Is male reproductive health at risk? Longitudinal semen analysis studies

Considerable controversy remains as to whether a decline in sperm production has occurred in normal men over the past 50 years. Semen analysis studies must log transform the sperm concentration data to obtain a normal distribution and obtain multiple (3-6) semen samples. These methodological procedures were followed in a longitudinal study (1972-93) of 510 healthy adult US men. Sperm concentration semen volume and sperm morphology data were obtained for samples obtained after 2-7 days of sexual abstinence. A median of 6 samples were obtained per subject. The geometric mean sperm concentrations ranged from 49.2 x 10 to the sixth power/ml in the first trial during 1972-73 to 51.96 in the last study during 1992-93. The highest geometric mean (76.4) was obtained during 1987-89. There was no significant decrease in sperm concentration semen volume or total sperm per ejaculate during the study period. Although these findings suggest there has been no decline in semen quality over the past 21 years such deterioration may have occurred in other geographic areas or in small vulnerable populations such as men exposed to environmental toxins.