The impact of genetic, environmental and life-style factors on male reproductive function

Abstract: Recent studies have indicated a decline in sperm number in the western world during the past 50 years, sperm concentration changing from 113 to 66 millions per mL. Furthermore, significant geographical differences in male reproductive function have been observed. In Finland, the sperm concentration was found to be substantially higher than in Denmark. In parallel, the incidence of testicular cancer (TC) and of congenital malformations of male genital organs is significantly higher in Denmark as compared to Finland. Previous studies have shown an association between decreased sperm quality and risk of TC. Recently, it was suggested that poor sperm quality, cryptorchidism, hypospadias and TC have a common cause and are symptoms of a so called Testicular Dysgenesis Syndrome (TDS). The aetiology of TDS is unknown but genetic, environmental and life-style related factors have been suggested as its causes. Genetic factors might, at least partly, explain the difference in male reproductive function between Denmark and Finland. However, Swedish and Danish populations are genetically similar and therefore any differences in reproductive parameters found between these two countries are most likely due to environmental and/or life-style related factors. The aim of this study was to compare reproductive parameters between Swedish and Danish men and to investigate the possible impact of environmental, life-style and genetic factors. All papers included in this thesis were based on investigations of Swedish military conscripts (n=305). Semen parameters of the Swedish conscripts were compared to previously published data on their Danish counterparts. Furthermore, reproductive parameters were evaluated in relation to exposure to persistent organohalogen pollutants (POP) and to smoking. Polymorphisms in the androgen receptor gene were also assessed. We found 30% higher sperm number as well as higher sperm concentration and semen volume in Swedish men as compared to Danish. Non-smoking men presented with 40% higher sperm number as compared to smokers. Exposure to POP, assessed by serum levels of CB-153, was associated with impairment of sperm motility but not with the number of spermatozoa. Androgen receptor CAG repeat number was only weakly associated with sperm parameters. Our data indicated that the reproductive function of Swedish adolescent men is superior to that of their Danish counterparts. Smoking is less prevalent in Sweden compared to Denmark and this could, at least partly, contribute to the difference in sperm number found between these countries.