Participants and procedures

Data are from the 2001–2003 Collaborative Psychiatric Epidemiologic Surveys (CPES). The CPES is a set of three nationally-representative cross-sectional householdsurveys (The National Comorbidity Survey Replication (NCS-R), The National Survey of American Life (NSAL), and the National Latino and Asian American Study (NLAAS)) conducted to estimate the prevalence of psychopathology in the adult (age ≥ 18) population and to assess treatment patterns, with specific attention to racial/ethnic minorities [29,30,31]. Additional details about the CPES study design and sampling approach are described elsewhere [29,30,31]. The CPES data used for this analysis are available through the Inter-University Consortium for Political and Social Research: https://www.icpsr.umich.edu/icpsrweb/ICPSR/studies/20240.

This analysis was limited to individuals with complete data on BMI, BED, and suicidality (N = 14,497), which represents 72% of the total CPES sample. Those excluded from the analytic sample (N = 5516) were older, more likely to be male, more likely to be white, and had more education than those included; poverty-to-income ratio and BMI were similar (Additional file 1: Table S1). Most of those excluded were from the NCS-R, which by design only asked the complete set of BED items on a random subset of 2980 participants [32].

Measures

Exposure ascertainment

Lifetime history of BED (with hierarchy) was assessed using the World Health Organization’s (WHO) expanded version of the Composite International Diagnostic Interview (CIDI) for DSM-IV [2]. BED case status was indicated if respondents endorsed binge eating, defined as (a) recurrent episodes of eating, in a discrete (2-h) period, an amount of food that is definitely larger than most people would eat during a similar period of time accompanied by (b) a sense of lack of control over eating, and (c) three or more cognitive or affective feelings during the binge (i.e., eating rapidly, eating until uncomfortably full, eating when not feeling hungry, eating alone due to feeling embarrassed by the amount of food consumed, feeling disgusted with oneself, depressed, or very guilty after overeating, or marked distress). These binge episodes had to occur at least 2 days a week for 6 months, and the binging could not be associated with use of compensatory behaviors (i.e. purging, fasting, excessive exercise), consistent with DSM-IV criteria. Individuals with bulimia or anorexia nervosa were excluded from the BED hierarchy diagnosis. Lifetime history of any binge episode was defined as criteria a and b only, and with duration of two days/week for at least three months. BMI (kg/m2) was calculated from self-reported weight and height. It was treated as a continuous variable (centered on the sample mean: 27 kg/m2). As a sensitivity analysis we also evaluated BMI as a categorical variable using WHO categories (< 18.5, 18.5 to < 25 (reference group), 25.0 to < 30 and ≥ 30).

Outcome ascertainment

Lifetime suicidality was indexed by a CIDI module that assessed suicidal ideation / intent (i.e., “seriously thought about committing suicide” or “made a plan for committing suicide”) and suicide attempt, including the age of onset and recency of suicidality. For this analysis two dichotomous variables were created: for the main analysis we examined lifetime (ever/never) suicidality (ideation and/or intent), and for the sensitivity analyses we examined past-year suicidality; for the sensitivity analysis individuals who endorsed suicidality only prior to the past year were excluded (n = 2030).

We also conducted a post-hoc analysis examining lifetime history of attempting suicide as an outcome. Because of the skip-pattern of the CIDI, history of suicide attempt was only asked of those who endorsed suicidality; however, for this analysis we created a new variable indexing lifetime history of suicide attempt by recoding respondents who had not seriously considered suicide as a “no” for history of attempting suicide, as prior studies of this outcome have done. Due to some missing data on the attempt question, this analysis was limited to 13,079 respondents.

Covariates

All covariates were assessed by self-report and included age (in years, mean-centered at 43.4), race/ethnicity, gender, marital status, education and Income-to-needs ratio. Race/ethnicity was categorized as Asian, Hispanic, Black, and Non-Latino White, with Black as the reference group. Education was categorized as high school education or less (reference group) vs. more than high school. Marital status was categorized as currently married (reference group), formerly married, and never married. Income-to-needs ratio is a measure of socioeconomic status calculated by dividing household income by the Census poverty threshold for that household size, [33] categorized into quintiles. We also considered smoking and medical comorbidities as confounders. Lifetime history of medical conditions (including arthritis, chronic pain, headaches, stroke, heart disease, hypertension, chronic lung disease, diabetes, and cancer) were summed and was categorized as zero (reference group), one, two, and three or more conditions for analysis. Smoking status was available on a subset of participants (N = 9648) and was categorized as current, former, and never smoker (reference group).

Analytic approach

Initial bivariate relationships between BED, suicidality and covariates were assessed using Scott-Rao chi-square tests. To address the first hypothesis, weighted logistic regression models were fit to test the association between binge eating behavior and lifetime history of suicidality as the dependent variable. Three nested models were fit for both BED and binge episodes: Model 1 was unadjusted, Model 2 was adjusted for BMI. Model 3 was adjusted for BMI and sociodemographic characteristics, and Model 4 was additionally adjusted for number of chronic health conditions; we also fit models additionally adjusted for smoking status as a sensitivity analysis. Weighted logistic regression models were fit to assess the relationship between BMI and suicidality using a similar nested model approach. To test the second hypothesis, we evaluated whether a quadratic term on BMI improved model fit, indicating a curvilinear relationship with suicidality. To test the third hypothesis, logistic regression models were fit that included interaction terms between BED (and binge eating) and BMI. To evaluate whether these relationships were similar for men and women these models were then fit within strata of sex. As a sensitivity analysis, all models were refit to examine the relationship between BED, binge eating, and BMI with past-year suicidality. Finally, we conducted two post-hoc sensitivity analyses: first, we refit all models examining binge eating as the exposure while excluding the 271 cases of BED from the analysis; and second, we refit all models to examine the outcome of lifetime history of suicide attempt rather than suicidality.

Goodness-of-fit was assessed using the Wald test. All analyses were conducted using STATA/IC 11.2 survey procedures to account for the complex sampling design and all p-values refer to two-tailed tests.