Temporal Trends in Semen Quality Among 271,545 Chinese Healthy Men From 1981 to 2019

Abstract

Background: Recent studies reported a decrease of sperm count around the world, however, little data from China was included. In China, declines in sperm quality remain controversial. Therefore, this study attempted to explore the temporal trends in sperm quality of Chinese healthy males from 1981 to 2019. Methods: Based on the protocol provided by Levine et al, data extracted from Pubmed, Science Director, Embase, China National Knowledge Infrastructure (CNKI) and Wanfang Data were collected to assess changes of sperm concentration (SC) and total sperm count (TSC) in recent decades using simple liner regression and meta-regression before and after adjusting for potential covariates including fertility group, region group, mean age, abstinence time, sperm collection and counting methods and whether individual provides more than one sample selection of population. Moreover, subgroups, categorizing based on geographic region or fertility status, were also conducted. Findings: A total of 102 studies with 271,545 individuals who provided semen samples from 1981 to 2019 were finally extracted for the present meta-regression analysis. SC declined significantly, on average, 0.43% per year with an overall decline of 16.3% between 1981 and 2019 (slope in unadjusted simple regression models -0.848 million/ml/year; 95% CI: -1.392 to -0.304; P = 0.002; slope in adjusted meta-regression models = -0.854; −1.452 to -0.630; P < 0.001). Trends for TSC was similar to that for SC with 0.89% per year and 33.08% overall decline from 1981 to 2019 (slope in unadjusted simple regression models = -2.063 million/year; 95% CI: -3.840 to -0.287, P = 0.023; slope in adjusted meta-regression models = -2.536; -4.052 to -1.022; P = 0.001). In subgroup meta-regression analysis, the slopes in model could be modified by fertility and region group (PSC for interaction = 0.031 and PTSC for interaction = 0.006). Fertility males in northern China had continuous declines in both SC (slope= -2.393; -3.964 to -0.822; P = 0.006) and TSC (slope= -9.675; -16.295 to -3.054; P = 0.010). Similarity, unselected group (unknown fertility males) in northern China also showed significant decreases in both SC (slope= -0.866; -1.403 to -0.329; P = 0.002) and TSC (slope= -1.806; -3.744 to -0.131; P = 0.047). Meanwhile, in southern China, only SC had significant down trends in fertility individuals (slope= -0.997; -1.736 to -0.258; P = 0.008). No changes in SC or TSC were seen in other groups separately. Results changed minimally in multiple sensitivity analyses, and there was no statistical support for the use of a nonlinear model. Interpretation: The present study was the first study to assess semen quality among 271,545 Chinese general healthy men in the recent 4 decades and our result indicated a serious reproductive health warning that sperm quality in general healthy Chinese men decreases between 1981 and 2019. Further studies on causes of the decreases are urgently needed. Funding Statement: This research was financially supported by National Natural Science Funding of China (to DZ) and Natural Science Funding of Shaanxi Province (to DZ). Declaration of Interests: All authors declare no conflict of interest.