Cigarette smoking and semen quality

Cigarette smoking as a cause of delay in conception

Epidemiological studies relating cigarette smoking to the ability to conceive and maintain a pregnancy provide information on the clinical significance of smoking on reproductive health. Cigarette smoking by females has significantly increased in the decades after World War II, and now has an average initiation at ages 18–20 years. Maternal smoking is a hazard to the general health, the reproductive health and the life of both mother and child. Gestational smoking renders the fetus a passive smoker. This can result in fetal and neonatal death and in reduced fecundity of adult daughters.

Smoking and reproduction

In the Netherlands, approximately 30% of all women of reproductive age smoke, compared with 36% of men.

Cigarette smoking is associated in women with a dose-related reduction in fecundity and fertility and in men with a reduction in semen quality. Smoking has a negative effect on pregnancy: increased rates of antepartum bleeding and placenta praevia have been described. Smoking is also associated with increases in the rates of spontaneous abortion, low birth weight and perinatal death. Some tobacco-related perinatal deaths are due to an increased risk of serious malformation. Children of mothers who smoke are admitted twice as often to hospital for pulmonary problems. However, studies on maternal smoking and childhood cancer have proved inconclusive.

Is smoking a risk factor for decreased semen quality? A cross-sectional analysis

BACKGROUND

Previous studies suggest a deleterious effect of cigarette smoking on semen quality, but their results have not been consistent. We studied the association between current smoking and semen characteristics and hormonal levels in a large group of healthy men.

METHODS

From 1987 to 2004, seven separate occupational or environmental semen quality studies were co-ordinated by our department. A total of 2562 men participated, each providing semen and blood sample and answering a questionnaire about lifestyle and factors related to health. Appropriate semen and smoking data were available for 2542 men.

RESULTS

Adjusting for study, age and other covariates, we observed an inverse dose-response relation between smoking and semen volume, total sperm count and percentage motile sperm. Heavy smokers had a 19% lower sperm concentration than non-smokers. We found a positive dose-response relationship between smoking and testosterone, LH and the LH/free testosterone ratios.

CONCLUSION

Current smoking in adult life moderately impairs the semen quality. It is well known that semen quality is associated to fecundity. Therefore, it would be sensible to advise men to abstain from smoking to avoid decreased fecundity.

Lack of association between smoking and DNA fragmentation in the spermatozoa of normal men

Male factor infertility patients can have anomalies in their sperm nuclei, displaying high levels of loosely packaged chromatin and damaged DNA. The primary objectives of this study were to compare the extent of DNA fragmentation in the spermatozoa of healthy light and heavy smokers versus non-smokers, and to investigate its correlation with concentrations of the smoking markers cotinine and cadmium. A secondary objective was to compare the concentrations of blood cadmium and serum cotinine with corresponding concentrations in seminal plasma. Ninety-seven healthy male volunteers were divided into three groups: non-smokers, light and heavy smokers. There was no difference between the three groups with respect to age, number of ejaculations per week, serum testosterone concentration, and parameters of semen analysis. The percentages of DNA fragmentation in spermatozoa were not statistically different in the heavy smokers (12.11%), light smokers (11.66%) and non-smokers (20.41%). Serum and seminal plasma concentrations of cotinine were significantly higher in heavy smokers compared with the other groups (P < 0.0001). Median values for blood cadmium concentration were higher in heavy smokers (4.50 microg/l) than in light smokers (0.20 microg/l) and non-smokers (0.20 microg/l) (P < 0.001). Cadmium concentration in seminal plasma was significantly higher in heavy smokers (0.20 microg/l) than in light smokers (0.10 microg/l) and non-smokers (0. 10 microg/l) (P < 0.05). In summary, our results indicate no association between smoking and DNA fragmentation in the spermatozoa of healthy men.

Effects of cigarette smoking on semen characteristics of a population in Mexico

A study of semen quality was conducted in 197 smoking and 161 non-smoking men undergoing initial infertility investigation. The men were allocated into groups according the number of cigarettes smoked per day < 10 (n = 57), 11-20 (n = 115), and > 20 cigarettes (n = 25). Smokers had significantly poorer sperm density (P < .005), a lower percentage of viability (P < .007), a lower percentage of normal sperm morphology (P < .005), and the percentage of motile sperm was lower (P < .005). These parameters were worse in the heavy smoking groups. Thus the present study corroborates reports of detrimental effects of cigarette smoking on sperm characteristics. Further studies are needed to explain the mechanism by which smoking affects spermatogenesis.

An electron microscope study of the axonemal ultrastructure in human spermatozoa from male smokers and nonsmokers

OBJECTIVE

To investigate possible abnormalities or deterioration of the sperm axonemal ultrastructure in men who have smoked a large quantity of cigarettes (> 20 per day) for a prolonged period.

DESIGN

Semen specimens were collected by patients via masturbation; qualitative characteristics of the sperm were assessed and ultrastructural analysis of the sperm axoneme was performed using standard operating procedures for electron transmission microscopy.

SETTING

The Andrology Institute of Lexington, Lexington, Kentucky, and the Department of Histology and Embryology, University of Salonika, Greece (collaborative effort).

PATIENT(S)

Twenty-nine men (mean age +/- SD, 30.7 +/- 2.1 years) who smoked a mean (+/- SD) of 30.7 +/- 2.1 cigarettes per day for 10.7 +/- 0.7 years and 15 men who never smoked (mean age +/- SD, 30.4 +/- 2.2 years) participated in this study.

MAIN OUTCOME MEASURE(S)

Ultrastructural organization of the sperm axoneme in male smokers and nonsmokers.

RESULT(S)

Changes in the number and the arrangement of axonemal microtubules were noted in the smoker group when compared to the nonsmoker group. The incidence of axonemal abnormalities was higher in spermatozoa from smokers compared with that in spermatozoa from nonsmokers.

CONCLUSION(S)

Smoking a large quantity of cigarettes per day, under the conditions of the current study, severely affected the ultrastructure of the flagellum and, more specifically, it affected the axoneme of the human spermatozoon.

Effects of seminal plasma from cigarette smokers on sperm viability and longevity

OBJECTIVE

To evaluate the effects of cigarette smoking on the ability of seminal plasma (SP) to maintain sperm viability.

DESIGN

Clinical randomized study. Spermatozoa from cigarette smoking or nonsmoking subjects were reconstituted in SP from smokers and nonsmokers and in modified Ham's F-10 medium, followed by sperm quality assessment during a 48-hour incubation period.

SETTING

Andrology Institute of Lexington, Lexington, Kentucky.

PATIENT(S)

Twenty men who had been smoking cigarettes for longer than 3 years (30 cigarettes per day or more) and 20 nonsmokers participated in this study.

MAIN OUTCOME MEASURE(S)

Improvement in sperm viability by removal of SP--and associated detrimental factors present in the SP--from smoker subjects.

RESULT(S)

The results obtained indicate that the quality of spermatozoa obtained from nonsmokers was superior to that of smokers. The SP from the two patient groups had a definite effect on their respective sperm quality, i.e., beneficial effects for the nonsmokers, detrimental effects for the smokers. Exposure of spermatozoa from the nonsmokers to SP from the smokers resulted in a significant reduction in sperm viability. However, exposure of spermatozoa from the smokers to SP from the nonsmokers or to Ham's F-10 medium yielded significant improvements in sperm viability.

CONCLUSION(S)

The detrimental effects of smokers' SP on nonsmokers' spermatozoa was prominent and a rather unique phenomenon. The results generated in this study could be of clinical significance since removal of smokers' SP and subsequent reconstitution and incubation in physiological media seems to enhance the viability, longevity, and possibly the fertilizing ability of these spermatozoa for use in various assisted reproductive technologies.

Smoking and male reproduction: a review

Because of the large number of men worldwide who smoke and the fact that cigarette smoke contains known mutagens and carcinogens, there has been concern that smoking may have adverse effects on male reproduction. A review of the epidemiological literature indicates that cigarette smoking is associated with modest reductions in semen quality including sperm concentration, motility and morphology. The associations between male smoking and sperm concentration and motility are stronger among studies of 'healthy' men (e.g. volunteers and sperm donors) than among men from infertility clinic populations. Smoking has also been associated with alterations in hormone levels in males, for example increases in the levels of oestrone and oestradiol. Despite modest reductions in semen quality and altered hormone levels among smokers compared to non-smokers, studies have not shown a reduction in male fertility in association with paternal smoking. There is some evidence to suggest that paternal smoking is associated with congenital anomalies and childhood cancer (with ORs in positive studies generally < 2.0). Smoking has not been shown to be mutagenic to human spermatozoa, although studies have been small and have had methodological shortcomings. It is concluded that, although smokers as a group may not experience reduced fertility, men with marginal semen quality who wish to have children may benefit from quitting smoking, since several small studies indicate the potential for improved semen quality after quitting smoking. More research on the benefits of quitting smoking among men with marginal semen quality is needed. Methodological improvements in studies aimed at clarifying the association between paternal smoking and reproductive and developmental outcomes in offspring should include obtaining accurate paternal smoking dose information, evaluating smoking exposure information in relation to various time windows (e.g. prior to conception, during gestation), and controlling for potential confounders and modifying factors such as age and maternal smoking habits. More sensitive and specific laboratory assays and increased sample sizes are required to establish whether smoking induces mutations in human spermatozoa.

Does cigarette smoking impair natural or assisted fecundity?

OBJECTIVES

To assess the effects of female and male smoking on natural and assisted fecundity.

DESIGN

A systematic review of published studies was conducted, identifying reports using on-line and hand search techniques.

INCLUDED STUDIES

Potentially relevant articles were screened for inclusion based on the following criteria: comparative study (cohort or case control) with clinical pregnancy or live birth reported among smokers and nonsmokers.

EXPOSURE

Cigarette smoking.

MAIN OUTCOME MEASURES

Time to conceive; conceptions per subject or per cycle; spontaneous abortion rate.

RESULTS

Thirteen relevant studies of natural conception were identified. All but one demonstrated a negative association between smoking and fecundity (odds ratio [OR] for conception or live birth 0.33 to 1.0). Seven studies of IVF-GIFT yielded a common odds ratio for conception of 0.57 (95% confidence interval 0.42 to 0.78). Seven studies evaluating spontaneous abortion suggested a small increased risk among female smokers (OR 0.83 to 1.8). Twenty-one studies assessing smoking in men demonstrated no consistent effect on sperm quality. None of the four studies evaluating fertility in male smokers demonstrated significant impairment.

CONCLUSION

This body of literature suggests a small but clinically significant detrimental effect of female smoking on both time to conception and spontaneous abortion risk. Variability between studies, particularly in terms of adjustment for confounding factors, undermines the strength of these conclusions. However, the consistent dose-response effect in both the spontaneous conception and abortion literature and a return to normal fecundity among exsmokers suggest a causal association. The effect of male smoking on fecundity is probably far less significant.

Effects of cigarette smoking on human semen quality

The effects of cigarette smoking on sperm quality were evaluated from a group of males undergoing initial screening for infertility. Out of a total of 674 males, 618 (selected based on established criteria) were studied. Detailed smoking history was obtained by direct interview. Tests were conducted on semen characteristics (volume, sperm density, viability, motility, and morphology). Smokers had significantly poorer sperm density (p < .04), a lower percentage of normal sperm morphology (p < .001) and a higher percentage of headpiece spermatozoa defects (p < .01) compared with the nonsmokers. Significant trends were also observed for different categories of cigarette-years with sperm density, percentage of normal spermatozoa morphology, and percentage of spermatozoa with headpiece defect. Cigarette smoking appears to affect sperm density and the morphology of spermatozoa, especially the headpiece. A dose-response relationship of cigarette smoking and spermatogenesis is suggested.

Mutagenic lifestyles? A review of evidence of associations between germ-cell mutations in humans and smoking, alcohol consumption and use of 'recreational' drugs

In humans, associations between germ-cell mutations and hypothetical aetiological factors can be investigated by (1) examining the relationship between the factor of interest and conditions known to be of genetic aetiology; (2) examining the relationship between conditions of unknown aetiology and route of exposure, especially paternal preconceptional exposure. As regards smoking, alcohol and 'recreational' drugs, the first approach has been applied in studies of retinoblastoma, Wilms' tumour and chromosomal anomalies. Only Down's syndrome has received intensive investigation, in relation to maternal smoking during pregnancy; the relative risks would be compatible with there being no association in all recognized conceptuses. The second approach has been applied in studies of sperm quality, miscarriage, congenital anomalies and childhood cancer. The available studies do not show a consistent relationship between smoking and sperm quality; there are few data on the effects of the other exposures. There are a substantial number of studies of childhood cancer and smoking by the father; the majority do not indicate any relationship. Some studies of childhood cancer suggest a positive association with use of 'recreational' drugs by the parents, but it has not been possible to clarify which route of exposure, or the specific type of drug which may be involved. Use of molecular techniques to detect individual genetic changes should enable progress to be made in elucidating the origin of mutation. In the meantime, public health actions are justified on the basis of the known non-genetic effects of these agents.

Ethnography, epidemiology and infertility in Egypt

Infertility in the developing world has been relatively neglected as an international health problem and a topic of social scientific and epidemiological inquiry. In this study, we examine factors placing poor urban Egyptian men and women at risk of infertility, and we explore the sociocultural and political-economic contexts in which these health-demoting factors are perpetuated. Our approach to the problem of Egyptian infertility attempts an explicit merging of ethnographic and epidemiological research designs, methods of data collection and analysis, and interpretive insights to provide improved understanding of the factors underlying infertility in the urban Egyptian setting.

Use of a sealed minichamber for direct observation and evaluation of the in vitro effect of cigarette smoke on sperm motility

OBJECTIVE

To determine the in vitro effect of cigarette smoke on sperm motility and survival in an attempt to find a possible association with clinical studies that had pointed to the existence of such an effect in vivo.

DESIGN

Laboratory experiments in which the effect of cigarette smoke on human sperm placed in a sealed minichamber was directly observed and determined by motion analysis.

PATIENTS

High-quality fresh semen specimens were obtained from healthy donors and used for the experimental studies.

INTERVENTIONS

Various doses of filtered and nonfiltered cigarette smoke, collected by an improvised manual smoking machine, were streamed at a rate of 2 mL/s into sealed chambers containing samples of washed spermatozoa. Evaluation of the changes in sperm motility was performed in real time by direct microscopical observation and repeated determinations by the multiple exposure photography technique until their complete immobilization.

RESULTS

Streaming of 100 mL of cigarette smoke induced a dramatic drop in sperm motility, which caused sperm immobilization in about 15 minutes. This effect showed a clear dose-response relationship either with the amounts streamed or with the time during which sperm were exposed to cigarette smoke. The harmful effect was almost the same whether sperm were exposed to filtered or nonfiltered cigarette smoke. The role of carbon monoxide and hydrogen cyanide on these findings was studied separately, and it was shown that the inhibitory effect was not due to the presence of these two important components of cigarette smoke.

CONCLUSIONS

The clear evidence of the in vitro harmful effect of crude cigarette smoke on sperm motility points to the possibility that in heavy smokers certain toxic agents may reach mature spermatozoa or their precursors via the blood stream and induce their harmful effect on sperm motility in vivo.

Cigarette smoking and sperm quality

The effect of cigarette smoking on conventional semen parameters (volume, total sperm count, sperm count/ml, total motility, progressive motility, morphology) was studied retrospectively in 90 healthy patients (50 non-smokers, 40 smokers) of our infertility clinic. Both groups, comparable in age, height and weight, were subdivided into two age groups (less than 28 years, greater than or equal to 28 years). Smokers were found to have sperm volumes significantly smaller than non-smokers of the same age. No additional effects on sperm parameters were found. Cigarette smoking revealed no detrimental effect on spermatogenesis.

Cigarettes, alcohol and marijuana are related to pyospermia in infertile men

The relationship of current use of cigarettes, marijuana and alcohol to the parameters of seminal fluid analysis, sperm penetration assay and sperm autoimmunity was studied in 164 men from infertile couples. Current cigarette smokers, marijuana users and heavy alcohol users showed greater numbers of leukocytes in the seminal fluid than did nonusers (p less than 0.02, less than 0.007 and less than 0.01, respectively). In addition, cigarette smokers had lower sperm penetration assay scores than nonsmokers (median 2.5 versus 8.0, p = 0.05). Users of cigarettes, marijuana or alcohol showed no decrease in sperm count, motility or percentage of oval sperm, and no difference in prevalence of antisperm antibodies compared to nonusers. After controlling for past sexually transmitted diseases and multiple substance exposures in a multivariate model, use of cigarettes (p = 0.006), marijuana (p = 0.12) or alcohol (p = 0.098) continued to be associated with a trend toward increased number of seminal fluid leukocytes. Cigarette smoking continued to show a significant decrease in sperm penetration assay score (p = 0.03).

Cigarette smoking and male reproduction

The effects of cigarette smoking on male reproduction were studied through measuring the serum estradiol (E2), prolactin (PRL), and total testosterone (T). Smoking men had higher levels of E2 and PRL but normal T compared to nonsmokers. Raised E2 and PRL may be among the mechanisms through which cigarette smoking impairs male reproduction.

Cigarette smoking and semen quality in men of reproductive age

The effect of cigarette smoking on conventional semen parameters was studied in voluntary men of reproductive age (n = 190). Special attention was focused on sperm motility and its quantitative and qualitative change in vitro during the observation period. The sperm output war normal in both smokers (n = 54) and non-smokers (n = 110), but semen volume was smaller (p less than 0.03) in heavy smokers (greater than 16 cigarettes/day) than non-smokers. In sperm morphology there was no difference between study groups. The only clear difference between men with different smoking habits was in the percentual change in the sperm motility during 24 hours. At the time of first examination, the sperm motility was better (p less than 0.02) in heavy smokers than those who smoked less than 16 cigarettes per day and the motility decreased more rapidly (p less than 0.007) in heavy smokers than non-smokers. The objectively measured initial mean velocities of the whole sperm population and of the progressive spermatozoa were slightly higher in subgroup of smokers than in non-smokers. The rapid decrease in the survival spermatozoa in smokers may be uneconomical and harmful in respect of fertility.

Effect of tobacco consumption on semen quality of a population of hypofertile males

Effect of tobacco use (by chewing or smoking) on semen quality has been seen. Semen analysis of 119 tobacco chewers and 219 smokers was compared with those of 288 control patients. Some decrease in the ejaculate volume, sperm density, and total count was observed in tobacco users, but it was statistically insignificant. No difference was found in other parameters, like motility and morphology. It is concluded that tobacco use by chewing or smoking is not associated with impaired semen quality in males selected from an idiopathically hypofertile population.

Interrelationships of cigarette smoking, testicular varicoceles, and seminal fluid indexes

Data on cigarette smoking, testicular varicoceles, seminal fluid indexes, and oligospermia were examined in 160 young men without known disease and in 94 husbands in infertile couples. The combination of smoking and testicular varicoceles is strongly related to the incidence of oligospermia, defined as sperm count less than or equal to 20 X 10(6)/ml, in each sample. Smokers with testicular varicoceles, in each sample, had a disproportionately high incidence of oligospermia. In the combined sample of 254 men, the smokers with testicular varicoceles had an incidence of oligospermia approximately ten times greater than that in nonsmokers with testicular varicoceles and approximately five times greater than that in men who smoked but were without testicular varicoceles. This relationship of cigarette smoking and testicular varicoceles to oligospermia has not been previously reported. The pathophysiologic basis of the interaction between smoking and varicoceles was theorized to be due to an increased secretion of catecholamines from the adrenal medulla, induced by cigarette smoking. The elevated catecholamine concentrations in the renal vein would then reach the testes via retrograde flow down the internal spermatic vein in men with testicular varicoceles, resulting in seminiferous tubule damage.

Semen quality of infertile couples--comparison between smokers and non-smokers

Comparison of semen quality was undertaken between 60 smoking and 50 non-smoking men attending infertility investigation. As far as possible, other factors which might influence semen quality were eliminated. The men were allocated into groups according to sperm density and number of cigarettes smoked per day. The percentage of motile sperm in heavy smokers with oligozoospermia and the total sperm count were lower, the difference being significant at the 1% and 5% levels, respectively. No correlation was found in percentage of sperm with morphologically abnormal heads, midpieces or tails. Heavy smoking may have a detrimental effect on the motility of sperm. Further studies are needed to explain the mechanisms by which smoking affects spermatogenesis.

Sperm quality of healthy smokers, ex-smokers, and never-smokers

The possible effects of cigarette smoking on sperm quality were investigated in a blind study of 333 healthy male volunteers 19 to 40 years of age. All subjects with clinically proven abnormalities, operations, or inflammatory diseases of the genital organs, exposure to radiation exceeding routine x-ray examination, or medication were excluded, and the data from 150 smokers, 37 ex-smokers, and 52 never-smokers were evaluated. There was a small but insignificant decrease in sperm density from never-smokers to ex-smokers and to smokers. Eight smokers (6%) had sperm counts less than 1 X 10(6)/ml, whereas none of the ex-smokers or never-smokers fell into this category. This difference, however, is not statistically significant (P = 0.084). No statistically significant effect of smoking habits on sperm density, motility, and morphologic features was detected. It is concluded that smoking does not affect the motility and morphologic features of sperm in healthy adult men. The diminished sperm density in heavy smokers may be related to factors associated with smoking.

Cigarette smoking and its possible effects on sperm

The possible effects of cigarette smoking on sperm were evaluated by comparison of the quality of sperm from 103 smokers and 135 nonsmokers in a blind study. Smokers were found to possess significantly (P less than 0.001) decreased density (number) and motility of their sperm than nonsmokers. Morphologic abnormalities, particularly bicephalia, although prevalent among individual smokers, did not differ significantly (P greater than 0.9) when a comparison of smokers versus nonsmokers was made as a whole. Based on these observations and those of others demonstrating the presence of the mutagenic properties of smoke condensates, we suggest that decreases in sperm density and motility in cigarette smokers may be reflective of smoke condensate-induced mutagenic spermatogenital alterations.

Scoring sperm morphology from fertile and infertile cigarette smokers using the scanning electron microscope and image analysis

Image analysis was applied to photographs of sperm samples obtained using a scanning electron microscope. This technique is too time-consuming for routine use but could, if automated, provide an objective assessment of sperm morphology. In order to test the technique, sperm samples were evaluated from four groups of men: fertile and infertile smokers and fertile and infertile nonsmokers. There was a significant increase in the numbers of abnormalities in samples from infertile men. There was no association between the numbers of abnormal sperm and cigarette smoking.

Testicular function in potential sperm donors: normal ranges and the effects of smoking and varicocele

Testicular exocrine (semen analysis) and endocrine (plasma LH, FSH, prolactin and testosterone) function was assessed in 119 consecutive healthy men presenting for screening as potential sperm donors. Since these volunteers were unbiased with respect to their fertility status, this sample of the general male population was suitable to determine normal ranges and the influence of a variety of physical (height, weight, standardized body weight, varicocele) and demographic (age, marital and fertility status, tobacco and alcohol consumption) factors on normal human testicular endocrine and exocrine function, without the confounding effects of bias in selection of subjects. The statistical distribution of all seminal parameters was non-gaussian, but cube-root transformation of the data normalized the distribution, allowing for parametric statistical analysis. The median (and 95% confidence limits) for the various semen parameters was 73.0 (10.6-235.3) million sperm per ml; 189.0 (12.6-868) million sperm per ejaculate; 50.4 (5.9-181.9) million motile sperm per ml; 133.0 (6.9-661.7) million motile sperm per ejaculate; 54.0 (7.0-172.9) million morphologically normal sperm per ml and 138.5 (7.5-672) million morphologically normal sperm per ejaculate. Testicular volume was correlated positively with measures of physique such as standardized body weight (r = 0.25, P less than 0.01) and body surface area (r = 0.30, P less than 0.002), and negatively with plasma levels of FSH (r = -0.31), P less than 0.002) but not LH. Sperm output was positively correlated with testicular volume (r = 0.28, P less than 0.005) and negatively correlated with plasma FSH (r = -0.31, P less than 0.002) and plasma LH (r = -0.31, P less than 0.002). Smoking was associated with a highly significant reduction in sperm output and motility. Men with varicocele (25%) were significantly taller, had slightly lower haemoglobin levels and moderate left (but not right) testicular atrophy, but neither seminal nor hormonal parameters were different from men without varicocele. There was no difference in any markers of human testicular function between men according to marital or fertility status, grades of moderate alcohol consumption or the presence of low titres of sperm antibodies.

Prolactin and pituitary-gonadal function in cigarette smoking infertile patients

Serum prolactin (PRL) was significantly lower in smokers, compared with non-smokers in 233 males and 250 females referred to our infertility clinics. In subjects smoking 10 cigarettes or more per day, the mean serum PRL was 22% and 20% lower in men and women, respectively. In cigarette smoking men serum testosterone was significantly higher and semen volume lower, while neither serum luteinizing hormone (LH) or follicle stimulating hormone (FSH), sperm density, motility of morphology differed between smokers and non-smokers. It is possible that the higher serum testosterone levels in smokers are due to their lower bodyweight, and that the lower semen volume may be due to an effect of nicotine on the contractility of the deferental ducts. Cigarette smoking may increase central dopaminergic tonus and reduce PRL levels, but it is unknown whether or not this is of biological significance in relation to reproductive function.