Home›Allergy & Immunology› Serum complement C3 levels are elevated in polycystic ovary syndrome, meta-analysis finds
Serum complement C3 levels are elevated in polycystic ovary syndrome, meta-analysis findsHigher Levels of Complement C3 Protein Found in People with Polycystic Ovary Syndrome
Frontiers in MedicinePublished August 21, 2026DOI ↗Editorial oversight: Dr. Amelia Tan, PhD · Internal Medicine & Chronic Disease
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Key Takeaway
Consider serum C3 as an exploratory inflammatory marker in PCOS, but await prospective validation before clinical use.
This meta-analysis pooled data from 915 individuals with polycystic ovary syndrome (PCOS) and controls to compare serum complement C3 levels. The primary outcome was the difference in C3 levels between the two groups. The analysis found that C3 levels were significantly higher in PCOS patients than in controls, with a standardized mean difference (SMD) of 0.73 (95% CI: 0.54–0.93). Heterogeneity was moderate (I² = 47.1%, P = 0.092).
The findings suggest that complement C3, a marker of low-grade inflammation, may be elevated in PCOS. However, the authors emphasize that this is an association only, not proof of causation, because the underlying studies were observational. The evidence is considered exploratory due to the observational design and limited evidence base.
The meta-analysis did not report on adverse events, tolerability, or other safety outcomes, as it focused on biomarker levels. The authors note that prospective studies are needed to validate the association and to determine whether C3 levels have clinical utility in PCOS management.
For clinicians, these findings are exploratory and should not change current practice. They may inform future research directions, but routine measurement of serum C3 in PCOS is not yet supported. The association aligns with the understanding that PCOS involves chronic low-grade inflammation, but more robust evidence is required before any clinical recommendations can be made.
How this fits prior evidence
This meta-analysis extends prior coverage by linking an inflammatory marker, serum complement C3, to PCOS. It complements earlier findings that dietary inflammatory index scores are associated with PCOS and that gut microbiota dysbiosis drives insulin resistance, both of which point to inflammation as a key pathway. The elevated C3 levels (SMD = 0.73) add to the inflammatory profile of PCOS, but the observational design limits causal interpretation, similar to the dietary and microbiota evidence. It does not directly address the therapeutic interventions previously covered, such as mindfulness or integrated TCM, but reinforces the inflammatory context in which those interventions might act.
Researchers looked at data from over 900 people to see if there was a link between certain proteins and polycystic ovary syndrome. They specifically measured the level of a substance called complement C3 in the blood.
The results showed that women with this condition had significantly higher levels of C3 compared to those without it. This suggests that the body's immune system might be reacting differently in people with this specific hormonal condition.
While these findings are interesting, they come from an observational study. This means the researchers can see a connection between the protein and the condition, but they cannot prove that one causes the other yet.
More research is needed to understand why these levels are higher. Future studies will help doctors determine if this protein could be used as a way to track health or identify symptoms in patients with polycystic ovary syndrome.
What this means for you:
Women with polycystic ovary syndrome show higher levels of the C3 protein, suggesting a link to immune activity.
Common questions
What is complement C3?
Complement C3 is a protein in your blood that is part of the immune system. It helps fight infections and is also involved in inflammation. Higher levels can indicate inflammation in the body.
Does this mean PCOS causes high C3 levels?
No. This analysis only shows a link, not cause and effect. The studies were observational, so we can't say PCOS causes higher C3. More research is needed to understand the relationship.
Should I get my C3 levels tested if I have PCOS?
This finding is exploratory and not ready for clinical use. There is no recommendation to test C3 levels in PCOS based on this analysis. Talk to your doctor about any concerns you have.
BackgroundComplement C3 is a key effector molecule of the innate complement system, which participates in inflammatory responses, immune regulation and the maintenance of metabolic homeostasis. Consistency and evidence grade regarding the association between serum C3 levels and polycystic ovary syndrome (PCOS) remain controversial. This systematic meta-analysis aims to assess changes of C3 levels in PCOS patients.MethodWe systematically searched PubMed, Scopus, Web of Science, Cochrane Central Register of Controlled Trials (CENTRAL), China National Knowledge Infrastructure (CNKI), VIP Chinese Science and Technology Journal Database (VIP) and Wanfang Database for studies concerning PCOS and C3, from database inception to December 31, 2025. Literature screening, data extraction and risk of bias assessment using the Newcastle-Ottawa Scale (NOS) were independently performed by two investigators. Sensitivity analysis was performed by sequentially omitting each individual study to verify the robustness of the pooled results. Funnel plots were adopted for preliminary evaluation of publication bias. Subgroup analysis was used to explore potential effect modifiers. All statistical analyses were conducted using R software (version 4.6.0) to guarantee the scientific validity and reliability of the findings.ResultsA total of 6 studies meeting the predefined inclusion criteria were included, enrolling 915 individuals. C3 levels were higher in PCOS patients than controls (SMD = 0.73, 95% CI: 0.54–0.93), with moderate heterogeneity (I²=47.1%, P = 0.092). No significant difference was observed between subgroups. Sensitivity analysis confirmed the robustness of the overall association.ConclusionThis meta-analysis suggests that circulating C3 levels are elevated in PCOS. However, due to the observational design and limited evidence, these findings are exploratory. Prospective studies are needed to validate this association.Systematic review registrationhttps://www.crd.york.ac.uk/PROSPERO/, identifier CRD420251121390.
