Systematic review of the literature on triclosan and health outcomes in humans

Abstract

The ability of epidemiologic evidence to inform regulatory decisions is largely dependent on the coherence and quality of the published literature. This systematic review examines the quality and consistency of studies assessing health outcomes associated with exposure to triclosan (TCS), an antimicrobial chemical with a short physiologic half-life. We used elements of the Biomonitoring, Environmental Epidemiology, and Short-Lived Chemicals instrument to evaluate aspects of study quality. Each methodological domain – overall design, exposure assessment, and data analysis – was categorized according to three tiers where Tier 1 indicated the highest quality. We also examined consistency of methods, results and reporting as considerations for weight of evidence (WOE) assessment. Studies were considered sufficiently comparable if they addressed the same or similar research questions. Forty-two studies met the criteria for inclusion. Only one randomized cross-over clinical trial of TCS was assigned to Tier 1 for all three domains. Most other studies were assigned to Tier 3 for at least one domain. Although the available literature examined more than 100 different health endpoints and reported hundreds of different measures of association, few studies were considered comparable. For reported measures of association, most were not significantly different from the null; the few statistically significant results represented isolated findings without a discernable across- or within-study pattern. We conclude that the current body of epidemiologic literature does not allow a meaningful WOE assessment due to methodological limitations of individual studies and lack of inter-study consistency. On the other hand, methodologically stronger studies may be used to inform future research.

Keywords:

• Triclosan
• epidemiology
• systematic review
• ICC
• short-lived chemical
• anti-androgen
• BEES-C
• PI(E)CO

Acknowledgements

The authors thank Dr. Brian Slezak of Colgate-Palmolive for his minor editorial comments on the manuscript. We also thank the six anonymous reviewers selected by the journal Editor for their thoughtful comments on the manuscript.

Declaration of interest

The employment affiliations of the authors are shown on the cover page. The authors have sole responsibility for the writing and content of this paper. LaKind Associates is a private consulting firm specializing in strategic risk management, assessment of human exposures and health risks, biomonitoring, state-of-the-science reviews, and environmental regulatory review; LaKind Associates consults to governmental and private sectors. The academic institutions with which the authors are affiliated are traditional academic institutions. All authors consult to both industry and government and conduct research with industry, government, and academia. The research was supported via funding from Colgate-Palmolive Company to LaKind Associates, with subcontracts to the two other coauthors. Colgate-Palmolive was not involved in the design, collection, management, analysis, or interpretation of the information in the manuscript; or in the preparation of the manuscript. This work is the exclusive professional work product of the three authors. While Colgate-Palmolive had the opportunity to offer comments on the draft manuscript, the findings and conclusions in this manuscript are those of the authors and do not necessarily represent the views of Colgate-Palmolive or any institutions with which the authors are affiliated. None of the authors have appeared in any legal or regulatory proceedings within the past 5 years related to the contents of the paper nor have been engaged to make such appearances in the future.

Supplemental material

Supplemental material for this article is available online here.

Additional information

Funding

The research was supported via funding from Colgate-Palmolive Company to LaKind Associates, with subcontracts to the two other coauthors.