American Journal of Epidemiology
ª The Author 2009. Published by the Johns Hopkins Bloomberg School of Public Health.
All rights reserved. For permissions, please e-mail: [email protected].
Vol. 170, No. 5
DOI: 10.1093/aje/kwp166
Advance Access publication July 9, 2009
Original Contribution
Association of Higher Parental and Grandparental Education and Higher School
Grades With Risk of Hospitalization for Eating Disorders in Females
The Uppsala Birth Cohort Multigenerational Study
Jennie Ahrén-Moonga, Richard Silverwood, Britt af Klinteberg, and Ilona Koupil
Initially submitted February 23, 2009; accepted for publication May 19, 2009.
Eating disorders are a leading cause of disease burden among young women. This study investigated associations of social characteristics of parents and grandparents, sibling position, and school performance with
incidence of eating disorders. The authors studied Swedish females born in 1952–1989 (n ¼ 13,376), thirdgeneration descendants of a cohort born in Uppsala in 1915–1929. Data on grandparental and parental social
characteristics, sibling position, school grades, hospitalizations, emigrations, and deaths were obtained by register
linkages. Associations with incidence of hospitalization for eating disorders were studied with multivariable Cox
regression, adjusted for age and study period. Overall incidence of hospitalization for eating disorders was 32.0/
100,000 person-years. Women with more highly educated parents and maternal grandparents were at higher risk
(hazard ratio for maternal grandmother with higher education relative to elementary education ¼ 6.5, 95% confidence interval: 2.2, 19.3, adjusted for parental education). Independent of family social characteristics, women with
the highest school grades had a higher risk of eating disorders (hazard ratio ¼ 7.7, 95% confidence interval: 2.5,
24.1 for high compared with low grades in Swedish, adjusted for parental education). Thus, higher parental and
grandparental education and higher school grades may increase risk of hospitalization for eating disorders in
female offspring, possibly because of high internal and external demands.
anorexia nervosa; eating disorders; education; family; parents; siblings; social class
Abbreviations: ICD, International Classification of Diseases; UBCos, Uppsala Birth Cohort.
There are concerns about increasing rates of mental illness
such as eating disorders, self-inflicted injuries, and selfreported stress among young women in Sweden (1) and other
industrialized parts of the world (2, 3). According to the
Diagnostic and Statistical Manual of Mental Disorders:
DSM-IV (4), eating disorders are divided into the main
diagnoses of anorexia nervosa, bulimia nervosa, eating disorder not otherwise specified, and binge eating disorder.
Together, these disorders constitute one of the leading causes
of disease burden in terms of years of life lost through death
or disability for young women (5), with a peak age at onset
occurring at a developmentally sensitive time in the midteens. Respective lifetime prevalence rates for full and partial
anorexia nervosa in women range from 0.9% to 4.3% (6–8)
and from 1.5% to 7% for full and partial bulimia nervosa
(6, 9). Studies of time trends in eating disorders show that
the incidence and prevalence of anorexia nervosa and bulimia
nervosa are stabilizing in Western countries (10), whereas the
prevalence of eating disorder not otherwise specified and of
binge eating disorder continues to increase (11, 12).
Eating disorders are usually explained by multifactorial
models including psychological, social, and biological risk
factors. However, little research has attempted to bring together information about various types of risk factors and
explore interactions among parental health and social characteristics, early-life environment, and individual aspirations in influencing the risk and long-term outcome of
eating disorders.
Correspondence to Dr. Jennie Ahrén-Moonga, CHESS, Karolinska Institutet/Stockholm University, Sveavägen 160, 106 91 Stockholm, Sweden
(e-mail: [email protected]).
566
Am J Epidemiol 2009;170:566–575
Eating Disorders and Educational Background in Females 567
Common risk factors for anorexia nervosa and bulimia
nervosa are gender, ethnicity, family history of eating disorders or depression, elevated weight and shape concerns,
negative self-evaluation, abuse, and general psychiatric
morbidity (13, 14). Additional risk factors for anorexia
nervosa include childhood sleeping problems, overanxious parenting, obsessive-compulsive personality traits,
perfectionism, family discord, high parental demands,
and high levels of physical exercise (13, 15). Evolutionary
biologists (16–18) have argued that people restrict their
eating as a result of comparing themselves with those who
are successful and in response to fears of loss of status.
Studies in humans support a role for social rank in eating
pathology (19), and results from twin studies confirm the
role of genetic factors in the development of eating disorders (20).
Evidence that the conditions in which children live have
long-term effects on their health is well established (21) and
lends support to policies to reduce child disadvantage as part
of strategies to address health inequalities. However, earlier
studies on family social circumstances and eating disorders
in daughters have not provided conclusive results: a review
of eating disorders and socioeconomic position concluded
that eating disorders were not restricted to certain social
groups (22), whereas a cohort study from Sweden showed
a higher prevalence of anorexia nervosa in higher socioeconomic groups. Results from the latter study also showed that
children with an earlier foster-home placement or children
of parents who had been treated for psychiatric disorders
were at increased risk of developing eating disorders (23).
Moreover, families with a higher prevalence of deaths of
a first-degree relative and with a higher prevalence of depression in mothers were overrepresented among anorexia
nervosa cases (24).
Family structure and sibling position have also been studied as potential risk factors for eating disorders. Eating disorders have been shown to be more common in families
with poor structure and multiple conflicts (25). No clear
associations between birth order or sex of siblings and eating disorders were found in a study by Gowers et al. (26),
whereas higher birth order and fewer brothers were associated with anorexia nervosa in a study by Eagles et al. (27).
A qualitative study of women recovering from anorexia nervosa found that the relationship between patients and siblings
tended to be characterized by antagonism, rivalry, and little
warmth (28). Canetti et al. (29) reported that anorectic patients, compared with healthy controls, perceived their parents as less caring and their fathers as more controlling.
While changes in cognitive ability and neuropsychological functioning in patients with chronic, severe eating disorders have been documented (30, 31), much less is known
about school performance and the incidence of eating disorders. Earlier research on cognitive functioning and eating
disorders mostly focused on IQ, suggesting that patients
with eating disorders have IQ scores within or slightly
higher than the normal range (32, 33). Furthermore, Dura
and Bornstein (34) found that school achievement, as measured by reading, spelling, and arithmetic, of patients with
anorexia nervosa was much better than predicted by their IQ
scores.
Am J Epidemiol 2009;170:566–575
We hypothesized that high and low school achievement
may be common among females at risk of eating disorders
and may partly reflect the role of family educational background in the etiology of eating disorders. The aim of our
study was to investigate social and family background factors and school performance in relation to incidence of hospitalization for eating disorders among females in a large,
multigenerational Swedish cohort.
MATERIALS AND METHODS
Study participants and register linkage
We studied associations of family social characteristics
and school performance with incidence of hospitalization
for eating disorders among Swedish females, third-generation
descendants of the Uppsala Birth Cohort (UBCoS). The
original UBCoS consists of 14,193 males and females born
in Uppsala University Hospital from 1915 to 1929 (first
generation). All subsequent generations born to UBCoS
members until 2002 have been traced through the MultiGeneration Register that made it possible to identify the
offspring of the original cohort if they were born in 1932
or later and resident and registered in Sweden at least once
during 1961–2002. The Multi-Generation Register also provided information about the identity of the other biological
(or adoptive) parent of the children (second generation) and
grandchildren (third generation), and we could thus reconstruct the family links for all subsequent generations born
until the end of 2002. Register-based data on grandparental
and parental social characteristics, school grades at age
15 years, and hospitalizations for eating disorders were obtained by linkages through unique personal identification
numbers and covered a follow-up period from 1960 to
2002 (35).
There were 14,338 females in the third generation of
UBCoS, who were born in 1952–1989. We excluded 330
(2.3%) who were adopted into UBCoS families and an
additional 414 (2.9%) who were born outside of Sweden
themselves or whose parent(s) were born outside of
Sweden.
Because the diagnostic criteria for anorexia nervosa include amenorrhea, the start of the study period was set to
age 12 years. Another 218 (1.5%) women who had died,
emigrated, or already been hospitalized for an eating disorder by this age were also excluded, leaving data on 13,376
women in the analysis.
Information on parental educational level was obtained
from the census and the Longitudinal Database for Education, Income and Occupation (LOUISE) databases and
was analyzed in 3 categories as ‘‘elementary’’ (<10
years), ‘‘secondary’’ (11–12 years), and ‘‘postsecondary’’
(13 years). Mother’s and father’s gross income was obtained from the Longitudinal Database for Education, Income and Occupation and was analyzed in tertiles.
Grandparental education was obtained from census data
and was analyzed in 2 categories as ‘‘elementary’’ or
‘‘higher.’’ Information on sibling position and sex of siblings was generated from information obtained from the
Multi-Generation Register.
568 Ahrén-Moonga et al.
School performance
Information on school performance was obtained from
the Swedish National Agency for Education and concerned
the grades earned during the last year of compulsory school
(typically age 15 years). The data were based on 2 different
grading systems. In the first study period, Sweden had a national relative grading system. Grades ranged from 1 to 5; 5
was the highest. Teachers were guided through national
achievement tests given in English (year 8) and mathematics
and Swedish (year 9). In the school year 1995–1996, a new
criterion-referenced grading system was introduced, with
grades divided into 4 levels: IG (not pass), G (pass), VG
(pass with distinction), and MVG (pass with special distinction) and prespecified skills required for different levels
(36). Because there was no obvious objective way to reconcile the grades over the 2 periods, we chose to analyze them
separately. However, because there were very few eating
disorders events among females with school grades from
the later period (3 or 4, depending on the school subject),
we ultimately analyzed grades from the earlier period only.
Grades for Swedish language, biology, physics, history,
mathematics, and English, and a combined average grade,
were used in this analysis.
During 1988–1996, mathematics and English were offered at 2 different levels, basic and advanced. The lack of
an objective method for combining the grades across levels
again led us to analyze the levels separately. Because there
were very few eating disorders events among females taking
the basic level (8 in mathematics and 3 in English), we
analyzed only those females taking the advanced level.
Definitions of eating disorders
Data on eating disorders were obtained from the hospital
discharge register, and we combined the information from
all versions of the International Classification of Diseases
(ICD) (37) used during the study period. The study subjects
were classified as having eating disorders if any of the following diagnoses and codes were included on the discharge
record for hospitalizations at age 12 years or older: ICD,
Eighth Revision: 306.5 (feeding disturbances); ICD, Ninth
Revision: 307.1 (anorexia nervosa) and 307.5 (other and
unspecified disorders of eating); ICD, Tenth Revision: F50
(eating disorders), F50.0 (anorexia nervosa), F50.1 (atypical
anorexia), F50.2 (bulimia nervosa), F50.3 (atypical bulimia), F50.4 (overeating), F50.5 (vomiting associated with
other psychosocial disturbances), F50.8 (other eating disorders), and F50.9 (eating disorders, unspecified). Separate
analysis for a subgroup of patients with anorexia nervosa
was based on diagnoses from ICD, Ninth Revision (code
307.1) and ICD, Tenth Revision (codes F50.0, F50.1).
Statistical methods
Associations of social characteristics and school performance with incidence of eating disorders were studied by
using multivariable Cox regression models, adjusted for age
and study period. The standard errors of the estimates were
calculated allowing for the potential correlations caused by
subjects sharing the same parents or grandparents. Because
school grades were observed at age 15 years, the study
period in analyses concerning school performance did not
begin until this age. For all other risk factors, exposure
began at age 12 years. Data for women who died or emigrated before the end of follow-up (the end of December
2002) were censored at the date of death or emigration. All
analyses were performed by using Stata software: Stata/IC
version 10.0 for Macintosh and Stata/SE version 10.0 (38).
RESULTS
The 13,376 third-generation UBCoS females included in
the analyses were born between 1952 and 1989 to 9,648
different mothers. Tables 1 and 2 summarize the available
data for each risk factor considered. The proportion of missing data ranged from 1.9% to 4.0% for the parental social
characteristics and from 1.2% to 3.5% for the grandparental
education variables. Regarding school subjects offered at
only a single level, grades were missing for 8.5%–18.2%
of females (calculated as a percentage of those born within
the period for which school grades based on the earlier
grading system were available (January 1973–July 1982)).
In mathematics and English, grades were missing for 9.7%
and 11.3%, respectively, of females who did not have basiclevel grades. In each analysis, the sample size was further
affected by the need to maintain a consistent sample when
adjusting for additional risk factors.
In the analyses concerning parental social characteristics,
grandparental education, and sibling position, where the
study period began at age 12 years, 454 females died or
emigrated before the end of follow-up. There were 55 cases
of eating disorders recorded among the 13,376 study subjects, who altogether completed 171,837 years of follow-up.
The overall incidence rate of eating disorders was 32.0 per
100,000 person-years. Anorexia nervosa accounted for
50.9% of the recorded cases of eating disorders.
In age- and period-adjusted analyses, both higher parental
education and higher parental income were associated with
increased risk of eating disorders in daughters, although the
trend for father’s income was not statistically significant
(Table 3). The effect became weaker and not statistically
significant after additional adjustment for the other parent’s
characteristic, with the exception of the linear trend of risk
of eating disorders over tertiles of maternal income that
remained borderline significant even when adjusted for father’s income (Table 3). We did not find evidence of interaction between the respective parental social characteristics
regarding their associations with eating disorders in daughters (P ¼ 0.18 for maternal and paternal education and P ¼
0.89 for maternal and paternal income).
Risk of eating disorders was substantially increased for
women with more highly educated maternal grandmothers
(Table 4). This increased risk was only partly confounded by
maternal grandfather’s and parents’ education. The fully
adjusted hazard ratio associated with a higher than elementary compared with an elementary education for maternal
grandmothers was 6.5 (95% confidence interval: 2.2, 19.3).
Age- and period-adjusted analysis also indicated an increased risk of eating disorders for women with maternal
Am J Epidemiol 2009;170:566–575
Eating Disorders and Educational Background in Females 569
Table 1. Distribution of Parental Education and Income and of Grandparental Education Among the 13,376 Eligible Third-Generation Uppsala
Birth Cohort Females Born in 1952–1989, Sweden
Eating Disorders
No.
%
No. of
Events
Person-years
at Risk
Anorexia Nervosa
Crude Incidence
Rate/100,000
Person-years
No. of
Events
Person-years
at Risk
Crude Incidence
Rate/100,000
Person-years
11.7
Parental education and income
Mother’s education
Elementary
2,791
21.3
10
42,592
23.5
5
42,670
Secondary
6,365
48.5
21
80,468
26.1
11
80,562
13.7
Postsecondary
3,968
30.2
22
43,358
50.7
11
43,413
25.3
Missing
252
Father’s education
Elementary
3,552
27.7
12
51,747
23.2
3
51,816
5.8
Secondary
5,664
44.1
17
71,212
23.9
8
71,267
11.2
Postsecondary
3,625
28.2
22
38,644
56.9
13
38,770
33.5
7
51,526
13.6
Missing
535
Mother’s income
Lowest
4,312
32.9
13
51,446
25.3
Medium
4,406
33.6
15
55,995
26.8
5
56,073
8.9
Highest
4,399
33.5
25
58,773
42.5
15
58,842
25.5
Missing
259
Father’s income
Lowest
4,139
32.2
11
54,307
20.3
2
54,392
3.7
Medium
4,337
33.8
17
54,542
31.2
11
54,569
20.2
Highest
4,362
34.0
23
52,292
44.0
12
52,406
22.9
Missing
538
Grandparental education
Maternal grandmother
Elementary
6,981
95.8
18
96,142
18.7
10
96,242
10.4
Higher
307
4.2
4
2,842
140.7
2
2,863
69.9
Missing
86
Maternal grandfather
Elementary
6,179
86.9
17
85,910
19.8
9
85,989
10.5
Higher
934
13.1
5
9,884
50.6
3
9,905
30.3
Missing
261
Paternal grandmother
Elementary
6,256
95.2
33
75,448
43.7
15
75,575
19.4
Higher
318
4.8
1
2,955
33.8
1
2,955
33.8
Missing
95
Paternal grandfather
Elementary
5,475
85.9
27
66,755
40.4
11
66,875
16.4
Higher
900
14.1
6
8,655
69.3
5
8,661
57.7
Missing
294
grandfathers with a higher education; however, that association became weaker and nonsignificant after adjustment for
maternal grandmother’s education.
In the analyses concerning parental social characteristics
and grandparental education, we found no evidence that
included subjects differed from those who were not included
Am J Epidemiol 2009;170:566–575
in terms of the crude incidence of eating disorders. However, excluded subjects were often born a little earlier (results not shown).
Analyses of sibling position and sex of siblings indicated
a protective effect of a larger family and the presence of
older siblings and brothers in particular, but none of the
570 Ahrén-Moonga et al.
Table 2. Distribution of Variables Regarding Grades in School Subjects Among the 5,632 Eligible Third-Generation Uppsala Birth Cohort
Females Born in 1952–1989, Sweden
Eating Disorders
No.
%
No. of
Events
Person-years
at Risk
Anorexia Nervosa
Crude Incidence
Rate/100,000
Person-years
No. of
Events
Person-years
at Risk
Crude Incidence
Rate/100,000
Person-years
Combined average
Low
1,416
27.5
5
14,826
33.7
2
14,836
13.5
Medium
1,818
35.3
7
18,774
37.3
2
18,806
10.6
High
1,921
37.3
14
19,456
72.0
7
19,477
35.9
Missing
477
Swedish
Low
2,579
50.2
6
26,863
22.3
2
26,876
7.4
Medium
2,041
39.7
11
20,951
52.5
4
20,991
19.1
High
517
10.1
9
5,074
177.4
5
5,085
98.3
Missing
495
Biology
Low
2,518
53.1
7
26,293
26.6
2
26,313
7.6
Medium
1,696
35.7
8
17,346
46.1
3
17,362
17.3
High
532
11.2
4
5,190
77.1
3
5,195
57.7
Missing
886
29.7
3
30,312
9.9
Physics
Low
2,914
61.6
9
30,289
Medium
1,408
29.8
5
14,357
34.8
1
14,371
7.0
High
407
8.6
5
4,002
124.9
4
4,007
99.8
Missing
903
26.2
2
26,759
7.5
History
Low
2,565
55.7
7
26,727
Medium
1,573
34.1
3
16,187
18.5
2
16,192
12.4
469
10.2
7
4,621
151.5
2
4,632
43.2
High
Missing
1,025
Mathematics
Low
Medium
High
Basic level
Missing
1,745
59.6
5
17,891
27.9
1
17,907
5.6
912
31.2
6
9,311
64.4
3
9,318
32.2
271
9.3
4
2,634
151.9
3
2,640
113.6
2,208
496
English
Low
2,210
56.4
8
23,020
34.8
5
23,036
21.7
Medium
1,349
34.4
9
13,786
65.3
2
13,808
14.5
362
9.2
4
3,532
113.3
3
3,538
84.8
High
Basic level
Missing
1,209
502
effects were statistically significant (results not shown). The
hazard ratio associated with having one or more younger
sisters was of borderline significance (hazard ratio ¼ 1.68,
95% confidence interval: 0.97, 2.91).
In the analyses concerning school performance, where the
study period began at age 15 years, 28 cases of eating disorders were observed among the 5,632 eligible study sub-
jects during 56,235 person-years of follow-up, giving an
incidence rate of 49.8 per 100,000 person-years. Anorexia
nervosa accounted for 42.9% of the recorded cases of eating
disorders.
The trend in risk of eating disorders over average school
grades indicated some evidence of higher risk for females in
the highest grade category (Table 5), a result that became
Am J Epidemiol 2009;170:566–575
Eating Disorders and Educational Background in Females 571
Table 3. Hazard Ratios for Hospitalization for Eating Disorders Among 12,565 Third-Generation Uppsala Birth Cohort Females, Born in 1952–
1989, With Nonmissing Data on Mother’s Education, Father’s Education, Mother’s Income, and Father’s Income, Sweden
Minimally Adjusteda
HR
95% CI
Additionally Adjustedb
P Value
P Value
for Linear
From
Trend
Wald Test
HR
95% CI
Fully Adjustedc
P Value
P Value
for Linear
From
Trend
Wald Test
HR
95% CI
P Value
P Value
for Linear
From
Trend
Wald Test
Mother’s education
Elementary
1
Secondary
1.25 0.55, 2.85
0.60
1
Postsecondary
2.16 0.94, 4.95
0.07
0.05
1
1.20 0.51, 2.80
0.68
1.66 0.60, 4.57
0.33
0.31
1.15 0.50, 2.66
0.74
1.40 0.51, 3.80
0.51
0.51
Father’s education
Elementary
1
Secondary
0.95 0.45, 2.00
0.90
1
Postsecondary
2.04 1.00, 4.19
0.05
0.05
1
0.90 0.42, 1.95
0.79
1.66 0.67, 4.15
0.28
0.28
0.86 0.39, 1.87
0.70
1.47 0.58, 3.74
0.41
0.41
Mother’s income
Lowest
1
Medium
1.35 0.61, 3.01
0.46
1
Highest
2.15 1.03, 4.52
0.04
0.03
1
1.30 0.58, 2.88
0.52
1.98 0.95, 4.15
0.07
0.06
1.26 0.58, 2.76
0.56
1.70 0.84, 3.48
0.14
0.13
Father’s income
Lowest
1
Medium
1.45 0.68, 3.09
0.34
1
Highest
1.88 0.91, 3.89
0.09
0.08
1
1.37 0.64, 2.92
0.41
1.67 0.81, 3.46
0.16
0.16
1.36 0.64, 2.90
0.42
1.38 0.66, 2.90
0.39
0.40
Abbreviations: CI, confidence interval; HR, hazard ratio.
Adjusted for age and study period.
b
Additionally adjusted for other parental variable within the same domain (e.g., HR for mother’s education adjusted for father’s education, HR for
mother’s income adjusted for father’s income).
c
Additionally adjusted for the remaining variables in the table.
a
weaker after adjustment for parental education. Of the specific subjects studied, we noted a markedly increased risk of
eating disorders for females with the highest grade in the
Swedish language. Receiving the highest grades in biology,
physics, history, mathematics, and English was also associated with a higher risk of incidence of eating disorders in
study subjects. These effects were slightly reduced after
adjustment for parental education. The linear trends in increasing risk of eating disorders over increasing grades in
physics, history, mathematics, and English remained borderline statistically significant after adjustment for parental education, whereas the associations with grades from other
subjects studied lost statistical significance.
There was some evidence that crude incidence rates of
eating disorders were higher among subjects not included in
the school performance analyses compared with those included (results not shown). However, the number of events
of eating disorders in the excluded subjects was small.
Despite the fact that the statistical power of analyses restricted to females with anorexia nervosa was very limited,
we repeated the above analyses by restricting the outcome to
anorexia nervosa only for all risk factors apart from school
grades (where the reduced sample size meant that insufficient eating disorders events were observed, Table 1). Results of these analyses were largely consistent with the
reported associations of social characteristics and sibling
position with any diagnosis of eating disorders.
Am J Epidemiol 2009;170:566–575
DISCUSSION
The most important finding in the present study was the
increased risk of hospitalization for an eating disorder
among daughters of more highly educated parents. There
was a doubled risk of eating disorders associated with postsecondary education relative to elementary education, and
a significant linear trend was observed. It is noteworthy that,
in line with this trend, a higher than elementary education
for maternal grandmothers indicated a 6-fold increased risk
of eating disorders relative to elementary education, a result
that was significant even when adjusted for grandfather’s
and parental education. Thus, parental social characteristics
and maternal social background appeared to be associated
with risk of hospitalization for eating disorders among
daughters. Together, those findings indicate a role of high
internal and external demands in the etiology of eating
disorders.
Furthermore, we found a higher risk of eating disorders
among females with the highest grades. Even after adjusting
for parental education, there was a marked increase in risk
of eating disorders among females with the highest grades in
Swedish language and some evidence of increased risk of
eating disorders with increasing grades in several other
subjects.
A main limitation of our study is that we could study the
risk of only hospitalization for eating disorders and could
572 Ahrén-Moonga et al.
Table 4. Hazard Ratios for Hospitalization for Eating Disorders Among Third-Generation Uppsala Birth Cohort Females, Born in 1952–1989,
With Nonmissing Data on Maternal Grandmother’s Education, Maternal Grandfather’s Education, Mother’s Education, and Father’s Education
(n ¼ 6,548) and on Paternal Grandmother’s Education, Paternal Grandfather’s Education, Mother’s Education, and Father’s Education
(n ¼ 6,102), Sweden
Minimally Adjusteda
HR
95% CI
Additionally Adjustedb
P Value
From
Wald Test
HR
95% CI
Fully Adjustedc
P Value
From
Wald Test
HR
95% CI
P Value
From
Wald Test
2.18, 19.31
0.001
0.42, 3.47
0.72
0.06, 3.89
0.48
0.36, 3.67
0.82
Maternal grandparents
Grandmother
Elementary
1
Higher
9.54
1
3.28, 27.81
<0.001
7.77
1.08, 8.12
0.04
1.35
1
2.59, 23.25
<0.001
6.49
0.49, 3.68
0.56
1.21
0.57
0.46
Grandfather
Elementary
1
Higher
2.95
1
1
Paternal grandparents
Grandmother
Elementary
1
Higher
0.77
1
0.10, 5.87
0.80
0.53
1
0.06, 4.53
Grandfather
Elementary
1
Higher
1.46
1
0.58, 3.70
0.42
1.56
1
0.57, 4.29
0.39
1.15
Abbreviations: CI, confidence interval; HR, hazard ratio.
Adjusted for age, study period, and year of birth of grandparent included in the model.
b
Additionally adjusted for other grandparental variable corresponding to the same parent (e.g., HR for maternal grandmother’s education
adjusted for maternal grandfather’s education, HR for paternal grandmother’s education adjusted for paternal grandfather’s education).
c
Additionally adjusted for maternal and paternal education.
a
not include cases of eating disorders diagnosed and treated
in outpatient care. This limitation necessarily meant that our
analysis was restricted to the most severe cases of eating
disorders that required hospitalization. On the other hand, it
is most likely that, during the period of follow-up, and the
earlier years of follow-up in particular, clinically diagnosed
eating disorders cases would be admitted to inpatient care.
The analyses presented in this paper were adjusted for age
and calendar period and thus also indirectly address problems with changing diagnostic and treatment practices over
the period of our study.
There is a slight possibility that our outcome was influenced by differential health-care-seeking behavior by families with different social positions or different levels of
parental education. It is plausible that, for example, parents
with a higher education might seek medical help for their
daughters earlier or be more active in requesting access to
inpatient care. Latzer et al. (39) found a higher educational
level among parents of eating disorders patients than in the
general population in Israel and interpreted this finding
as a likely consequence of systematic differences in helpseeking patterns. Earlier research on help-seeking behavior
regarding eating disorders also showed that individuals from
ethnic minorities were less likely to seek help (39–41).
Although subjects born outside of Sweden themselves or
with parents who were born outside of Sweden were excluded from our study, it is possible that the results also
partly reflect differences in help-seeking behavior rather
than differences in the incidence of eating disorders. Although concerns about equity in access to health care have
been voiced in Sweden recently (42), access to health services during the period of follow-up was generally good,
with no financial barriers to use of hospital care in particular.
Because information used for our analysis is based on
data included in routine registers, validity of our results
depends on the quality and completeness of the register data
and a correct linkage of data between the respective registers. The hospital discharge register is unlikely to be complete; however, we believe that the relatively small
proportion of missing data did not lead to serious bias in
our analysis.
Although we would have preferred to use school-grade
data from both school grading systems, the lack of an objective method of combining the grades and the scarcity of
eating disorders events during the more recent period meant
that grades from only the earlier period could be utilized.
Future analysis of associations between school grades under
the more recent grading system and eating disorders risk is
important to assessing whether the trends we observed are
common to both grading systems. Our inability to analyze
basic-level mathematics and English grades because of
a small number of events could also potentially have introduced bias. Reassuringly, the results obtained were in line
with those observed for other school subjects.
It is unlikely that misclassification of the risk factors differed between subjects with and without eating disorders
Am J Epidemiol 2009;170:566–575
Eating Disorders and Educational Background in Females 573
Table 5. Hazard Ratios for Hospitalization for Eating Disorders Among Third-Generation Uppsala Birth Cohort Females, Born in 1952–1989,
With Data on Grades in School Subjects, Mother’s Education, and Father’s Education, Sweden
Minimally Adjusteda
No.
HR
Combined average
95% CI
P Value
From
Wald Test
1
Medium
1.17
0.33, 4.16
0.81
High
2.66
0.87, 8.10
0.09
1
2.55
0.87, 7.44
0.09
High
9.61
3.20, 28.88
<0.001
1
2.46
0.80, 7.54
0.12
High
4.11
1.09, 15.57
0.04
0.06
1.04
0.29, 3.80
0.95
2.15
0.71, 6.50
0.17
0.13
<0.001
2.46
0.84, 7.21
0.10
9.28
2.91, 29.56
<0.001
2.01
0.56, 7.19
0.28
3.01
0.63, 14.39
0.17
1.26
0.37, 4.23
0.71
4.28
1.12, 16.32
0.03
0.71
0.19, 2.66
0.62
5.34
1.56, 18.28
0.01
2.13
0.64, 7.06
0.22
4.79
1.13, 20.32
0.03
1.96
0.70, 5.43
0.20
3.19
0.78, 13.06
0.11
<0.001
1
0.02
0.14
4,552
Low
1
Medium
1.52
0.48, 4.78
0.48
High
5.57
1.75, 17.77
0.004
1
0.02
0.08
4,435
Low
1
Medium
0.83
0.21, 3.31
0.8
High
6.85
2.32, 20.17
<0.001
1
0.01
0.04
2,824
Low
1
Medium
2.31
0.71, 7.57
0.17
High
5.62
1.49, 21.19
0.01
English
P Value
for Linear
Trend
4,569
Medium
Mathematics
P Value
From
Wald Test
1
Low
History
95% CI
4,948
Medium
Physics
HR
1
Low
Biology
P Value
for Linear
Trend
4,965
Low
Swedish
Fully Adjustedb
1
0.01
0.04
3,780
Low
1
1
Medium
2.18
0.81, 5.84
0.12
High
3.82
1.10, 13.23
0.04
0.02
0.08
Abbreviations: CI, confidence interval; HR, hazard ratio.
Adjusted for age and study period.
b
Additionally adjusted for maternal and paternal education.
a
(nondifferential misclassification), meaning that any misclassification would lead to attenuation of the hazard ratios.
Although we would not expect substantial misclassification
of risk factors, this possibility suggests that the true associations may be greater than those observed. Because the outcome we considered was hospitalization for eating
disorders, it is unlikely that significant outcome misclassification occurred, although the possibility of true eating
disorders cases being misdiagnosed does exist. This misclassification would result in the true incidence of eating
disorders being higher than that observed and, if misdiagnosis was associated with the risk factors examined, could
bias the results.
The proportion of subjects missing from analyses involving parental and grandparental risk factors was low,
Am J Epidemiol 2009;170:566–575
so the effects of any selection bias are unlikely to be substantial. Excluded subjects were generally similar to included subjects, although, in analyses of school
performance, there was some evidence of a higher incidence of eating disorders among excluded subjects. If we
thought that the excluded subjects were likely to be those
with lower school attainment, then their exclusion could
explain some or all of the observed trends of increasing
risk of eating disorders with increasing school grades.
However, the number of eating disorders events among
excluded subjects was low, so these observations should
not be overinterpreted.
The unique feature of our study was our ability to combine data on 2 social indicators of both mothers and fathers
and to study associations with the educational level of
574 Ahrén-Moonga et al.
maternal and paternal grandparents. Moreover, we are not
aware of other large studies of the incidence of eating
disorders in groups with different levels of school
performance.
Our finding of a higher risk of eating disorders for
females with high school grades may indicate high ambition in those females, partly supporting the findings of
relatively higher school achievement than expected by IQ
scores among patients with anorexia nervosa (34). Our
findings, particularly regarding the high risk of eating disorders among females with high grades in Swedish language, may also, more speculatively, reflect cognitive
strategy preferences among females with eating disorders, especially those with anorexia nervosa, for details/
accuracy closely related to traits reflecting control and
perfectionism (43).
Although the results concerning siblings and birth order
are not conclusive, there is some indication that having older
brothers may reduce the risk of eating disorders, whereas
having younger sisters may increase the risk. However,
these findings should be interpreted cautiously because of
the lack of statistical significance. Early studies have suggested that patients with eating disorders have more sisters
(44), and more recent reports found that anorexia nervosa
patients had fewer brothers than controls did (27). The number of siblings might be related to other aspects of the family
setting such as internal relationships, family climate, and
attitudes.
A negative childhood climate has been suggested as a risk
factor for development of eating disorders, especially bulimia nervosa (45), and physical or psychological abuse in
childhood is recognized as a risk factor for psychiatric disorders in general (46, 47). Our results on associations between eating disorders and family characteristics are
consistent with earlier findings (23) in that we also found
an indication of a higher risk of eating disorders for females
from socially advantaged families. Although we do not
think that quality of parenting is systematically worse
among highly educated parents or mothers with high income, we cannot exclude the possibility that problems regarding certain aspects of parenting, such as time and
parental engagement during sensitive periods of development, may mediate the effects seen in our analysis. In our
view, the increased risk of eating disorders for granddaughters of more highly educated maternal grandmothers further
supports a role of high internal and external demands in
shaping the incidence patterns of eating disorders found in
our study.
Despite the improving survival of adolescent patients
with anorexia nervosa in Sweden (48), it is generally believed that our lack of understanding of etiology still hampers the development of more effective treatments for eating
disorders (18, 49). The results of the present study emphasize the importance of multigenerational information and
longitudinal research, as highlighted by others (49, 50),
and point to the need for future research on various types
of risk factors and interactions between parental health and
social characteristics, early-life environment, and individual
psychological factors in assessing the risk and long-term
outcome of eating disorders.
ACKNOWLEDGMENTS
Author affiliations: Department of Woman and Child
Health, Karolinska Institutet, Stockholm, Sweden (Jennie
Ahrén-Moonga, Britt af Klinteberg); CHESS, Centre for
Health Equity Studies, Karolinska Institutet/Stockholm
University, Stockholm, Sweden (Jennie Ahrén-Moonga,
Britt af Klinteberg, Ilona Koupil); Department of Epidemiology and Population Health, London School of Hygiene
and Tropical Medicine, London, United Kingdom (Richard
Silverwood); and Department of Psychology, Stockholm
University, Stockholm, Sweden (Britt af Klinteberg).
The UBCoS Multigenerational Study is supported by
grants from the Swedish Council for Working Life and Social Research and the Swedish Research Council. J. A. M.
has received financial support from Queen Silvia’s Jubilee
Fund for research on children and disability. I. K. is currently funded by the Swedish Council for Working Life and
Social Research. B. a. K. was supported by grants from the
Swedish Foundation for Health Care Sciences and Allergy
Research.
The study was approved by the regional ethics committee
in Stockholm (Dnr 03-117, 04-944T).
The authors thank Rawya Mohsen and Bitte Modin for
help with data management.
Parts of this work were presented at the European Public
Health Association (EUPHA) Conference, November 5–8,
2008, Lisbon, Portugal.
Conflict of interest: none declared.
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