The Disappearing Sperms: Analysis of Reports Published Between 1980 and 2015

Abstract

Reports regarding the changes in sperm concentration in different counties of the world are inconsistent. Furthermore, the reports that sprung up from specific epidemiological and experimental examinations did not include data of prior studies or geographical variations. The current study, following a previous report of massive fall in semen volume over the past 33 years, attempts to delineate the trend of altering sperm concentrations and factors responsible for this by reviewing article published from 1980 to July 2015 with geographic differences. The current study identified an overall 57% diminution in mean sperm concentration over the past 35 years ( r = -.313, p = .0002), which, when analyzed for each geographical region, identified a significant decline in North America, Europe, Asia, and Africa. An increasing trend of sperm concentration was identified only in Australia. The association of male age with such a trend ( R² = .979) is reported. The authors also correlated male fertility with sperm concentration. Thus, this comprehensive, evidence-based literature review aims to concisely and systematically present the available data on sperm concentration from 1980 to 2015, as well as to statistically analyze the same and correlate male health with the declining pattern of sperm count in a single scientific review to serve the scientific research zone related to reproductive health. It points to the threat of male infertility in times ahead.

Keywords: semen quality; sperm concentration; sperm count.

Figure 1.

(A) Temporal decline in sperm concentration (×10⁶/mL) (r = −.313, p = .0002, R² = .098); bubble size corresponds to the number of men in study. (B) Changes in sperm concentrations from 1980 to 2015 shown as Box-and-Whisker plots. White bands indicate the median values for each duration. The Y-intercept shows median (71.6 × 10⁶/mL), and the regression band (y = −3.92x + 87.72, R² = .460) indicates significant decline from 1980 to 2015.

Figure 2.

(A) Correlation plot shows significant decline in sperm concentration in North America (r = −.435, p = .007), but no such alteration in South America (B). It has decreased 36.49% in North America (C) and only 4.22% in South America (D) from 1980 to 2015. A comparative overview of Carlsen et al., 1992 and this study reveals a further 28.25% decline after that report in North America (E). Wafer plot reveals that New York and Connecticut have the highest sperm count (F).

Figure 3.

(A) Correlation plots of non-American continents showed significant reduction in sperm concentrations in Europe (r = −.307, p = .02) (A), Asia (r = −.560, p = .004) (B), and Africa (r = −.597, p = .02) (D), while Australia showed an increasing trend in sperm concentration over time (r = .167, p = .788) (C). Mean sperm concentrations reflected similar trends (a-d).

Figure 4.

Possible mechanism of action of environmental toxicants, lifestyle factors, obesity, and systemic diseases in lowering sperm count in ageing male (red arrows show inhibition, blue arrows show stimulation, purple arrows indicate decrease, and blue arrows indicate increase in hormone levels).