Semen quality and male reproductive health: the controversy about human sperm concentration decline

Concern about the effect of environmental changes on male reproductive heal th has grown in recent years to become a major preoccupation in some develo ped countries. A possible decline in human sperm concentration was suggeste d in the early seventies following studies in the US. In 1992 a metaanalysi s of 61 articles published by Carlsen et al. concluded that the mean sperm count of healthy men had declined by 1% per year over the previous 50 years . From 1995 and onwards, some retrospective, longitudinal analyses of the s perm count of fertile or infertile men contradicted this while others did n ot. The demonstration of a geographical variation in sperm concentration, b etween and within countries or regions, appears to be less controversial. T he amplitude of the difference observed cannot only be explained by methodo logical or confounding factors, and must to some extent be attributed to et hnic, genetic or environmental factors. As many of the published studies su ffer from imprecision regarding the description of population characteristi cs and confounding factors, and were not designed with controlled and stand ardised methodology, the debate remains open. Prospective studies in well-d efined cohorts of men in various populations are required to evaluate the p otential effect of external factors on male reproductive health. These stud ies should not be limited to the analysis of sperm concentration, as this m ay not be the best biomarker of testis function and human fertility.