Data from an animal study showed that an EtOH-rich diet can affect testicular function, with consequences on the semen quality. In fact, EtOH-fed mice showed compromised integrities of the testis and seminal vesicles, and altered weight of the prostate, which resulted in increased germ cell desquamation, decreased sperm concentrations, and increased abnormal sperm morphologies
[123][51]. Besides the alterations in the semen quality (lower sperm concentration, motility, and percentage of normal forms), Rahimipour et al. also reported reduced DNA condensation and integrity in mice fed with ethanol compared to controls, along with increased apoptotic rates
[85][52]. In addition, in vitro experiments showed an accelerated acrosomal loss occurring during the sperm capacitation of human and animal sperm incubated in ethanol, further reducing their fertilizing ability
[124,125,126,127][53][54][55][56]. This is probably due to the capacity of ethanol to alter lipid fluidity and membrane permeability through the oxidation of the membranes’ lipids and proteins
[127][56]. In rats, decreased sperm motility was observed after exposure to EtOH, as well as changes in the meiotic divisions, reduced gametes viability, and a higher rate of sperm with poorly condensed chromatin
[86,87][57][58]. In humans, a case study reported severe oligoasthenoteratozoospermia in an alcoholic man, which evolved into cryptozoospermia, and then azoospermia after a few years
[91][59]. In 2017, a meta-analysis investigated the impact of alcohol intake on semen quality by analyzing evidence from 18 cross-sectional studies
[93][60]. The authors concluded that daily alcohol consumption results in a worsened semen quality, particularly in terms of the semen volume and the sperm morphology. However, this effect was not reported for occasional drinkers, while the authors observed even better sperm motility in occasional drinkers than never drinkers, despite all the limitations identified in their analysis
[93][60]. In fact, the association between semen quality and the amount of alcohol consumed is still controversial. Surprisingly, Ricci et al. observed a positive correlation between semen volume and concentration, and moderate alcohol consumption (equal to 4–7 units/week), suggesting that a limited consumption of alcohol may improve semen quality
[96][61]. This might be explained by the fact that some compounds present in alcoholics drinks (i.e., natural flavonoids, and polyphenols in red wine) have antioxidant and anti-inflammatory activities, and they reportedly have a positive influence on semen quality (particularly by improving sperm motility, concentration, and survival) at low concentrations
[128,129,130,131][62][63][64][65]. However, a cross-sectional study including 8344 healthy men did not report any association between low/moderate alcohol consumption and semen quality
[81][29]. Similarly, other studies failed to identify any coherent dose–response pattern in the semen parameters depending on the degree of alcohol consumption
[83,88,132,133,134][31][66][67][68][69]. Boeri et al. suggested that the correlation between alcohol consumption and alterations in the semen parameters might be directly proportional to the amount of alcohol consumed. In fact, the semen parameters were reportedly worse in samples of heavy rather than moderate drinkers
[89][70]. Several recent studies of different global geographic regions have confirmed the negative impact of heavy alcohol consumption on semen quality. In fact, in China, a cross-sectional study conducted in 2020 reported reduced sperm concentrations in 55 heavy drinkers suffering from secondary infertility
[88][66], while in Italy, 45 heavy drinkers with primary infertility showed reduced sperm concentrations and motilities compared to moderate drinkers or abstainers
[89][70]. Similarly, an inverse association between sperm counts and alcohol consumption was observed in a Brazilian population of 167 infertile men
[90][71], while a large study conducted on a Danish population of 1221 men showed a direct association between worsening semen quality and increasing alcohol intake
[92][72]. Other studies have also confirmed a higher rate of sperm DNA fragmentation and chromatin decondensation in heavy drinkers
[89,90,94,95][70][71][73][74].
The differences in the study designs, and the discrepancies in the published studies, make it challenging to draw any conclusions regarding the association between the amount of alcohol consumed and the semen quality. Hence, much research is still warranted in this regard.