Spatiotemporal trends in human semen quality

Abstract

Over the past four decades, studies of various designs have reported spatial and temporal trends in human semen quality. Several standardized-methodology studies in homogeneous populations that compare specific cities within a country or a continent provide clear evidence of geographical differences in sperm production, even over short distances within the same country. Human sperm production is widely believed to be declining over time, but evidence from the scientific literature is less clear. Studies based on repeated cross-sectional data from a single centre have shown mixed results. Among the numerous retrospective studies conducted in a single centre, only some included homogeneous groups of men and appropriate methods, and most of them suggest a temporal decrease in human sperm production in the geographical areas considered. Conclusions reporting temporal trends in sperm production that came from existing retrospective multicentre studies based on individual semen data and those using means, medians or estimates of sperm production are questionable, owing to intrinsic limitations in the studies performed. Regardless of study design, studies on the percentage of motile or morphologically normal spermatozoa are still limited by the inherent variability in assessment. Overall, available data do not enable us to conclude that human semen quality is deteriorating worldwide or in the Western world, but that a trend is observed in some specific areas. To understand these trends and contrasts in sperm and semen quality, prospective studies should be encouraged and combined with assessment of the male exposome.

Trends in semen parameters of infertile men in South Africa and Nigeria

“…Nigeria also had significantly lower sperm concentration compared to South Africa which is of mixed races. It is not clear if our findings are of any racial correlations, however, Auger et al, reported that black men had significantly lower sperm concentrations than white men and Hispanics 44 . Furthermore, exposure to the pesticide, DDT [1,1,1-trichloro-2,2-bis (chlorodiphenyl)ethane] and its main metabolite, p,p′-dichlorodiphenyl-dichloroethylene (p,p′-DDE) has been associated with the declining trend of semen quality in malaria stricken parts of African countries 45 .…”

Global warming and testis function: A challenging crosstalk in an equally challenging environmental scenario

“…In numerical terms, a systematic review and meta regression analysis by Levine et al involving 185 studies that accounted complexively 42,935 men from unselected Western countries, estimated a variation of −0.70×10 6 cells/mL per year in sperm concentration and −5.33×10 6 cells per year in total sperm count/ejaculate over the period of time between 1973 and 2011 ( Bahadur G et al, 1996 ; Levine et al, 2017 ). An exhaustive discussion of this topic, highlighting major strengths, criticisms, and claims of a possible causal relationship between sperm count, lifestyle, and environmental factors is provided in the review by Auger et al (2022 ). In any case, a strong parallelism is evident between the environmental modifications associated with human activities following the industrial revolution and the variations in the seminal parameters documented in the same period of time ( Auger et al, 2022 ; Damon Matthews and Wynes, 2022 ).…”

“…An exhaustive discussion of this topic, highlighting major strengths, criticisms, and claims of a possible causal relationship between sperm count, lifestyle, and environmental factors is provided in the review by Auger et al (2022 ). In any case, a strong parallelism is evident between the environmental modifications associated with human activities following the industrial revolution and the variations in the seminal parameters documented in the same period of time ( Auger et al, 2022 ; Damon Matthews and Wynes, 2022 ). The global nature of climatic warming, therefore, raises doubts about the possible role of ambient temperature as an environmental interferent on the quality of human semen as an index of testis function.…”

Male Germ Cell Telomeres and Chemical Pollutants

“…These hormone levels often fluctuate along a lifespan, which may lead to organismal decay and infertility when they decrease. Thus, an increase in age in males has a significant negative impact on testicular function, sperm functionality and, consequently, fertilization [1,2]. Gamete quality is also impaired by an imbalance in the redox status [3] and the continuous accumulation of genetic mutations [4,5], including Y-chromosome microdeletions [6] and DNA alterations [7] with reduced repair capacity [8].…”