Factors Associated with Premenstrual Syndrome among Nursing Students Based on the Theory of Unpleasant Symptoms

Background: This study aimed to explain premenstrual syndrome (PMS) in nursing students based on the Theory of Unpleasant Symptoms (TOUS). PMS includes physiological factors (pain intensity during clinical practice, sleep quality), psychological factors (neuroticism, stress), situational factors (attitudes toward menstruation, sex role stereotypes) that influence symptoms. Therefore, thoroughly investigating the correlates of PMS among nursing students is necessary. Method: Data were collected from March 2022 to May 2022 through a cross-sectional study of female students using a self-reported questionnaire. A total of 330 female students (in the fourth grade) enrolled in the nursing department of a college in G city were recruited via convenience sampling. Independent t-test and one-way ANOVA were used to explore differences in PMS, with Scheffe’s test performed post hoc. We analyzed correlations using Pearson’s correlation and performed multiple regression analyses to investigate the factors influencing PMS. Results: PMS was positively significantly correlated with menstrual pain intensity during clinical practice (r = 0.51, p < 0.01), attitudes toward menstruation (r = 0.15, p < 0.01), neuroticism (r = 0.37, p < 0.01) and stress (r = 0.39, p < 0.01), but negatively correlated with sleep quality (r = −0.38, p < 0.01). The results of multiple regression analysis showed that menstrual pain intensity during clinical practice ( β = 0.42), sleep quality ( β = −0.23), neuroticism ( β = 0.17) and stress ( β = 0.21) affected PMS. The regression model was significant (F = 44.64, p < 0.001) and explanatory power was 44%. Conclusion: The findings of this study identified physiological and psychological factors influencing PMS. Developing an appropriate understanding of these influencing factors and customized interventions may be associated with the improvement of PMS in female college students enrolled in the Department of Nursing


Introduction
Many women experience menstruation, which is a reproductive function, a symbol of sexual identity, and an important indicator of a woman's health [1]. However, various symptoms that occur before and during menstruation periodically cause discomfort in women's daily activities, with some individuals experiencing serious physical and psychological symptoms [2,3]. Because of this, many women have a negative perception of menstruation. Premenstrual syndrome (PMS) is a mixed set of symptoms that may occur between 2 and 14 days before the onset of menstruation and usually ends shortly after menstruation begins [4]. PMS includes physical, behavioral, and emotional clinical symptoms that vary in severity and timing between individuals. Symptoms can include breast tenderness, abdominal bloating, back pain, irritability, anxiety, tension, depression, difficulty controlling emotions, sleep disturbance, poor concentration, and social withdrawal [1,5,6].
Although the etiology of PMS has not yet been fully identified, it seems that physiological, psychological and situational factors are interrelated, and that changes in neurotransmitters [23,24], psychological factors [25], stress, and hormones [26,27] are probably the primary contributors to the symptoms [28,29]. Nevertheless, few studies have been conducted to comprehensively explain PMS in nursing students based on a theoretical model. Independent and partially investigated studies have been able to explain isolated relationships between factors, but it has been difficult to determine the total influence of physiological, psychological, and situational factors that are specific to nursing students and are often interrelated.
Considering the multidimensional aspect of PMS, applying an integrated evaluation to investigations on the syndrome is necessary. The Theory of Unpleasant Symptoms (TOUS) [30] suggests that, in many conditions related to illness or stress, an individual's physiological, psychological, and situational factors may affect symptoms simultaneously and in complex ways. The physiological factors include body systems that normally regulate an individual's energy level; psychological factors include an individual's state of mental or mood and their emotional responses to an illness; and situational factors include how an individual's social and physical experiences may affect their symptoms [30]. This theory was initially developed to explain the symptoms of dyspnea and fatigue, but it has progressed to provide a conceptual framework for understanding symptoms in a variety of contexts and to help manage, improve, and prevent unpleasant symptoms [31]. Previous studies have used the TOUS to examine experiences of symptoms have focused on patients with serious illnesses, such as breast cancer and colorectal cancer with non-recurrent, nonperiodic symptoms [32][33][34], but few research has used the TOUS framework to explain PMS in nursing students, who repeatedly and regularly experience unpleasant symptoms that can affect their daily lives and lead to declines in their health-related quality of life [35,36].
Even with the high prevalence and negative impacts of PMS, these symptoms have been inadequately treated in female university students [37,38]. The primary barriers to effective administration may be associated with a lack of accurate understanding about the factors related to PMS. Consequently, recognizing and understanding factors associated with PMS are critical to establishing a customized management strategy that can alleviate its symptoms. This study was therefore designed to explain PMS in nursing students based on TOUS theory [30,39], which attributes symptom experience to various factors that influence symptoms, and to provide a comprehensive understanding of how physiological factors (i.e., menstrual pain intensity during clinical practice [28,40,41] and sleep quality [36,42]), psychological factors (i.e., neuroticism [43] and stress [44][45][46]), and situational factors (i.e., attitudes towards menstruation [47][48][49] and sex role stereotypes [50,51]) influence PMS in female college nursing students.
Therefore, in this study, we constructed a theoretical model with preliminary hypotheses based on TOUS ( Figure 1) and examined the correlates of PMS among female college students in the Nursing Department at X University using the physiologic, psychological and situational factors. Specifically, we aimed to examine the effects of these factors on PMS, help design a foundation for developing nursing intervention programs that can create health coping strategies for women in this population who are experiencing PMS.

Ethical Approval
Ethical approval was granted by the Ethics Committee at the author's university [blinded for review]. All participants were provided with relevant information, including study design, objectives, and the data collection process prior to data collection. In addition, we assured participants that their responses were confidential, that no private identifying information would be exposed, that the data would be used for the state research purpose only, and that participants could withdraw their consent to be involved in the study from any time.

Study Design
A cross-sectional study using a self-reported questionnaire was used to collect the data among female students between Mar 2022 and May 2022.

Participants
We recruited a convenience sample of 4 th grade students in the nursing department at X university in G city, Republic of Korea. The inclusion criteria were having experienced menstruation regularly for at least the previous six consecutive months, not having any medical disease, including pelvic disorders, understanding the purpose of this study, and voluntarily agreeing to participate. Those who had a history of childbirth or miscarriage were excluded. The required sample size for this study, estimated using the G*Power 3.1 program, was 328 participants (power .80, effect size .15 and significance level .05). Accounting for the dropout rate, 340 questionnaires were distributed, of which 337 were returned. However, seven questionnaires included invalid responses. Therefore, 330 questionnaires were ultimately used for analysis.

Data Collection
Data were collected from March 2022 to May 2022. A total of 330 female students (grade 4th) enrolled in the nursing departments of the four nursing colleges in G city were recruited via convenience sampling. The investigator described the objectives of the study and requested the students' cooperation. Questionnaires were provided only to those who voluntarily agreed in writing to be involved in the study. The self-reported questionnaire was completed in about 20 minutes, and was returned from participants in packs shortly after completion.

PMS
PMS was measured using the Korean Menstrual Symptom Scale (KMSS) for university developed by Lee et al. [52]. In the 37 items scale, items were measured using a 5-point Likert scale (1 = not at all, 5= very severe), whrere a higher score indicates more severe PMS symptoms. It includes 8-items on negative emotions, 7 items on changes in activity levels, 9 items on physical symptoms, 4 items on mood changes, 4 items on changes in concentration, and 5 items on water retention. We assessed the reliability using Cronbach's α, which was .96 when the instrument was developed and .97 in this study Volume

Menstrual pain intensity during clinical practice
Menstrual pain intensity was measured using a 10 point Numeric Rating Scale (NRS), with 0 being no menstrual pain and 10 being the most severe.

Sleep Quality
Sleep quality was measured using the Korean Sleep Scale A by Oh et al. [53]. This scale consist of 15 items in total, including 8 items on sleep pattern, 4 items on sleep assessment, 1-item on sleep outcome, 2 items on sleep disruptors. Each item is rated on a 4 point Likert scale (1 = always true, 4= not at all). A higher total score indicates a higher sleep quality. We assessed the reliability using Cronbach's α, which was .75 when the instrument was developed and .88 in this study.

Neuroticism
Neuroticism was measured using the International Personality Item Pool (IPIP) developed by Goldberg [54], translated by Yu and Lee [55]. Among the five personality traits, only the 10 items for neuroticism scale was adopted in this study. Each item is rated on 5 point Likert scale (1 = not at all, 4 = always true). A higher total score indicates a higher level of neuroticism. We assessed the reliability using Cronbach's α that were .90 at the time of instrument development, .82 in this study

Stress
Stress was measured using the Stress Scale for Korean Nursing Students developed by Yoo et al. [56]. This scale consists of 59 items in total, including 39 items on college-based stress and 20 items on clinical-based stress. Each item is rated on a 5 point Likert scale (0 = not at all, 4 = always true). A higher total score indicates a higher level of perceived stress. We assessed the reliability using Cronbach's α, which was .94 and .92 for collegebased and clinical-based stress, respectively, when the instrument was developed and.96 for both college-based and clinical-based stress in this study

Attitudes toward Menstruation
Attitudes toward menstruation was measured using the Menstrual Attitude Questionnaire developed by Yang et al. [57]. This scale consist of 21 items in total, including 8 items on women's secret, 5 items on women's burden, 5-items on traditional feminity, 3 items on women's symbol. Each item is rated on 7 point Likert scale (1 = very positive, 7 = very negative). A higher total score indicates more negative attitudes toward menstruation. . We assessed the reliability using Cronbach's α, which was 0.82 at the time of the instrument's development and 0.85 in this study.

Sex Role Stereotype
Sex role stereotype was measured using the self-reported questionnaire developed by Kim and Kim [58], modified by Koh et al [59]. This scale consist of 27 items in total, including 7 items on family-oriented sex role, 6 items on social psychology, 6 items on intellectual characteristics, 4 items on social activity, 4 items on appearance. Each item is rated on 5 point Likert scale (1 = strongly agree, 5 = strongly disagree). A higher total score indicates more conservative sex role stereotypes based on biological sex. We assessed the reliability using Cronbach's α, which was 0.83 at the time of the instrument's development, 0.88 in a modified study and 0.87 in this study.

General and menstruation related information questionnaire
General and menstruation related information include age, body mass index (BMI), menarche age, family history of PMS, regularity of menstrual cycle, average menstrual period, average menstrual cycle, volume of menstruation, the degree of difficulty in daily life, menstrual pain intensity during usual day and clinical practice.

Statistical Analysis
Data analysis was performed using SPSS ver. 27.0. General and menstruation-related characteristics, sleep quality, attitudes toward menstruation, sex role stereotypes, neuroticism, stress, and PMS were analyzed using descriptive statistics. We analyzed the differences in PMS according to general and menstruation-related characteristics by independent t-test and one-way ANOVA, with Scheffe's test post hoc. We examined the correlates between menstruation pain intensity during clinical practice, sleep quality, attitudes toward menstruation, sex role stereotypes, neuroticism, stress, and PMS using Pearson's correlation coefficients. Multiple linear stepwise regression analysis was performed to identify the correlates of PMS. Variables that were statistically significant in the univariate analysis were included in the multivariate analysis. A variance inflation factor (VIF) value of 10 or less indicates that there is no problem with multicollinearity, and the VIF of this study ranged from 1.02 to 1.51. For all of the above statistical analyses, the significance level and confidence interval were p< .05 and 95%, respectively.

Results
A total of 337 nursing students experiencing PMS were initially enrolled in the study. A total of 7 cases were excluded due to missing responses; therefore 330 responses were included for data analyses.  Table 1 shows the general and menstruation-related characteristics of the participants. The highest proportion of participants were between 12 and 13 years old at the onset of menarche (n=164, 49.7%) and had regular menstrual cycles (n=212, 64.2%). Of these, 152 (46.1%) participants answered that their average menstrual cycle length was between 26 and 30 days, with 60.3% reporting that their average menstrual period was 6 days or less in length. Of the participants, 231 (70%) of them stated that their menstruation was of average volume. The degree of menstrual pain was assessed by Numeric Rating Scale (NRS), which resulted in a mean pain level of 5.28±2.54 and 5.38±2.57 in usual day and clinical practice, respectively. The level of pain experienced by individuals in decreasing sequence was 7-10 points (severe; n=132, 40%), 4-6 points (moderate; n=113, 34.2%), and 1-3points (mild; n=85, 25.8% on clinical practice. By measuring and analyzing the variables for the characteristics, we obtained the following results: Significant differences in PMS were demonstrated in family history (F = 3.068, p = 0.002) and regularity of menstrual cycle (F = −2.26, p = 0.024). In the post hoc testing, volume of menstruation, the degree of difficulty in daily life and menstrual pain intensity during a normal day and clinical practice showed significant differences. Large volumes of menstruation, the highest degree of difficulty in daily life and a menstrual pain intensity of 7-10 points (severe) on a normal day and clinical practice were found to have a significantly higher PMS score than small volumes of menstruation, low degrees of difficulty and 1-3-point pain intensity (mild) ( Table 1).

Mean ± SD t/F (p)
Age ( Table 2 shows the analysis results for the relationship between the participant's PMS and major variables. . PMS was significantly positively correlated with menstrual pain intensity during clinical practice (r = 0.51, p < 0.01), neuroticism (r = 0.37, p < 0.001), stress (r = 0.39, p < 0.001) and attitudes toward menstruation (r = 0.15, p = 0.008). In contrast, PMS was negatively correlated with sleep quality (r = −0.38, p < 0.001) ( Table 2). Thus, participants with poor sleep quality, negative attitudes towards menstruation, severe menstrual pain intensity and high levels of neuroticism and stress experienced more severe PMS.

Influencing factors for PMS (N=330)
In order to identify the relevant factors affecting PMS, the multiple regression model of the independent variables (menstrual pain intensity during clinical practice, sleep quality, neuroticism, stress, attitudes toward menstruation and sex role stereotypes) was analyzed. The tolerance limits were all above 0.1, and the variance inflation factors (VIF) ranged from 1.02 to 1.51, which did not exceed 10, confirming that there was no evidence of multicollinearity. The Durbin-Watson statistic was 1.824, which is close to the criterion value of 2, indicating that there was no correlation between the independent variables, so the regression model is reasonable.
The regression model of the independent variables (menstrual pain intensity during clinical practice, sleep quality, attitudes toward menstruation, sex role stereotypes, neuroticism and stress) was significant (F = 44.64, p < 0.001), and its explanatory power was 44%. The independent variable of sleep quality (t = −5.37, p < 0.001) was found to have an inverse effect on PMS, while menstrual pain intensity during clinical practice (t = 9.69, p < 0.001), neuroticism (t = 3.70, p < 0.001) and stress (t = 4.50, p < 0.001) were found to have a positive effect on PMS. As a result of multiple regression analysis, menstrual pain intensity during clinical practice (β = 0.42), sleep quality (β = −0.23), stress (β = 0.21) and neuroticism (β = 0.17) were shown to affect PMS (Table 3).
In other words, when levels of menstrual pain intensity during clinical practice, stress, and neuroticism were higher and sleep quality was lower, PMS symptoms were higher.

Discussion
Attempts to evaluate PMS among female college students in the department of nursing are worthwhile, and we investigated the relationship between physiological, psychological, and situational factors based on TOUS. The results showed that psychophysiological factors, such as menstrual pain intensity during clinical practice, sleep quality, neuroticism, and stress were significant independent determinants of PMS in the studied population with combined explanatory power of 44%.
Studies have shown that PMS is a common symptom in menstrual disorders and has a relatively high proportion of prevalence. In this study, the mean age of participants was 22.14 ± 1.32 years, and their mean age at menarche was 12.48 ± 1.61 years, which was lower than in a previous study [44]. Those with a family history of PMS were significantly more likely to have severe PMS, consistent with previous research [60]. Approximately 70.0% of subjects were shown to have average volume of menstruation, while 17.9% was shown to have large volume of menstruation, and subjects with heavier bleeding had tendency to have statistically significant more severe PMS. In addition, between PMS and regularity of menstrual cycle had significant association. Also, more than 70% of the subjects were complained that over 4-point menstrual pain during usual day and clinical practice. These results were in alignment with previous research [60,61]. This was significantly higher than the proportion of middle school girls who reported moderate to severe pain in one recent study (59.9%) [62], but similar to the proportion of college students reporting this level of pain in another study (78.5%) [45].
Physiological factors as menstrual pain intensity during clinical practice, sleep quality were related to PMS based on the results of multivariable analysis, which is consistent with previous study [63]. The mean menstrual pain intensity of nursing students was 5.38/10 and 2.3 points higher than that of the perimenopausal women (43 to 53 years), while 0.84 points lower than that of the adolescent girls [64,65]. Menstrual pain is a subjectively perceived health condition, and the level of pain was shown to be higher among adolescents, college students, and postmenopausal women who had relatively high physical health. The mechanism of the relationship between menstrual pain and PMS is not yet fully understood, but it is likely that when the duration of exposure to previously unexperienced pain is shorter, a higher level of pain intensity is perceived. In this study, menstrual pain intensity during clinical practice was particularly identified as the major determinant affecting PMS, which can be suggested as meaning that the complex symptoms of PMS are highly related to pain. In nursing students in particular, research is needed to expose another unfamiliar environment due to the nature of nursing education; clinical practice is reported to be a stressful situation that causes high anxiety and tension, leading to difficulties in coping with stress [66,67]. Stressful situation elevates the level of cortisol, and stress has been shown to be higher during clinical practice than during typical days in nursing students. This high level of stress makes it easier to feel pain at a higher level, which has been found to be one of the factors that exacerbates PMS. Also, similar to the findings of an earlier study examining nursing students [68], sleep quality was also identified as having a statistically significant negative effect on PMS, with higher sleep quality being associated with lower PMS severity. This supports previous research that suggests that worse sleep quality can alter estrogen and progesterone concentrations, leading to PMS [40]. In another study, sleep quality was decreased in 71.6% of general university students and 89% of nursing students, and nursing students in particular had lower sleep quality than general university students due to stress caused by the heavy learning load involving theory, practice, and responsibility for patient care [68]. Therefore, intervention strategies to alleviate PMS through satisfied sleep needs are crucial for nursing students.
The results of regression analysis showed that neuroticism and stress were positively correlated with PMS, which corresponded with prior research [54,[69][70][71]. The more neurotic an individual is, the more likely they are to experience PMS. Neuroticism is the personality trait that refers to the tendency to be emotionally sensitive, moody, easily anxious, depressed, overly worried, and susceptible to negative emotions [54,69,70]. Higher levels of neuroticism are associated with more negative moods in daily life and more life stress [70], which may lead to more negative responses to premenstrual physical symptoms and attitudes toward menstruation, higher perceived depression and stress, and more PMS. In addition, the higher stress, the more PMS were experienced. This is supported by several previous studies which have reported that increasing or chronic stress can lead to hormonal imbalance and contribute to PMS [6,20,46,72,73]. Furthermore, a similar study reported that stress was the most important predictor of PMS in female college students [74], and another study reported that women were more vulnerable to stress, indicating that they suffered more severe PMS, such as recurrent physical symptoms and difficulty concentrating before menstruation. Therefore, daily stress can be considered as a factor that aggravates the severity of PMS in female college students, and practical intervention programs should be developed to improve the ability to cope with life stress appropriately. In terms of stress, we found that nursing students in their fourth year, when the burden of clinical practice, employment, and national examinations was increased, had a higher level of stress than in the first and second years (before clinical practice begins), which was also higher than that of general university students [20,75,76]. These findings suggest that nursing students' stress related to clinical practice was mostly above average and can have a negative impact on their health. As a result, intervention strategies are needed to help nursing students alleviate PMS through proper stress control. Volume  Although attitudes toward menstruation were positively correlated with PMS, it was not identified as a significant determinant of PMS. Previous studies have shown that negative attitudes toward menstruation lead to excessive perception of premenstrual bodily changes, which exacerbate the physical, cognitive, behavioral and social symptoms of PMS, supporting the present findings [37,51,68,77]. In addition, high-stress environments result in negative attitudes toward menstruation, and female college students with negative attitudes toward menstruation had a 6.25-fold increased risk of clustering into the premenstrual dysphoric disorder group compared to female college students with normal and mild PMS [78], suggesting that PMS and menstrual attitudes are closely related. The more women experience pain, negative emotions, and daily restrictions associated with each recurrent menstrual period, the more negative their attitudes toward menstruation become, which in turn exacerbates PMS.
Sex role stereotypes were not significantly associated with PMS and were not an influencing factor. In Korea, there was less interest in women's unique experiences, such as menstruation, due to the traditional culture of masculinity and patriarchy. Studies in Western cultures, however, have shown that menstruation has been considered an important indicator of women's health throughout Western history, and various studies have been conducted on the phenomenon [51,[79][80][81][82]. In particular, these studies suggested that PMS is more likely to be experienced in the context of low acceptance of women's roles related to sex role stereotypes or negative attitudes towards menstruation [51,80,83]. In addition, the distinction between sex roles has been blurred and sex role stereotypes are disappearing in the current society. Thus, sex role may not be a situational factor that has a significant effect on PMS.
However, there are some limitations of this study. First, this was a cross-sectional study performed only in a single location and restricted population as nursing students, which may have reduced the representativeness of the sample. Thus, generalizing the findings of this study to all college students in Korea should be approached with caution. Second, the inherent potential biases of a self-reported questionnaire include inevitable recall bias. Third, the design of this study as a cross-sectional study may be inadequate for establishing a clear causal relationship. Despite these limitations, the study specifically measured the extent of PMS experienced by female nursing students and investigated the predictors of PMS, including four major factors (menstrual pain intensity during clinical practice, sleep quality, neuroticism and stress).
As nursing students are future healthcare providers, they may benefit from under-standing the physiological and psychological factors of PMS and acquiring accurate knowledge to form a positive coping strategies for PMS it rather than focusing on the negative aspects of menstruation.

Conclusions
This study was designed to investigate the correlates of premenstrual syndrome between the variables suggested by the TOUS (menstrual pain intensity during clinical practice, sleep quality, attitudes towards menstruation, sex role stereotypes, neuroticism and stress) among female university students enrolled in the Department of Nursing, and identified menstrual pain intensity during clinical practice, sleep quality, neuroticism and stress as influencing factors of PMS. These findings suggest that healthcare providers could alleviate PMS through physiopsychological interventions such as relieving men-strual pain, enhancing sleep quality, converting the personal trait of neuroticism and controlling stress levels. By doing so, this study on the correlates of PMS can contribute the crucial evidence with the management of and interventions for PMS in nursing students with PMS.
Funding: This research received no external funding.Institutional Review Board Statement: All experimental procedures were approved. Ethical clearance was approved by the Ethics Committee of Chonnam National University, Gwang-Ju (protocol No. 1040198-220120-HR-005-01) under the Declaration of Helsinki. This study was conducted in accordance with ethical standards and na-tional and international laws. All participants signed an informed consent form after receiving instructions regarding the possible risks and benefits and were assured of their privacy, confidentiality and anonymity. The participants were free to stop participating at any time in the experiment without giving a reason for their decision.

Informed Consent Statement:
We obtained informed consent from all participants enrolled in the study. Written informed consent was obtained from the participant(s) to publish this paper. Data Availability Statement: Data supporting the study results can be provided by request sent to the corresponding author's email.

Conflicts of Interest:
The author declares no conflicts of interest.