Seasonality in human semen quality of smokers and non-smokers: effect of temperature
Robert Knzle1, Michael D. Mueller1, Alexander W. Huber1, Heinz Drescher2, Nick A. Bersinger1
1Department of Obstetrics and Gynaecology,
University of Berne, Berne, CH-3010, Switzerland
Asian J Androl 2004 Sep; 6: 243-247
Keywords: sperm quality; seasonal temperature; fertility; smoking
Aim: To analyse the possible effect of seasonal variation on semen parameters. Methods: The participants consisted of 1688 men attending the andrology laboratory between 1991 and 1997 for reduced fertility in the couple. Semen analysis was performed according to the WHO manual. The 84 individual months of the study period were each assigned to one of the three groups according to the average monthly outside temperature; Group A (temperature <4.4 ), Group B (4.4 - 13.3 ) and Group C (>13.3 ). Results: When comparing the different sperm parameters, the morphology was significantly better in Group C. However, when the smokers were analysed separately, this difference disappeared and significant seasonal variations were found in sperm density, total sperm count, motility and total motile sperm; they were deteriorated in the warmer season. In non-smokers, no such negative effect of increased temperature was observed. Conclusion: Sperm quality is influenced by seasonal factors. Increased environmental temperature, (maybe also light exposure) has an additional negative effect on the spermatogenesis in smokers, leading to reduced sperm quality in men with borderline fertility.
Assessment of semen quality is based on the evaluation of several parameters, including semen volume, sperm density, total sperm count, sperm motility and sperm morphology. It is now accepted that these parameters can be influenced by various factors such as smoking [1-3], lifestyle  and high scrotal temperature, and may be also seasons of the year. Most studies performed in temperate climates showed a minimum of the sperm count in summer and higher densities in winter or spring [6-9]. However no significant differences in other semen parameters could be observed as a function of the month of the year in other studies. Chia et al  did not see a significant seasonal variation in semen volume and density of men who live in the tropics. Ombelet et al  examined seasonal variation in sperm count, motility and morphology without observing any differences in these parameters, neither did others find a circannian rhythm except a reduced motility in the spring . Nevertheless, fluctuations in testicular temperature or changes in daily exposure to light may be responsible for seasonal variations of sperm quality, which could be induced by an endogenous biological clock occurring annually by changes in the length of daylight. The causal mechanisms of this process are far from being fully understood .
Seasonal variation in sperm quality may result in lower conception rates in summer as one of the possible factors being responsible for a reduced birth rate in spring. In this study we aimed to investigate whether semen quality was subject to circannian rhythmicity and if smoking habits had an effect on this variability in a part of the world with a temperate climate, but with a wide range of temperatures, such as Western Europe.
2 Materials and methods
2.1 Participants and sample collection
Men attending the andrology laboratory between 1991 and 1997 for reduced fertility in the couple were included in this retrospective study. Only the first sperm evaluation was taken into account in this analysis and samples from patients with azoospermia or having had vasectomy or vasovasostomy were excluded. Semen samples were collected by ejaculation into a special sterile container (Telast SA, Prverenges, Switzerland) after two to seven days of sexual abstinence. Most ejaculates were collected at the laboratory, but some at home and delivered immediately to the laboratory without allowing to cool. All analyses were performed within two hours.
A total of 1688 samples, with clinical data and smoking behaviour on record, fulfilled the criteria and were included in the study. All analyses were performed in the same laboratory (MCL) and no methodological changes were made during the study period.
2.2 Semen analysis
The semen analysis consisted in the determination of sample volume, sperm density, total sperm count, progressive motility, vitality and morphology as described by the WHO . Total sperm count and total motile sperm were calculated from the observed data.
The sperm motility was assessed by computer assisted sperm analysis (CASA), using an ATS 20-J.C. analyser (Diffusion International, Fresnele, France) based on the principle of negative phase contrast microscopy. Oligozoospermic samples were manually analysed with a Makler chamber using an Olympus BH-2 microscope (Japan). The morphology was assessed under the microscope after staining with a kit based on fast green, eosin and thiacin (Diff-Quick, Dade Diagnostica, Switzerland). The laboratory continuously takes part in multicentre quality control trials.
2.3 Statistical analyses
The 84 individual months of the study period (1991 to 1997) were assigned to three groups according to the average monthly temperature in Berne, obtained retrospectively from the Swiss National Bureau of Meteorology (Liebefeld, Berne, Switzerland). Table 1 shows the average monthly temperatures observed during the collection period. The following temperature cut-offs between the groups were calculated in order to obtain three groups of an identical total time span (28 months each): Group A, less than 4.4 ; Group B, 4.4 - 13.3 ; and Group C, more than 13.3 .
Table 1. Average monthly temperature in during the study period (July 1991 to May 1997).
Data were analysed by Student's t-test or, in case of significantly different standard deviations (predominantly for total sperm count), with the Welch's approximate test. A P value of 0.05 or less indicated a significant difference between two seasonal groups.
The study sample consisted of 1688 participants of whom 1064 (63 %) were non-smokers. Group A (cold) consisted of 635 semen samples, Group B (medium), 522 samples and Group C (warm), 531 samples. The fraction of smokers was 38.5 % (n=240), 30.4 % (n=190) and 31.1 % (n=194) in temperature groups A, B and C, respectively. No significant associations were found between smoking habits and temperature groups.
When analysing the mean values of different sperm parameters as a function of the 3 groups, only the morphology showed significant differences (A vs. C and B vs. C) with higher values in Group C (Table 2). A similar trend was seen when comparing the non-smokers alone between these groups, with a significantly better morphology in Group C than in the others. When the smokers were analysed separately, the morphology was not significantly different, while significant seasonal variations were found for sperm density (A vs. C), total sperm count (A vs. C and B vs. C), motility (B vs. C) and total motile sperm (A vs. C) with lower values in C. Non-smoker semen donors in warmer months (C) were significantly younger than those recruited during the cold period (A) (Table2).
Table 2. Sperm parameters as a function of temperature. Group A (<4.4 ), B (4.4 - 13.3 ) and C (>13.3 ) in the total population, smokers and non-smokers. Data in meanSD.a Total motile sperm = total sperm countprogressive motility/100. bP<0.05 compared to smokers. eP <0.05, Group A versus Group C; hP<0.05, Group B versus Group C.
Hence, a deleterious effect on sperm quality associated with the warmer season was observed in smokers only, i.e. sperm samples collected in the summer months were of a significantly reduced quality in the smoking population. This effect cannot be attributed to age, since the non-smokers were slightly older.
A number of biological rhythms are known to exist in man, such as the rhythm of the pituitary response to luteinising hormone-releasing hormone (LHRH) and the circadian rhythm in the excretion of prolactin or steroid hormones. Some studies describe a chronobiological fluctuation in semen parameters with a decrease in semen quality during the summer months and an increase in winter and spring [7, 8, 15]. This seasonal rhythmicity may be induced by an endogenous clock which is influenced by seasonal changes in temperature or light exposure ; however the causal relations and mechanisms are not understood and the reported results are contradictory to some extent. Other studies did not find any seasonal variation in semen parameters [9, 11]. The lack of significant periodicity in these studies may be explained by the large variation in individual semen parameters in the population, which could also be influenced by external factors, such as length of abstinence, different smoking habits [1, 3], sedentary working style , varying age [7, 16] or different daily light exposure . Details on these factors, which could be potential confounders, are not available, but we do not think that bias could have been introduced by them since the large number of samples is likely to be randomly distributed.
Politoff et al
 demonstrated a circannual rhythm in spermatogenesis using 2697 spermiograms
from fertile and subfertile men, with the lowest sperm parameter values
observed in July, August, September, and December , and the highest in
February and November. Statistical significance (P = 0.017) was
reached for the month of September. In the normal spermiogram population
alone, a similar rhythmicity was found, with sperm densities between 20
and 250106/mL (first spermiograms
) and a minimum value again in September but which did not quite reach
statistical significance (P =
One could hypothesize that in patients with an already reduced sperm quality such as smokers, the effects of environmental temperature and maybe light and lifestyle would have an additional deleterious influence on the spermatogenesis. This would also be in agreement with Politoff et al  who found a more pronounced decrease in sperm density in a population with oligozoospermia than in the control population during the summer.
In conclusion, sperm quality is influenced by a number of external factors, of which some are seasonal. Environmental factors such as temperature and light could have an additional negative effect on spermatogenesis and sperm quality in men with borderline fertility.
Zhang JP, Meng QY, Wang Q, Zhang
LJ, Mao YL, Sun ZX. Effect of smoking on semen quality of infertile men
in Shandong, China. Asian J Androl 2000; 2: 143-6.
Nick A. Bersinger, Ph.D., University
Department of Clinical Research, Inselspital KKL G3-825, Berne, CH-3010,