Blood lead concentration among oral/inhaled opium users: systematic review and meta-analysis

Abstract

Lead is a poisonous heavy metal with various known side effects. The effect of opium on raising blood lead concentration (BLC) has been investigated with no general agreement. In Iran, the number of lead poisoning cases has raised among the opium-addicted population. This systematic review and meta-analysis aim to combine the results of previous studies with the Iranian population to investigate the effect of opium on BLC. In this systematic review, PubMed/Medline, Web of Sciences, Embase, and Scopus were searched for studies using the Iranian population to compare the BLC of opium-addicted cases and non-addicted controls till January 2020. A random-effects model was used to pool the results. I-square test was used to assess the heterogeneity of the studies. The effect sizes were standardized mean differences (proxied by Hedges’ g) followed by a 95% confidence interval. Of 417 initial articles, 13 studies met the inclusion criteria to be considered in the meta-analysis. The sample size of eligible studies ranged from 40 to 131 (mean 81.83, SD 27.6). All studies were focused on adults with mean age ranged from 33.5 to 65.15 years old (overall mean 49.0, SD 7.66). There were 13 studies included with 18 Hedges’ g effect sizes. Using a random effect model, the pooled effect size was g_w = 2.48 (95% CI: 1.58–3.39) and statistically significant in favor of opium-addicted participants. Moreover, heterogeneity was 96.6% ($I^2=96.6,$ Q(17) = 504.95, p < 0.001). For studies with large Hedges’ g effect sizes (> 4) identified as outliers and removed from meta-analysis. The pooled Hedges’ g effect size reduced to 1.39 (95% CI: 0.94–1.85), still highly significant in favor of higher levels of lead in the opium-addicted group. The funnel plot appeared symmetrical confirmed by Egger's test (t = 1.87, p = 0.088), indicating no publication bias present.

Keywords:

• Blood lead
• opium
• addiction
• oral and inhalation consumption
• poisoning

Acknowledgments

The authors sincerely acknowledge the advice of the editor and also the comments of the anonymous reviewer who was selected by the editor. Also, the authors would like to convey an appreciation of Dr Lukasz J. Binkowski and Dr Martyna Błaszczyk for their nice comments in editing the manuscript.

Declaration of interest

The authors take complete accountability for the content of this paper. The employment affiliations of the authors are shown on the cover page. All authors have contributed to the preparation of this article. This paper has had little financial support to be designed and provided. The authors declare no conflict of interest in this study. None of the authors have participated in any legal, regulatory, or advocacy activities during the last 5 years related to the contents of this paper. This study has been carried out with financial support from Kermanshah University of Medical Sciences (Grant number: 1399/990692; Ethics code: IR.KUMS.REC.1399.751).

Author contributions

VF, MP, and BM generated the idea and design of the study. BM and FR searched the literature in databases, wrote some parts of the manuscript. NA and BM participated in statistical analyses and edited the result part. VF, MP, NA, BM, and FR reviewed the manuscript. NA and BM wrote the discussion section, and with VF and MP, supervised all parts of the revision part of the manuscript. BM acted as the corresponding author.