The sitting men: A systematic review of spare and working time exposure to sedentariness in relation to semen parameters.

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Over the past few decades, several studies have found that semen quality parameters have steadily declined over time. Many hypotheses have been made to explain this finding, among which a sedentary lifestyle has been investigated. To synthesize the current evidence, we performed a systematic review of published papers reporting on the relationship between sedentary habits and semen parameters. Embase and PubMed were systematically searched for papers published in English up to May 2023. We included all full-text observational papers that reported the relationship between sedentariness and semen parameters. Article selection adhered to the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) guidelines. Sixteen observational studies were ultimately included, six in healthy men and ten in men from Fertility Clinics. They encompassed a total of 13,509 men, with 9877 being healthy men and 3632 presenting at Fertility Clinics for initial assessment. In terms of semen volume, no association emerged in the six studies involving healthy men: however, results in men referring to fertility clinics mainly showed no association, with one indicating a decline and one higher volume. Twelve studies did not report differences in sperm concentration, while one study in men from Fertility Clinics and two in healthy men observed a decline in this parameter with increasing time spent on TV watching or sedentary posture in spare time. Total sperm count was found to be similar across groups of inactivity, except for one study that showed a significant decrease when men from Fertility Clinics spent more time watching TV. No significant differences were reported in sperm motility across all studies, with only one study, among those addressing sperm morphology, indicating a lower percentage of normal forms in men watching TV more than 3h per day. Finally, three studies conducted in men referring to Fertility Clinics analyzed the sperm DNA fragmentation index. Two of these studies found a higher DNA fragmentation index in men spending more time per day in a sitting posture. This review suggests a weak association between time spent sitting during spare time and sperm concentration, but the findings are inconsistent, highlighting the need for further research.