JPM | Free Full-Text | Decrease in Sperm Parameters in the 21st Century: Obesity, Lifestyle, or Environmental Factors? An Updated Narrative Review

JPM | Free Full-Text | Decrease in Sperm Parameters in the 21st Century: Obesity, Lifestyle, or Environmental Factors? An Updated Narrative Review

Cigarette smoking is identified as a worldwide health problem that contributes to different illnesses and is a cause of premature death. Data suggest that smoking, especially during the preconception time, might negatively impact DNA methylation patterns, thus causing sperm DNA fragmentation and aneuploidy [21,22]. A model to assess the germline age based on sperm DNA methylation at specific loci was developed to estimate the individual’s chronological age with a high degree of accuracy [21]. Moreover, cigarette smoking has been associated with an infertility risk factor and is strongly associated with male sterility [22]. Beal and collaborators analysed the current literature on the subject and found that half of the studies reviewed demonstrated no significant impairment in semen parameters. In contrast, about 40% of the remaining studies found evidence of modest impairment in one or more semen parameters (number, motility, and morphology) when the number of cigarettes smoked per day increased [22]. In addition, the authors reported that paternal smoking during the preconception time was associated with an increased cancer risk in offspring [22]. A study by Sharma and collaborators [23], investigating 5865 men, showed that cigarette smoking is correlated with a decrease in sperm motility and number and that deterioration of sperm parameters is more evident in smoking individuals. Studies have observed that smoking can increase the time for pregnancy: in infertile couples undergoing assisted reproductive treatment (ART), male smoking contributes to a 44% reduction in pregnancy rate after in vitro fertilisation [21]. Smoking exerts its greatest negative impact on genome integrity, where 70% of publications reported some level of smoking-related damage to the genome and epigenome, which might raise the rate of chromosomal aberrations [21,22,23]. A study by Linschooten and colleagues reported that men who smoked during the six months prior to conception were “four times more likely to pass on tandem repeat minisatellite mutations to their children” [24]. Furthermore, the results from meta-analyses provide convincing evidence that paternal preconception smoking significantly raises the risk of cancer in offspring [22]. Most tobacco products contain over 4000 different chemicals and constituents, including nicotine and heavy metals. Between these, cadmium and lead have been individually linked to impaired sperm quality, as has tobacco smoke in general. Smoking appears to reduce sperm concentration, motility, viability, and normal morphology; also, it is associated with DNA damage and leads to the generation of reactive oxygen species (ROS) [25,26]. A study by Pant and co-authors [27] has investigated the correlation between lead and cadmium with sperm quality. They studied fertile and infertile individuals between 20 and 43 years of age. The semen assessment was performed according to the 2010 WHO guidelines. The authors reported that cadmium and lead levels were significantly increased in infertile males. Also, an adverse correlation was found between the seminal concentration of cadmium and lead and sperm numbers, motility, and abnormal forms. One of the main mechanisms involved between smoking and semen impairment seems to be associated with an increase in ROS; cigarette smoking represents a source of pro-oxidants and free radical generators, which can induce oxidative damage and a reduction of redox scavengers in the peripheral blood [28]. Due to this concern, Kiziler and colleagues [29] scrutinised the level of lead and cadmium in seminal plasma and blood, as well as the level of antioxidant defences, in particular, glutathione S-transferase (GST) and reduced glutathione (GSH), in the seminal plasma and spermatozoa from 50 infertile men versus 45 healthy fertile individuals. The authors found that lead and cadmium concentration as well as ROS levels in the smokers’ infertile group were significantly increased compared to the fertile men and the group of nonsmoking infertile males (p 30]. However, another concern greatly studied in male factor infertility is represented by DNA damage in the male germ line, which can be associated with damage to genetic integrity, a reduced fertilisation rate, poor embryo development, and an increased risk of miscarriage [30,31]. Even so, the specific details of the DNA lost integrity are not well elucidated; however, it seems that it is highly associated with DNA compaction during the final stages of spermiogenesis and the damage induced by oxidative stress (OS) [32]. A specific enzyme, 8-oxoguanine DNA glycosylase 1 (OGG1), is involved in the DNA repair pathway in human spermatozoa. Interestingly, it has been elucidated by Smith and collaborators [33] that the activity of this enzyme is significantly reduced when cadmium is present; thus, this heavy metal can be considered as an inhibitor of OGG1 in a time- and dose-dependent manner. However, even though enough scientific evidence suggests that smoking might impair male infertility, more than one-third of male adults worldwide continue to use tobacco, making it perhaps one of the most widespread contributors to declining male fertility [26].

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And in case you missed it, here is our ultimate road trip playlist is the perfect mix of podcasts, and hidden gems that will keep you energized for the entire journey


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