pii: sp- 00256-15
SLEEP DUR ATION/SLEEP QUALIT Y
Inverse U-shaped Association between Sleep Duration and Semen Quality: Longitudinal Observational Study (MARHCS) in Chongqing, China Qing Chen, PhD1; Huan Yang, PhD1; Niya Zhou, MM1; Lei Sun, PhD1; Huaqiong Bao, MM2; Lu Tan, MAgr1; Hongqiang Chen, BSc1; Xi Ling, BE1; Guowei Zhang, PhD1; Linping Huang, MPH1; Lianbing Li, MD2; Mingfu Ma, MD2; Hao Yang, MD2; Xiaogang Wang, BSc1; Peng Zou, BSc1; Kaige Peng, PhD1; Taixiu Liu, BSc1; Zhihong Cui, PhD1; Lin Ao, PhD1; Till Roenneberg, PhD3; Ziyuan Zhou, PhD4; Jia Cao, PhD1 Institute of Toxicology, College of Preventive Medicine, Third Military Medical University, Chongqing, China; 2Chongqing Institute of Science and Technology for Population and Family Planning, Chongqing, China; 3Centre for Chronobiology, Institute for Medical Psychology, University of Munich, Munich, Germany; 4Department of Environmental Health, College of Preventive Medicine, Third Military Medical University, Chongqing, China 1
Study Objectives: To investigate the association between sleep duration and semen parameters as well as reproductive hormone levels. Methods: We designed a cohort of male college students in Chongqing, China. A total of 796 subjects were recruited in 2013 and 656 (82.4%) were followed up in 2014. Each time, semen and peripheral blood samples were collected for semen quality and reproductive hormone measurement. Sleep duration was estimated by revised Munich Chronotype Questionnaire. In 2014, sleep quality was also measured by Pittsburgh Sleep Quality Index (PSQI). Results: There was a substantial inverse U-shaped association between sleep duration and two semen parameters (semen volume and total sperm number), with 7.0–7.5 h/day of sleep showing highest parameters. Either longer or shorter sleep was associated with decreased semen parameters in a dose-response manner (P = 0.002 and 0.001, respectively). Sleeping > 9.0 h was associated with a 21.5% (95% confidence interval 9.2, 32.2) reduction in semen volume and 39.4% (23.3, 52.1) reduction in total sperm number; sleeping ≤ 6.5 h was associated with 4.6% (−10.5, 22.3) and 25.7% (−1.2, 60.1) reduction. Increase of the two parameters was found in those who changed sleep duration toward 7.0–7.5 h/day from 2013 to 2014. The U-shaped association was independent from PSQI and was replicated in another dataset of 1,346 males. No association found between sleep duration and reproductive hormone. Conclusions: Either restricted or excessive sleep may impair semen quality. Further research is needed to validate this finding. Keywords: reproductive hormone, semen, sleep duration Citation: Chen Q, Yang H, Zhou N, Sun L, Bao H, Tan L, Chen H, Ling X, Zhang G, Huang L, Li L, Ma M, Yang H, Wang X, Zou P, Peng K, Liu T, Cui Z, Ao L, Roenneberg T, Zhou Z, Cao J. Inverse u-shaped association between sleep duration and semen quality: longitudinal observational study (MARHCS) in Chongqing, China. SLEEP 2016;39(1):79–86. Significance Based on a cohort and another cross-sectional study, we for the first time showed an inverse U-shaped association between sleep duration and semen parameters and indicated that either restricted or excessive sleep may reduce semen quality. The potential effect of sleep duration on semen quality deserves attention given the global prevalence of nontraditional sleep schedules and the potential impact on male reproductive health. Further work is needed to confirm the casual relationship of sleep duration and semen quality in independent populations.
INTRODUCTION With artificial lighting and “24/7” lifestyle in modern society, the sleep duration of human beings has been quite different from what it was before. There was 1–2 h difference of the sleep duration between the people nowadays and those living 50 to 100 years ago1; sleeping less than 6 h or over 9 h now accounts for about one third of adults.2 Unfortunately, cumulative evidence has suggested that both restricted and excessive sleep duration may induce various unfavorable outcomes such as cognitive, coronary and gastrointestinal disorders.3–5 The effect of sleep duration on reproductive health has also been cause for concern in recent years. Several reports suggest that sleep duration was associated with the testosterone level in males.6,7 However, as to its influence over semen quality, which reflects the fertility of males more directly,8–10 evidence is still sparse. In 2007, we measured sleep duration and semen quality in 1,346 Chinese males but only examined the hypothesis of linear correlation, finding null results.11 In 2013, Jensen et al.12 studied sleep disturbance, another dimension of sleep, and reported a U-shaped association with semen quality in Danish males. The authors find it difficult to interpret this type of association; but interestingly, as the authors mentioned, U-shaped association was common in studies about another dimension of sleep—the sleep duration, which was unfortunately not investigated in their study. Recently, an animal study reported that SLEEP, Vol. 39, No. 1, 2016
restriction of sleep duration led to declined semen quality.13 However, there has been no evidence linking sleep duration with semen quality in population until now. Considering the emerging evidence of regional or global decrease in semen quality (especially the total sperm number) in the recent decades,14–16 whether the sleep duration could modify the semen quality deserves investigation. Since 2013 we have established a cohort to investigate the effect of environmental and socio-psycho-behavioral factors on male reproductive health in China (the MAle Reproductive Health in Chongqing college Students, MARHCS study). Semen quality and reproductive hormone levels were analyzed for the subjects. As to the evaluation of sleep, both quantity (sleep duration) and quality were measured. Based on this cohort, here we show our findings about the relation between sleep duration and semen quality (as well as reproductive hormone levels), with consideration for the influence of sleep quality. METHODS Study Design The MARHCS cohort was designed to investigate the influence of environmental and socio-psycho-behavioral factors on male reproductive health. The baseline was established within the voluntary male college students in the University 79
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Town of Chongqing in June 2013. The subjects donated biological samples (semen and peripheral blood for assessment for semen quality and reproductive hormone levels) and answered a composite questionnaire of socio-psycho-behavioral factors including the sleep related issues. Then, according to the lecture schedule of the college, some of the students moved from the rural campus (University Town) to the urban campus for higher grade education after September 2013, resulting in distinct living circumstances between the moved students and ones who stayed. The participants were followed up for the first time in June 2014. More details could be found elsewhere.17 The associations between sleep duration and semen parameters were first analyzed for the baseline data (2013) and then replicated in the follow-up data (2014), with adjustment for sleep quality. Furthermore, change of sleep duration and semen parameters between the 2 y were compared in order to investigate whether there was an association between change of sleep duration and change of semen parameters. The study was approved by the ethics committee of Third Military Medical University. We obtained written informed consent from all the participants.
Laboratory Manual for the Examination and Processing of Human Semen.18 The analyses began as soon as the sample liquefied. The semen volume was assessed by weighing, assuming the density of semen to be 1 g/mL. The sperm concentration and progressive motility was measured by the Sperm Class Analyzer 5.3.00 (MICROPTIC S.L., Barcelona, Spain). Total sperm number was calculated as sperm concentration multiplied by semen volume. The sperm morphology was assessed with semen smears prepared with 10 μL of well-mixed semen. Assessment of Serum Reproductive Hormone Levels The serum levels of the following six hormones were measured on the Beckman Unicel DXI 800 Immunoassay System (Beckman Coulter Inc., Brea, CA, USA): follicle-stimulating hormone, luteinizing hormone, estradiol, progesterone, testosterone, and prolactin. Questionnaire The information of socio-psycho-behavioral factors was collected by a composite questionnaire, within which a modified Munich Chronotype Questionnaire (MCTQ) was used to estimate the sleep duration. The MCTQ estimated the sleep duration by identifying certain time points. It had been proved to be an accurate and precise tool for the measurement of sleep time in population.19 Average night sleep duration and average midday sleep duration could be measured separately, and entire sleep duration was calculated as the sum of night duration and midday duration. In the following context, the sleep duration indicated average entire sleep duration unless there was a particular explanation. Details of sleep duration estimation can be found in the supplemental material. Information regarding age, tobacco smoking, alcohol consumption, and intake of tea, cola, and coffee was also collected by the composite questionnaire. In the 2014 survey, the Pittsburgh Sleep Quality Index (PSQI) was also included to measure the sleep quality of the subjects.20,21 The total score of PSQI ranges from 0 to 21, with higher scores indicating poorer sleep quality.
Participants The participants were recruited by the following criteria: older than 18 y; abstinence period between 2 and 7 days; sophomores studying in the University Town of Chongqing city. Those who met any of the following criteria were excluded: (1) previous diagnosis by urologist with any of the listed conditions: inflammation of urogenital system, epididymitis, testicular injury, incomplete orchiocatabasis; (2) treatment history of varicocele; (3) detected by the urologist at the field of recruitment as any of the following conditions: absence of prominentia laryngea, absence of pubes, abnormal breast, abnormal penis, absence of testis, epididymal knob or varicocele. A total of 872 males participated; 796 of them were eligible and the remaining 76 were excluded due to ineligible abstinence period (n = 33), urogenital disorders (n = 36), or failure to provide semen sample (n = 7). In June 2014, 656 of the 796 eligible subjects (82.4%) were followed up and finished all the procedures. No significant difference of sleep duration or semen parameters was found between the followed-up students and the lost ones.
Statistical Methods Because the semen parameters and reproductive hormone levels were of skewed distribution, we used nonparametric Jonckheere-Terpstra test and Spearman correlation to examine the association between the semen parameters and the sleep duration. Next, multivariate linear regression was implemented to adjust for age, body mass index (BMI), period of abstinence, tobacco smoking, alcohol consumption, and intake of tea, cola, and coffee. To fit the prerequisite of linear regression, the outcome variables were analyzed on a logarithmic scale and back-transformed to obtain the percentage of change for each parameter. The locally estimated scatter plot smoothing (LOESS) method was also used to help illustrate the associations. This method was especially useful to represent the nonlinear relation between variables, e.g., the U-shaped relation. Furthermore, multilevel model was also used to analyze the sleep-semen association by integrating the data of both 2013 and 2014. Wilcoxon signed rank test was used to compare how
Assessment of Semen Quality Before the time of each interview, we sent Emails and text messages to each subject reminding him to keep his abstinence period between 2 and 7 days when participating in the interview. Furthermore, although we recommend the subjects to make an appointment for interview, they could change it to another appropriate date in case that occasional ejaculation such as during intercourse, masturbation, or nocturnal emission occurred. Following the World Health Organization (WHO)-recommended masturbation method,18 the semen samples were collected in an isolated room near the laboratory, delivered to the laboratory right after ejaculations, and incubated at 37°C until analysis. Semen volume, sperm concentration, total sperm number, progressive motility, and morphology were analyzed by professional clinician following the WHO SLEEP, Vol. 39, No. 1, 2016
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the semen parameters and sleep duration in 2013 differ from those in 2014 for the individuals. In each analysis, cases with missing data for any variable involved were excluded. The statistical analyses were carried out by SPSS version 15.0 (SPSS Inc., Chicago, IL, USA) and SAS version 9.1 (SAS Institute Inc., Cary, NC, USA).
Table 1—Demographic characteristics, sleep duration, semen parameters, and reproductive hormone levels of the subjects. Demographic Characteristics Age, y
RESULTS Characteristics of the Subjects The characteristics of the subjects can be found in Table 1. The median of entire sleep duration was 7.8 (interquartile range: 7.3, 8.3) h/d, of which 7.2 h (interquartile range: 6.8, 7.7) was night sleep and 0.5 h (interquartile range: 0.2, 0.8) was midday sleep. The semen samples were collected between 8:30 to 20:00, with more samples collected in the afternoon and evening (562 collected after 12:00, 71%) than in the morning. No significant correlation was found between timing of semen collection and sleep duration of the subjects. Sleep Duration and Semen Parameters: Cross-Sectional Analysis The relation of sleep duration and semen parameters was first investigated with the data collected in the baseline survey (2013). The semen parameters of the subjects with different sleep duration were listed in Table 2. An inverse U-shaped association was observed between the entire sleep duration and two of the semen parameters (semen volume and total sperm number) with 7.0–7.5 h/d as the “turning point”: in a dose-response manner, the semen parameters increased with longer sleep duration for those whose sleep duration was below 7.0 h/d; but for those whose sleep duration was over 7.5 h/d, the semen parameters decreased with longer sleep duration. To illustrate the sleep-semen relationship more intuitively, the fitting curve drawn by the LOESS method was also provided (Figure 1). Compared to the subjects sleeping for 7.0–7.5 h/d, those who slept > 9.0 h/d or ≤ 6.5 h/d had lower parameters (semen volume: 3.5 mL versus 2.8 mL or 3.2 mL, P = 0.249 or P = 0.015 respectively; total sperm number: 203.9 millions versus 126.2 millions or 145.1 millions, P = 0.001 or P < 0.0001 respectively). After adjustment for potential confounders, compared to sleeping for 7.0–7.5 h/d, sleeping for over 9 h/d was associated with a 21.5% reduction in semen volume (95% confidence interval: 9.2, 32.2) and 39.4% reduction in total sperm number (23.3, 52.1); sleeping for less than 6.5 h/d was associated with 4.6% (−10.5, 22.3) and 25.7% (−1.2, 60.1) reduction in the two parameters (Table 3 and Figure 1). Then we calculated sleep duration “distance”, which indicated the magnitude of difference between a subject’s sleep duration and 7.0–7.5 h/d (details in Table 4). The association between that “distance” and semen parameters were analyzed to represent the average change of semen parameters with each unit of sleep duration different from 7.0–7.5 h/d. After adjusting for potential confounders, each hour of sleep duration “distance” was averagely associated with 8.1% (−13.5, −2.6) and 12.0% (−21.7, −1.7) reduction in the two semen parameters. No significant association was detected between sleep duration and other semen parameters. SLEEP, Vol. 39, No. 1, 2016
20 (20 to 21)
Abstinence period, days
4 (3 to 6)
Body mass index
Tobacco smoking Never Ever Current
593 30 171
74.7% 3.8% 21.5%
Alcohol consumption Never Ever Current
409 10 374
51.4% 1.3% 47.2%
Tea intake Never Ever Current
512 123 159
64.5% 15.5% 20.0%
Cola intake, bottles/w 0 6
273 404 100 17
34.4% 50.9% 12.6% 2.1%
Coffee intake, cups/w 0 6
605 154 21 14
76.2% 19.4% 2.6% 1.8%
20.9 (19.6 to 22.7)
Sleep Duration* Entire sleep duration, h/d Night sleep duration, h/d Midday sleep duration, h/d
n 738 734 752
Semen Parameters Semen volume, mL Sperm concentration, millions/mL Total sperm number, millions Progressive motility, % Morphologically normal spermatozoa, %
n 771 3.4 (2.4 to 4.5) 795 53.8 (32.3 to 84.6) 770 183.6 (97.7 to 300.6) 795 55.5 (43.6 to 68.8) 791 8.4 (6.4 to 10.3)
Reproductive Hormone Levels Follicle-stimulating hormone, mIU/mL Luteinizing hormone, mIU/mL Estradiol, pg/mL Progesterone, ng/mL Testosterone, ng/mL Prolactin, ng/mL
n 774 3.5 (2.6 to 4.9) 772 4.0 (3.1 to 5.1) 770 19 (10 to 27) 757 0.5 (0.3 to 0.8) 749 4.2 (3.5 to 5.1) 764 10.1 (8.1 to 13.7)
7.8 (7.3 to 8.3) 7.2 (6.8 to 7.7) 0.5 (0.2 to 0.8)
Values presented as median (25th to 75th percentile) or percentage. *Of the 796 eligible subjects, 58 (7.3%) reported in the Munich Chronotype Questionnaire that they did not have a regular workday/ free-day schedule and had distinct sleep duration in these days. The weekly average of entire sleep duration could be estimated for 738 subjects (92.7%). As to night sleep and midday sleep, 734 (92.2%) and 752 subjects were available (94.5%, including those who did not have midday sleep), respectively.
The associations between semen parameters and night duration or midday duration were also investigated, both showing 81
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Figure 1—Association between sleep duration and semen parameters without and with adjustment for potential confounders. Univariate analyses between sleep duration and semen volume (A) and total sperm number (B) are represented as regression curve (thick solid line) by the locally estimated scatter plot smoothing (LOESS) method. The thin horizontal line indicates the turning point of the curve. C and D represent the results of multivariate analyses adjusted for potential confounders including age, body mass index, abstinence period, smoking, alcohol consumption, and intake of tea, coffee and cola. The 7.0–7.5 h/d sleep is defined as the reference group (triangle).
similar trend as that of semen parameters and entire sleep duration, although some results were not statistically significant (Table S1 and Table S2, supplemental material). No association was found between sleep duration and reproductive hormone levels (Table S3, supplemental material). The follow-up data (2014) was also used to validate the sleep-semen association found in the baseline data (2013), and the results were in concordance with those of the baseline data investigation. Then we integrated the data of the 2 y by multilevel model, and the associations remained significant (Table 4). In the 2014 survey we also measured the sleep quality by PSQI, because there had been study suggesting that sleep disturbance was associated with semen parameters.12 The median of PSQI in the subjects was 5 (interquartile range: 3, 6). Although PSQI was correlated with sleep duration and the two semen parameters in univariate analyses (Figure S1, supplemental material), adjustment for PSQI conferred little difference on the association between sleep duration and semen parameters (Table 4), whereas PSQI become insignificant in the regression models (data not shown). There is a possibility that sleep related medication influenced the sleep-semen association and this needs investigation. SLEEP, Vol. 39, No. 1, 2016
According to the information collected by PSQI in 2014, the prevalence of medication taking is quite low (5 out of 656, 0.8%; only 1 took medicine more than once per week, accounting for 0.2%) and no significant association was found between sleep duration and medication intake. Change of Sleep Duration Versus Change of Semen Parameters: Comparison between 2013 and 2014 We investigated the difference of average sleep duration for the whole population between the 2 y. No significant difference was found when compared directly (Table 5). However, when investigating the individual change of sleep duration from 2013 to 2014, we found a significant inverse association between the sleep duration in 2013 and the change of sleep duration (Spearman correlation: P < 0.0001): the more the subject slept in 2013, the higher reduction in sleep duration was seen in 2014, vice versa (Figure S2, supplemental material). Interestingly, this regression curve crossed the horizontal axis at the point of 7.8 (h/d), which was close to the turning point (7.0–7.5 h/d) of the sleep-semen association. For those sleeping ≤ 7.0 h/d in 2013, the sleep duration significantly increased in 2014; whereas for those sleeping > 7.5 h/d in 2013, 82
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Table 2—Semen parameters of the subjects with different sleep duration (univariate analysis).
Sleep Duration, h/d n a P trend ≤ 6.5 45 6.5–7.0 83 7.0–7.5 (reference) 140 7.5–8.0 187 8.0–8.5 148 8.5–9.0 81 > 9.0 54 a P trend
Semen Volume, mL 0.216 3.2 (2.2 to 4.4) 3.5 (2.3 to 4.5) 3.5 (2.5 to 4.8) 3.6 (2.7 to 4.7) 3.4 (2.5 to 4.5) 3.4 (2.4 to 4.4) 2.8 (2.1 to 3.4) 0.006
Sperm Concentration, millions/mL 0.039 53.8 (28.0 to 74.3) 48.0 (32.1 to 85.8) 58.4 (36.9 to 89.7) 49.4 (31.7 to 77.8) 57.6 (36.5 to 88.2) 54.9 (34.0 to 86.8) 41.9 (26.6 to 84.0) 0.300
Total Sperm Number, Progressive Motility, millions % 0.008 0.221 145.1 (90.1 to 242.0) 54.3 (43.0 to 62.0) 186.3 (87.5 to 292.5) 58.1 (42.5 to 70.3) 203.9 (120.2 to 359.6) 57.2 (44.2 to 70.8) 187.3 (97.7 to 290.3) 53.6 (42.4 to 68.8) 217.4 (110.9 to 341.4) 54.0 (43.4 to 70.2) 188.4 (122.7 to 293.0) 58.3 (42.5 to 67.2) 126.2 (66.2 to 229.8) 56.0 (45.9 to 68.3) 0.020 0.723
Morphologically Normal Spermatozoa, % 0.024 7.5 (5.5 to 10.0) 7.9 (5.4 to 10.4) 9.0 (7.0 to 10.6) 8.3 (6.1 to 10.3) 8.1 (6.6 to 10.2) 8.5 (6.5 to 9.8) 8.8 (5.6 to 10.6) 0.218
Values presented as median (25th to 75th percentile). a Test for trend (Jonckheere-Terpstra test) was performed respectively in the two subsets in which the subjects’ sleep duration were ≤ 7.5 h/d and > 7.0 h/d.
Table 3—Association between sleep duration and semen parameters adjusted for potential confounders (multivariate analysis).
Sleep Duration, h/d n P trend a ≤ 6.5 45 6.5–7.0 83 7.0–7.5 140 7.5–8.0 187 8.0–8.5 148 8.5–9.0 81 > 9.0 54 P trend a
Semen Volume, Sperm Concentration, % change % change 0.498 0.073 −4.6 (−22.3 to 10.5) −18.4 (−49.5 to 6.2) −3.6 (−17.5 to 8.6) −18.3 (−43.3 to 2.4) Reference Reference 1.6 (−7.8 to 11.9) −19.6 (−31.5 to −5.6) −1.1 (−10.6 to 9.5) −4.7 (−19.8 to 13.2) −5.6 (−16.6 to 6.9) −4.8 (−22.1 to 16.2) −21.5 (−32.2 to −9.2) −23.5 (−38.5 to −4.7) 0.002 0.313
Morphologically Total Sperm Number, Progressive Motility, Normal Spermatozoa, % change % change % change 0.028 0.065 0.088 −25.7 (−60.1 to 1.2) −7.5 (−18.6 to 2.5) −8.9 (−23.0 to 3.5) −24.9 (−54.7 to −0.9) −4.8 (−13.9 to 3.6) −9.2 (−22.0 to 2.2) Reference Reference Reference −20.4 (−32.9 to −5.5) −7.5 (−14.1 to −0.4) −6.8 (−14.4 to 1.5) −7.0 (−22.9 to 12.1) −4.2 (−11.0 to 3.1) −2.4 (−9.7 to 5.5) −12.0 (−29.6 to 9.9) −5.7 (−13.4 to 2.6) −8.8 (−17.7 to 0.9) −39.4 (−52.1 to −23.3) −2.4 (−11.1 to 7.1) −6.9 (−17.0 to 4.4) 0.014 0.860 0.195
Because the semen parameters were skewed distributed, they were analyzed on a logarithmic scale and back-transformed to obtain the percentage of change (with 95% confidence interval given in the brackets) for each parameter, adjusted for age, body mass index, abstinence period, smoking, alcohol consumption, and intake of tea, coffee, and cola. a Tests for trend were performed respectively for the two subsets in which the subjects’ sleep duration were ≤ 7.5 h/d or > 7.0 h/d. The categorical variable of sleep duration was inserted into the linear regression model, assuming the association to be linear.
Table 4—Change of semen parameters with each hour of sleep duration “distance” from 7.0–7.5 h/d.
Sleep Duration Distance from 7.0–7.5 h/d a 2013 data c 2014 data c 2014 data additionally adjusted for PSQI d 2013 & 2014 data integrated c
Semen Volume % change per h/d 95% CI of distance b −8.1 −13.5 to −2.6 −5.3 −10.5 to 0.2 −5.2 −10.5 to 0.2 −5.7 −9.2 to −2.1
P 0.004 0.058 0.060 0.002
Total Sperm Number % change per h/d of distance b 95% CI −12.0 −21.7 to −1.7 −11.0 −20.8 to −0.7 −10.4 −20.0 to 0.0 −9.3 −16.1 to −2.2
P 0.023 0.038 0.050 0.011
The sleep duration was transformed into ordinal categories in increment of 0.5 h/d as listed in Table 2. The “distance” between each two neighboring categories was defined as 1 (for example, the distance between 7.0–7.5 h/d and 6.5–7.0 h/d was defined as 1, the distance between 7.0–7.5 h/y and 8.0–8.5 h/d was 2). b The change of semen parameters with each hour “distance” of sleep duration from 7.0–7.5 h/d. Because the semen parameters were skewed distributed, they were analyzed on logarithmic scale and back-transformed to obtain the percentage of change in each parameter. Then the results were multiplied by 2 to represent the change of the semen parameters with 1 h/d distance as each unit of “distance” indicates 0.5 h/d. c Adjusted for age, body mass index, abstinence period, smoking, alcohol consumption, and intake of tea, coffee, and cola. d In addition to age, body mass index, abstinence period, smoking, alcohol consumption, and intake of tea, coffee and cola, Pittsburgh Sleep Quality Index (PSQI) was also adjusted for. CI, confidence interval. a
the 2014 sleep duration decreased (Table 5). Considering the inverse U-shaped sleep-semen association we found, we SLEEP, Vol. 39, No. 1, 2016
further investigate whether there was an increase of semen parameters (especially of semen volume and total sperm number) 83
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Table 5—Comparison of sleep duration and semen parameters between 2013 and 2014. Variables Sleep duration, h/d All subjects a Subjects with ≤ 7.0 h sleep in 2013 (n = 95) Subjects with7.0–7.5 h sleep in 2013 (n = 115) Subjects with > 7.5 h sleep in 2013 (n = 382) Semen parameters b Semen volume, mL Sperm concentration, millions/mL Total sperm number, millions Progressive motility, %
2013 7.8 (7.3 to 8.3) 6.7 (6.4 to 6.8) 7.3 (7.2 to 7.4) 8.2 (7.8 to 8.6) 3.4 (2.4 to 4.5) 54.7 (31.8 to 84.4) 185.1 (98.8 to 299.2) 55.2 (43.4 to 68.0)
7.8 (7.3 to 8.4) 7.3 (6.7 to 7.8) 7.5 (7.0 to 8.0) 8.0 (7.5 to 8.6)
0.408 < 0.0001 0.001 < 0.0001
3.6 (2.7 to 4.6) 51.8 (33.0 to 81.7) 193.4 (109.2 to 311.8) 57.0 (44.8 to 67.7)
0.002 0.855 0.025 0.777
Values presented as median (25th to 75th percentile). a Because 64 of the 656 followed-up subjects (9.8%) reported in the Munich Chronotype Questionnaire that they did not have a regular workday/free-day schedule and had distinct sleep duration in these days (either in 2013 or in 2014), sleep duration could be estimated and compared between the two interviews for 592 subjects (90.2%). b Because the measurement of sperm morphology for 2014 samples is still underway, the comparison of this parameter is not available now.
Table 6—Individual change of sleep duration and change of semen parameters between the 2 y. Change of Sleep Duration a Closer to 7.0–7.5 h/d Identical Further from 7.0–7.5 h/d
nb 190 182 220
Semen Volume, mL 2013 2014 3.2 (2.4 to 4.2) 3.5 (2.7 to 4.4) 3.5 (2.5 to 4.6) 3.7 (2.7 to 4.9) 3.5 (2.4 to 4.7) 3.4 (2.7 to 4.5)
P 0.097 0.083 0.791
Total Sperm Number, millions 2013 2014 181.5 (83.6 to 279.0) 186.1 (105.6 to 305.8) 196.8 (105.1 to 300.1) 196.0 (118.0 to 313.5) 183.9 (106.3 to 306.9) 189.5 (102.5 to 325.4)
P 0.042 0.254 0.431
Values presented as median (25th to 75th percentile range). a “Change of sleep duration” indicates whether the subject’s sleep duration in 2014 had become closer to 7.0–7.5 h/d compared to the condition in 2013. The sleep duration was transformed into ordinal categories in increments of 0.5 h/d as listed in Table 2. The distance between each two neighboring categories was defined as 1 (for example, the distance between 7.0–7.5 h/d and 7.5–8.0 h/d was defined as 1, the distance between 7.0–7.5 h/d and 8.0–8.5 h/d was 2). If the distance between the subject’s sleep duration and 7.0–7.5 h/d in 2014 was smaller than the distance in 2013, the subject was assigned to the “closer” subgroup; if larger, the “further” subgroup; the rest were assigned to the “identical” subgroup. b Because 64 of the 656 followed-up subjects (9.8%) reported in the Munich Chronotype Questionnaire that they did not have a regular workday/free-day schedule and had distinct sleep duration in these days (either in 2013 or in 2014), sleep duration could be estimated and compared between the two interviews for 592 subjects (90.2%).
that improper sleep duration may impair semen quality. More interestingly, in those who had altered their sleep duration toward 7.0–7.5 h/d, increase of the semen parameters was found, further indicating the sleep-semen association. However, the increase of semen parameters in those who change their sleep duration toward “proper” length seemed small (though significant), indicating that the damage of semen quality, if recoverable, may need a long time to recover or it was not completely reversible. The current findings may deserve public concern as untraditional sleep behavior has become quite common in modern society. In China, about 33% of the male adults have sleep duration either ≤ 6 h or ≥ 9 h22; a similar phenomenon (36%) was also reported in the US.2 Hence, the potential influence of sleep duration on male reproductive health, if true, could be widespread and not ignorable, especially considering the unfavorable global situation of semen quality and infertility.14,16,23,24 To our knowledge, the current study is the first report about inverse U-shaped association between sleep duration and semen quality. Actually, as early as 2007 we had investigated the sleep-semen relation in another population of 1,346 males,11
along with this change of sleep duration in the population. As expected, semen volume increased from 3.4 mL in 2013 to 3.6 mL in 2014 (P = 0.002); total sperm number increased from 185.1 millions to 193.4 millions (P = 0.025); no significant difference was found in other parameters. Furthermore, we investigated whether the increase of the two semen parameters was associated with the change of sleep duration. We calculated individual “distance” between the subject’s sleep duration and 7.0–7.5 h/d in 2013 and 2014 respectively, and divided the subjects into three groups depending on whether that “distance” had become smaller (assigned to “closer” group), identical (“identical” group), or larger (“further” group) from 2013 to 2014 (details in Table 6). Increase of the semen parameters was found in the “closer” group but not in the “further” group. DISCUSSION Based on a cohort of male adults, we found an inverse Ushaped association between sleep duration and semen quality. Either excessive or restricted sleep was associated with reduction of semen quality in a dose-response manner, suggesting SLEEP, Vol. 39, No. 1, 2016
Sleep Duration and Semen Quality—Chen et al.
regular life ahead of each interview, and this method has limitation to represent all details of the subjects’ sleep duration; for example, sleep duration in free days or workdays was not analyzed separately (because the amount of free days is distinct among the subjects, it seems not proper to analyze the effect of free-day sleep duration or workday duration directly), and occasional change of sleep duration in the days immediately before the interview was not investigated. Third, though we found similar results in two populations, both of them were investigated in Chongqing of China, and particular bias from regional characteristics may not be excluded. Also, some other potential confounders were not investigated here, including environmental exposure, depression, and socioeconomic status. The results of the current study should be interpreted with caution and further replications would be needed. We did not investigate clinical diagnosed infertility as an outcome in our study. It is to be noted that abnormal semen parameters do not necessarily indicate infertility. However, there has been a large amount of evidence showing that the semen parameters, including total sperm number, are associated with reproductive outcome and could be used as a predictor of pregnancy probability.8,9 Our results indicate the necessity to investigate the influence of sleep duration over infertility in the future. In summary, based on the data of a reproductive health cohort in China, we for the first time found an inverse U-shaped relation between sleep duration and semen parameters. Both too long and too short sleep duration were associated with decreased semen volume and total sperm number. Furthermore, this sleep-associated semen impairment seemed to be reversible, indicating the potential of sleep “correction” not only for prevention but also for therapy. Because untraditional sleep behavior is common in modern society, our results may have important implications for global public health.
though we did not realize at that time the possibility of Ushaped relation and only reported null linear association. Here we reanalyzed that data and found a result similar to that of the student cohort (Table S4, supplemental material). The 2007 population is with substantially distinct demographic characteristics and semen quality compared to the student population, indicating the generalizability of our findings. Interestingly, in a cross-sectional study of 953 Danish men, Jensen investigated the relationship of sleep disturbance and semen parameters, and also found an inverse U-shaped association.12 However, the authors found it difficult to interpret the mechanism. Our study also showed an association between sleep quality and semen parameters, but it became insignificant when sleep duration was adjusted for, indicating that association observed by Jensen et al. might be because of the correlation between sleep quality and sleep duration. Indeed, inverse U-shaped relation has been found between sleep duration and various phenotypes of different systems.3–5 However, the underlying mechanism is not clear. There are studies suggesting that improper sleep duration raises the risk of obesity, which is well known to impair reproductive function.25–28 However, obesity (BMI ≥ 28.0 according to the reference norm for Chinese adults29) was uncommon in our population (21/796, 2.6%); even after adjustment for BMI, the sleep-semen association remained significant. As in the study by Jensen et al.,12 no association was found between sleep duration and reproductive hormone in our study, so reproductive hormones might not be the mechanism either. Actually, although there are reports of positive results, other researchers argued that reproductive hormones were not associated with sleep duration.30,31 Some other research indicates the circadian clock could be involved.32–34 It seems plausible that the improper sleep duration may disrupt the circadian clock, leading to subsequent impairment of semen quality. The students in our study were young and had not yet planned to have children; those with urogenital disease were excluded. Hence it is unlikely that the subjects had knowledge of their semen quality or fertility potential. Thus, the possibility that psychological stress from infertility had influenced the sleep behavior could be avoided.35,36 However, the possibility of reverse causation may not be completely ruled out. Other researches of sleep usually measured the sleep duration by simply asking the subjects how many hours they slept, only obtaining limited information that could be biased.37 Actigraphy was a precise tool for sleep measurement, but the high expense limited its application in epidemiological studies. In the current study we adopted the MCTQ, which proved to be accurate and reliable in measuring the sleep time.19 In addition, having been applied in millions of subjects around the world,1 it offers an opportunity to replicate our findings in other populations in the future. The current study has several main limitations. First, only one semen sample was collected during each interview, probably introducing intraindividual variability of semen quality. This, as well as the rhythmical endocrine of reproductive hormone, could lead to nondifferential misclassification, and thereby underestimation of the potential association. Second, we only calculated the average sleep duration in the subjects’ SLEEP, Vol. 39, No. 1, 2016
ABBREVIATIONS BMI, body mass index LOESS, locally estimated scatter plot smoothing MARHCS (study), the male reproductive health in Chongqing college students MCTQ, Munich Chronotype Questionnaire PSQI, Pittsburgh Sleep Quality Index REFERENCES 1. Roenneberg T. Chronobiology: the human sleep project. Nature 2013;498:427–8. 2. Schoenborn CA, Adams PE. Health behaviors of adults: United States, 2005-2007. Vital Health Stat 10 2010:1–132. 3. Patel SR, Ayas NT, Malhotra MR, et al. A prospective study of sleep duration and mortality risk in women. Sleep 2004;27:440–4. 4. Liu Y, Wheaton AG, Chapman DP, Croft JB. Sleep duration and chronic diseases among US adults age 45 years and older: evidence from the 2010 Behavioral Risk Factor Surveillance System. Sleep 2013;36:1421–7. 5. Ananthakrishnan AN, Khalili H, Konijeti GG, et al. Sleep duration affects risk for ulcerative colitis: a prospective cohort study. Clin Gastroenterol Hepatol 2014;12:1879–86. 6. Leproult R, Van Cauter E. Effect of 1 week of sleep restriction on testosterone levels in young healthy men. JAMA 2011;305:2173–4. 7. Penev PD. Association between sleep and morning testosterone levels in older men. Sleep 2007;30:427–32.
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ACKNOWLEDGMENTS The authors thank the fieldworkers for their help and the interviewees for their cooperation.
SUBMISSION & CORRESPONDENCE INFORMATION Submitted for publication May, 2015 Submitted in final revised form June, 2015 Accepted for publication July, 2015 Address correspondence to: Jia Cao, PhD, Institute of Toxicology, College of Preventive Medicine, Third Military Medical University, Chongqing 400038, China; Tel: (023) 6875 2289, Fax: (023) 6875 2276; Email: [email protected]
Ziyuan Zhou, PhD, Department of Environmental Health, College of Preventive Medicine, Third Military Medical University, Chongqing 400038, China; Tel: (023) 6875 2294; Fax: (023) 6877 2390; Email: [email protected]
DISCLOSURE STATEMENT This was not an industry supported study. This work was supported by the Key Program of National Natural Science Funding of China (grant number 81130051), National Natural Science Funding of China (grant number 81402660, 81202276) and National Scientific and Technological Support Program (grant number 2013BAI12B02). The authors have indicated no financial conflicts of interest. Qing Chen, Huan Yang, and Niya Zhou contributed equally to this work.
Sleep Duration and Semen Quality—Chen et al.