Counting your sperm before they fertilize: are sperm counts really declining?

Abstract

A purported global decline in sperm counts has been a source of controversy since the early 1990s. Numerous studies performed since then, as well as reanalysis of the original data, show either no changes, or even increases, in sperm concentrations over time. In this review, we discuss the 1992 meta-analysis that initiated the continuing debate on whether sperm concentrations are declining, and the community discussion surrounding it over the past two decades. We also highlight studies evaluating sperm concentrations performed since the initial study that produced different results, and conclude that no definitive cause for a decrease in sperm counts has been established, and the effects of geography and environment on sperm counts are unclear.Approximately 15% of couples are considered infertile, with a male factor implicated in up to 50% of cases, underscoring the essential contribution of the male in conception. 1 However, only over the past two decades have we begun to understand the degree to which men contribute to a couple's infertility, which historically was attributed to the female partner. One quarter or more of infertile men have an unknown cause for their infertility, and while recent work suggests that many of these etiologies are genetic, we cannot exclude the impact of environmental factors on the male reproductive system, which have been incompletely defined.Work over recent decades has identified a potential decline in sperm concentrations, with at least one explanation being an increase or change in environmental pollutant levels. In 1992, a meta-analysis of sperm concentrations derived from 61 papers dating between 1938 and 1990 involving semen quality from 14 476 men found that both sperm concentrations and seminal volumes had dropped significantly during that period. 2 This was followed in 1993 by a manuscript suggesting that this decrease in sperm concentrations was partly due to environmental contamination with estrogenic compounds. However, there was little evidence identifying estrogens in the geographical areas where sperm concentrations appeared to be declining, or other evidence directly linking estrogenic pollution with declines in male fertility. 3 These works triggered a continuing discourse and numerous investigations to evaluate the verity of these claims. However, current data have failed to demonstrate a decrease in either sperm concentrations or male fertility.Owing to the large amount of unclear and confounding data, it is difficult to determine whether male fertility rates are truly declining. Fertility assessment in both men and women is made more difficult by the wide range of sperm concentrations that can result in pregnancy. Indeed, sperm count alone cannot define the fertility potential of a couple. Nevertheless, from the authors' viewpoint, the available data do not support a global decline in sperm concentrations or male fertility. We highlight the limitations of the original work claiming this decline, and show that current data, including data by the authors of the...

The effects of advanced paternal age on fertility

“…Proficiency programs are now in place allowing interlaboratory comparisons of accuracy. 42 The studies discussed in this review make comparisons that are clouded by regional variations as well as methodological bias; results further complicated by the baseline variability observed in the semen analyses of normal males. 42 In conclusion, this review has summarized the current state of knowledge of advanced paternal age and its effects on semen quality, reproductive success and offspring health.…”

“…42 The studies discussed in this review make comparisons that are clouded by regional variations as well as methodological bias; results further complicated by the baseline variability observed in the semen analyses of normal males. 42 In conclusion, this review has summarized the current state of knowledge of advanced paternal age and its effects on semen quality, reproductive success and offspring health. We are currently moving towards an era where a man's reproductive age is considered as important as the females; 90 however, further work is required to elucidate the strength of these associations.…”

“…41 However, the ability to establish a link between environmental toxins and male fertility is difficult. 42 DNA damage may also result as a consequence of oxidative stress. This can occur owing to numerous conditions including repeated infections and obstruction.…”

Hormone Signaling in the Testis

“…Lipophilic hormone binding to their receptors often results in the translocation of the ligand-receptor complex to specific regulatory DNA sites in the genome and the alteration of gene expression patterns ( Figure 16.4(B)). The stages of the cycle were identified by means of 14 of the 19 steps of spermiogenesis (numbers [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19]. 15 15 16 16 a Roman numeral shows the cell types present in one of the cellular associations found in cross-sections of seminiferous tubules.…”

“…Glucocorticoids secreted by the adrenal in response to adrenocorticotrophic hormone (ACTH) can influence fertility at three levels: (1) in the hypothalamus, to suppress release of GnRH; (2) in the pituitary, to perturb LH and FSH secretion; and (3) within the testis, to influence steroidogenesis and spermatogenesis directly (reviewed in Ref. 575).…”