Is the application of Kohl to eyes associated with increased blood lead levels in children? A meta-analysis

Abstract

A controversial disagreement about the association between eye-worn Kohl and increased blood lead level (BLL) in children has been raised. We investigated such association in children aged <7 years. According to PRISMA, we performed a meta-analysis, rated the confidence in the body of human evidence, and translated the confidence ratings into levels of evidence. Detection bias related to exposure assessment, selection, and confounding were the main biases in the 14 included studies. Meta-analyses suggested a significant association between increased BLL and exposure to Kohl: odds ratio was 3.64, but heterogeneity was high (inconsistency I2=59%); pooled weighted mean difference was 5.81, but heterogeneity was high (I2=91.4%). Publication bias was ruled out in odds ratio meta-analysis. Leaving-one-out, subgroups, and meta-regression analyses showed that study quality and type of BLL testing devices were sources of heterogeneity. Biases, high heterogeneity and study size were all factors that limited evidence of the causal relationship between eye-worn Kohl and increased BLL.