Binge eating disorder and depressive symptoms among females of child-bearing age: the Korea Nurses' Health Study

The target population was 7,267 female Registered Nurses (RNs) aged 20 to 45 years, who were in their childbearing years. Nurses with either psychiatric comorbidities or history of using psychiatric drugs were excluded. These nurses have either been medically diagnosed with depression or have taken any psychiatric drugs including Selective Serotonin Reuptake Inhibitator (SSIR) type antidepressants, other antidepressants, or Minor tranquilizers. The data was collected from July of 2013 to September of 2015 via online survey through voluntary participation. Participants had completed the first and second surveys as part of the Korea Nurses’ Health Study [12]. The Korea Nurses’ Health Study is a grand-scale research that the Korean Nurses Association and Korea Centers of Disease Control and Prevention jointly conducted using a similar survey protocol and format of the Nurses’ Health Study 3 (NHS 3) [13] of the United States. The first baseline study was conducted for 3 years, from March 2013 to December 2015. The KNHS consisted of six modules including two special modules asking about one’s early stages of pregnancy and postpartum experiences with consent in case the participants got pregnant or gave birth. This study utilized the data from the first phase of the KNHS. The second phase of the KNHS has been underway since 2016 and is scheduled to be completed in 2018. The first survey, which served as baseline data, was closed while the other surveys are still open.

All the survey questionnaires used in this study were translated and back-translated into Korean, modified, and redeemed to suit the Korean context after discussions with an advisory committee of multidisciplinary experts. In this research, we measured whether one has binge eating disorder with 10 questions of self-report measures using the diagnostic criteria (definition of binge eating episode) of Diagnostic and Statistical Manual of Mental Disorders, fifth edition (DSM-5) [1]. The last question was a negative-form question related to inappropriate compensatory behaviors and was converted into positive-form for this research. For each question, participants could answer with either “yes” or “no,” and the BED criteria of DSM-5 was met if she answered “yes” for both of the questions: 1) did you eat an amount of food that is definitely larger than most people would eat in a similar period of time under similar circumstances in a discrete period of time? and 2) did you feel a sense of lack of control over eating? Once a participant responded “yes” to both of these questions, then five additional questionnaires were asked. These questions were: a) did you eat much more rapidly than normal? b) did you eat until feeling uncomfortably full?, c) did you eat large amounts of food when not feeling physically hungry?, d) did you eat alone because of feeling embarrassed by how much you eat?, and e) did you feel disgusted with yourself, depressed, or very guilty after overeating? Participants who answered “yes” to at least 3 of the above 5 questions and “yes” to ‘did you feel often upset both during and after the binge eating?’ and ‘did you experience binge eating episodes at least once a week over the past 3 months?’ were categorized as experiencing binge eating disorder. Additionally, we excluded participants who answered “yes” to a question regarding inappropriate compensatory behaviors like laxatives, diuretics, and self-induced vomiting.

We measured the degree of self-reported depressive symptoms using the Patient Health Questionnaire (PHQ-9), which is a self-report instrument with 9 questions. The possible score range is 0–27, divided into 0–4, 5–9, 10–14, 15–19, and above 20, representing minimal, mild, moderate, moderately severe, and severe depressive symptoms respectively. The higher the score, the severer one’s depressive symptom [14]. The Cronbach’s alpha value in our study was 0.90, and that of the original research by Arroll et al. was 0.87 [15].

In order to find the association between BED and depressive symptoms, this research considered potential confounders through literature reviews. Confounders included a) age [11], level of education [16], annual income [11], and marital status [16] as socio-demographic factors, b) alcohol consumption [17], body mass index (BMI) [11], self-rated health [18], sleep [19], stress [20] as health-behavior factors and c) shift work as a work-related factor [11].

Stress, a control variable in this study, was measured using the Perceived Stress Scale-4 (PSS-4) [21], which consists of 4 questions regarding the frequency of emotions and thoughts during the last 30 days. The possible score range is 0–16; the higher the score, the greater the degree of stress. For sleep, another control variable, we used the Jenkins Sleep Questionnaire [22], which consists of 4 questions about the amount of sleep during the last 30 days, with possible score range of 0–20; a high score implies a sleep disorder. We measured self-rated health using one question asking if a participant think of herself as healthy in three categories, which are good, fair, and poor.

Out of the 7,267 nurses, 6.9% (n = 502) nurses had symptoms for BED. Distributions of key variables with and without BED as well as the differences between the two groups by key variables are presented in Table 1. According to the descriptive analysis, 81.3% of nurses displayed some levels of depressive symptoms (from mild to severe), and majority of them were younger than 30 years old (42.9%) or in the ages between 30 and 39 (45.5%). Majority of the study participants had completed either a 3-year college (51.7%) or 4-year university (42.9%), had earned either annual income in ranges of $30,000–39,999 (42.0%) or $40,000–49.999 (37.8%), and were single (76.1%). With regard to health related characteristics and shift work, majority of the nurses consumed alcohol occasionally (70.2%), had a normal BMI (61.8%), rated their health as fair (50.7%), expressed some levels of sleep problems (14.9% with the least sleep problems) and stress (26.1% with the lowest level of stress), and worked shifts (77.9%).

Multicollinearity was examined with no variance inflation factor (VIF) values over 10 [23]. Spearman’s correlation analyses showed that all variables showed moderate correlation below 0.6 (Table 2), which justified proceeding to conduct multivariable ordinal logistic regression [24]. Table 3 shows the results of the multivariable ordinal logistic regression analysis. In model 2, socio-demographic characteristics, such as age, level of education, annual income, and marital status, were controlled; health behaviors including alcohol consumption, BMI, self-rated health, sleep, and stress were included as control variables in Model 3. In the final model (Model 4), shift work was also included. Out of the control variables, age (40 years old and older), alcohol consumption (frequent drinkers), self-rated health, sleep problems, and stress were associated with depressive symptoms in the final model. Overall, after adjusting for confounders, nurses with binge eating disorders had 1.80 times the risk of experiencing a greater severity of self-reported depressive symptoms when compared to those without BED. Table 3 shows that as we add more confounders, both the Nagelkerke R-square values and the risk of nurses with binge eating disorders to experience a greater severity of depressive symptoms increase.