The increasing use of artificial light at night and the modern lifestyle '' 24/7 '' have led individuals to adopt sleep/wake schedules that are inconsistent with their internal biological clock, which is referred to as '' daily desynchronization '' (Roenneberg and others, 2019).
QUESTION TO STUDY:
Is peri-day desynchronisation a risk factor for male reproductive damage in semen parameters and/or reproductive hormones?
SUMMARY OF RESPONSES:
Peri-day desynchronization correlates with a decrease in sperm count, which has improved after weakening peri-day desynchronization.
WHAT'S ALREADY KNOWN:
Peri-day desynchronisation due to work (shift work) and non-work-related causes is common worldwide and has been found to be associated with a decrease in female fertility, but it is not clear whether it harms men's reproductive health.
TEST DESIGN, SIZE, DURATION:
Hybrid studies have been conducted. (i) Cross-cutting survey of 1346 Chinese in 2007 were used to analyse the relationship between sperm/hormone biomarkers and work-related peri-day desynchronisation, which was divided into rotational shift work and permanent shift work compared to shift-free work. (ii) A cohort of 796 Chinese students between 2013 and 2014 was used to analyse the relationship between semen/hormone biomarkers and non-work-related peri-day desynchronisation (between school days and holidays). (iii) A biomarker identified simultaneously in both populations has been additionally verified in male C57BL/6J mice kept in conditions simulating peri-day desynchronisation.
MAIN RESULTS AND ROLE OF THE CASE:
Among sperm/hormone biomarkers, sperm count was lower in shift workers who had a higher risk of low
sperm count, as determined by the Chinese Ministry of Health (total sperm count/ejaculate <120 10 6)
(1/4 1.26; 95% CI 1.05-1.52).