The association between environmental exposures to chlordanes, adiposity and diabetes-related features: a systematic review and meta-analysis

Abstract

Chlordane compounds (CHLs) are components of technical chlordane listed in the Stockholm convention on persistent organic pollutants identified as endocrine disrupting chemicals (EDCs) and may interfere with hormone biosynthesis, metabolism or action resulting in an unbalanced hormonal function. There is increasing scientific evidence showing EDCs as risk factors in the pathogenesis and development of obesity and obesity-related metabolic syndromes such as type 2 diabetes, but there is no systematized information on the effect of CHLs in humans. Our aim is to identify the epidemiological data on the association between CHLs with adiposity and diabetes using a systematic approach to identify the available data and summarizing the results through meta-analysis. We searched PubMed and Web of Science from inception up to 15 February 2021, to retrieve original data on the association between chlordanes, and adiposity or diabetes. For adiposity, regression coefficients and Pearson or Spearman correlation coefficients were extracted and converted into standardized regression coefficients. Data were combined using fixed effects meta-analyses to compute summary regression coefficients and corresponding 95% confidence intervals (95% CI). For the association between chlordanes and diabetes, Odds ratios (ORs) were extracted and the DerSimonian and Laird method was used to compute summary estimates and respective 95% CI. For both, adjusted estimates were preferred, whenever available. Among 31 eligible studies, mostly using a cross-sectional approach, the meta-analysis for adiposity was possible only for oxychlordane and transchlordane, none of them were significantly associated with adiposity [(β = 0.04, 95% CI 0.00; 0.07, I² = 89.7%)] and (β = 0.02, 95% CI - 0.01; 0.06), respectively. For diabetes, the estimates were positive for all compounds but statistically significant for oxychlordane [OR = 1.96 (95% CI 1.19; 3.23)]; for trans-nonachlor [OR = 2.43 (95% CI 1.64; 3.62)] and for heptachlor epoxide [OR = 1.88 (95% CI 1.42; 2.49)]. Our results support that among adults, the odds of having diabetes significantly increase with increasing levels of chlordanes. The data did not allow to reach a clear conclusion regarding the association with adiposity.

Figure 1

Systematic review flowchart.

Figure 2

Meta-analysis of studies evaluating the association of oxychlordane with body mass index (BMI). Beta coefficients and corresponding 95% CI (horizontal lines). The size of the black square indicates the study’s weight in the analysis (weights are from fixed-effects analysis). The centre of the open diamond indicates the summary estimate and its width represents the 95% CI.

Figure 3

Meta-analysis of studies evaluating the association of trans-nonachlor with body mass index in adults. Beta coefficients and corresponding 95% CI (horizontal lines). The size of the black square indicates the study’s weight in the analysis (weights are from fixed-effects analysis). The centre of the open diamond indicates the summary estimate and its width represents the 95% CI.

Figure 4

Meta-analysis of studies evaluating the association of oxychlordane with diabetes-related features. Odds ratios and corresponding 95% CI (horizontal lines). The size of the black square indicates the study’s weight in the analysis (weights are from fixed-effects analysis). The centre of the open diamond indicates the summary estimate and its width represents the 95% CI.

Figure 5

Meta-analysis of studies evaluating the association of trans-nonachlor with diabetes-related features in adults. Odds ratios and corresponding 95% CI (horizontal lines). The size of the black square indicates the study’s weight in the analysis (weights are from fixed-effects analysis). The centre of the open diamond indicates the summary estimate and its width represents the 95% CI.

Figure 6

Meta-analysis of studies evaluating the association of heptachlor epoxide with diabetes-related features in adults. Odds ratios and corresponding 95% CI (horizontal lines). The size of the black square indicates the study’s weight in the analysis (weights are from fixed-effects analysis). The centre of the open diamond indicates the summary estimate and its width represents the 95% CI.