Ambient air pollutants and sperm quality in healthy Italian young men: a multicenter prospective cohort study with repeated measures.

Infertility is becoming a global public health issue, with male fertility declining worldwide in recent decades. Although air pollution is suspected to affect sperm quality, evidence is still controversial. The objective is to assess the potential relationship between air pollution and male infertility in healthy Italian young men, with a multicenter prospective cohort study. A sample of 345 males was enrolled in 2018-2019 in three polluted areas in North, Central, and South Italy. Participants received repeated examinations of semen quality parameters including sperm concentration, total and progressive motility, volume, and normal morphology. PM2.5, PM10, NO2, and O3 concentrations were used for estimating air pollution exposure during the 0-90, 0-9, 10-14, and 70-90 days before each semen examination. Linear mixed-effects models with subject-specific random intercept were employed, considering several climatic and behavioral factors as potential confounders. A 1 μg/m3 increase in PM2.5 during the 10-14 days interval was linked to a 1.3 % rise in sperm concentration and count (95 % Confidence Intervals [CIs]: 0.5 %-2.2 %, 0.4 %-2.2 %), with covariates held unchanged. Similarly, a 1 μg/m3 increase in PM10 during the same interval corresponded to 1.2 % and 1.1 % increases in sperm concentration and count, respectively (95 % CIs: 0.5 %-1.9 %, 0.3 %-2 %). Moreover, an increasing trend emerged in motility and normal morphology with increasing O3 exposure during the 0-90 and 70-90 days intervals. Due to the limited range of variability of outdoor air pollutants observed in this study, larger studies with a wider range of individual exposures are necessary to clarify air pollution's impact on male infertility.