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Summary of dissertation

EDMaRC PhD dissertation defence
In September 21st, 2018 the EDMaRC Ph.D student cand.scient. Lærke Priskorn will defend her dissertation at the Panum Institute, University of Copenhagen. 
Title: Semen quality in young Danish men – prenatal factors and adult lifestyle
Supervisors: Professor Katharina Main, MD, PhD Niels Jørgensen, and Professor Tina Kold.  

Summary: Total fertility rates in Denmark are below the replacement level of 2.1 children per woman and have been for several decades. Social and economic factors influence fertility trends, but biological capacity to reproduce, including semen quality, may also play a role. Besides being associated with fertility chances, semen quality also seems to be a predictor of a man’s long-term general health. Thus, the significance of decreased semen quality should not be neglected as a large proportion of young Danish men have poor semen quality, and the average sperm count is lower than in Danish men examined in the 1940s. The causes of the poor semen quality in Danish men are widely unknown.
To elucidate the trends in semen quality and potential prenatal factors and adult lifestyle influencing semen quality in Danish men we analysed data from an ongoing study of semen quality with annual cross-sectional investigations between 1996 and 2016, including a total of 7,012 men from the general population. Study participants completed a questionnaire; delivered a semen sample, assessed for semen volume, sperm concentration, motility and morphology; had a blood sample drawn, analysed for serum concentrations of reproductive hormones, and had a physical examination, including measurement of anogenital distance (AGD, distance from anus to external genitalia) from 2012 onwards.

We observed that semen quality during the study period was stable but low. 35% of the men were categorized as having low semen quality taking the World Health Organization’s reference levels for semen quality into account. Both prenatal factors and adult lifestyle seem to influence semen quality in Danish men. A subgroup of 1,106 men had AGD measured as a marker of in utero androgen action and thus foetal masculinization programming.  The proportion of men exposed in utero to maternal smoking declined during the study period, but despite a confirmation of the previously reported association between maternal smoking during pregnancy and lower semen quality in sons, the large decline in the proportion of exposed men did not result in an overall improvement of semen quality among Danish men. Thus, other factors are likely responsible for maintaining the observed low semen quality. Also adult lifestyle is important, and in 1,210 men the association between sedentary behaviour and testicular function (semen quality and reproductive hormones) was examined. This study showed that more time spent watching television, but not time spent in front of a computer, was associated with lower sperm concentration and total sperm count, e.g. men who watched television more than 5 hours per day had an adjusted sperm concentration of 37 million/mL compared to 52 million/mL in men who watched very little television or none at all (p-value for difference <0.05).

Our results suggest that the low semen quality in Danish men are likely due to a wide range of factors that in combination affect the semen quality. This can have a negative impact on couples’ biological ability to reproduce, which is a burden for the couples and for society as well. Further research should investigate the interplay between different exposures with adverse effects on semen quality and the link between reproductive and long-term general health in men, which is poorly understood.
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