Sleep behavior is associated with over two-fold decrease of sperm count in a chronotype-specific pattern: path analysis of 667 young men in the MARHCS study

Recent studies have shown that the reduction of sperm count is associated with sleep behaviors, including restricted/excessive sleep duration, late sleep time midpoint, and shift of sleep midpoint time (social jetlag). Chronotype is suggested to regulate sleep behaviors; however, the relationship between chronotype and human sperm count is unknown. The relationship between sleep behaviors and human sperm count, when sleep behaviors as well as chronotype are controlled is also unclear. We performed a path analysis of the data obtained from 667 Chinese men recruited into the MARHCS (Male Reproductive Health in Chongqing College Students) study. Chronotype, sleep duration, sleep time midpoint, and social jetlag were estimated by the Munich Chronotype Questionnaire. Sperm count was measured by computer-aided sperm analysis. The comprehensive relationship between chronotype, all sleep behaviors, and sperm count was tested by path analysis, in which the standardized residual of sperm count was used for adjustment of age, abstinence period, body mass index, tobacco smoking, alcohol drinking, and intake of tea, cola, and coffee. Our major findings are: (1) Chronotype negatively correlated with sleep duration (correlation coefficient (R) = -0.32, P < .001) and positively correlated with sleep midpoint (R = 0.65, P < .001) and social jetlag (R = 0.37, P < .001). (2) Sleep duration (U-shape transformed; R = -0.11, P = .005), sleep midpoint (R = -0.09, P = .021), and social jetlag (R = -0.12, P = .001), respectively, correlated with sperm count in univariate analysis. The relationship between sleep midpoint and sperm count disappeared when social jetlag was controlled. (3) Path analysis showed that chronotype is connected with sperm count through two pathways: via sleep duration (standardized path coefficient = -0.09, 95% CI: -0.17 to -0.01, P = .030) and via social jetlag (standardized path coefficient = -0.09, 95% CI: -0.17 to -0.01, P = .031). For men of earlier, intermediate, and later tertile of chronotype, the sleep-duration-related decrease of sperm count was separately estimated to be 16.3%, 12.8%, and 11.6%, while the social-jetlag-related decrease of sperm count was estimated to be 9.3%, 12.8%, and 19.2%. The total effect of sleep behaviors on sperm count was estimated to be 25.7%, 25.6%, and 30.7%, with an average of 27.4% for men of different chronotypes. The present study showed that men of earlier chronotype were prone to restricted/excessive sleep duration, while men of later chronotype were prone to social jetlag, both of which correlated with reduced sperm count, suggesting that chronotype may modulate the sleep behaviors and exert dual effects on sperm count via different sleep behaviors, leading to a ubiquitous sperm decline. Men of different chronotypes should take care to avoid different types of improper sleep behaviors, so as to prevent such deleterious effect on sperm count.