more than double in patients who eventually died compared with survivors (16.7 vs. 7.2 pg/mL, p<0.001), and IL-6 was an independent predictor within a composite inflammaging score that carried a hazard ratio of 2.42 (95% CI 1.74-3.37) comparing high versus low scores [1]. Among community-dwelling older adults specifically, the Iowa 65+ Rural Health Study (n=1,293 healthy, non-disabled adults) found the highest IL-6 quartile carried twice the mortality risk of the lowest quartile, and elevation of both IL-6 and CRP together was associated with 2.6-fold higher mortality risk [2]. The Framingham Heart Study similarly found higher IL-6 and TNF-alpha levels were associated with increased mortality in older adults, and the Health ABC cohort found elevated IL-6 was more strongly associated with cancer death specifically (hazard ratio 1.63) than with cancer incidence, suggesting IL-6 may reflect a systemic vulnerability to poor outcomes once disease is present rather than purely driving disease onset [2].

How to measure it: standard clinical or research immunoassay, ELISA or high-sensitivity multiplex, from a blood serum or plasma sample, reported in picograms per milliliter [3]. Levels show substantial day-to-day and assay-to-assay variability, and acute illness or infection can transiently spike IL-6 far above baseline chronic-inflammation levels, so single measurements during acute illness are not representative of someone's baseline inflammaging status.

How to intervene on it: aerobic exercise, weight loss in individuals with obesity, and treating underlying chronic infections or periodontal disease can lower chronic IL-6 elevation in observational and small trial data; several IL-6 pathway inhibitor drugs exist for autoimmune disease (e.g., tocilizumab) but are not established or approved as longevity interventions given their immunosuppressive risks, and no trial has shown that pharmacologically lowering IL-6 in otherwise healthy older adults extends lifespan.

Critics note IL-6 elevation is a downstream marker of many different underlying processes, including occult infection, obesity, smoking, and periodontal disease, so an elevated level is diagnostically non-specific and requires clinical context rather than being treated as a standalone red flag [3]. The strong association between IL-6 and cancer death rather than cancer incidence specifically also raises the possibility that IL-6 partly reflects an already-present disease burden rather than acting as a pure early-warning marker [4][5].

Bryan Johnson's Blueprint protocol tracks IL-6 as part of its routine inflammatory panel, an n=1 self-report [6].

The plain takeaway: chronic IL-6 elevation is one of the most consistently validated blood-based predictors of mortality risk in older adults across multiple independent large cohorts, but because it is a non-specific marker of many different inflammatory triggers, an elevated reading should prompt investigation into underlying causes rather than treatment of the number itself.