Impact of Tobacco Cigarette Smoking on Semen Quality and Serum Levels of Sex Hormones in Men: A Cross‐Sectional Population‐Based Study

ABSTRACT

Background and Aims

The detrimental effect of tobacco cigarette smoking on human health has been reported in previous studies. The aim of the current study is to assess the effect of tobacco cigarette smoking on sperm quality and serum levels of sex hormones in men from the Jordanian population.

Method

In this study, 145 smoker men and 136 nonsmoker men were recruited. Semen analysis including ejaculate volume, sperm concentration, sperm total mobility and sperm morphology, was performed for comparison between cigarette smokers and non‐cigarette smokers. Serum concentrations of total testosterone, luteinizing hormone, and follicle‐stimulating hormone were also assessed in all subjects.

Results

Results from this study showed a significant statistical reduction in ejaculate volume (2.14 ± 0.03 mL vs. 2.65 ± 0.02 mL, p < 0.001) and sperm quality (sperm concentration, sperm total motility and sperm morphology) in smokers compared to non‐smokers. It also showed that smokers had statistically significant decreases in serum total testosterone hormone and follicular‐stimulating hormone levels (400.17 ± 4.29 IU/L and 6.23 ± 0.02 IU/L), respectively compared to non‐smokers (510.15 ± 5.17 IU/L and 7.75 ± 0.52 IU/L), respectively (p < 0.05). Smokers exhibited a notably higher level of serum luteinizing hormone compared to non‐smokers, with statistical significance (8.34 ± 0.03 IU/L vs. 7.04 ± 0.05 IU/L, p < 0.001).

Conclusion

Tobacco cigarette smoking showed an obvious reduction in ejaculate volume and sperm quality as well as altered levels of serum sex hormones in Jordanian men.

1. Introduction

Tobacco cigarette smoking is a major public health problem worldwide, with tremendous harmful health consequences on humans. In 2025, it is predicted that the prevalence of tobacco cigarette smoke in both sexes will reach 19.8%, while the prevalence among men is to reach 32.9% [1].

Cigarette smoke contains approximately 600 ingredients, which, when burned, produce over 7000 chemicals. Some examples of these toxic ingredients include nicotine, carbon monoxide, heavy metals, and benzene. Nicotine aggregates are a key component of the particulate phase of cigarette smoke [2]. Considering that smoke from tobacco cigarette contains more than 30 chemicals known to be carcinogenic, mutagenic, or allergenic, it is speculated that smoking directly harms human germ cells [3].

Jordan, an Arab and Middle Eastern nation, alarmingly is ranked as the highest tobacco‐using country in the world. The percentage of nicotine use among Jordanian males was 80% in 2000 [4].

Several studies found that cigarette smoking affects reproductive health in both men and women [5, 6]. Smoking damages the male reproductive system [7], affecting sperm production in the testes [8], and causes an imbalance in the endocrine system [9]. The exact mechanisms by which chemicals in tobacco cigarette smoke affect fertility in humans are not fully clear.

Seminal fluid analysis is a diagnostic procedure used to assess sperm quality, serving as a tool to diagnose male infertility. It involves examining semen volume, total sperm count, sperm concentration, sperm motility, and sperm morphology [10].

Although several studies examining the impact of smoking on semen characteristics in fertile men have been published so far, conflicting and inconsistent results have been reported [11, 12, 13]. To our knowledge, there has been no recent, comprehensive, population‐based study assessing the impact of cigarette smoking on serum sex hormones and semen quality in the Jordanian population. It is imperative to conduct thorough research in this field.

This study aims to examine the effects of smoking tobacco cigarettes on sperm quality and serum sex hormone levels in Jordanian men. It also aims to enhance our understanding of the mechanisms through which cigarette smoke may impact men's reproductive health.

2. Materials and Methods

2.1. Ethics Approval

This study was performed in line with the principles of the Declaration of Helsinki. Approval was granted by the Research Ethics Committee of the faculty of Pharmacy at Jadara University and filed under PHARM‐JA‐2/2024.

2.2. Study Population

The present observational population‐based study was carried out from June 2022 to March 2023. A total of 281 male subjects aged 22 to 45 years voluntarily participated in this study. Of these, 145 were fertile tobacco cigarette smokers, and 136 were fertile non‐smokers who served as controls. Signed informed consent forms were obtained from all participants included in the study. A pre‐test Performa was used to collect participants details such as age, weight, height and history of chronic disease.

2.3. Exclusion Criteria

Participants with a history of taking medications or having conditions or procedure known to affecting men reproductive health were excluded from the study. Individuals with malignancy, hypertension, diabetes, arthritis, epilepsy, tuberculosis, endocrin, liver or kidney diseases confirmed by laboratory diagnosis were also excluded from the current study.

2.4. Seminal Fluid Collection and Analysis

Participants were directed to abstain from ejaculation for 3–5 days prior providing semen samples, which were collected by masturbation into labeled sterile plastic containers. The semen specimens were collected either at a private infertility center or brought from home within 30 min after ejaculation. The samples were left for 20 min to liquefy at 37°C. Normal saline was used to wash the sperm and eliminate the seminal plasma.

The physical properties of sperms were assessed at a private infertility center by microscopic examination using a Zeiss Primo Star microscope (Carl Zeiss AG, Oberkochen, Germany) by experienced technicians according to the World Health Organization 2010 guidelines [14].

2.5. Blood Collection and Analysis

The blood samples were collected and processed in a private diagnostic laboratory. Blood samples were withdrawn from the participants between 8:00 and 10:00 a.m. and transferred into clean and labelled blood tubes. Samples were left at room temperature for 15 min to clot. After blood samples centrifugation at 5000g for 10 min, serum samples were transferred into new clean and labelled 1.5 mL Eppendorf tubes for analysis. Serum levels of total testosterone (TT), luteinizing hormone (LH), and follicular‐stimulating hormone (FSH) in the samples were measured using the Cobas 501 auto‐analyzer (Roche Diagnostics GmbH, Mannheim, Germany) and recorded.

2.6. Statistical Analysis

A two‐tailed, unpaired Student's t‐test assuming unequal variances was used to assess the statistical significance of differences between the smokers and the control groups. All data were analyzed using the GraphPad Prism 10 application for MacBook (GraphPad Software Inc., San Diego CA, USA). All results are expressed as the mean ± standard error of the mean (SEM). p < 0.05 was considered to be statistically significant.

3. Results

3.1. Demographic Characteristics

Our results showed that the mean age ±SEM of smokers (33.82 ± 0.35 years) was significantly higher than that of the controls (29.92 ± 0.22 years, p < 0.001, Table 1). The mean BMI of the smokers was also significantly higher compared with the controls (26.17 ± 0.13 kg/m² vs. 24.86 ± 0.14 kg/m², p < 0.001, Table 1).

Table 1.

Demographic characteristics of the participants.

Characteristic	Controls group n = 136	Smokers group n = 145	p value
Age (years)	29.92 ± 0.22	33.82 ± 0.35	p < 0.001
BMI (kg/m2)	24.86 ± 0.14	26.17 ± 0.13	p < 0.001

Note: Results are expressed as the mean ± SEM. p < 0.05 was considered to be statistically significant. Compared with the control group. BMI is body mass index.

3.2. Seminal Fluid Analysis

This study also showed that the seminal fluid analysis parameters in the smokers' group were significantly different compared to the controls group (Table 2). In this regard, the mean ejaculate volume of semen was (2.14 ± 0.03 mL) in smokers, which is significantly lower than the mean ejaculate volume in the controls (2.65 ± 0.02 mL, p < 0.001).

Table 2.

Seminal profile parameters in smokers and controls groups.

Parameter	WHO reference range	Controls group n = 136	Smokers group n = 145	p value
Ejaculate volume (mL)	> 1.5 mL	2.65 ± 0.02	2.14 ± 0.03a	p < 0.001
Sperm conc. (million/mL)	> 15 m/mL	46.75 ± 0.33	37.81 ± 0.34a	p < 0.001
Sperm total motility %	> 40%	47.89 ± 0.34	43.81 ± 0.21a	p < 0.001
Sperm morphology	> 4% normal shape	4.96 ± 0.03	3.90 ± 0.04a	p < 0.001

Note: Results are expressed as the mean ± SEM. Statistical significance was considered when p < 0.05.

^aIndicates statistically significant difference compared with the control group.

Additionally, the mean sperm concentration in the smokers was significantly lower than the mean sperm concentration in the control group (37.81 ± 0.34 million sperm/mL semen vs. 46.75 ± 0.33 million sperm/mL semen, p < 0.001) (Table 2).

Moreover, the percentage of sperm total motility and sperm morphology were significantly different in smokers compared to controls (Table 2). Smokers exhibited a significantly reduced percentage of sperm total motility (43.81% ± 0.21%) compared with the controls (47.89% ± 0.34%, p < 0.001). Similarly, the percentage of sperm morphology was also reduced in the smokers compared to the controls (3.90% ± 0.04% normal shape vs. 4.96% ± 0.03% normal shape, p < 0.001, Table 2).

3.3. Serum Sex Hormone Levels

The main serum levels of TT, LH, and FSH sex hormones were measured in smokers and controls groups (Table 3). The main serum TT and FSH levels were significantly reduced in smokers compared to controls (400.17 ± 4.29 IU/L vs. 510.15 ± 5.17 IU/L and 6.23 ± 0.02 IU/L vs. 7.75 ± 0.52 IU/L), respectively (p < 0.05). The main serum LH level was found to be significantly increased in the smokers compared to controls (8.34 ± 0.03 IU/L vs. 7.04 ± 0.05 IU/L, p < 0.001).

Table 3.

Serum sex hormone levels in smokers and controls groups.

Analyte	Reference range	Controls group n = 136	Smokers group n = 145	p value
TT	300–1000 ng/dL	510.15 ± 5.17	400.17 ± 4.29a	p < 0.001
LH	2–9 IU/L	7.04 ± 0.05	8.34 ± 0.03a	p < 0.001
FSH	2–12 IU/L	7.75 ± 0.52	6.23 ± 0.02a	p = 0.004

Note: Results are expressed as the mean ± SEM. Statistical significance was considered when p < 0.05.

^a Indicates statistically significant difference compared with the controls group. TT is total testosterone, LH is Luteinizing hormone, FSH is follicular‐stimulating hormone.

4. Discussion

The prominent finding in the current study is the deleterious consequence of cigarette smoking on men reproductive health through altering ejaculate volume, sperm concentration, sperm motility and sperm morphology among fertile males. Our study also showed that cigarette smoking affects the serum levels of TT, LH, and FSH in fertile males.

Cigarette smoking has a teratogenic effect in humans. Cigarette smoke comprises over 4000 components, including nicotine, tar, carbon monoxide, and polycyclic aromatic hydrocarbons [15], which have detrimental consequence on human health in general and on fertility in particular. Tobacco smoke content of nicotine and its metabolite cotinine, can pass the blood‐testis barrier, subsequently harm germ cells to varying degrees [3].

4.1. Smoking and Sperm Quality

Several studies have assessed the effect of various types of tobacco consumption including cigarette smoking [16, 17], e‐cigarette [17] and hookah smoking [18], on the seminal fluid analysis parameters in humans, yielding mixed and conflicting results. Seminal fluid analysis parameters include ejaculate volume, sperm concentration, sperm motility, and sperm morphology [14]. These discrepancies in the reported results may be due to variability between populations or differences in sampling methods in the different studies. Inadequate consideration of smoking habit or the potential confounding and modifying effects of other factors such as age as well as lack of statistical power in some studies may account for the contradictory findings.

Broadly speaking, cigarette smoking has been shown to reduce semen quality in men. Our findings in the current study are consistent with similar studies that have detected an association between cigarette smoking and reduced ejaculate volume of seminal fluid [19, 20, 21] and sperm concentration [20, 22]. The current study also found a reduction in total sperm motility percentage, which is in agreement with the decrease in sperm motility observed by Henriques et al. [22, 23], however, this finding contradicts that of Tang et al. [20].

Our study has shown an increase in abnormal sperm morphology in cigarette smokers. This is in alignment with another study that found sperm morphology was significantly lower in the infertile smokers' group compared to the infertile non‐smokers group [24]. However, in contrast to this finding, another study found no effect of in vitro tobacco‐ treatment (1 mg/mL) of human sperms on sperm morphology [25].

Spermatogenesis is the biological process of transformation and differentiation of spermatogonial stem cells into spermatozoa within 74 days in the seminiferous tubules of the testes [26]. Several underlying mechanisms of cigarette smoking effect on semen quality have been suggested. This includes the influence of chemicals in the cigarette smoke on the activity of accessory sex glands (such as seminal vesicle, prostate and urethral glands), which regulate semen volume through their secretions [27]. Additionally, chemicals in tobacco cigarette smoke increase levels of reactive oxygen species in the smokers' body as well as semen, which in turn deteriorate semen quality through inducing sperm DNA fragmentation [28], an increase in inflammatory response in the genitourinary system in men [29], promoting sperm apoptosis [30] and lipid peroxidation of the polyunsaturated fatty acids in the sperms' plasma membrane [3]. Furthermore, a decrease in the activity of antioxidant enzymes such as glutathione peroxidase (GPx‐1, 4) and a reduction in the mRNA expression of glutathione reductase enzyme in the spermatozoa of smoking men may mediate the reduction in sperm quality in smokers [31]. Moreover, chemicals in cigarette smoke decrease sperm quality in males, which can be mediated through seminal zinc level reduction [32]. Cigarette smoking can also reduce the mitochondrial activity in spermatozoa, leading to a low fertilization capacity [30]. Tobacco smoke alters the microRNA expression in sperm and DNA methylation pattern [3].

Nicotine, an abundant chemical in the cigarette smoke is able to penetrate the blood‐testis barrier and affect the process of spermatogenesis [3]. A higher seminal concentration of nicotine (100 ng/mL) reduced the percentage of viable spermatozoa and promoted spermatozoa apoptosis with DNA fragmentation or altered the chromatin compactness. Nicotine induced mouse Leydig cell apoptosis and inhibited androgen biosynthesis [8]. Heavy metals such as cadmium and lead in cigarette smoke when accumulate in seminal fluid may reduce the semen quality through inhibiting 8‐oxoguanine DNA glycosylase 1 enzyme, which is involved in the DNA repair pathway in human spermatozoa [33].

4.2. Effect of Smoking on Sex Hormones

Cigarette smoking has been shown to alter serum sex hormone levels in men. Enormous conflicting results have been reported regarding the effect of cigarette smoking on specific serum sex hormone levels in men. To this regard, it has been reported that cigarette smoking reduces the serum sex hormone levels [34, 35]. Nonetheless, nonsignificant differences in levels of serum FSH, LH, and TT in cigarette smokers compared to non‐smokers have also been reported [36, 37]. A third trend of studies found that cigarette smoking increases serum sex hormone levels [38]. The causes behind these discrepancies remain unclear but can be attributed to the variations between the experimental groups in different studies.

Effect of cigarette smoking on serum TT level, in particular, have been discrepant [27]. In alignment with other studies [39], our result showed a significant reduction in serum TT levels in smoking men compared to no‐smoking men. This finding contradicts what has been reported previously [11, 38]. Surprisingly, high serum TT level may, in turn, promote health risk behaviors such as cigarette smoking as well [11].

It has also been reported that cigarette smoking increased serum LH in smoking men compared to nonsmoking men [40] This finding is in agreement with our finding in the current study. However, several other studies found no association between cigarette smoking and serum LH levels [34, 41].

The current study also found a significant reduction in serum FSH level in smoking men compared to nonsmoking men. This finding is consistent with another study that reported a reduced serum FSH level when more than 10 cigarettes were smoked per day [42]. Nevertheless, this finding is in contrast to an earlier study by Mitra et al., which reported on the effect of cigarette smoking on serum levels of FSH [43].

Several theories have been proposed elucidating the mechanisms by which cigarette smoking alters serum levels of TT, LH, and FSH. Chemicals in the cigarette smoke can affect the hypothalamic‐pituitary axis through stimulation of growth hormone, cortisol, and vasopressin and oxytocin release [44]. The hypothalamus produces gonadotropin‐releasing hormone (GnRH) which, in turn, stimulates the gonadotropic cells in the anterior pituitary gland to produce LH. This hormone stimulates Leydig cells in the testes to produce TT hormone.

The reduced levels of serum TT observed in smoking men in our study seem to be caused by the direct toxic effect of cigarette smoke on Leydig cells per se, through various mechanisms including chronic hypoxia, oxidative stress, and the effect of nicotine on the hypothalamus‐pituitary‐gonadal axis [45]. A previous study using an animal model and histological examination showed that cigarette smoking led to the destruction of Leydig cells and a smaller number of these cells in the testis [45]. A potential and plausible mechanism by which cigarette smoking may alter serum TT levels in smokers is the direct damage to Leydig cells in the testis. This damage could lead to a decrease in key enzymes involved in TT production (NR5A1, CYP11A1, and 3b‐HSD1), or by triggering cell death through increased levels of proapoptotic proteins like Bax and caspase‐3, while decreasing levels of the antiapoptotic protein Bcl‐2 [39]. Moreover, it has also been suggested that chemicals in the cigarette smoke may lead to elevated serum TT levels by reducing the conversion of this hormone to estradiol [46].

Although LH and FSH work together in the reproductive system, an explanation for the unexpectedly increased serum LH levels in the smokers observed in this study may be due to direct downregulation in LH receptor (LHCGR) protein in smokers due to the effect of chemicals in cigarette smoke on the impairment of the LHCGR (encoded by Lhcgr gene) gene expression process and its effect on transcription factors [47]. Decreased serum FSH levels in smokers in this study may suggest testicular failure in the smokers, a pathological condition in which the seminiferous tubules in the testes are damaged due to chemicals in cigarette smoke [43].

Our study has some limitations. The effect of cigarette smoking on reproductive health in men might be confounded by other lifestyle factors such as coffee consumption habit, which is normally associated and concurrent with cigarette smoking, as well as alcohol intake. However, the latter confounder is rare in the study population due to cultural and religious reasons. The lack of accurate smoking dose information is another limitation in this current study. Information on the average number of cigarettes smoked per day is essential to assess the dose–response relationship between smoking habits and male reproductive health which is recommended in future work.

5. Conclusion

This study corroborated that cigarette smoking reduces sperm quality and alters the serum levels of sex hormones in Jordanian men. Observations in the current study may have important implications for couples seeking conception.

Author Contributions

Ibrahim Al‐Odat: conceptualization, formal analysis, visualization, investigation, supervision, methodology, writing – original draft, writing – review and editing, validation, software, project administration. Saad Al‐Fawaeir: conceptualization, data curation, formal analysis, methodology, investigation.

Consent

The authors have nothing to report.

Conflicts of Interest

The authors declare no conflicts of interest.

Transparency Statement

The lead author Ibrahim Al‐Odat affirms that this manuscript is an honest, accurate, and transparent account of the study being reported; that no important aspects of the study have been omitted; and that any discrepancies from the study as planned (and, if relevant, registered) have been explained.

Data Availability Statement

The data that support the findings of this study are available from the corresponding author upon reasonable request.