Lifestyle and Environment · Environmental Exposures
RRM Academy Synopsis
Two insecticide classes are linked to lower sperm concentration in men
Men with more exposure to organophosphate and carbamate insecticides had lower sperm concentration, a meta-analysis found. It pooled 20 studies of 1,774 men. Reviewers rated the evidence moderate in quality and sufficient in strength.
Key Findings
- Pooling 20 studies and 1,774 adult men, the standardized mean difference in sperm concentration was -0.30 (95% CI: -0.49, -0.10), with lower values in the more-exposed men.
- In subgroup analyses, the organophosphate estimate was double the carbamate estimate, and the occupational estimate was larger than the environmental one. The estimate stayed negative in direction in every analysis.
- In the six studies that controlled for age and smoking and for effect modifiers such as coexposures, abstinence time, and medical risk factors, the estimate stayed negative but shrank and lost significance.
- Among the 25 studies in the review, 21 used a cross-sectional design, 2 were case-control studies, and 2 were cohort studies.
- The reviewers rated the overall quality of evidence as moderate and the strength of evidence as sufficient for an association between higher exposure and lower sperm concentration.
Interpretation
The review pooled results from many separate studies into one estimate. The studies were observational, and 21 of 25 measured exposure and sperm concentration at one point in time. The authors note that the mainly cross-sectional literature makes causal inference challenging. They add that mechanistic and animal evidence indicate the association may be causal. Participants were adult men. Eighteen of the 25 studies assessed occupational exposure, such as work on farms and in factories. Studies of other sperm measures were left out.
RRM Context
Low sperm concentration often leads to a male factor diagnosis, the authors note. Restorative reproductive medicine sees unexplained infertility as undiagnosed. The approach looks for root causes in both partners. The review reports an association between two insecticide classes and low sperm concentration.
Abstract
Background
Evidence of the negative impacts of contemporary use insecticides on sperm concentration has increased over the last few decades; however, meta-analyses on this topic are rare.
Objectives
This investigation assessed the qualitative and quantitative strength of epidemiological evidence regarding adult exposure to two classes of contemporary use insecticides-organophosphates (OPs) and N-methyl carbamates (NMCs)-and sperm concentration using robust and reproducible systematic review and meta-analysis methods.
Methods
Three scientific databases (PubMed, Scopus, and Web of Science), two U.S. government databases (NIOSHTIC-2 and Science.gov), and five nongovernmental organization websites were searched for relevant primary epidemiological studies published in any language through 11 August 2022. Risk of bias and strength of evidence were evaluated according to Navigation Guide systematic review methodology. Bias-adjusted standardized mean difference effect sizes were calculated and pooled using a three-level, multivariate random-effect meta-analysis model with cluster-robust variance estimation.
Results
Across 20 studies, 21 study populations, 42 effect sizes, and 1,774 adult men, the pooled bias-adjusted standardized mean difference in sperm concentration between adult men more- and less-exposed to OP and NMC insecticides was -0.30 (95% CI: -0.49, -0.10; PSatt<0.01). Sensitivity and subgroup analyses explored statistical heterogeneity and validated the model robustness. Although the pooled effect estimate was modified by risk of bias, insecticide class, exposure setting, and recruitment setting, it remained negative in direction across all meta-analyses. The body of evidence was rated to be of moderate quality, with sufficient evidence of an association between higher adult OP and NMC insecticide exposure and lower sperm concentration.
Discussion
This comprehensive investigation found sufficient evidence of an association between higher OP and NMC insecticide exposure and lower sperm concentration in adults. Although additional cohort studies can be beneficial to fill data gaps, the strength of evidence warrants reducing exposure to OP and NMC insecticides now to prevent continued male reproductive harm. https://doi.org/10.1289/EHP12678.
