Original Articles
Standardized mortality in eating disorders—a quantitative summary of previously published and new evidence

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Abstract

Ten eating disorder (ED) populations were reviewed using the standardized mortality ratio (SMR) presenting new evidence for several studies. In eight of the ten samples, strong evidence (in one sample weak evidence and in one sample no evidence) supports an hypothesis of elevated SMR. We found strong evidence for an increase in SMR for anorexia nervosa (AN), whereas no firm conclusions could be drawn for bulimia nervosa (BN). Bias caused by loss to follow-up was quantified and found nonnegligable in some samples (possible increase in SMR from 25% to 240%). We did not find a significant effect of gender or time period on SMR. Survival analysis showed a significant difference among the life-tables for males and females; female risk of death averaged 0.59% per year, whereas all male deaths occurred within the first 2 years after presentation. Weight at presentation had a highly significant effect on SMR, and lower weight at presentation was associated with higher SMR. Age at presentation exerted a significant unimodal effect on SMR; aggregate overall SMR was 3.6 for the youngest age group (<20 years), 9.9 for those aged 20–29 years, and 5.7 for those aged ⩾30 years at presentation. Length of follow-up had a highly significant inverse effect on SMR; maximal SMR was 30 for female AN patients in the first year after presentation. A statistically significant increase in SMR was documented for at least up to 15 years after presentation. One study indicated a treatment effect on SMR. New evidence on causes of death suggests there are more deaths from suicide and other and unknown causes and fewer deaths related to ED than previously reported. Our findings have both research and clinical implications, with the most important clinical implication being the need for vigorous and well-directed treatment efforts from the initial presentation for treatment. An important research implication is that no single measure of mortality is sufficient; that is, only a combination of different statistics will maximize the available information.

Introduction

Recent reviews 1, 2, 3, 4 on course and outcome in anorexia nervosa (AN) have highlighted the limited knowledge behind the assumptions concerning mortality in the eating disorders AN and bulimia nervosa (BN). The use of some measure of standardized mortality is recommended 1, 2, but so far most investigators have reported only crude mortality rates, recently summarized by Sullivan [5], who used a weighted linear regression approach. He summarized 42 studies, totaling 3006 AN patients, and found 178 deaths (5.9%). Thirty-eight of these studies reported on cause of death for 164 probands; 54% of these died from complications of the eating disorder, 27% from suicide, and the remaining 19% from unknown or other causes. The mortality rate per decade of follow-up was 5.6%.

Few studies have used more sophisticated statistical analyses. Isager et al. [6] and Emborg [7] used survival analyses, and the latter investigation applied several types of regression in the predictor analysis (multiple regression, logistic regression, and Cox's regression) as well as SMR (standardized mortality ratio) and crude mortality rate. As those results are not fully available at this time, we cannot present them in detail.

Four studies on standardized mortality ratio (SMR) in eating disorders are known to us 8, 9, 10, 11. None has used standardized rate ratio (SRR) 12, 13. The present article will emphasize SMRs in ED, but we mention crude mortality rates when appropriate. We compare findings from the existing four publications with additional data from five studies from southern Scandinavia 14, 15, 16, 17, 18 using identical methodology to the extent data permit.

In Scandinavia we have access to reliable registers 19, 20, which provide high ascertainment rates both for vital status and for causes of death. These registers have been put under much scrutiny after the recent political changes in Eastern Europe where people have been aware of the abuse of health information by the authorities. In what follows, we provide an example of the proper use of such valuable data.

Our aim is to show the state of the art in the field of SMR applied to ED, including recommendations for further research. We examine the merits and shortcomings of the different measures of mortality: crude mortality rate, SMR, SRR, survival analysis, and mathematical modeling.

Section snippets

Materials

Characteristics of the studies are summarized in Table 1 Table 2a, and Table 2b (note: overall mortality in Table 1 Table 2a, and Table 2b encompasses all ED diagnoses and both genders).

Method

Computerized and manual searches of the literature revealed four relevant studies 8, 9, 10, 11. Now, our five studies 14, 15, 16, 17, 18 can be added to the database. We applied robust methodology in our approach to the problems of standardized mortality 12, 13. SMR is defined as the observed mortality divided by expected mortality. For the smaller samples we used a personal computer and the person-years method 12, 27 when analyzing the expected mortality of each individual. The sum of the

Effect of gender

Crude mortality: Some studies do not contain any males 9, 11, 14. Patton [8] did not report specifically on mortality by gender, but, on the other hand, he did not mention gender as one of the significant predictors of mortality. In none of the following studies was a significant effect of gender documented when analyzing the 2×2 table of mortality by gender: Tolstrup et al. [15]: Fisher's exact test, p=0.36; Møller-Madsen et al. [16]: chi-square=0.64, df=1; p=0.43 (controlling for diagnosis

Discussion

The eating disorders AN and BN are serious illnesses that place a heavy burden on the afflicted individual, their families, and care delivery systems. The burden consists of developmental delays and a lack of fulfillment of the individual's potential, emotionally, socially, intellectually, and sexually [39]. These patients are in danger of chronicity [24] with increased use of psychiatric as well as somatic bed-days [11]. Besides this direct personal and societal cost, there are the costs

Acknowledgements

Acknowledgments—Fru C. Hermansen Mindelegat, the Foundation for Research into Mental Disorders (Grant No. 75), Dansk Psykiatrisk Forskningsfond af 1967, and Gangstedfonden have given generous support to the Danish studies 15, 16, 17, 18. The Sjöbring Foundation and the Crafoord Foundation generously supported the Swedish studies (14, 22–24) over a number of years. Methodological and statistical advice was received from the consultant service (No. 94134/94) of the Danish Medical Research

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