Ambient ozone pollution is associated with decreased semen quality: longitudinal analysis of 8945 semen samples from 2015 to 2018 and during pollution-control period in Beijing, China / 亚洲男科学杂志(英文版)

Previous studies suggest that air pollution has a negative effect on semen quality. However, most studies are cross-sectional and the results are controversial. This study investigated the associations between air pollutants (PM2.5, PM10, SO2, NO2, CO, and O3) and semen quality among sperm donation candidates, especially when the air pollution was artificially controlled in Beijing, China. We analyzed 8945 semen samples in the human sperm bank of Peking University Third Hospital (Beijing, China) from October 2015 to May 2018. Air pollution data during the entire period (0-90 days prior) and key stages (0-9, 10-14, and 70-90 days prior) of sperm development were collected from the China National Environmental Monitoring Centre. The association between air pollutants and semen parameters (sperm concentration and progressive motility) was analyzed by a mixed model adjusted for age, abstinence duration, month, and average ambient temperature. Only O3during key stages of 0-9 days and 10-14 days and the entire period was negatively associated with sperm concentration between 2015 and 2018 (P < 0.01). During the period of air pollution control from November 2017 to January 2018, except for the increase in O3concentration, other five pollutants' concentrations decreased compared to those in previous years. In this period, the sperm concentration decreased (P < 0.001). During the pollution-control period, O3exposure 10-14 days prior was negatively associated with sperm concentration (95% CI: -0.399--0.111; P < 0.001). No significant association was found between the other five pollutants and semen quality during that period. Our study suggested that only O3exposure was harmful to semen quality. Therefore, O3should not be neglected during pollution control operation.

Ambient ozone pollution is associated with decreased semen quality: Longitudinal analysis of 8945 semen samples from 2015 to 2018 and during pollution-control period in Beijing, China / 亚洲男科学杂志(英文版)

Previous studies suggest that air pollution has a negative effect on semen quality. However, most studies are cross-sectional and the results are controversial. This study investigated the associations between air pollutants (PM2.5, PM10, SO2, NO2, CO, and O3) and semen quality among sperm donation candidates, especially when the air pollution was artificially controlled in Beijing, China. We analyzed 8945 semen samples in the human sperm bank of Peking University Third Hospital (Beijing, China) from October 2015 to May 2018. Air pollution data during the entire period (0-90 days prior) and key stages (0-9, 10-14, and 70-90 days prior) of sperm development were collected from the China National Environmental Monitoring Centre. The association between air pollutants and semen parameters (sperm concentration and progressive motility) was analyzed by a mixed model adjusted for age, abstinence duration, month, and average ambient temperature. Only O3 during key stages of 0-9 days and 10-14 days and the entire period was negatively associated with sperm concentration between 2015 and 2018 (P 0.01). During the period of air pollution control from November 2017 to January 2018, except for the increase in O3 concentration, other five pollutants' concentrations decreased compared to those in previous years. In this period, the sperm concentration decreased (P 0.001). During the pollution-control period, O3 exposure 10-14 days prior was negatively associated with sperm concentration (95% CI: -0.399--0.111; P 0.001). No significant association was found between the other five pollutants and semen quality during that period. Our study suggested that only O3 exposure was harmful to semen quality. Therefore, O3 should not be neglected during pollution control operation.

Estudio epidemiológico de casos y autocontroles: una aproximación conceptual y metodológica / Case crossover studies: a conceptual and methodological approach

Los estudios de casos y autocontroles se clasifican como una variante de los estudios de casos y controles. Se han mencionado en la literatura científica desde hace aproximadamente 18 años, y son empleados en investigaciones epidemiológicas con exposiciones agudas o transitorias que pueden generar un evento en salud (infarto agudo del miocardio, asma, lesiones, enfermedades infectocontagiosas, entre otras). Para su manejo se requiere definir conceptos tales como disparadores, tiempo de inducción, periodo de caso, periodo de control. Su uso es limitado en la evaluación de exposiciones crónicas o no intermitentes. Por otro lado, este diseño reduce sesgos de selección, de información, de confusión y el sobrepareamiento. Una de sus ventajas es que requieren menor tamaño de muestra que un estudio clásico de casos y controles, donde los periodos de control se pueden obtener del mismo sujeto, sin la necesidad de entrevistar a otro tipo de controles. No obstante, para el cálculo del tamaño de la muestra se debe tener encuenta el enfoque de diseños pareados. Éste es un diseño donde los principios teóricos de homogeneidad, simultaneidad y representatividad se cumplen de manera singular.

Case crossover studies are considered as a variant of case control studies, and they have been included in the scientific literature since approximately eighteen years ago. They have also been used in epidemiological research on acute or intermittent exposures that may lead to a number of events including heart attack or cardiac arrest, injuries, asthma, etc. Application of this particular study design requires defining concepts such as: triggers, induction time, case period and control period. Its use is limited in studies on chronic exposures. On the other hand, this type of design may reduce selection and misclassification bias, confounding, and overmatching. Another advantage is that it requires a small sample size because the same case can be used as its own control in one or several periods. Nevertheless, sample size calculation must be assessed as a matched case-control study. This is a type of study in which theoretical principles are accomplished in a sui generis manner.