The Prognostic Value of Serum Interleukin-6 Concentrations for 9 Cardiovascular and Mortality Outcomes

Background

Interleukin-6, often abbreviated as IL-6, is a signaling protein made by immune cells and other tissues during inflammation. In recent years, IL-6 has attracted major attention because inflammation is now recognized as a key driver of cardiovascular disease, not just a bystander. Researchers have therefore asked a practical question: if someone has higher IL-6 in their blood, does that mean they are more likely to develop heart attack, stroke, heart failure, atrial fibrillation, or die from cardiovascular causes?

This study, from the Cross Cohort Collaboration, was designed to answer that question using data from large, multiethnic prospective cohorts. By pooling individual-level information from many studies, the investigators could test whether IL-6 is linked to a wide range of cardiovascular and mortality outcomes in real-world community populations, not just in one narrowly defined group.

Why IL-6 matters

IL-6 is part of the body’s immune response. When inflammation is activated, IL-6 helps regulate the production of other inflammatory molecules and acute-phase proteins such as high-sensitivity C-reactive protein, or hsCRP. Persistent low-grade inflammation can damage blood vessels, worsen atherosclerosis, and contribute to plaque instability, thrombosis, cardiac remodeling, and metabolic dysfunction.

Because of this biology, IL-6 has become a promising therapeutic target. Drugs that block the IL-6 pathway are already used in some inflammatory diseases, and researchers are increasingly interested in whether reducing IL-6 signaling could lower cardiovascular risk as well. However, before IL-6 inhibition can be broadly considered for cardiovascular prevention, it is important to know how strongly IL-6 is associated with future cardiovascular events across different populations and clinical settings.

Study design

The investigators harmonized participant-level data from 14 prospective cohorts, including 59,396 adults. All participants had baseline blood IL-6 measurements and follow-up data for one or more of nine prespecified outcomes:

1. Myocardial infarction
2. Stroke
3. Atrial fibrillation
4. Heart failure
5. Total coronary heart disease (CHD)
6. Total cardiovascular disease (CVD)
7. All-cause mortality
8. CVD-specific mortality
9. CHD-specific mortality

The analysis used multivariable-adjusted Cox proportional hazards models, which are standard methods for estimating the relative risk of events over time while accounting for important confounding factors such as age, sex, race, and clinical variables.

IL-6 was examined in two ways: by quartiles, which compare people with low, intermediate, and high levels, and as a continuous variable after logarithmic transformation, which helps handle skewed biomarker distributions.

The study also asked whether the relationship between IL-6 and outcomes differed in important subgroups, including people with:

– Chronic kidney disease
– Diabetes
– Different levels of hsCRP
– Different body mass index categories
– Secondary prevention populations, meaning individuals who already had cardiovascular disease

Finally, the researchers assessed discrimination, or how much IL-6 improves risk prediction, by comparing models that included clinical factors alone versus models that also included IL-6, hsCRP, or both.

Main findings

The median IL-6 concentration was 1.91 pg/mL. The average age of participants was 63.6 years, 67.6% were women, and 20.6% were Black. Follow-up was long, with a median duration reaching 15.8 years for cardiovascular mortality.

Across the full cohort, higher IL-6 concentrations were associated with greater risk of all nine outcomes. In other words, as IL-6 levels rose, so did the likelihood of heart attack, stroke, heart failure, atrial fibrillation, CHD, broader CVD, and death from any cause or cardiovascular causes.

The strongest association was seen for CHD-specific mortality. Participants in the highest IL-6 quartile had more than double the risk of dying from CHD compared with those in the lowest quartile, with an adjusted hazard ratio of 2.12 (95% CI: 1.88-2.39).

The weakest association was observed for myocardial infarction, although it was still significant and clinically meaningful, with an adjusted hazard ratio of 1.45 (95% CI: 1.28-1.64).

These results suggest that IL-6 is not only linked to a single cardiovascular endpoint, but to a broad spectrum of outcomes involving both incident disease and mortality.

Subgroup analyses

One of the most important strengths of this study is that the associations remained robust across key subgroups. The relationship between higher IL-6 and worse outcomes was generally consistent regardless of:

– Diabetes status
– Chronic kidney disease status
– hsCRP level
– Body mass index category
– Secondary prevention status

This matters because cardiovascular inflammation is often more complex in people with obesity, diabetes, renal disease, or prior cardiovascular events. The fact that IL-6 retained predictive value across these groups supports the idea that IL-6-mediated inflammation is a common pathway in cardiovascular risk rather than a marker limited to one specific patient type.

Risk prediction and clinical relevance

The investigators also tested whether IL-6 improved discrimination beyond traditional clinical risk factors and hsCRP. IL-6 alone offered modest additional predictive value for several outcomes, including stroke, heart failure, CVD, CHD, and mortality.

This finding is important but should be interpreted carefully. In clinical practice, a biomarker can be strongly associated with disease yet still add only a modest amount to risk prediction models, especially when established factors such as age, blood pressure, diabetes, smoking, cholesterol, and kidney function are already included. That appears to be the case here: IL-6 is a strong biologic signal and a meaningful marker of risk, but it is not a stand-alone screening tool.

Its value may be greatest in helping to identify patients in whom inflammatory pathways are especially active and who might benefit from more intensive prevention strategies or future anti-inflammatory therapies.

How these findings fit into current cardiovascular science

Cardiovascular prevention has traditionally focused on controlling blood pressure, lipids, blood sugar, smoking, and weight. The growing evidence around IL-6 reinforces a newer concept: inflammation is a parallel and important target.

The present study supports several key ideas:

– Inflammation contributes to both atherosclerotic events and heart failure-related outcomes.
– IL-6 is linked not just to disease occurrence but also to death, especially CHD-related death.
– The association is consistent in diverse populations, which increases confidence that the results are generalizable.
– Even after accounting for hsCRP, IL-6 still carries information, suggesting it may reflect inflammatory biology not fully captured by CRP alone.

Taken together, the findings add weight to the hypothesis that therapies targeting the IL-6 pathway could have cardiovascular benefits. However, observational association does not prove that lowering IL-6 will automatically reduce events. Randomized trials are still needed to confirm whether IL-6 inhibition improves outcomes in broad cardiovascular populations and to identify which patients would benefit most.

Clinical interpretation

For clinicians, this study suggests that a higher IL-6 level may identify patients at elevated long-term cardiovascular and mortality risk, even in community-based cohorts and across multiple clinical subgroups. IL-6 may be especially useful as part of a broader inflammatory risk profile, alongside hsCRP and traditional cardiometabolic measures.

For patients, the practical message is that chronic inflammation is not just a laboratory concept. It is closely tied to heart and vascular health. Measures that reduce inflammation indirectly, such as weight management, physical activity, smoking cessation, blood pressure control, lipid lowering, diabetes control, and kidney disease management, remain foundational. Future therapies may also specifically target inflammatory pathways such as IL-6.

Strengths and limitations

This study has several major strengths:

– Very large sample size
– Multiethnic cohorts
– Harmonized individual-level data
– Long follow-up period
– Multiple cardiovascular and mortality outcomes
– Analyses across important clinical subgroups

There are also limitations to keep in mind. As an observational analysis, it cannot prove causation. IL-6 was measured at baseline, so changes over time were not fully captured. Residual confounding is always possible, even with careful adjustment. In addition, although the cohorts were diverse, biomarker assays and cohort characteristics may differ somewhat across studies.

Still, the consistency of the findings across endpoints and subgroups makes the overall message compelling.

Conclusion

In this large pooled analysis of 14 prospective cohorts involving nearly 60,000 participants, higher serum IL-6 concentrations were strongly and consistently associated with nine cardiovascular and mortality outcomes. The relationship remained evident across major cardiometabolic subgroups, chronic kidney disease status, and secondary prevention settings.

These results strengthen the case that IL-6-mediated inflammation plays a broad role in cardiovascular risk. They also support continued research into IL-6 as both a biomarker and a therapeutic target in cardiovascular prevention.

Reference

Yao Z, Dardari ZA, LaMonte MJ, et al. The Prognostic Value of Serum Interleukin-6 Concentrations for 9 Cardiovascular and Mortality Outcomes: The Cross Cohort Collaboration (CCC). Journal of the American College of Cardiology. 2026; PMID: 42201287.