Blood lead levels and male reproductive hormones: A systematic review and meta-analysis

Present study aimed to systematically review and synthesise quantitative evidence on association between occupational Lead (Pb) exposure and male reproductive hormones (MRH) and sperm quality from the existing literature. Observational studies investigating the effects of Pb exposure on MRH, sperm-count and sperm motility are systematically searched in PubMed, Scopus and EMBASE databases since inception to May 2019. The PRISMA guidelines are adhered during the entire study procedure and details such as participant characteristics, occupational Pb exposure, MRH, sperm-count and sperm motility from individual articles are extracted to the perform meta-analysis. Sub-group analysis and sensitivity analysis are additionally explored. Further, meta-regression is executed to investigate the influence of participant's age, duration of workplace Pb exposure on the individual outcome parameters. We observed that otherwise normal (fertile) male participants from all studies were within the age range of 25–45 years. Male employees occupationally exposed to Pb exhibited significantly higher blood Pb, lower sperm-count, poor sperm motility and higher serum prolactin levels as compared to the Pb unexposed males. The testosterone, follicle stimulating hormone and luteinising hormone levels of the occupationally Pb exposed participants are comparable to that of unexposed comparators. Studies included for synthesising quantitative evidence had unacceptable levels of heterogeneity. Explorative subgroup or meta-regression analysis had no additional results to the study. Lastly, included studies were driven by publication bias (positive results) and low powered (small sample size) studies. Thus, Pb exposure at workplaces is detrimental to male reproductive function, with lower sperm-count and higher prolactin levels. However, to enumerate the precise quantity of Pb exposure detrimental on male reproductive functions, high quality longitudinal studies with large cohorts are needed.