A systematic review of eating disorder prevalence in the Nordic countries: 1994–2016

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Nordic Psychology
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A systematic review of eating disorder prevalence in the Nordic countries: 1994–2016
Camilla Lindvall Dahlgren, Kristin Stedal & Line Wisting
To cite this article: Camilla Lindvall Dahlgren, Kristin Stedal & Line Wisting (2017): A systematic review of eating disorder prevalence in the Nordic countries: 1994–2016, Nordic Psychology, DOI: 10.1080/19012276.2017.1410071
To link to this article: https://doi.org/10.1080/19012276.2017.1410071
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© 2017 The Author(s). Published by Informa UK Limited, trading as Taylor & Francis Group. This is an Open Access article distributed under the terms of the Creative Commons Attribution-NonCommercial-NoDeriva- tives License (http://creativecommons.org/licenses/by-nc-nd/4.0/), which permits non-commercial re-use, distribution, and reproduction in any medium, provided the original work is properly cited, and is not altered, transformed, or built upon in any way.
A systematic review of eating disorder prevalence in the Nordic countries: 1994–2016 CAMILLA LINDVALL DAHLGREN  , KRISTIN STEDAL & LINE WISTING
Correspondence address: Camilla Lindvall Dahlgren, Regional Department for Eating Disorders, Division of Mental Health and Addiction, Oslo University Hospital, Ullevål HF, Oslo, Norway. Email: [email protected]
Abstract Objective: The objective of this study was to systematically review the literature on eating disorder prevalence in the Nordic countries (i.e. Denmark, Finland, Iceland, Norway and Sweden) between 1994 and 2016. Method: Three online databases, PubMed, PsycINFO and SveMed+, searches were conducted, targeting articles on prevalence, incidence and epidemiology of eat- ing disorders (EDs). The review was performed in accordance with Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines, and was limited to Internation- al Classification of Diseases 10th revision (ICD-10) and the Diagnostic and Statistical Manual of Mental Disorders 4th Edition (DSM-IV) ED diagnoses published between 1994 and 2016. Results: A total of 19 studies fulfilled inclusion criteria and were included in the study. Results revealed that anorexia nervosa (AN) and binge eating disorder (BED) prevalence ranges in females are lower in the Nordic countries compared to Europe in general, and slightly higher for bulimia nervosa (BN). Discussion: The current review shows that there is an imperative need for studies investigating the prevalence of EDs in the Nordic countries by employing a methodology which allows for a formal diagnosis. The notable lack of two-stage designs in the studies reviewed ren- ders concern regarding the validity of the obtained prevalence rates. It is essential that future studies employ standardized methodologies as these will allow for comparison across geograph- ic regions, genders and ages, facilitating mapping of prevalence rates over time.
Keywords: review, prevalence, eating disorders, Nordic countries, DSM-IV, ICD-10, DSM-5
Introduction Eating disorders (EDs) are serious mental illnesses characterized by irregular eating patterns and severe distress concerning body shape and weight. Anorexia nervosa (AN) is associated with a high risk of premature death (Kask et al., 2016) and is recognized by persistent efforts to lose weight despite being severely underweight, and significant concerns regarding body image. Bulimia nervosa (BN) is characterized by episodes of binge eating followed by compensatory behaviours. Historically, AN and BN have been the most widely studied EDs. However, eating disorders not otherwise specified (EDNOS) was the most frequently reported ED using the fourth version of the Diagnostic and Statistical Manual of Mental Disorders (DSM-IV) (American
1Regional Department for Eating Disorders, Division of Mental Health and Addiction, Oslo University Hospital, Ullevål HF, Postboks 4950 Nydalen, 0424 Oslo, Norway
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Psychiatric Association, 1994). Recently, the DSM-IV was replaced by the DSM-5 (American Psy- chiatric Association, 2013) which resulted in a number of changes to the diagnostic ED cate- gories. A few of the most substantial revisions were to lower the diagnostic threshold for AN and BN, and to introduce binge eating disorder (BED) as an independent ED diagnosis. In addi- tion, the diagnostic categories pica, rumination disorder and avoidant/restrictive food intake disorder (ARFID) were added to the DSM-5 “Feeding and Eating Disorders”. The changes in the DSM-5 were introduced to help minimize broad generalizations of EDs, and is expected to have important implications for ED prevalence rates in the years to come. Some of these implication have already been confirmed by studies investigating the prevalence of EDNOS (Machado, Gon- calves, & Hoek, 2013) as well as AN and BN (Mustelin et al., 2016; Smink, van Hoeken, Oldehinkel, & Hoek, 2014; Trace et al., 2012).
For many years, EDs have been claimed to be represented predominantly in Western coun- tries, and although there is evidence of potential biological markers (Cerasa et al., 2015) it is well known that cultural beliefs and attitudes influence the development of EDs (Makino, Tsuboi, & Dennerstein, 2004) BN, in particular, seems to be a culture-bound syndrome (Keel & Klump, 2003). The influence of sociocultural factors on EDs was recently emphasized in a study by Nakai and colleagues (Nakai, Nin, & Noma, 2014) where a conflict between the influence of western culture and traditional Japanese values, as well as a growing media-oriented culture was put forth as an explanation for the dramatic increase in ED prevalence rates in Japan. Because EDs are influenced by sociocultural factors, both on a local and global level (Becker & Fay, 2006) it is important to obtain prevalence rates within targeted geographical areas. Unfortunately, popu- lation-based prevalence studies are both time-consuming and financially demanding to imple- ment. In addition, they will often be limited by small sample sizes and selection bias. Therefore, systematic reviews of prevalence studies can be particularly helpful. By synthesizing studies assessing prevalence rates across countries with similar standards of living, socio-economic sta- tus and culture, it is possible to obtain better estimates of the number of individuals affected by the illness in question. Lately, there has been a marked increase in studies reviewing the preva- lence of EDs across geographic regions including Africa (van Hoeken, Burns, & Hoek, 2016), Asia (Pike & Dunne, 2015) and Europe (Keski-Rahkonen & Mustelin, 2016). In their recent European review, Keski-Rahkonen and Mustelin demonstrate great variability in prevalence rates across European countries. However, there are some limitations to the study methodology as the liter- ature was not reviewed through a systematic process using specific review criteria. In addition, only studies published in 2015 and the first half of 2016 were included, leaving out a substan- tial proportion of studies of relevance. Finally, comparisons between countries included in the review are likely to be obscured by socio-economic differences. The authors compare prevalence rates from Finnish and German communities, as well as students from Serbia and the Canary Islands. Poverty rates and income inequalities in the Nordic countries have been reported to be lower, compared to some Southern European countries (Andersen et al., 2007), and correlations between socio-economic conditions and mental illnesses are well documented (Adler & Ostrove, 1999; Everson, Maty, Lynch, & Kaplan, 2002; Hudson, 2005). In sum, it is necessary to obtaining local prevalence rates to minimize the effects of sociocultural and economic factors. The Nordic region is one local area of interest.
The Nordic region consists of some of the most affluent countries in the world, including Den- mark, Finland, Iceland, Norway and Sweden. In addition to the close geographic proximity, the countries are also similar in terms of standard of living, socio-economic status and culture. The
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“Nordic Model” promotes health and welfare policies which aim to ensure good public health, provide a high level of social security and diminish social inequalities (Andersen et al., 2007). To the authors’ knowledge, no studies have previously investigated the prevalence of EDs in the Nordic region. A systematic review of the prevalence of EDs in the Nordic region could provide a valuable point of reference when planning ED treatment, allocating resources, evaluating out- comes and to be able to identify an aggregated estimate of the economic burden of EDs in this region. Further, a systematic review of the prevalence of EDs in the Nordic region during the DSM-IV period may help facilitate rate comparisons between existing and future studies, and has the potential of informing the development of new prevalence studies. The aim of this study was thus to systematically review the literature on ED prevalence in the Nordic countries between 1994 and 2016. The review was conducted in accordance with Preferred Reporting Items for Sys- tematic Reviews and Meta-Analyses (PRISMA) guidelines (Moher et al., 2015).
Methods Search strategy The literature was reviewed in November 2016 using the three databases PubMed, PsycINFO and SveMed+. A librarian at the Medical Library, Oslo University Hospital (OUS), developed this search strategy. To update the initial search, an additional search was performed in November 2016. All publication titles were screened initially by the first author. Eligibility was established by reading abstracts and full texts. A detailed search strategy is available in Appendix 1.
Eligibility criteria
Publications that examined prevalence, incidence and epidemiology of EDs in the Nordic coun- tries (Denmark, Finland, Iceland, Norway and Sweden) were targeted, and were reviewed accord- ing to the following criteria:
(1) Articles published between January 1994 and November 2016 (initial search) (2) Articles that were written in English or had an available published English translation (3) Articles presenting ED prevalence rates using the ICD-10 or DSM-IV (4) Articles that described methods used to assess prevalence
No exclusions for age or gender were applied. Both cross-sectional and longitudinal studies were included.
Exclusion criteria
Books, book chapters, editorials, commentaries, reviews, errata, prevalence studies in clinical samples (e.g. psychiatric outpatients), studies presenting data where diagnostic measures were unclear and articles using diagnostic systems preceding DSM-IV (e.g. DSM-III) or ICD-10 (World Health Organisation, 1992) (e.g. ICD-8 and ICD-9) or a combination of diagnostic systems (e.g. DSM-III and DSM-IV) were omitted. All omitted review articles were screened for additional refer- ences. Inclusions and exclusions were tracked and registered (see Figure 1).
Title, abstract and article selection
Publication titles in studies sourced through the search strategy outlined in Appendix 1 were initially reviewed by the first author (CLD). Where titles were ambiguous, abstracts were also screened at this stage. Full texts were retrieved and assessed for eligibility by the three authors
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(CLD, KS & LW). Full texts were divided between the three authors, which, after having been examined were labelled “include”, “exclude” or “inconclusive”. Inconclusive texts were discussed. Agreement was reached for all inconclusive texts. None of the reviewers were blind to the authors of the texts, nor their affiliations.
Figure 1. The PRISMA flow diagram describing the literature screening process.D ow
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Results The PRISMA literature search: 1994–2016 The PubMed, PsycINFO and SveMed+ searches produced 389 titles, which, after duplicates had been removed, were reduced to 347. In the title screening process, publications with titles corre- sponding to obviously ineligible texts (e.g. “Gastronomy and diet in 18-month-old children with congenital heart defects”) were initially removed, whereas equivocal (e.g. “Eating Disorders – an overview”) and plausible titles (e.g. “Epidemiology of eating disorders in children and adoles- cents) were retained. Consequently, 233 out of the 347 publications were omitted based on the lack of title relevance. 114 titles were retained. Retained titles were equally divided between the three authors (CLD, KS & LW) who first screened potential eligibility using inclusion and exclu- sion criteria based on abstracts, and subsequently, established eligibility by reading full texts. An additional 51 texts were excluded in the abstract extraction phase, and after having read full texts, another 44 articles were omitted. No additional studies were found through the screening of review articles. All in all, 19 studies were included in the review. A more detailed overview of the screening process is presented in Figure 1.
Search summary
19 studies met inclusion criteria and were included in the review. No studies meeting inclusion criteria were published prior to 1999. Table 1 summarizes all included studies between 1999 and 2016. Studies are grouped based on study design (i.e. 2-stage design studies, interviews only and self-reports) and listed in chronological order. One study did not report study design, and was listed under the table heading “OTHER” (Goodman, Heshmati, Malki, & Koupil, 2014). Assessments of the following full-threshold diagnoses were reported: ED, AN, BN, BED and EDNOS. Although not recognized as its own disorder in the DSM-IV, prevalence of BED was assessed in the majority of the included studies. As it now is, i.e. in the DSM-5, considered a distinct diagnostic category, BED was included in the current review for comparative purposes.
Sample characteristics Demographics
Nine (47.4%) of the included studies were Finnish, six (31.6%) were Swedish, three (15.8%) were Norwegian, and one (5.3%) study reported prevalence rates in Iceland. No studies from Denmark fulfilled inclusion criteria. Out of the nine Finnish studies, four were based on the same study sample (Keski-Rahkonen et al., 2009, 2007, 2006; Mustelin et al., 2016). This was also true for two of the Swedish studies (Ghaderi & Scott, 1999, 2001). A total of ten studies reported prevalence for females only, whereas one study reported rates for males only. The eight remaining studies reported prevalence rates for both females and males. Ages ranged from 12 to 55, with 13 the vast majority (68.4%) of studies reporting ED prevalence rates in individuals 18 years and above. Five studies (26.3%) reported rates in adolescents and young adults ranging in age from 14 to 20, and the final study had a mixed sample including children, adolescents and adults (ages 12–36).
Sample size and setting
Sample sizes ranged from 595 to 2 015 862, with the majority of studies (N = 15) reporting prev- alence rates from samples ranging from 500 to 4500 participants. Three studies presented data
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from samples ranging in size from 10 000 to 30 000. One study had a sample size just above two million (N = 2 015 862) with ED cases identified using the Swedish national inpatient, outpatient, or death registers based on ICD-10 between 1997 and 2010. Nearly fifty per cent (N = 9) of the included studies had collected data from twin registries. These studies were either Finnish or Swedish. Five study samples were drawn from the general population, and the remaining five studies had assessed prevalence in student populations.
Data collection Design
Ten (52.6%) of the included studies followed what is known to be the gold standard in assessing prevalence rates; the two-stage design. Here, one or more self-report questionnaires were used to screen for ED risk, followed by an interview to establish ED diagnosis. One (5.8%) study used an interview alone to assess ED prevalence, and seven (36.8%) studies employed one or more self-reports. The final study had collected diagnostic data from national inpatient, outpatient, or death registers based on ICD-10, but without specifying the design of the study.
Assessment
In sum, 13 different assessment instruments had been used for either screening purposes or to assign specific ED diagnoses. The instrument most commonly applied to determine ED diag- noses was the SCID (First, Spitzer, Robert, Gibbon, & Williams, 1996) (all SCID interview formats included), which was used in eight (42.1%) out of the 19 included studies. All but one of these was conducted in Finland. The SEDs self-report questionnaire (Ghaderi & Scott, 2002) was used for diagnostic assessment in four (21.1%) studies. The Survey for Eating Disorders (SEDs) was only used in Swedish or Norwegian prevalence studies. A wide array of additional instruments was used to determine ED diagnoses, all of which were based on DSM-IV (American Psychiatric Asso- ciation, 1994) or ICD-10 (World Health Organisation, 1992) criteria, but without being specified any further (see Table 1).
Point- and lifetime prevalence rates
Point prevalence refers to the proportion of a population presenting with a condition at a specific point in time, whereas lifetime prevalence refers to the proportion of individuals who, at any point in their life up to the time of assessment, has suffered from the condition in ques- tion. In studies where overall lifetime ED prevalence differentiated between females and males (regardless of assessment method), rates ranged from 7.0% (Isomaa, Marttunen, Kaltiala-Heino, & Isomaa, 2010) to 17.9% (Kjelsas, Bjornstrom, & Gotestam, 2004) in females, and from .1% (Isomaa et al., 2010) to 6.5% (Kjelsas et al., 2004) in males. AN and/or BN lifetime prevalence rates were most commonly reported in 2-stage design studies, with AN rates ranging from .2 to 2.9% in females (Raevuori et al., 2008) and from .0% (Isomaa et al., 2010) to .4% (Raevuori et al., 2008) in males. BN rates ranged from .0% (Isomaa et al., 2010) to 2.3% (Lähteenmäki et al., 2014) in females, and from .0% (Isomaa et al., 2010; Raevuori et al., 2008) to .4% (Kjelsas et al., 2004) in males. Point prevalence was most commonly reported in studies using the self-report design, with all but one study (Kjelsas et al., 2004) assessing ED prevalence in females, or females and males. Here, female point prevalence for overall ED rates ranged from 2.6% (Ghaderi & Scott, 1999) to 8.0% (Kjelsas et al., 2004) and AN rates ranged from .0% (Ghaderi & Scott, 1999) to .5%. (Litmanen,
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Frojd, Marttunen, Isomaa, & Kaltiala-Heino, 2016) BN prevalence rates ranged from .5% (Kjelsas et al., 2004) to 3.0% in females (Litmanen et al., 2016). BED rates were only reported in two out of the ten 2-stage design studies, with point prevalence rates being .6 and 1.5% for females, and .2 and .0% for males. In self-report studies, BED point prevalence rates ranged from .3 to 1.2% in females, whereas the corresponding range for lifetime prevalence rates was 1.0–5.8%.
Discussion The current study systematically reviewed studies of ED prevalence in the Nordic countries between 1994 and 2016. In addition to discrepant results regarding reported prevalence rates, we found significant variability across studies in terms of study design, measures applied to determine diagnoses and sample characteristics. Finland was the country with most studies (N = 9), all drawn from the same register (FinnTwin16). A majority of the reviewed studies uti- lized the gold standard 2-stage design; all of which were Finnish. The majority of the Norwegian (N = 3) and Swedish (N = 6) studies had assessed ED prevalence using self-report measures. None…