A decade of WHO 2010. Total sperm number temporal trend and role of lifestyle factors

After a huge decline in sperm concentration between 1938 and 1991 was reported, many researchers investigated the possibility of a worsening of human sperm quality. Despite massive efforts, published evidence is still controversial. Similarly, the role of lifestyle factors on semen parameters is debated. We conducted a monocentric Italian study to evaluate the total sperm number trend over the last 10 years (from 2010 to 2019). Additionally, we evaluated the association between lifestyle factors and total sperm number in order to identify possible damaging factors. We performed a retrospective study analyzing subjects aged 18-55 years who had their semen analyzed between 2010 and 2019. A total of 3329 subjects were included: 1655 subjects referred to our department (Department of Experimental Medicine, Sapienza University of Rome, Roma, Italy) for idiopathic infertility and 1674 subjects referred for preconceptional or andrological screening with no confirmed andrological diseases. Semen samples were examined according to World Health Organization (WHO) 2010 criteria by two seminologists with the same training and the same equipment. For statistical evaluations, only total sperm number (×106 per ejaculate) was taken into consideration. We detected no significant changes in mean total sperm number during the last decade, in either the entire population or the two subgroups (infertile group and control group). In a multivariate analysis total sperm number was significantly associated with the history of infertility, body mass index (BMI) and cigarette smoking. Our results suggest that infertile men are "vulnerable" subjects, particularly susceptible to several negative factors, many of which still remain unknown. Our study highlights the need for studies addressing men's lifestyle in order to find and reduce deleterious agents.