Year of birth and sperm count in 10 Danish occupational studies

Abstract

Objectives Several reports indicate a secular decline of human sperm counts. It is still not known if these findings are artifacts related to shortcomings in the data and applied methodologies. Even less is known about possible mechanisms, but it has been proposed that potential changes may be related to disruption of the hormonal regulation of testicular development in prenatal life. The objective of this study was to examine whether sperm count was related to year of birth. Methods An analysis was made of the sperm count of 1196 men participating in 10 cross-sectional occupational sperm studies in 3 regions of Denmark from 1986 through 1995. Results The median sperm concentration was 63 million per milliliter for men born in 1937-1949 and 52 million per milliliter for men born in 1970 or later, and the median total sperm was 206 million and 117 million, respectively. The inverse relationship between sperm concentration and year of birth was statistically significant even after adjustment for duration of sexual abstinence, season of the year, and study population. However, bias because of differential participation related to age and fertility or lack of comparability across the populations cannot be ruled out. C O~C~U S~O~~S The apparent decline of sperm count with increasing year of birth is compatible with the hypothesis of a common risk factor for male reproductive health operating in prenatal life or early childhood, but the evidence is circumstantial. Age-related selection bias is an alternative and perhaps not a less likely explanation.

Lipid concentrations and semen quality: the LIFE study

“…Some data have shown that sperm count rates have declined over the last 50 years with current reference ranges of approximately 15 million/mL (Swan, Elkin et al , 2000; Swan and Elkin, 1999; Swan, Elkin et al , 1997; Bonde, Kold et al , 1998; Rolland, Le Moal et al , 2103; Cooper, Noonan et al , 2010; Fisch, Goluboffe et al , 1996). However, other data are equivocal with regard to global semen quality parameters (Fisch 2013).…”

Is human fertility declining?

“…In addition, evidence is emerging that semen quality is lower among younger cohorts. A meta-analysis of semen quality of normal Danish men suggested a birth cohort-related decline in semen quality [70], and the trend seems to continue as the younger cohorts born around 1980 had the lowest sperm counts of all cohorts examined (Fig. 2) [69].…”

Continuously Proliferative Stem Germ Cells Partially Repopulate the Aged, Atrophic Rat Testis after Gonadotropin-Releasing Hormone Agonist Therapy1

“…Although controversial, gradual but steady declines in the number and quality of sperm [1][2][3] as well as levels of biologically available or free serum testosterone (T) [4,5] have been reported with advancing age. Agerelated differences in the human testis include reductions in volume or number of T-producing Leydig cells and changes in the morphology and number of germ-cell-supporting Sertoli cells, either of which may contribute to the age-related degeneration of germ cells during spermatogenesis [6][7][8][9][10].…”