Introduction
Approximately 50% of individuals with an eating disorder abuse or are dependent on alcohol or illicit substances compared with approximately 9% of the general population (Holderness et al. Reference Holderness, Brooks-Gunn and Warren1994; The National Center on Addiction and Substance Abuse at Columbia University, 2003). Of individuals with a substance-use disorder, more than 35% report some form of an eating disorder (The National Center on Addiction and Substance Abuse at Columbia University, 2003) compared with lifetime prevalence estimates of approximately 5% for women in the United States (Hudson et al. Reference Hudson, Hiripi, Pope and Kessler2007). While it has been established that the co-occurrence between eating disorders and substance use exists, prevalence varies markedly across studies (Holderness et al. Reference Holderness, Brooks-Gunn and Warren1994), which is partially attributable to study design and methodology. Most studies have not compared substance use across the various subtypes of eating disorders often due to small sample sizes, particularly for anorexia nervosa (AN). Additionally, most research on eating disorders and substance use has focused on alcohol, tobacco or broadly defined illicit drug use. Finally, few studies include a non-eating disorder control group, which is necessary in order to make meaningful comparisons between those with and without an eating disorder.
Substances associated with eating disorders include alcohol, tobacco, cannabis, cocaine, heroin and amphetamines (The National Center on Addiction and Substance Abuse at Columbia University, 2003; Bulik et al. Reference Bulik, Klump, Thornton, Kaplan, Devlin, Fichter, Halmi, Strober, Woodside, Crow, Mitchell, Rotondo, Mauri, Cassano, Keel, Berrettini and Kaye2004a, Reference Bulik, Slof, Sullivan, Rounsaville and Kranzlerb; Blinder et al. Reference Blinder, Cumella and Sanathara2006; Root et al. Reference Root, Pinheiro, Thornton, Strober, Fernandez-Aranda, Brandt, Crawford, Fichter, Halmi, Johnson, Kaplan, Klump, La Via, Mitchell, Woodside, Rotondo, Berrettini, Kaye and Bulik2009) and patterns of association vary across eating disorder subtypes. Those who endorse binge eating, including those with bulimia nervosa (BN) and a lifetime history of both AN and BN (ANBN), tend to exhibit higher levels of licit and illicit drug use (Herzog et al. Reference Herzog, Keller, Sacks, Yeh and Lavori1992; Wiederman & Pryor, Reference Wiederman and Pryor1996; Ross & Ivis, Reference Ross and Ivis1999; The National Center on Addiction and Substance Abuse at Columbia University, 2003; Hudson et al. Reference Hudson, Hiripi, Pope and Kessler2007; Root et al. Reference Root, Pinheiro, Thornton, Strober, Fernandez-Aranda, Brandt, Crawford, Fichter, Halmi, Johnson, Kaplan, Klump, La Via, Mitchell, Woodside, Rotondo, Berrettini, Kaye and Bulik2009), including use of diet pills (Reba-Harrelson et al. Reference Reba-Harrelson, Von Holle, Thornton, Klump, Berrettini, Brandt, Crawford, Crow, Fichter, Goldman, Halmi, Johnson, Kaplan, Keel, LaVia, Mitchell, Plotnicov, Rotondo, Strober, Treasure, Woodside, Kaye and Bulik2008), than individuals with AN or no eating disorder. For example, females with purging symptoms are more likely to report frequent alcohol use and binge drinking than females without eating disorder symptoms (Adams & Araas, Reference Adams and Araas2006). Conversely, females who report alcohol problems and/or binge drinking were more likely to report recent eating disorder symptoms (Wiederman & Pryor, Reference Wiederman and Pryor1996; Field et al. Reference Field, Austin, Frazier, Gillman, Camargo and Colditz2002; The National Center on Addiction and Substance Abuse at Columbia University, 2003). Further, research suggests that those with BN and those with ANBN have a higher prevalence of lifetime alcohol abuse and/or dependence than individuals with AN (Bulik et al. Reference Bulik, Klump, Thornton, Kaplan, Devlin, Fichter, Halmi, Strober, Woodside, Crow, Mitchell, Rotondo, Mauri, Cassano, Keel, Berrettini and Kaye2004a). However, of those with AN, there is higher prevalence of alcohol abuse and/or dependence in the binge and/or purge subtype of AN (ANBP) than restricting AN (RAN; Blinder et al. Reference Blinder, Cumella and Sanathara2006). Finally, those with BN are also more likely to report illicit drug use, particularly amphetamines, barbiturates, marijuana, tranquilizers and cocaine (The National Center on Addiction and Substance Abuse at Columbia University, 2003), with the heaviest illicit drug use found among females who binge and purge.
Tobacco use is also more common among individuals with eating disorders compared with those without (Anzengruber et al. Reference Anzengruber, Klump, Thornton, Brandt, Crawford, Fichter, Halmi, Johnson, Kaplan, LaVia, Mitchell, Strober, Woodside, Rotondo, Berrettini, Kaye and Bulik2006) and, as with alcohol, patterns of use vary across eating disorder category and subtype. Anzengruber et al. (Reference Anzengruber, Klump, Thornton, Brandt, Crawford, Fichter, Halmi, Johnson, Kaplan, LaVia, Mitchell, Strober, Woodside, Rotondo, Berrettini, Kaye and Bulik2006) found that women with BN or ANBP had a higher prevalence of cigarette use compared with women with RAN, who had a similar prevalence as women without an eating disorder. Although cigarettes are the most studied form of tobacco, cigarette use in Sweden appears to be declining while tobacco use remains constant (Wersall & Eklund, Reference Wersall and Eklund1998; Furberg et al. Reference Furberg, Lichtenstein, Pedersen, Bulik and Sullivan2006). This is partly attributable to the increased use of snus, a form of oral smokeless tobacco that has been popular in Sweden for decades, particularly among men (Furberg et al. Reference Furberg, Lichtenstein, Pedersen, Bulik and Sullivan2006), and has recently been test marketed in the United States. Snus is a less harmful and more discreet form of tobacco (Lewin et al. Reference Lewin, Norell, Johansson, Gustavsson, Wennerberg, Biorklund and Rutqvist1998; Lagergren et al. Reference Lagergren, Bergstrom, Lindgren and Nyren2000; Osterdahl et al. Reference Osterdahl, Jansson and Paccou2004) and thus may be a more appealing tobacco product. However, to date, no published data have been reported on snus use among those with an eating disorder.
Most research on substance use and eating disorders has focused on either BN or broadly defined AN with few studies comparing substance use across subtypes of AN. Root et al. (Reference Root, Pinheiro, Thornton, Strober, Fernandez-Aranda, Brandt, Crawford, Fichter, Halmi, Johnson, Kaplan, Klump, La Via, Mitchell, Woodside, Rotondo, Berrettini, Kaye and Bulik2009) examined substance use across several AN subtypes and reported differences in prevalence of substance-use disorder across AN subtypes, with more in the ANBN group reporting a substance-use disorder than those in the RAN and purging AN groups, supporting previous research (Eddy et al. Reference Eddy, Keel, Dorer, Delinsky, Franko and Herzog2002). Root et al. (Reference Root, Pinheiro, Thornton, Strober, Fernandez-Aranda, Brandt, Crawford, Fichter, Halmi, Johnson, Kaplan, Klump, La Via, Mitchell, Woodside, Rotondo, Berrettini, Kaye and Bulik2009) also report that cannabis was the most frequently used substance by women with AN, including the RAN group, and that individuals who purged were more likely to report substance use than those who did not purge. Although informative, this sample was collected for a study of the genetics of eating disorders which recruited male and female probands affected with AN. The present study explores these issues in depth in a population-based sample.
The purpose of this study was to extend previous research by examining the prevalence of substance-use behaviors across eating disorder groups relative to individuals with no history of eating disorders in a large population-based female sample. Specifically, we: (1) compared the prevalence of substance use across four eating disorder groups relative to a non-eating disorder referent; (2) determined whether substance use, and specifically, which substances, are more common in those with ANBP compared with RAN; (3) investigated the prevalence of snus use across eating disorder groups; and (4) conducted pairwise comparisons for each substance across eating disorder groups to determine which groups report significantly more substance use and to also report effect sizes for significant comparisons. Our approach focuses on lifetime history for both eating disorders and substance use. Lifetime use models are a necessary first step in the advancement to more complex models assessing casual mechanisms (Kendler & Prescott, Reference Kendler and Prescott1999; Eaves et al. Reference Eaves, Silberg, Foley, Bulik, Maes, Erkanli, Angold, Costello and Worthman2004). For example, the ultimate liability to alcohol dependence in an individual who has never been exposed to alcohol is unknown. Thus, lifetime use is an important variable for any substance because it is prerequisite to developing abuse or dependence.
Method
Participants
Participants were from the Screening Twin Adults: Genes and Environment (STAGE) cohort of the Swedish Twin Registry (STR; Lichtenstein et al. Reference Lichtenstein, Sullivan, Cnattingius, Gatz, Johansson, Carlstrom, Bjork, Svartengren, Wolk, Klareskog, de Faire, Schalling, Palmgren and Pedersen2006), a large population-based prospective sample of Swedish twins born between 1959 and 1985 (Lichtenstein et al. Reference Lichtenstein, Sullivan, Cnattingius, Gatz, Johansson, Carlstrom, Bjork, Svartengren, Wolk, Klareskog, de Faire, Schalling, Palmgren and Pedersen2006). Using web-based questionnaires (or computer-assisted telephone interviews for those preferring this method), data were collected on most common complex diseases including information on eating disorders and substance use. Kappa values were calculated for several components and were based on 100 respondents who were first tested using the web-based questionnaire and then retested 2–5 months later using the computer-assisted telephone interview for the purpose of assessing test–retest reliability across the two methods. Kappa for the eating disorder section was 0.76 and for the substance-use section was 0.66, suggesting agreement between the web-based questionnaire and the telephone interview. The current study consisted of a total of 13 297 female participants; males were not included given the low prevalence of eating disorders.
Measures
Eating disorder diagnosis
Lifetime history of broadly defined eating disorders was assessed using an expanded, online Structured Clinical Interview for the Diagnostic and Statistical Manual, 4th edition (DSM-IV) (SCID)-based instrument designed to collect detailed information about course and severity of eating disorders. Due to low prevalence using narrow definitions, we focused on broadly defined eating disorder groups.
Table 1 presents criteria used to define eating disorder groups. For the primary analyses, participants were classified into one of five groups based on lifetime history of eating disorders: (1) no eating disorder; (2) AN; (3) BN; (4) ANBN; and (5) binge eating disorder (BED). For secondary analyses, the AN group was subdivided into RAN and ANBP.
Table 1. Criteria used for eating disorder diagnosisFootnote a
BMI, Body mass index.
a Based on DSM-IV criteria.
Substance use
Eighteen substance-use items from the SCID were included. Information on abuse/dependence was available only for alcohol. Thus, all items were based on use (not abuse or dependence) with the exception of alcohol abuse/dependence which required the DSM-IV criteria for either abuse or dependence (APA, 2000). Binge drinking was defined as either four or more bottles of beer, four or more glasses of wine (>600 ml), or three or more shots of liquor (>180 ml) at one time. Occasional smoker was defined as smoking less than one cigarette per day on average but more than just having tried a cigarette and includes those who report only smoking on weekends. Regular smoking was defined as ever having smoked at least once per day. Occasional snus was defined as more than just trying snus but less than once per day on average. Regular snus was defined as using snus at least once per day. Diet pills-weekly was defined as over-the-counter and prescription diet pill use at least once per week. The remaining substance-use items – cannabis, hallucinogens, opioids, sedatives, and stimulants – were categorized based on two criteria: (1) lifetime use, and (2) used more than 10 times per month. Two variables for each substance were created (e.g. cannabis 10 times per month; cannabis-ever). Due to low prevalence, diet pills-ever and hallucinogens 10 times per month were dropped from the analyses. Polysubstance 10 times per month was defined as having used at least two illicit substances at least 10 times per month. Polysubstance-ever was defined as ever having tried at least two illicit substances.
Statistical analyses
Prevalence was calculated for the eating disorder groups and the referent across all substance-use measures. Logistic regression analyses were conducted using generalized estimating equations (GEE) with proc genmod (SAS version 9.1; SAS Institute Inc., Cary, NC, USA) to test for statistically significant differences in substance use across eating disorder groups. GEE allows for the correlated nature of the twin data to be controlled. Comparisons for each substance across pairs of eating disorders groups (e.g. AN, BN) were conducted to determine which eating disorder groups reported significantly more substance use and to report their associated effect sizes (i.e. odds ratios). In order to assess differences in substance use within the AN group, secondary logistic regression analyses were conducted to compare the RAN and ANBP subgroups. Given that there were 18 tests (one for each substance-use variable), p values were adjusted using the method of false discovery rate (FDR; Benjamini & Hochberg, Reference Benjamini and Hochberg1995), which controls for the expected proportion of type I errors (i.e. rejecting the null hypothesis when it is true). It is the expected proportion of false positives (type I) among all rejected hypotheses (type I and type II) at the desired significance level. For example, in our study an FDR cutoff of 0.05 was selected, implying that we allowed one expected false positive out of 20. All analyses were performed using sas version 9.1 (SAS Institute Inc.).
Results
Of the sample, 94% reported no history of an eating disorder, 3% reported AN (RAN, n=197; ANBP, n=181), 2% BN, 1% ANBN and <1% BED (Table 2).
Table 2. Demographic characteristics across the four eating disorder groups and the no-eating disorder group
Values are given as mean (standard deviation).
ED, Eating disorder; AN, anorexia nervosa; BN, bulimia nervosa; ANBN, lifetime history of AN and BN; BED, binge eating disorder; BMI, body mass index.
Demographics
Table 2 presents demographic information across the eating disorder groups and the referent group. Participants ranged in age from 20 to 47 years with a mean age of 34 years (s.d.=7.66). The mean for highest lifetime adult body mass index (BMI) was greatest among the BED group and the mean for lowest lifetime adult BMI was lowest among the ANBN group.
Prevalence of substance use across eating disorder groups
Table 3 presents prevalence estimates of substance use across the groups and provides odds ratios for statistically significant pairwise comparisons across eating disorder subtypes. Due to space limitations, we only present the statistically significant pairwise comparisons; however, a complete list of all 130 pairwise comparisons can be found in the Supplementary material (available online).
Table 3. Prevalence of substance use items across eating disorder groups and odds ratios for statistically significant pairwise comparisons
ED, Eating disorder; AN, anorexia nervosa; BN, bulimia nervosa; ANBN, lifetime history of AN and BN; BED, binge eating disorder; CI, confidence interval.
Asterisks in the ‘Substance-use item’ column represent omnibus statistical significance across all groups.
a The BED group was removed from the analysis due to an empty cell.
* p<0.05, ** p<0.01.
Overall, statistically significant differences for prevalence across groups were found for alcohol abuse/dependence, diet pills-weekly, cannabis 10 times per month, cannabis-ever, hallucinogens-ever, opioids 10 times per month, opioids-ever, sedatives 10 times per month, sedatives-ever, stimulants 10 times per month, stimulants-ever, polysubstance 10 times per month and polysubstance-ever. No statistically significant differences across groups were found for binge drinking, occasional smoking, regular smoking, occasional snus and regular snus.
Alcohol
The prevalence of alcohol abuse/dependence differed across groups with the AN, BN and ANBN groups more likely to have had alcohol abuse/dependence relative to the referent. Across eating disorder groups (not relative to the referent), the BN and ANBN groups were more likely to have had alcohol abuse/dependence relative to the AN group. No statistically significant group differences emerged for the prevalence of binge drinking.
Tobacco
No statistically significant group difference emerged for regular smoking, occasional smoking, occasional snus or regular snus.
Diet pills
A statistically significant difference across groups was found for diet pills-weekly. The AN, BN and ANBN groups were more likely to use diet pills-weekly relative to the referent. Across eating disorder groups (not relative to the referent), (1) the ANBN group was more likely to use diet pills-weekly relative to the AN, BN and BED groups, and (2) the BN group was more likely to use diet pills-weekly relative to the AN and BED groups.
Illicit drugs
Cannabis
Statistically significant group differences were found for cannabis 10 times per month and cannabis-ever. Individuals in the AN and BN groups were more likely to use cannabis 10 times per month relative to the referent. Those in the AN, BN, ANBN and BED groups were more likely to use cannabis-ever relative to the referent.
Hallucinogens
Statistically significant group differences emerged for hallucinogens-ever, with the AN group more likely to use hallucinogens-ever relative to the referent.
Opioids
There was a statistically significantly difference across groups for opioids 10 times per month and opioids-ever. Individuals in the AN group were more likely to use opioids 10 times per month relative to the referent and the AN and BN groups were more likely to use opioids-ever relative to the referent.
Sedatives
Statistically significantly differences across groups were found for sedatives 10 times per month and sedatives-ever. The AN and BN groups were more likely to use sedatives 10 times per month relative to the referent, and the AN, BN, ANBN and BED groups were more likely to use sedatives-ever relative to the referent.
Stimulants
Across groups, statistically significant differences emerged for stimulants 10 times per month and stimulants-ever. The AN group was more likely to use stimulants 10 times per month relative to the referent. Those in the AN and BN groups were more likely to use stimulants-ever compared with the referent.
Polysubstance use
Statistically significant differences across groups were found for polysubstance 10 times per month and polysubstance-ever. The AN group was more likely to engage in polysubstance 10 times per month relative to the referent, and the AN, BN and ANBN groups were more likely to engage in polysubstance-ever relative to the referent.
Secondary analyses – substance use for RAN and ANBP
Prevalence was statistically significantly higher in the ANBP group compared with the RAN group for alcohol abuse/dependence (15% v. 9%, p<0.05), diet pills-weekly (35% v. 9%, p<0.01), stimulants-ever (12% v. 5%, p<0.01) and polysubstance-ever (24% v. 15%, p<0.01). The ANBP group was 1.93 times more likely than the RAN group to have alcohol abuse/dependence [χ2=4.08, p<0.043, 95% confidence interval (CI) 1.02–3.66], 5.76 times more likely to use diet pills-weekly (χ2=38.68, p<0.001, 95% CI 3.22–10.31), 2.86 times more likely to endorse stimulants-ever (χ2=6.87, p<0.009, 95% CI 1.28–6.38) and 1.74 times more likely to engage in polysubstance-ever (χ2=4.40, p<0.036, 95% CI 1.04–2.92). No statistically significant differences emerged for the remaining substances.
Discussion
This study represents the largest and most detailed exploration to date of a wide range of substance use in eating disorders in a population-based sample of Swedish women and presents novel epidemiological information on eating disorders and substance use. Three broad themes emerged from the analyses. First, consistent with previous research, the prevalence of substance use was higher in all eating disorder groups than the referent, indicating that substance use is not limited to any particular eating disorder presentation. Second, in contrast with previous studies (Anzengruber et al. Reference Anzengruber, Klump, Thornton, Brandt, Crawford, Fichter, Halmi, Johnson, Kaplan, LaVia, Mitchell, Strober, Woodside, Rotondo, Berrettini, Kaye and Bulik2006), tobacco use was not elevated in women with eating disorders relative to the referent. Third, the observation that women with AN report elevated substance-use behaviors challenges previously held beliefs that substance use is uncommon in women with AN (Wiederman & Pryor, Reference Wiederman and Pryor1996; Herzog et al. Reference Herzog, Franko, Dorer, Keel, Jackson and Manzo2006) and the finding that the RAN and ANBP subgroups differed on alcohol abuse/dependence, weekly diet pill use, stimulant use and polysubstance use adds to the literature examining substance use across varying presentations of AN.
Although no differences in prevalence emerged for binge drinking across the eating disorder groups relative to the referent, those in the AN, BN and ANBN groups were at increased risk for alcohol abuse/dependence relative to the referent. Observed prevalence in the BN and ANBN groups (approximately 22%) is consistent with previous research reporting prevalences of alcohol abuse or dependence of 25% for BN and 14% for ANBN (Bulik et al. Reference Bulik, Klump, Thornton, Kaplan, Devlin, Fichter, Halmi, Strober, Woodside, Crow, Mitchell, Rotondo, Mauri, Cassano, Keel, Berrettini and Kaye2004a). These findings could reflect the elevated relative risk of alcohol-use disorders among individuals with BN compared with AN (Kaye et al. Reference Kaye, Lilenfeld, Plotnikov, Merikangas, Nagy, Strober, Bulik, Moss and Greeno1996, Reference Kaye, Greeno, Moss, Fernstrom, Fernstrom, Lilenfeld, Weltzin and Mann1998). However, follow-up analyses revealing that those in the ANBP group were at elevated risk relative to the RAN group suggests that increased risk of alcohol abuse/dependence among those with bulimic symptoms or personality traits such as impulsivity (Bulik et al. Reference Bulik, Klump, Thornton, Kaplan, Devlin, Fichter, Halmi, Strober, Woodside, Crow, Mitchell, Rotondo, Mauri, Cassano, Keel, Berrettini and Kaye2004a) may also be particular risk factors for the binge/purge subtype of AN. One possible explanation is that substance use may reflect attempts to reduce negative affect (i.e. shame and guilt) associated with bingeing and purging (Stice & Shaw, Reference Stice and Shaw2002).
For the AN group, additional hypotheses exist. One possible explanation is that the reinforcing effect of alcohol and other drugs is enhanced by the food deprivation associated with the illness (Carroll & Meisch, Reference Carroll, Meisch, Thompson, Dews and Barrett1984; Bulik et al. Reference Bulik, Klump, Thornton, Kaplan, Devlin, Fichter, Halmi, Strober, Woodside, Crow, Mitchell, Rotondo, Mauri, Cassano, Keel, Berrettini and Kaye2004a). Additionally, alcohol (and drug) use may assist with the regulation of affect including prominent anxiety symptoms seen in those with AN (Godart et al. Reference Godart, Flament, Lecrubier and Jeammet2000; Bulik et al. Reference Bulik, Klump, Thornton, Kaplan, Devlin, Fichter, Halmi, Strober, Woodside, Crow, Mitchell, Rotondo, Mauri, Cassano, Keel, Berrettini and Kaye2004a). Overall, our finding of alcohol abuse/dependence in the AN group, particularly the ANBP group, extends a growing body of literature supporting substance-use behaviors among women with AN (von Ranson et al. Reference von Ranson, Iacono and McGue2002; Bulik et al. Reference Bulik, Klump, Thornton, Kaplan, Devlin, Fichter, Halmi, Strober, Woodside, Crow, Mitchell, Rotondo, Mauri, Cassano, Keel, Berrettini and Kaye2004a; Root et al. Reference Root, Pinheiro, Thornton, Strober, Fernandez-Aranda, Brandt, Crawford, Fichter, Halmi, Johnson, Kaplan, Klump, La Via, Mitchell, Woodside, Rotondo, Berrettini, Kaye and Bulik2009).
Regarding tobacco use, in contrast to previous research (Anzengruber et al. Reference Anzengruber, Klump, Thornton, Brandt, Crawford, Fichter, Halmi, Johnson, Kaplan, LaVia, Mitchell, Strober, Woodside, Rotondo, Berrettini, Kaye and Bulik2006), we did not find differences across the groups in cigarette use or snus use. It is possible that as snus use increases in the female population in Sweden, differences across groups may become detectable. It is also possible that tobacco products are being used among women both with and without an eating disorder as a weight-control measure, thus resulting in no differences between groups.
Consistent with previous research (Roerig et al. Reference Roerig, Mitchell, de Zwaan, Wonderlich, Kamran, Engbloom, Burgard and Lancaster2003; Reba-Harrelson et al. Reference Reba-Harrelson, Von Holle, Thornton, Klump, Berrettini, Brandt, Crawford, Crow, Fichter, Goldman, Halmi, Johnson, Kaplan, Keel, LaVia, Mitchell, Plotnicov, Rotondo, Strober, Treasure, Woodside, Kaye and Bulik2008), diet pill use was elevated in all eating disorder groups. The ANBN group was at particularly elevated risk (i.e. approximately 15 times more likely than the referent). Diet pill use has been associated with purging, novelty seeking, and several axis I and axis II disorders (Reba-Harrelson et al. Reference Reba-Harrelson, Von Holle, Thornton, Klump, Berrettini, Brandt, Crawford, Crow, Fichter, Goldman, Halmi, Johnson, Kaplan, Keel, LaVia, Mitchell, Plotnicov, Rotondo, Strober, Treasure, Woodside, Kaye and Bulik2008) which could explain why both the BN and ANBN groups, who tend to score higher on measures of novelty seeking (Cassin & von Ranson, Reference Cassin and von Ranson2005; Reba et al. Reference Reba, Thornton, Tozzi, Klump, Brandt, Crawford, Crow, Fichter, Halmi, Johnson, Kaplan, Keel, LaVia, Mitchell, Strober, Woodside, Rotondo, Berrettini, Kaye and Bulik2005; Fernandez-Aranda et al. Reference Fernandez-Aranda, Jimenez-Murcia, Alvarez-Moya, Granero, Vallejo and Bulik2006), reported more use than the AN group.
The very high diet pill use in women with ANBN and the greater risk for diet pill use in the ANBP group compared with the RAN group are consistent with a previous report (Reba-Harrelson et al. Reference Reba-Harrelson, Von Holle, Thornton, Klump, Berrettini, Brandt, Crawford, Crow, Fichter, Goldman, Halmi, Johnson, Kaplan, Keel, LaVia, Mitchell, Plotnicov, Rotondo, Strober, Treasure, Woodside, Kaye and Bulik2008) in which diet pill use was similar across purging BN, ANBN and ANBP. Because we were not able to assess temporal ordering of substance use and eating disorder symptoms, it is not known if the ANBN group used the diet pills during the time of their AN diagnosis, their BN diagnosis, or throughout both illnesses. We speculate that those with ANBN, who by definition have a history of low weight, may seek out more extreme weight loss measures than individuals with BN with no history of AN because they may continue to strive for previously achieved low weight.
Turning to the use of illicit drugs, all eating disorder groups reported greater use of illicit drugs and polysubstance use relative to the referent. Similar prevalences across eating disorder groups for cannabis-ever, hallucinogens-ever and stimulants-ever support previous research (Wiederman & Pryor, Reference Wiederman and Pryor1996; Root et al. Reference Root, Pinheiro, Thornton, Strober, Fernandez-Aranda, Brandt, Crawford, Fichter, Halmi, Johnson, Kaplan, Klump, La Via, Mitchell, Woodside, Rotondo, Berrettini, Kaye and Bulik2009). Additionally, the BN and ANBN groups had higher risk for several illicit substances including cannabis, opioids, sedatives and stimulants, which supports previous research (The National Center on Addiction and Substance Abuse at Columbia University, 2003; Herzog et al. Reference Herzog, Franko, Dorer, Keel, Jackson and Manzo2006; Hudson et al. Reference Hudson, Hiripi, Pope and Kessler2007), as well as for polysubstance-ever.
Unexpectedly, the AN group was at increased risk for all illicit drug use categories and polysubstance-ever relative to the referent, indicating that drug use is of concern across all eating disorder subtypes (von Ranson et al. Reference von Ranson, Iacono and McGue2002). Extending the AN findings further, AN subtype comparisons revealed that stimulants-ever was the only illicit substance that was more frequently reported in the ANBP group relative to the RAN group, adding to the literature suggesting that illicit drug use is not limited to those with binge eating or purging subtypes of AN. The attraction of stimulant use in the AN group might in part rest with their appetite-suppressant and increased metabolic effects (Hudson et al. Reference Hudson, Weiss, Pope, McElroy and Mirin1992; Wiederman & Pryor, Reference Wiederman and Pryor1996; Hsieh et al. Reference Hsieh, Yang, Chiou and Kuo2005) and the attraction of cannabis and sedatives for their sedating effects (Swinbourne & Touyz, Reference Swinbourne and Touyz2007).
One possible explanation for increased polysubstance use in those with eating disorders is the association between polysubstance use and impulsivity (Steiger & Bruce, Reference Steiger and Bruce2007) and novelty-seeking (Conway et al. Reference Conway, Kane, Ball, Poling and Rounsaville2003), which is also elevated in individuals with eating disorders, particularly BN. Because individuals with polysubstance use have high rates of psychiatric co-morbidity (Lynskey et al. Reference Lynskey, Agrawal, Bucholz, Nelson, Madden, Todorov, Grant, Martin and Heath2006) and often relapse after substance-abuse treatment (Marshall, Reference Marshall1994), replication and additional attention to polysubstance use with eating disorder populations is warranted.
Findings that illicit drug use is occurring across eating disorder groups support a study in which greater pathological eating behavior was associated with not just alcohol and tobacco but also cannabis use and other illicit substances (Ross & Ivis, Reference Ross and Ivis1999). It is possible that these findings can be explained given genetic research associating family history (Lachman, Reference Lachman2006) to both substance use and eating disorders (Slof-Op ‘t Landt et al. Reference Slof-Op 't Landt, van Furth, Meulenbelt, Slagboom, Bartels, Boomsma and Bulik2005; Pinheiro et al. Reference Pinheiro, Sullivan, Bacaltchuck, Prado-Lima and Bulik2006; Bulik et al. Reference Bulik, Sullivan, Tozzi, Furberg, Lichtenstein and Pedersen2006, Reference Bulik, Slof-Op 't Landt, van Furth and Sullivan2007). Genetics influence liability to substance-use disorder, with research suggesting that substance use among monozygotic twin pairs is two to four times greater compared with dizygotic twin pairs (Lachman, Reference Lachman2006). Heritability estimates for alcoholism are often 50% or greater, 40% to 70% for tobacco and 25% to 80% for other substances including illicit drugs (Prescott et al. Reference Prescott, Madden and Stallings2006). Regarding eating disorders, family studies have demonstrated that both AN and BN tend to be increased in relatives of affected probands compared with relatives of unaffected probands (Lilenfeld et al. Reference Lilenfeld, Kaye, Greeno, Merikangas, Plotnikov, Pollice, Rao, Strober, Bulik and Nagy1998; Pinheiro et al. Reference Pinheiro, Sullivan, Bacaltchuck, Prado-Lima and Bulik2006). Twin studies have reported heritability estimates between 33% and 84% for AN (Wade et al. Reference Wade, Bulik, Neale and Kendler2000; Slof-Op ‘t Landt et al. Reference Slof-Op 't Landt, van Furth, Meulenbelt, Slagboom, Bartels, Boomsma and Bulik2005; Bulik et al. Reference Bulik, Sullivan, Tozzi, Furberg, Lichtenstein and Pedersen2006, Reference Bulik, Slof-Op 't Landt, van Furth and Sullivan2007) and between 28% to 83% for BN (Bulik et al. Reference Bulik, Sullivan, Wade and Kendler2000), demonstrating considerable genetic effects for AN and BN. However, several lines of evidence suggest that eating disorders and substance use might not necessarily be influenced by shared genetic factors. Kendler et al. (Reference Kendler, Walters, Neale, Kessler, Heath and Eaves1995), in a twin study of six major psychiatric illnesses, did not find a strong genetic association between BN and alcoholism. Similarly, Lilenfeld et al. (Reference Lilenfeld, Kaye, Greeno, Merikangas, Plotnikov, Pollice, Rao, Strober, Bulik and Nagy1998) concluded that eating disorders and alcoholism were not co-transmitted in families. Lastly, Kaye et al. (Reference Kaye, Lilenfeld, Plotnikov, Merikangas, Nagy, Strober, Bulik, Moss and Greeno1996) reported that BN and substance-use disorders, including alcohol abuse and dependence, were transmitted independently. In contrast, one study has reported a moderate genetic correlation (r a=0.39) between broadly defined BN and drug-use disorders (Baker et al. Reference Baker, Mazzeo and Kendler2007). Additional work is required, including evaluations of both genetic and environmental factors and their interactions, in order to understand both the co-morbid profile and familial transmission of eating disorders and substance use.
Limitations
Limitations of our study must be considered. First, results cannot be generalized to other ancestry groups or to males. Second, because the study was not prospective, causal conclusions pertaining to the development of either eating disorders or substance-use behaviors cannot be discussed. Third, additional unexamined factors may have influenced the findings, including factors that may be associated with eating disorders and substance-use disorders. Of particular relevance is research indicating that depression/negative affect (Fernandez-Aranda et al. Reference Fernandez-Aranda, Pinheiro, Tozzi, Thornton, Fichter, Halmi, Kaplan, Klump, Strober, Woodside, Crow, Mitchell, Rotondo, Keel, Plotnicov, Berrettini, Kaye, Crawford, Johnson, Brandt, La Via and Bulik2007) and/or anxiety (Bulik et al. Reference Bulik, Klump, Thornton, Kaplan, Devlin, Fichter, Halmi, Strober, Woodside, Crow, Mitchell, Rotondo, Mauri, Cassano, Keel, Berrettini and Kaye2004a; Godart et al. Reference Godart, Perdereau, Curt, Rein, Lang, Venisse, Halfon, Bizouard, Loas, Corcos, Jeammet and Flament2006) are associated with the onset of both eating disorders and substance use. Fourth, one must consider whether any aspects of a twin population could limit generalizability of the observed prevalence of substance use and eating disorders to non-twin samples. By virtue of socializing together, twins may be more likely to be exposed to various substances and behaviors (e.g. one twin's exposure to cigarettes could increase the likelihood of the co-twin trying a cigarette). If this were the case, then we could expect prevalences in twins that are higher than the general population. That does not appear to be the case in these data as, for example, 11% of our sample was classified as regular smokers which is below the reported national prevalence of 20% in Swedish females aged 16–84 years (Strong & Bonita, Reference Strong and Bonita2003). Nonetheless, correlated exposure among twins and generalizability to non-twin samples is a potential weakness that must be considered when interpreting findings. Fifth, for polysubstance use, we only examined whether individuals were using more than two illicit substances either ever in their lifetime or at least 10 times per month; we did not examine which substances cluster together across individuals, nor did we include alcohol or tobacco use in these analyses. Future research would benefit from examining individuals’ substances of choice for polysubstance drug use in order to understand better differences in substance-use involvement across eating disorder groups. Last, the BED group is quite small in our sample (about 4%), which might be due in part to the much lower base rate of obesity in Sweden compared with the USA (Neovius et al. Reference Neovius, Janson and Rossner2006; Ogden et al. Reference Ogden, Carroll, Curtin, McDowell, Tabak and Flegal2006). As a result of the small sample, not all analyses could be conducted with the BED group. Thus, it is important to interpret the current findings with caution.
Conclusions
The results of this study add to the growing literature on eating disorders and substance use by further emphasizing that eating disorders may be associated with a range of substance-use behavior. The STAGE sample used in the current study provided extensive eating disorders and substance-use phenotyping, including snus use, which has never been reported before. This study represents the first large population-based study that was able to contrast substance-use patterns across AN, BN, ANBN and BED. Moreover, our secondary analyses allowed us to explore differences within AN subtypes in a non-treatment-seeking sample. Findings highlight the importance of screening for various types of substance use when examining and treating individuals with disordered eating. Although we cannot examine temporal patterns of onset, several possibilities exist, namely, the presence of an eating disorder may increase risk for substance use, substance use may increase risk for eating disorders, or a third underlying variable might increase risk for both eating disorders and substance use. Additional investigations incorporating patterns of onset will assist with determining how eating disorders and substance use mutually influence risk (Field et al. Reference Field, Austin, Frazier, Gillman, Camargo and Colditz2002; Stice & Shaw, Reference Stice and Shaw2002). Presenting comprehensive epidemiological data in order to characterize the sample fully was a necessary first step toward more advanced twin methodology exploring the complex genetic and environmental factors influencing liability to both traits. This is critically important given the heightened risk for physical complications, including suicide risk, among those with both an eating disorder and substance-use disorder (Keel et al. Reference Keel, Dorer, Eddy, Franko, Charatan and Herzog2003; Franko et al. Reference Franko, Dorer, Keel, Jackson, Manzo and Herzog2005).
Acknowledgements
T.L.R. was supported by National Institute of Health grant T32MH076694. This study was supported by grants CA-085739 (PI: P. F. Sullivan) and AI-056014 (Principal Investigator: P. F. Sullivan) from the National Institutes of Health. The STR is supported by grants from the Swedish Department of Higher Education and the Swedish Research Council.
Declaration of Interest
None.
Note
Supplementary material accompanies this paper on the Journal's website (http://journals.cambridge.org/psm).
