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Association between sleep duration and menstrual cycle irregularity in Korean female adolescents
Sleep Medicine 35 (2017) 62e66
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Sleep Medicine journal homepage: www.elsevier.com/locate/sleep
Original Article
Association between sleep duration and menstrual cycle irregularity in Korean female adolescents Ga Eun Nam a, Kyungdo Han b, Gyungjoo Lee c, * a
Department of Family Medicine, Sahmyook Medical Center, 82, Mangu-ro, Dongdaemun-gu, 02500 Seoul, Republic of Korea Biostatistics, College of Medicine, The Catholic University of Korea, 222 Banpo-daero, Seochogu, 65091 Seoul, Republic of Korea c College of Nursing, The Catholic University of Korea, 222 Banpo-daero, Seochogu, 65091 Seoul, Republic of Korea b
a r t i c l e i n f o
a b s t r a c t
Article history: Received 23 November 2016 Received in revised form 17 March 2017 Accepted 18 April 2017 Available online 8 May 2017
Objective: The association between sleep and the menstrual cycle in the adolescent population has been scarcely studied. This study aimed to investigate the association between sleep duration and menstrual cycle irregularity among female adolescents using nationwide representative data from the South Korean population. Methods: This population-based, cross-sectional study used the data collected from Korea National Health and Nutrition Examination Survey 2010e2012, and the data from 801 female adolescents were analyzed. Hierarchical multivariable logistic regression analysis was performed to assess the risk of menstrual cycle irregularity in relation to sleep duration. Results: Subjects with menstrual cycle irregularity accounted for 15% (N ¼ 120). The mean sleep duration in subjects with menstrual cycle irregularity was significantly shorter than that in those without (p ¼ 0.003). Menstrual cycle irregularity prevalence tended to decrease as sleep duration increased (p for trend ¼ 0.004), which was significantly different based on sleep duration and presence of depressive mood (p ¼ 0.011). Sleep duration 5 h per day was significantly associated with increased risk of menstrual cycle irregularity compared with that in the subjects whose sleep duration is 8 h per day even after adjusting for confounding variables. The odds ratios of menstrual cycle irregularity tended to increase for shorter sleep duration in all adjusted models. Conclusion: This study found a significant inverse association between sleep duration and menstrual cycle irregularity among Korean female adolescents. Increasing sleep duration is required to improve the reproductive health of female adolescents. © 2017 Elsevier B.V. All rights reserved.
Keywords: Adolescents Menstrual cycle irregularity Sleep duration
1. Introduction Women commonly experience irregular menstrual cycles during their reproductively fertile years, and menstrual cycle irregularity aggravates the frequency and degree of menstrual symptoms [1]. Moreover, irregular menstrual cycles have been shown to have implications for women's health. Menstrual cycle irregularity has been reported to be associated with serious health outcomes such as breast cancer, type 2 diabetes, cardiovascular disease, osteoporosis, and infertility [2e6]. In addition, evidence supporting the association between this condition and mental health problems has been increasing [7e12]. In particular, menstrual cycle abnormalities
* Corresponding author. Fax: þ82 02 2258 7779. E-mail address: [email protected] (G. Lee). http://dx.doi.org/10.1016/j.sleep.2017.04.009 1389-9457/© 2017 Elsevier B.V. All rights reserved.
were reported to be associated with symptoms of depressive disorders in high school girls [7], that seem to affect the female adolescents' quality of life and disturb active participation in academic performance and psychosocial functioning [13,14]. Although the objective definition of menstrual cycle irregularity has not been established, the prevalence of this condition has been reported to be high among adolescents [15e17]. In addition, the American Academy of Pediatrics recommended that menstrual cycle should be assessed with other vital signs, emphasizing the critical role of menstrual patterns in reflecting the overall health status of female adolescents [18]. Therefore, specific efforts should be made to identify associated factors to prevent menstrual cycle irregularity in the adolescent age group. Menstrual cycle regularity has been reported to be influenced by a variety of physical and mental conditions and health-related lifestyles [18]. Age at menarche, excessive exercise or rapid gain
G.E. Nam et al. / Sleep Medicine 35 (2017) 62e66
or loss of body weight has been explored as risk factors of menstrual cycle irregularity [19]. It is also caused by many medical conditions, such as pregnancy, endocrine disorders, and other chronic diseases [18]. In addition, mental health problems including depressive mood and psychological stress were also suggested as risk factors of menstrual cycle irregularity [9,13,19e21]. Recently, sleep has been gaining attention as an associated factor in menstrual cycle irregularity in adults. Romans et al. [22] concluded in their review that some studies showed significant associations between poorer sleep quality and premenstrual and menstrual phases. In general, women are well known to have higher prevalence of sleep disturbance than men [22], which suggests that sleep may be correlated with reproductive function in women. Also, puberty disrupts sleep onset, which can cause delayed bedtimes and low sleep quality [23]. Sleep is essential in the effective performance of various daily tasks in adolescents. Sleep patterns and quality contribute to successful academic achievement and holistic quality of life [24]. Inadequate sleep causes daytime malfunctioning, psychological and behavioral problems, and physical diseases including obesity [25]. Baker and Driver [26] issued that circadian disruption such as sleepeawake disorders may be associated with disturbance in the menstrual cycle [26]. Approximately a third of adolescents experience sleep disturbances [27], and only one in 10 adolescents is estimated to sleep more than 8 h, as recommended by the National Sleep Foundation [27]. The poor sleep pattern of adolescents seems to be associated with exposure to screen light including television watching and computer gaming, as well as after-school work and academic stress [28]. This may disturb the circadian rhythm, which affects the menstrual cycle of female adolescents. However, the association between sleep duration and menstrual cycle regularity has been scarcely studied in the adolescent population. Thus, this study aimed to identify the association between sleep duration and menstrual cycle irregularity among female adolescents using the nationwide representative data of the South Korean population. 2. Methods 2.1. Data source and study subjects This population-based, cross-sectional study used the data collected from the Korea National Health and Nutrition Examination Survey (KNHANES) 2010e2012. KNHANES has been conducting nationwide surveys annually since 1998, by the Division of Chronic Disease Surveillance under the Korea Centers for Disease Control and Prevention (KCDC) and the Korean Ministry of Health and Welfare. The survey aimed to assess the health and nutritional status of the non-institutionalized civilians of South Korea. The survey is composed of three parts: health interview, health examination, and nutritional surveys, and each part was conducted by trained investigators. The sampling units were defined based on the 2005 population and housing census in South Korea, which includes information regarding sex, age, and geographical area. A stratified, multi-staged, and clustered probability design with a rolling survey sampling model was used to select a representative sample of the non-institutionalized South Korean population. Of the 25534 individuals who participated in the KNHANES during 2010e2012, we excluded males (N ¼ 11616), those aged <12 or >18 years (N ¼ 12911), those who were diagnosed with epilepsy or attention deficit hyperactivity disease or were treated for these diseases (N ¼ 8), those before menarche (N ¼ 79), those who were pregnant or breastfeeding (N ¼ 0), and those with missing data (N ¼ 119). Finally, the data of 801 female adolescents were analyzed. Parental written informed consents were signed before
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participation in the survey for all study participants because they were minors. The institutional review board of the KCDC reviewed and approved the survey protocol. The data are accessible on the following website (http://knhanes.cdc.go.kr). 2.2. Assessment of sleep duration and menstrual cycle Sleep duration was self-reported from the following question: “How many hours do you sleep on average?” Sleep duration was classified into three categories: 5, 6e7, and 8 h. Subjects were asked to describe menstrual cycle regularity through the following question: “Do you have a regular menstrual cycle?” Subjects who responded “yes” were defined as having a regular menstrual cycle, whereas those who responded “no” were defined as having a menstrual cycle irregularity. 2.3. Covariates Sociodemographic and lifestyle characteristics of subjects were obtained by trained interviewers or by self-reported questionnaire. Monthly household income was divided into quartiles, and the lowest quartile of the total subjects was defined as a low income level. Subjects who had consumed one alcohol drink or more for at least one day during the month before the survey were defined as ever-drinkers, and those who had not, were defined as nondrinkers. For smoking status, based on the responses to the selfreported questionnaire, subjects who had smoked cigarettes at least one day during the month before the survey were defined as ever-smokers, and those who had not, were defined as nonsmokers. Physical activity was assessed using the Korean version of the International Physical Activity Questionnaire [29]. Subjects who exercised moderately for at least 30 min per session, more than five times per week, or those who exercised strenuously for at least 20 min per session more than three times per week were defined as regular exercisers. Subjects were asked to respond to the following question to assess their history of weight control attempts: “Have you ever attempted weight control?” In addition, information regarding the subjects' age at menarche was also collected. Psychological problems were investigated by providing questions regarding psychological stress and depressive mood. Psychological stress was assessed from the responses to the following question: “How much stress do you feel in your daily life?” Subsequently, subjects were asked to report the stress level as rare, mild, much, or severe. Based on the responses, subjects were classified into the low-stress group if they reported feeling stress rarely or mildly, and the high-stress group if they responded as feeling stress much or severely. Subjects were considered to have depressive mood when they answered “yes” to the following question: “Has your daily life been burdened by feelings of sadness or hopelessness for two continuous weeks or more during the previous year?” Trained staffs performed anthropometric measurements for all participants. Height and body weight were measured to the nearest 0.1 cm and 0.1 kg, respectively, with light clothing and without shoes, and body mass index (BMI) was calculated as body weight (kg)/height2 (m2). Waist circumference (WC) was measured to the nearest 0.1 cm at the midpoint between the lowest margin of the rib cage and iliac crest at the end of expiration. Blood samples were obtained after fasting for 8 h or more and were immediately processed and refrigerated. They were transported in cold storage to the Central Testing Institute in Seoul, Korea and then analyzed within 24 h. The blood hemoglobin level was measured using XE-2100D (Sysmex, Tokyo, Japan).
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2.4. Statistical analyses All statistical analyses were performed using the Statistical Analysis System (SAS, version 9.2; SAS Institute, Cary, NC, USA) survey procedure to account for complex sampling design and to provide nationwide representative estimates. The procedure included unequal probabilities of selection, oversampling, and nonresponse to make inferences regarding Korean adolescent participants. Data were expressed as mean ± standard error (SE) for continuous variables or as percentage (SE) for categorical variables. Baseline characteristics of the study subjects based on menstrual cycle regularity were compared using independent t-test for continuous variables or chi-square test for categorical variables. Prevalence of menstrual cycle irregularity based on sleep duration was compared using chi-square test, and then p for trend was obtained using a general linear model. Prevalence of menstrual cycle irregularity based on sleep duration and depressive mood was also compared using the chi-square test. Hierarchical multivariable logistic regression analysis was performed, and odds ratios (ORs) and 95% confidence intervals (CIs) were calculated to assess the risk of menstrual cycle irregularity in relation to sleep duration. Model 1 was adjusted for age and monthly household income as demographic variables. Model 2 was adjusted for variables adjusted in model 1 plus alcohol consumption, smoking status, physical activity, and weight loss attempt as health-related lifestyle characteristics. Model 3 was adjusted for variables adjusted in model 2 plus hemoglobin level, age at menarche, and BMI as physical information. Model 4 was adjusted for the variables in model 3 plus psychological stress and depressive mood as psychological problems. A p-value <0.05 was considered statistically significant.
height, body weight, BMI, WC, and hemoglobin level did not differ between subjects with and without menstrual cycle irregularity. The mean sleep duration was 6.6 ± 0.2 h and 7.1 ± 0.1 h in subjects with and without menstrual cycle irregularity (p ¼ 0.003), respectively. The rate of ever-smokers was higher in subjects with menstrual cycle irregularity than that in those without (p ¼ 0.023). Variables regarding monthly household income, alcohol consumption, physical activity, and weight loss attempts were not significantly different between the two groups. In addition, subjects with psychological stress were more likely to have menstrual cycle irregularity with a borderline significance (p ¼ 0.054). Subjects with depressive mood were also more likely to have menstrual cycle irregularity (p ¼ 0.001). 3.2. Prevalence of menstrual cycle irregularity according to sleep duration and the presence of depressive mood Fig. 1 presents the prevalence of menstrual cycle irregularity based on sleep duration. The prevalence tended to decrease as sleep duration increased (p for trend ¼ 0.004). Fig. 2 shows that the prevalence of menstrual cycle irregularity is significantly different based on sleep duration and the presence of depressive mood (p ¼ 0.011). Subjects with depressive mood were more likely to have menstrual cycle irregularity in subjects who sleep for 6 h per day (p ¼ 0.003). Among subjects who sleep for 5 h per day, the prevalence of menstrual cycle irregularity was not different according to the presence of depressive mood (p ¼ 0.763). 3.3. Risk of menstrual cycle irregularity in relation to sleep duration Table 2 shows the ORs (95% CIs) of menstrual cycle irregularity based on sleep duration. After adjusting for age and monthly
3. Results 3.1. Baseline characteristics of study subjects Table 1 describes the baseline characteristics of study subjects based on menstrual cycle irregularity. The subjects with irregular menstrual cycles accounted for 15% (N ¼ 120) of the total subjects. The mean age and mean age at menarche were significantly higher in subjects with menstrual cycle irregularity than that in those without (p ¼ 0.013 and 0.042, respectively). The mean values of Table 1 Baseline characteristics of Korean female adolescents based on the presence of menstrual cycle irregularity. Menstrual cycle irregularity
N Age (years) Height (cm) Body weight (kg) Body mass index (kg/m2) Waist circumference (cm) Hemoglobin (g/dL) Sleep duration (h) Monthly household income (the lowest quartile) Ever-alcohol drinker Ever-smoker Regular exerciser Weight loss attempt Age at menarche (years) High stress Depressive mood
pa
No
Yes
681 15.2 ± 0.1 160.2 ± 0.3 53.9 ± 0.4 21 ± 0.1 68.9 ± 0.4 13.1 ± 0.1 7.1 ± 0.1 15.6 (2.2)
120 15.7 ± 0.2 160.5 ± 0.6 55.5 ± 1.4 21.6 ± 0.6 69.7 ± 1.1 13.2 ± 0.1 6.6 ± 0.2 21.2 (4.4)
0.013 0.652 0.253 0.297 0.504 0.46 0.003 0.206
29 (2.2) 11.5 (1.6) 20.1 (1.8) 54.8 (2.2) 12.3 ± 0.1 28.1 (2) 11.1 (1.5)
29.1 20.4 18.8 56.1 12.6 38.1 24.7
0.991 0.023 0.772 0.832 0.042 0.054 0.001
(6.3) (4.2) (4) (5.7) ± 0.1 (5.1) (5.5)
Data are presented as mean ± standard error (SE) for continuous variables or percentage (SE) for categorical variables. a p-values were calculated using independent t-test for continuous variables or chi-square test for categorical variables.
Fig. 1. The prevalence of menstrual cycle irregularity based on sleep duration (p for trend ¼ 0.004).
Fig. 2. The prevalence of menstrual cycle irregularity based on sleep duration and the presence of depressive mood (p ¼ 0.011).
G.E. Nam et al. / Sleep Medicine 35 (2017) 62e66 Table 2 Odds ratios of menstrual cycle irregularity in relation to sleep duration in Korean female adolescents. Odds ratio (95% confidence interval) Model 1 Sleep 5 6e7 8 p for trend
duration (h) 3.08 (1.44e6.58) 1.87 (1.07e3.25) 1 0.003
Model 2
Model 3
Model 4
3.01 (1.35e6.73) 1.73 (0.98e3.03) 1 0.007
2.77 (1.21e6.30) 1.60 (0.86e2.99) 1 0.017
2.36 (1.02e5.47) 1.51 (0.81e2.82) 1 0.046
Odds ratios (95% confidence intervals) were calculated using multivariable logistic regression analysis, and p for trend was obtained from general linear model. Model 1 was adjusted for age and monthly household income (demographic variables). Model 2 was adjusted for variables in model 1 plus alcohol consumption, smoking status, physical activity, and weight loss attempt (health-related lifestyle variables). Model 3 was adjusted for variables in model 2 plus hemoglobin level, age at menarche, and body mass index (variables of physical condition). Model 4 was adjusted for variables in model 3 plus psychological stress and depressive mood (variables of psychological problems).
household income (model 1), subjects who slept for 6e7 h and 5 h per day were significantly associated with increased risk of menstrual cycle irregularity compared with those who slept for 8 h per day (OR [95% CI] ¼ 1.87 [1.07e3.25] for 6e7 h and 3.08 [1.44e6.58] for 5 h). After additionally adjusting for alcohol consumption, smoking status, physical activity, and weight loss attempts (model 2), sleeping 5 h per day was significantly associated with increased risk of menstrual cycle irregularity compared with those who slept for 8 h per day (OR [95% CI] ¼ 3.01 [1.35e6.73]). However, the OR of subjects who slept for 6e7 h did not show a significant association (OR [95% CI] ¼ 1.73 [0.98e3.03]) in model 2. After further adjustment for hemoglobin level, age at menarche, and BMI (model 3), subjects who slept for 5 h had a significantly higher OR of 2.77 (95% CI, 1.21e6.3) for menstrual cycle irregularity compared with subjects who slept for 8 h. However, the OR of subjects who slept for 6e7 h were not significant (OR [95% CI] ¼ 1.6 [0.86e2.99]) in model 3. After additional adjustment for psychological stress and depressive mood (model 4), subjects who slept for 5 h had a significantly higher OR of 2.36 (95% CI, 1.02e5.47) for menstrual cycle irregularity compared with subjects who slept for 8 h. The ORs of menstrual cycle irregularity tended to increase for the shorter sleep duration in all four models (p for trend for OR of 0.003, 0.007, 0.017, and 0.046 in models 1, 2, 3, and 4, respectively). 4. Discussion To the best of our knowledge, this is the first study with a large adolescent population that investigated the importance of sleep duration in relation to menstrual cycle regularity. The main finding of this study was a significant inverse association between sleep duration and menstrual cycle irregularity among South Korean adolescents aged 12e18 years. The association did not change even after adjusting for potential confounding factors including age, monthly household income, alcohol consumption, smoking status, physical activity, weight loss attempts, hemoglobin level, age at menarche, BMI, psychological stress, and depressive mood. In addition, among adolescents whose sleep duration was longer than 6 h, adolescents with depressive mood were more likely to have menstrual cycle irregularity than those without depressive mood. Adequate sleep stabilizes physiological circadian rhythmicity. Stable circadian rhythm affects both mood and menstrual cycle regularity, which are milestones of normal development in female adolescents [30]. Several studies have found that sleep quality is associated with the menstrual cycle phase [21,31]. Sleep quality
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decreases at the premenstrual phase and during menstruation or between menstrual cycles [21]. In adults, circadian rhythmicity is disrupted due to frequent shift change of work and increased menstrual cycle irregularities [32]. Disrupted sleep inhibits luteinizing hormone secretion, and shorter sleep duration may alter menstrual cycle in female adults working as shift workers [33]. Menstrual cycle irregularity may be linked with changes in luteinizing hormone pulsatility and amplitude, resulting from the disturbance of circadian rhythmicity [33,34]. However, the underlying mechanisms explaining the associations between sleep duration and menstrual cycle regularity in the adolescent age group have been poorly elucidated. This study found that shorter sleep duration is associated with increased risk of menstrual cycle irregularity in female adolescents. Baker and Driver [26] also emphasized that psychological stress or mood disturbance influences the menstrual cycle. Based on the annual report on the youths of South Korea in 2014, seven of 10 female adolescents were under high stress, and the rate for their optimal sleep duration decreased in 2014 compared with the result in 2006 [35]. The Korean Statistics raised the alarm that the leading cause of death in teens was suicide in 2012, which is highly related with depression [36]. It was estimated that 25% of adolescents aged 15e18 years experience depression including 14% with major depression and 11% with minor depression [37]. Premenstrual dysphoric disorder (PMDD) is a premenstrual mood disturbance, seriously affecting a teen's ability to function in their lives [26]. Both depression and PMDD had sleep disturbance including hypersomnia or insomnia as one of the symptoms to diagnose these diseases. In this study, in accordance with these previous findings, when adolescents have depressive mood although sleep duration is longer than 6 h, they were more likely to have menstrual cycle irregularity than those without depressive mood. The current study provides additional evidence that enough sleep with better mental health is essential to improve menstrual cycle regularity during adolescence, which is the critical period of healthy development. Putting together findings from previous studies and our study, public health providers should take into consideration the significance of the associations between sleep duration, depressive mood, and menstrual cycle irregularity in adolescents, suggesting an added vulnerability to disrupted circadian rhythm. This study added evidence that the significance of adequate sleep duration and psychological health to improve menstrual cycle regularity during the adolescent period. The present study has some limitations. First, the data used in this population-based study were collected by retrospective selfreport, which has a potential for recall bias. Second, the causal relationship should be cautiously interpreted in attempting to identify the relationships among variables due to the crosssectional design of this study. Third, this study could not consider various sleep features including subjective and objective sleep qualities, sleep timing, or circadian preference of the study participants due to lack of data from the KNHANES. Future study is needed to control those sleep-related factors to determine whether sleep duration is independently related with menstrual cycle irregularity. Fourth, menstrual cycle irregularity was assessed based solely on subjects' self-report which may be dependent on their subjective perceptions, without consideration of biomedical markers or hormone measurements. Further studies need to validate the parameters of menstrual cycle irregularity and to establish the definition of menstrual cycle irregularity. This study has several strengths as well; for instance, the study has reliable representatives based on the nationwide population dataset. It is the first study to identify the significant role of sleep duration in relation to menstrual cycle irregularity of adolescents, considering a variety of compounding variables, including
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demographic and lifestyle factors and physical and psychological health. In conclusion, the current study highlights the importance of adequate sleep duration with better mental health on menstrual cycle regularity of female adolescents. Surprisingly, few studies reported on the menstrual irregularities from the adolescent population although early gynecological age is influential in menstrual cycle instability. A replication study is needed to increase the reliability and validity of the findings of the current study. Specific intervention to increase sleep duration of adolescents is required at school and at the government level as well. Conflict of interest The ICMJE Uniform Disclosure Form for Potential Conflicts of Interest associated with this article can be viewed by clicking on the following link: http://dx.doi.org/10.1016/j.sleep.2017.04.009. References [1] Weller A, Weller L. Menstrual irregularity and menstrual symptoms. Behav Med 2002;27(4):173e8. [2] Harlow SD, Ephross SA. Epidemiology of menstruation and its relevance to women's health. Epidemiol Rev 1995;17(2):265e86. [3] Kaplan JR, Manuck SB. Ovarian dysfunction, stress, and disease: a primate continuum. ILAR J 2004;45(2):89e115. [4] Rowland AS, Baird DD, Long S, et al. Influence of medical conditions and lifestyle factors on the menstrual cycle. Epidemiology 2002;13(6):668e74. [5] Solomon CG, Hu FB, Dunaif A, et al. Long or highly irregular menstrual cycles as a marker for risk of type 2 diabetes mellitus. JAMA 2001;286(19):2421e6. [6] Solomon CG, Hu FB, Dunaif A, et al. Menstrual cycle irregularity and risk for future cardiovascular disease. J Clin Endocrinol Metab 2002;87(5):2013e7. [7] Bisaga K, Petkova E, Cheng J, et al. Menstrual functioning and psychopathology in a county-wide population of high school girls. J Am Acad Child Adolesc Psychiatry 2002;41(10):1197e204. [8] Chang PJ, Chen PC, Hsieh CJ, et al. Risk factors on the menstrual cycle of healthy Taiwanese college nursing students. Aust N Z J Obstet Gynaecol 2009;49(6):689e94. [9] Jarvelaid M. The effect of gynecologic age, body mass index and psychosocial environment on menstrual regularity among teenaged females. Acta Obstet Gynecol Scand 2005;84(7):645e9. [10] Toffol E, Koponen P, Luoto R, et al. Pubertal timing, menstrual irregularity, and mental health: results of a population-based study. Arch Women Ment Health 2014;17(2):127e35. [11] Yamamoto K, Okazaki A, Sakamoto Y, et al. The relationship between premenstrual symptoms, menstrual pain, irregular menstrual cycles, and psychosocial stress among Japanese college students. J Physiol Anthropol 2009;28(3):129e36. [12] Wang L, Wang X, Wang W, et al. Stress and dysmenorrhoea: a population based prospective study. Occup Environ Med 2004;61(12):1021e6. [13] Dorn LD, Negriff S, Huang B, et al. Menstrual symptoms in adolescent girls: association with smoking, depressive symptoms, and anxiety. J Adolesc Health 2009;44(3):237e43. [14] Hoppenbrouwers K, Roelants M, Meuleman C, et al. Characteristics of the menstrual cycle in 13-year-old Flemish girls and the impact of menstrual symptoms on social life. Eur J Pediatr 2016;175(5):623e30.
[15] Chan SS, Yiu KW, Yuen PM, et al. Menstrual problems and health-seeking behaviour in Hong Kong Chinese girls. Hong Kong Med J 2009;15(1):18e23. [16] Lee LK, Chen PC, Lee KK, et al. Menstruation among adolescent girls in Malaysia: a cross-sectional school survey. Singap Med J 2006;47(10):869e74. [17] Lee JC, Yu BK, Byeon JH, et al. A study on the menstruation of Korean adolescent girls in Seoul. Korean J Pediatr 2011;54(5):201e6. [18] American academy of pediatrics, American college of obstetrics and gynecologists. Menstruation in girls and adolescents: using the menstrual cycle as a vital sign. Pediatrics 2006;118(5):2245e50. [19] Jappe LM, Cao L, Crosby RD, et al. Stress and eating disorder behavior in anorexia nervosa as a function of menstrual cycle status. Int J Eat Disord 2014;47(2):181e8. [20] De Sanctis V, Bernasconi S, Bianchin L, et al. Onset of menstrual cycle and menses features among secondary school girls in Italy: a questionnaire study on 3,783 students. Indian J Endocrinol Metab 2014;18(Suppl. 1):S84e92. [21] Vale B, Brito S, Paulos L, et al. Menstruation disorders in adolescents with eating disorders-target body mass index percentiles for their resolution. Einstein (Sao Paulo) 2014;12(2):175e80. [22] Romans SE, Kreindler D, Einstein G, et al. Sleep quality and the menstrual cycle. Sleep Med 2015;16(4):489e95. [23] Carskadon MA, Acebo C, Jenni OG. Regulation of adolescent sleep: implications for behavior. Ann N Y Acad Sci 2004;1021:276e91. [24] Minges KE, Redeker NS. Delayed school start times and adolescent sleep: a systemic review of the experimental evidence. Sleep Med Rev 2016;28: 82e91. [25] Kira G, Maddison R, Hull M, et al. Sleep education improves the sleep duration of adolescents: a randomized controlled pilot study. J Clin Sleep Med 2014;10(7):787e92. [26] Baker FC, Driver HS. Circadian rhythms, sleep, and the menstrual cycle. Sleep Med 2007;8(6):613e22. [27] National Sleep Foundation. 2006 Sleep in America Poll. 2006. Retrieved from, https://sleepfoundation.org/sites/default/files/2006_summary_of_findings. pdf. [28] Foley LS, Maddison R, Jiang Y, et al. Presleep activities and time of sleep onset in children. Pediatrics 2013;131(2):276e82. [29] Oh JY, Yang YJ, Kim BS, et al. Validity and reliability of Korean version of international physical activity questionnaire (IPAQ) short form. J Korean Acad Fam Med 2007;28(7):532e41. [30] Crowley SJ, Acebo C, Carskadon MA. Sleep, circadian rhythms, and delayed phase in adolescence. Sleep Med 2007;8(6):602e12. [31] Baker FC, Driver HS. Self-reported sleep across the menstrual cycle in young, healthy women. J Psychosom Res 2004;56(2):239e43. [32] Labyak S, Lava S, Turek F, et al. Effects of shiftwork on sleep and menstrual function in nurses. Health Care Women Int 2002;23(6e7):703e14. [33] Hall JE, Sullivan JP, Richardson GS. Brief wake episodes modulate sleepinhibited luteinizing hormone secretion in the early follicular phase. J Clin Endocrinol Metab 2005;90(4):2050e5. [34] Baumgartner A, Dietzel M, Saletu B, et al. Influence of partial sleep deprivation on the secretion of thyrotropin, thyroid hormones, growth hormone, prolactin, luteinizing hormone, follicle stimulating hormone, and estradiol in healthy young women. Psychiatry Res 1993;48(2):153e78. [35] Statistics Korea and Ministry of Gender Equity and Family. 2015 Adolescent statistics. Statistics Korea and Ministry of Gender Equity and Family. 2015. Retrieved from, http://kostat.go.kr/portal/korea/kor_nw/2/6/1/index.board? bmode¼read&aSeq¼335384. [36] Chin YR, Choi K. Suicide attempts and associated factors in male and female Korean adolescents a population-based cross-sectional survey. Community Ment Health J 2015;51(7):862e6. [37] Kessler RC, Walters EE. Epidemiology of DSM-III-R major depression and minor depression among adolescents and young adults in the National Comorbidity Survey. Depress Anxiety 1998;7(1):3e14.
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Sleep Medicine journal homepage: www.elsevier.com/locate/sleep
Original Article
Association between sleep duration and menstrual cycle irregularity in Korean female adolescents Ga Eun Nam a, Kyungdo Han b, Gyungjoo Lee c, * a
Department of Family Medicine, Sahmyook Medical Center, 82, Mangu-ro, Dongdaemun-gu, 02500 Seoul, Republic of Korea Biostatistics, College of Medicine, The Catholic University of Korea, 222 Banpo-daero, Seochogu, 65091 Seoul, Republic of Korea c College of Nursing, The Catholic University of Korea, 222 Banpo-daero, Seochogu, 65091 Seoul, Republic of Korea b
a r t i c l e i n f o
a b s t r a c t
Article history: Received 23 November 2016 Received in revised form 17 March 2017 Accepted 18 April 2017 Available online 8 May 2017
Objective: The association between sleep and the menstrual cycle in the adolescent population has been scarcely studied. This study aimed to investigate the association between sleep duration and menstrual cycle irregularity among female adolescents using nationwide representative data from the South Korean population. Methods: This population-based, cross-sectional study used the data collected from Korea National Health and Nutrition Examination Survey 2010e2012, and the data from 801 female adolescents were analyzed. Hierarchical multivariable logistic regression analysis was performed to assess the risk of menstrual cycle irregularity in relation to sleep duration. Results: Subjects with menstrual cycle irregularity accounted for 15% (N ¼ 120). The mean sleep duration in subjects with menstrual cycle irregularity was significantly shorter than that in those without (p ¼ 0.003). Menstrual cycle irregularity prevalence tended to decrease as sleep duration increased (p for trend ¼ 0.004), which was significantly different based on sleep duration and presence of depressive mood (p ¼ 0.011). Sleep duration 5 h per day was significantly associated with increased risk of menstrual cycle irregularity compared with that in the subjects whose sleep duration is 8 h per day even after adjusting for confounding variables. The odds ratios of menstrual cycle irregularity tended to increase for shorter sleep duration in all adjusted models. Conclusion: This study found a significant inverse association between sleep duration and menstrual cycle irregularity among Korean female adolescents. Increasing sleep duration is required to improve the reproductive health of female adolescents. © 2017 Elsevier B.V. All rights reserved.
Keywords: Adolescents Menstrual cycle irregularity Sleep duration
1. Introduction Women commonly experience irregular menstrual cycles during their reproductively fertile years, and menstrual cycle irregularity aggravates the frequency and degree of menstrual symptoms [1]. Moreover, irregular menstrual cycles have been shown to have implications for women's health. Menstrual cycle irregularity has been reported to be associated with serious health outcomes such as breast cancer, type 2 diabetes, cardiovascular disease, osteoporosis, and infertility [2e6]. In addition, evidence supporting the association between this condition and mental health problems has been increasing [7e12]. In particular, menstrual cycle abnormalities
* Corresponding author. Fax: þ82 02 2258 7779. E-mail address: [email protected] (G. Lee). http://dx.doi.org/10.1016/j.sleep.2017.04.009 1389-9457/© 2017 Elsevier B.V. All rights reserved.
were reported to be associated with symptoms of depressive disorders in high school girls [7], that seem to affect the female adolescents' quality of life and disturb active participation in academic performance and psychosocial functioning [13,14]. Although the objective definition of menstrual cycle irregularity has not been established, the prevalence of this condition has been reported to be high among adolescents [15e17]. In addition, the American Academy of Pediatrics recommended that menstrual cycle should be assessed with other vital signs, emphasizing the critical role of menstrual patterns in reflecting the overall health status of female adolescents [18]. Therefore, specific efforts should be made to identify associated factors to prevent menstrual cycle irregularity in the adolescent age group. Menstrual cycle regularity has been reported to be influenced by a variety of physical and mental conditions and health-related lifestyles [18]. Age at menarche, excessive exercise or rapid gain
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or loss of body weight has been explored as risk factors of menstrual cycle irregularity [19]. It is also caused by many medical conditions, such as pregnancy, endocrine disorders, and other chronic diseases [18]. In addition, mental health problems including depressive mood and psychological stress were also suggested as risk factors of menstrual cycle irregularity [9,13,19e21]. Recently, sleep has been gaining attention as an associated factor in menstrual cycle irregularity in adults. Romans et al. [22] concluded in their review that some studies showed significant associations between poorer sleep quality and premenstrual and menstrual phases. In general, women are well known to have higher prevalence of sleep disturbance than men [22], which suggests that sleep may be correlated with reproductive function in women. Also, puberty disrupts sleep onset, which can cause delayed bedtimes and low sleep quality [23]. Sleep is essential in the effective performance of various daily tasks in adolescents. Sleep patterns and quality contribute to successful academic achievement and holistic quality of life [24]. Inadequate sleep causes daytime malfunctioning, psychological and behavioral problems, and physical diseases including obesity [25]. Baker and Driver [26] issued that circadian disruption such as sleepeawake disorders may be associated with disturbance in the menstrual cycle [26]. Approximately a third of adolescents experience sleep disturbances [27], and only one in 10 adolescents is estimated to sleep more than 8 h, as recommended by the National Sleep Foundation [27]. The poor sleep pattern of adolescents seems to be associated with exposure to screen light including television watching and computer gaming, as well as after-school work and academic stress [28]. This may disturb the circadian rhythm, which affects the menstrual cycle of female adolescents. However, the association between sleep duration and menstrual cycle regularity has been scarcely studied in the adolescent population. Thus, this study aimed to identify the association between sleep duration and menstrual cycle irregularity among female adolescents using the nationwide representative data of the South Korean population. 2. Methods 2.1. Data source and study subjects This population-based, cross-sectional study used the data collected from the Korea National Health and Nutrition Examination Survey (KNHANES) 2010e2012. KNHANES has been conducting nationwide surveys annually since 1998, by the Division of Chronic Disease Surveillance under the Korea Centers for Disease Control and Prevention (KCDC) and the Korean Ministry of Health and Welfare. The survey aimed to assess the health and nutritional status of the non-institutionalized civilians of South Korea. The survey is composed of three parts: health interview, health examination, and nutritional surveys, and each part was conducted by trained investigators. The sampling units were defined based on the 2005 population and housing census in South Korea, which includes information regarding sex, age, and geographical area. A stratified, multi-staged, and clustered probability design with a rolling survey sampling model was used to select a representative sample of the non-institutionalized South Korean population. Of the 25534 individuals who participated in the KNHANES during 2010e2012, we excluded males (N ¼ 11616), those aged <12 or >18 years (N ¼ 12911), those who were diagnosed with epilepsy or attention deficit hyperactivity disease or were treated for these diseases (N ¼ 8), those before menarche (N ¼ 79), those who were pregnant or breastfeeding (N ¼ 0), and those with missing data (N ¼ 119). Finally, the data of 801 female adolescents were analyzed. Parental written informed consents were signed before
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participation in the survey for all study participants because they were minors. The institutional review board of the KCDC reviewed and approved the survey protocol. The data are accessible on the following website (http://knhanes.cdc.go.kr). 2.2. Assessment of sleep duration and menstrual cycle Sleep duration was self-reported from the following question: “How many hours do you sleep on average?” Sleep duration was classified into three categories: 5, 6e7, and 8 h. Subjects were asked to describe menstrual cycle regularity through the following question: “Do you have a regular menstrual cycle?” Subjects who responded “yes” were defined as having a regular menstrual cycle, whereas those who responded “no” were defined as having a menstrual cycle irregularity. 2.3. Covariates Sociodemographic and lifestyle characteristics of subjects were obtained by trained interviewers or by self-reported questionnaire. Monthly household income was divided into quartiles, and the lowest quartile of the total subjects was defined as a low income level. Subjects who had consumed one alcohol drink or more for at least one day during the month before the survey were defined as ever-drinkers, and those who had not, were defined as nondrinkers. For smoking status, based on the responses to the selfreported questionnaire, subjects who had smoked cigarettes at least one day during the month before the survey were defined as ever-smokers, and those who had not, were defined as nonsmokers. Physical activity was assessed using the Korean version of the International Physical Activity Questionnaire [29]. Subjects who exercised moderately for at least 30 min per session, more than five times per week, or those who exercised strenuously for at least 20 min per session more than three times per week were defined as regular exercisers. Subjects were asked to respond to the following question to assess their history of weight control attempts: “Have you ever attempted weight control?” In addition, information regarding the subjects' age at menarche was also collected. Psychological problems were investigated by providing questions regarding psychological stress and depressive mood. Psychological stress was assessed from the responses to the following question: “How much stress do you feel in your daily life?” Subsequently, subjects were asked to report the stress level as rare, mild, much, or severe. Based on the responses, subjects were classified into the low-stress group if they reported feeling stress rarely or mildly, and the high-stress group if they responded as feeling stress much or severely. Subjects were considered to have depressive mood when they answered “yes” to the following question: “Has your daily life been burdened by feelings of sadness or hopelessness for two continuous weeks or more during the previous year?” Trained staffs performed anthropometric measurements for all participants. Height and body weight were measured to the nearest 0.1 cm and 0.1 kg, respectively, with light clothing and without shoes, and body mass index (BMI) was calculated as body weight (kg)/height2 (m2). Waist circumference (WC) was measured to the nearest 0.1 cm at the midpoint between the lowest margin of the rib cage and iliac crest at the end of expiration. Blood samples were obtained after fasting for 8 h or more and were immediately processed and refrigerated. They were transported in cold storage to the Central Testing Institute in Seoul, Korea and then analyzed within 24 h. The blood hemoglobin level was measured using XE-2100D (Sysmex, Tokyo, Japan).
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2.4. Statistical analyses All statistical analyses were performed using the Statistical Analysis System (SAS, version 9.2; SAS Institute, Cary, NC, USA) survey procedure to account for complex sampling design and to provide nationwide representative estimates. The procedure included unequal probabilities of selection, oversampling, and nonresponse to make inferences regarding Korean adolescent participants. Data were expressed as mean ± standard error (SE) for continuous variables or as percentage (SE) for categorical variables. Baseline characteristics of the study subjects based on menstrual cycle regularity were compared using independent t-test for continuous variables or chi-square test for categorical variables. Prevalence of menstrual cycle irregularity based on sleep duration was compared using chi-square test, and then p for trend was obtained using a general linear model. Prevalence of menstrual cycle irregularity based on sleep duration and depressive mood was also compared using the chi-square test. Hierarchical multivariable logistic regression analysis was performed, and odds ratios (ORs) and 95% confidence intervals (CIs) were calculated to assess the risk of menstrual cycle irregularity in relation to sleep duration. Model 1 was adjusted for age and monthly household income as demographic variables. Model 2 was adjusted for variables adjusted in model 1 plus alcohol consumption, smoking status, physical activity, and weight loss attempt as health-related lifestyle characteristics. Model 3 was adjusted for variables adjusted in model 2 plus hemoglobin level, age at menarche, and BMI as physical information. Model 4 was adjusted for the variables in model 3 plus psychological stress and depressive mood as psychological problems. A p-value <0.05 was considered statistically significant.
height, body weight, BMI, WC, and hemoglobin level did not differ between subjects with and without menstrual cycle irregularity. The mean sleep duration was 6.6 ± 0.2 h and 7.1 ± 0.1 h in subjects with and without menstrual cycle irregularity (p ¼ 0.003), respectively. The rate of ever-smokers was higher in subjects with menstrual cycle irregularity than that in those without (p ¼ 0.023). Variables regarding monthly household income, alcohol consumption, physical activity, and weight loss attempts were not significantly different between the two groups. In addition, subjects with psychological stress were more likely to have menstrual cycle irregularity with a borderline significance (p ¼ 0.054). Subjects with depressive mood were also more likely to have menstrual cycle irregularity (p ¼ 0.001). 3.2. Prevalence of menstrual cycle irregularity according to sleep duration and the presence of depressive mood Fig. 1 presents the prevalence of menstrual cycle irregularity based on sleep duration. The prevalence tended to decrease as sleep duration increased (p for trend ¼ 0.004). Fig. 2 shows that the prevalence of menstrual cycle irregularity is significantly different based on sleep duration and the presence of depressive mood (p ¼ 0.011). Subjects with depressive mood were more likely to have menstrual cycle irregularity in subjects who sleep for 6 h per day (p ¼ 0.003). Among subjects who sleep for 5 h per day, the prevalence of menstrual cycle irregularity was not different according to the presence of depressive mood (p ¼ 0.763). 3.3. Risk of menstrual cycle irregularity in relation to sleep duration Table 2 shows the ORs (95% CIs) of menstrual cycle irregularity based on sleep duration. After adjusting for age and monthly
3. Results 3.1. Baseline characteristics of study subjects Table 1 describes the baseline characteristics of study subjects based on menstrual cycle irregularity. The subjects with irregular menstrual cycles accounted for 15% (N ¼ 120) of the total subjects. The mean age and mean age at menarche were significantly higher in subjects with menstrual cycle irregularity than that in those without (p ¼ 0.013 and 0.042, respectively). The mean values of Table 1 Baseline characteristics of Korean female adolescents based on the presence of menstrual cycle irregularity. Menstrual cycle irregularity
N Age (years) Height (cm) Body weight (kg) Body mass index (kg/m2) Waist circumference (cm) Hemoglobin (g/dL) Sleep duration (h) Monthly household income (the lowest quartile) Ever-alcohol drinker Ever-smoker Regular exerciser Weight loss attempt Age at menarche (years) High stress Depressive mood
pa
No
Yes
681 15.2 ± 0.1 160.2 ± 0.3 53.9 ± 0.4 21 ± 0.1 68.9 ± 0.4 13.1 ± 0.1 7.1 ± 0.1 15.6 (2.2)
120 15.7 ± 0.2 160.5 ± 0.6 55.5 ± 1.4 21.6 ± 0.6 69.7 ± 1.1 13.2 ± 0.1 6.6 ± 0.2 21.2 (4.4)
0.013 0.652 0.253 0.297 0.504 0.46 0.003 0.206
29 (2.2) 11.5 (1.6) 20.1 (1.8) 54.8 (2.2) 12.3 ± 0.1 28.1 (2) 11.1 (1.5)
29.1 20.4 18.8 56.1 12.6 38.1 24.7
0.991 0.023 0.772 0.832 0.042 0.054 0.001
(6.3) (4.2) (4) (5.7) ± 0.1 (5.1) (5.5)
Data are presented as mean ± standard error (SE) for continuous variables or percentage (SE) for categorical variables. a p-values were calculated using independent t-test for continuous variables or chi-square test for categorical variables.
Fig. 1. The prevalence of menstrual cycle irregularity based on sleep duration (p for trend ¼ 0.004).
Fig. 2. The prevalence of menstrual cycle irregularity based on sleep duration and the presence of depressive mood (p ¼ 0.011).
G.E. Nam et al. / Sleep Medicine 35 (2017) 62e66 Table 2 Odds ratios of menstrual cycle irregularity in relation to sleep duration in Korean female adolescents. Odds ratio (95% confidence interval) Model 1 Sleep 5 6e7 8 p for trend
duration (h) 3.08 (1.44e6.58) 1.87 (1.07e3.25) 1 0.003
Model 2
Model 3
Model 4
3.01 (1.35e6.73) 1.73 (0.98e3.03) 1 0.007
2.77 (1.21e6.30) 1.60 (0.86e2.99) 1 0.017
2.36 (1.02e5.47) 1.51 (0.81e2.82) 1 0.046
Odds ratios (95% confidence intervals) were calculated using multivariable logistic regression analysis, and p for trend was obtained from general linear model. Model 1 was adjusted for age and monthly household income (demographic variables). Model 2 was adjusted for variables in model 1 plus alcohol consumption, smoking status, physical activity, and weight loss attempt (health-related lifestyle variables). Model 3 was adjusted for variables in model 2 plus hemoglobin level, age at menarche, and body mass index (variables of physical condition). Model 4 was adjusted for variables in model 3 plus psychological stress and depressive mood (variables of psychological problems).
household income (model 1), subjects who slept for 6e7 h and 5 h per day were significantly associated with increased risk of menstrual cycle irregularity compared with those who slept for 8 h per day (OR [95% CI] ¼ 1.87 [1.07e3.25] for 6e7 h and 3.08 [1.44e6.58] for 5 h). After additionally adjusting for alcohol consumption, smoking status, physical activity, and weight loss attempts (model 2), sleeping 5 h per day was significantly associated with increased risk of menstrual cycle irregularity compared with those who slept for 8 h per day (OR [95% CI] ¼ 3.01 [1.35e6.73]). However, the OR of subjects who slept for 6e7 h did not show a significant association (OR [95% CI] ¼ 1.73 [0.98e3.03]) in model 2. After further adjustment for hemoglobin level, age at menarche, and BMI (model 3), subjects who slept for 5 h had a significantly higher OR of 2.77 (95% CI, 1.21e6.3) for menstrual cycle irregularity compared with subjects who slept for 8 h. However, the OR of subjects who slept for 6e7 h were not significant (OR [95% CI] ¼ 1.6 [0.86e2.99]) in model 3. After additional adjustment for psychological stress and depressive mood (model 4), subjects who slept for 5 h had a significantly higher OR of 2.36 (95% CI, 1.02e5.47) for menstrual cycle irregularity compared with subjects who slept for 8 h. The ORs of menstrual cycle irregularity tended to increase for the shorter sleep duration in all four models (p for trend for OR of 0.003, 0.007, 0.017, and 0.046 in models 1, 2, 3, and 4, respectively). 4. Discussion To the best of our knowledge, this is the first study with a large adolescent population that investigated the importance of sleep duration in relation to menstrual cycle regularity. The main finding of this study was a significant inverse association between sleep duration and menstrual cycle irregularity among South Korean adolescents aged 12e18 years. The association did not change even after adjusting for potential confounding factors including age, monthly household income, alcohol consumption, smoking status, physical activity, weight loss attempts, hemoglobin level, age at menarche, BMI, psychological stress, and depressive mood. In addition, among adolescents whose sleep duration was longer than 6 h, adolescents with depressive mood were more likely to have menstrual cycle irregularity than those without depressive mood. Adequate sleep stabilizes physiological circadian rhythmicity. Stable circadian rhythm affects both mood and menstrual cycle regularity, which are milestones of normal development in female adolescents [30]. Several studies have found that sleep quality is associated with the menstrual cycle phase [21,31]. Sleep quality
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decreases at the premenstrual phase and during menstruation or between menstrual cycles [21]. In adults, circadian rhythmicity is disrupted due to frequent shift change of work and increased menstrual cycle irregularities [32]. Disrupted sleep inhibits luteinizing hormone secretion, and shorter sleep duration may alter menstrual cycle in female adults working as shift workers [33]. Menstrual cycle irregularity may be linked with changes in luteinizing hormone pulsatility and amplitude, resulting from the disturbance of circadian rhythmicity [33,34]. However, the underlying mechanisms explaining the associations between sleep duration and menstrual cycle regularity in the adolescent age group have been poorly elucidated. This study found that shorter sleep duration is associated with increased risk of menstrual cycle irregularity in female adolescents. Baker and Driver [26] also emphasized that psychological stress or mood disturbance influences the menstrual cycle. Based on the annual report on the youths of South Korea in 2014, seven of 10 female adolescents were under high stress, and the rate for their optimal sleep duration decreased in 2014 compared with the result in 2006 [35]. The Korean Statistics raised the alarm that the leading cause of death in teens was suicide in 2012, which is highly related with depression [36]. It was estimated that 25% of adolescents aged 15e18 years experience depression including 14% with major depression and 11% with minor depression [37]. Premenstrual dysphoric disorder (PMDD) is a premenstrual mood disturbance, seriously affecting a teen's ability to function in their lives [26]. Both depression and PMDD had sleep disturbance including hypersomnia or insomnia as one of the symptoms to diagnose these diseases. In this study, in accordance with these previous findings, when adolescents have depressive mood although sleep duration is longer than 6 h, they were more likely to have menstrual cycle irregularity than those without depressive mood. The current study provides additional evidence that enough sleep with better mental health is essential to improve menstrual cycle regularity during adolescence, which is the critical period of healthy development. Putting together findings from previous studies and our study, public health providers should take into consideration the significance of the associations between sleep duration, depressive mood, and menstrual cycle irregularity in adolescents, suggesting an added vulnerability to disrupted circadian rhythm. This study added evidence that the significance of adequate sleep duration and psychological health to improve menstrual cycle regularity during the adolescent period. The present study has some limitations. First, the data used in this population-based study were collected by retrospective selfreport, which has a potential for recall bias. Second, the causal relationship should be cautiously interpreted in attempting to identify the relationships among variables due to the crosssectional design of this study. Third, this study could not consider various sleep features including subjective and objective sleep qualities, sleep timing, or circadian preference of the study participants due to lack of data from the KNHANES. Future study is needed to control those sleep-related factors to determine whether sleep duration is independently related with menstrual cycle irregularity. Fourth, menstrual cycle irregularity was assessed based solely on subjects' self-report which may be dependent on their subjective perceptions, without consideration of biomedical markers or hormone measurements. Further studies need to validate the parameters of menstrual cycle irregularity and to establish the definition of menstrual cycle irregularity. This study has several strengths as well; for instance, the study has reliable representatives based on the nationwide population dataset. It is the first study to identify the significant role of sleep duration in relation to menstrual cycle irregularity of adolescents, considering a variety of compounding variables, including
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demographic and lifestyle factors and physical and psychological health. In conclusion, the current study highlights the importance of adequate sleep duration with better mental health on menstrual cycle regularity of female adolescents. Surprisingly, few studies reported on the menstrual irregularities from the adolescent population although early gynecological age is influential in menstrual cycle instability. A replication study is needed to increase the reliability and validity of the findings of the current study. Specific intervention to increase sleep duration of adolescents is required at school and at the government level as well. Conflict of interest The ICMJE Uniform Disclosure Form for Potential Conflicts of Interest associated with this article can be viewed by clicking on the following link: http://dx.doi.org/10.1016/j.sleep.2017.04.009. References [1] Weller A, Weller L. Menstrual irregularity and menstrual symptoms. Behav Med 2002;27(4):173e8. [2] Harlow SD, Ephross SA. Epidemiology of menstruation and its relevance to women's health. Epidemiol Rev 1995;17(2):265e86. [3] Kaplan JR, Manuck SB. Ovarian dysfunction, stress, and disease: a primate continuum. ILAR J 2004;45(2):89e115. [4] Rowland AS, Baird DD, Long S, et al. Influence of medical conditions and lifestyle factors on the menstrual cycle. Epidemiology 2002;13(6):668e74. [5] Solomon CG, Hu FB, Dunaif A, et al. Long or highly irregular menstrual cycles as a marker for risk of type 2 diabetes mellitus. JAMA 2001;286(19):2421e6. [6] Solomon CG, Hu FB, Dunaif A, et al. Menstrual cycle irregularity and risk for future cardiovascular disease. J Clin Endocrinol Metab 2002;87(5):2013e7. [7] Bisaga K, Petkova E, Cheng J, et al. Menstrual functioning and psychopathology in a county-wide population of high school girls. J Am Acad Child Adolesc Psychiatry 2002;41(10):1197e204. [8] Chang PJ, Chen PC, Hsieh CJ, et al. Risk factors on the menstrual cycle of healthy Taiwanese college nursing students. Aust N Z J Obstet Gynaecol 2009;49(6):689e94. [9] Jarvelaid M. The effect of gynecologic age, body mass index and psychosocial environment on menstrual regularity among teenaged females. Acta Obstet Gynecol Scand 2005;84(7):645e9. [10] Toffol E, Koponen P, Luoto R, et al. Pubertal timing, menstrual irregularity, and mental health: results of a population-based study. Arch Women Ment Health 2014;17(2):127e35. [11] Yamamoto K, Okazaki A, Sakamoto Y, et al. The relationship between premenstrual symptoms, menstrual pain, irregular menstrual cycles, and psychosocial stress among Japanese college students. J Physiol Anthropol 2009;28(3):129e36. [12] Wang L, Wang X, Wang W, et al. Stress and dysmenorrhoea: a population based prospective study. Occup Environ Med 2004;61(12):1021e6. [13] Dorn LD, Negriff S, Huang B, et al. Menstrual symptoms in adolescent girls: association with smoking, depressive symptoms, and anxiety. J Adolesc Health 2009;44(3):237e43. [14] Hoppenbrouwers K, Roelants M, Meuleman C, et al. Characteristics of the menstrual cycle in 13-year-old Flemish girls and the impact of menstrual symptoms on social life. Eur J Pediatr 2016;175(5):623e30.
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