The effect of coenzyme Q10 on morbidity and mortality in chronic heart failure (Q-SYMBIO trial)

Key finding

2-year double-blind multi-center RCT (n=420) in chronic heart failure found 300mg/day CoQ10 (ubiquinone) reduced cardiovascular mortality by 43% and major adverse cardiac events by 50% vs placebo.

OBJECTIVES: This randomized controlled multicenter trial evaluated coenzyme Q10 (CoQ10) as adjunctive treatment in chronic heart failure (HF). BACKGROUND: CoQ10 is an essential cofactor for energy production and is also a powerful antioxidant. A low level of myocardial CoQ10 is related to the severity of HF. Previous randomized controlled trials of CoQ10 in HF were underpowered to address major clinical endpoints. METHODS: Patients with moderate to severe HF were randomly assigned in a 2-year prospective trial to either CoQ10 100 mg 3 times daily or placebo, in addition to standard therapy. The primary short-term endpoints at 16 weeks were changes in New York Heart Association (NYHA) functional classification, 6-min walk test, and levels of N-terminal pro-B type natriuretic peptide. The primary long-term endpoint at 2 years was composite major adverse cardiovascular events as determined by a time to first event analysis. RESULTS: A total of 420 patients were enrolled. There were no significant changes in short-term endpoints. The primary long-term endpoint was reached by 15% of the patients in the CoQ10 group versus 26% in the placebo group (hazard ratio: 0.50; 95% confidence interval: 0.32 to 0.80; p = 0.003) by intention-to-treat analysis. The following secondary endpoints were significantly lower in the CoQ10 group compared with the placebo group: cardiovascular mortality (9% vs. 16%, p = 0.026), all-cause mortality (10% vs. 18%, p = 0.018), and incidence of hospital stays for HF (p = 0.033). In addition, a significant improvement of NYHA class was found in the CoQ10 group after 2 years (p = 0.028). CONCLUSIONS: Long-term CoQ10 treatment of patients with chronic HF is safe, improves symptoms, and reduces major adverse cardiovascular events. (Coenzyme Q10 as adjunctive treatment of chronic heart failure: a randomised, double-blind, multicentre trial with focus on SYMptoms, BIomarker status [Brain-Natriuretic Peptide (BNP)], and long-term Outcome [hospitalisations/mortality]; ISRCTN94506234).

Copyright © 2014 American College of Cardiology Foundation. Published by Elsevier Inc. All rights reserved. Abstract sourced from PubMed, a database of the U.S. National Library of Medicine. Displayed in the authors’ own words for context; our critique is in the sections below.

Critique

Q-SYMBIO is among the stronger supplement trials in the literature. Multi-center, double-blind, placebo-controlled, 2-year duration, and a hard clinical endpoint (cardiovascular mortality). The 43% mortality reduction represents a clinically meaningful effect size, not just statistical significance. The key interpretive nuance is that enrolled patients were already receiving optimal guideline-directed heart failure therapy, so the benefit represents an additive effect on top of standard care — applicable to a specific clinical context rather than general prevention in healthy adults.

What would be more convincing

Given the strength of this trial, what's missing is independent large-scale replication. A second 1,000+ patient multi-center RCT conducted in a different healthcare system would move CoQ10 in heart failure from 'likely beneficial' to 'guideline-recommended.' Smaller supporting trials exist but a definitive replication would close the case.

Reviewed 2026-04-21 · Opinion based on verifiable facts in the published paper.