A meta-analysis of epidemiologic studies of occupationally exposed styrene workers and micronuclei levels

Previous reviews and meta-analyses have reached different conclusions on whether high styrene exposure increase micronucleus frequencies. The most recent meta-analysis reports an increase in these frequencies related to styrene. We update this meta-analysis of micronucleus frequencies with additional studies not previously included, eliminate double counting of study subjects appearing in more than one publication, considered levels of styrene exposures in the analysis, assess publication bias, and examine consistency of findings across studies. Our meta-analysis used the standardized mean difference as the summary statistic since all studies assess the same outcome but use different comparison populations. The primary meta-analysis of the 12 studies of 516 styrene exposed workers and 497 non-exposed comparisons produces a meta-mean difference of 1.19 (95% CI 0. 20-2.18, random effects model), but there was substantial heterogeneity across studies (I² of 97.47, p-value <0.001, fixed effect model). We also observed that studies with higher styrene exposure had a higher mean standard difference compared with studies with lower styrene exposures. However, a longitudinal study did not find any association with styrene exposure and micronucleus frequencies. Given the lack of consistency across studies and the equivocal finding on exposure response, these data are insufficient to support a conclusion that an increase in micronucleus frequencies is due to styrene exposure.