Journal of Psychosomatic Research 69 (2010) 59 – 67
Common mental disorders and disability pension award: Seven year
follow-up of the HUSK study
Ann Kristin Knudsen a,⁎, Simon Øverland a , Helene Flood Aakvaag a , Samuel B. Harvey b ,
Matthew Hotopf b , Arnstein Mykletun a,c
a
Research Section of Mental Health Epidemiology, Department of Health Promotion and Development, Faculty of Psychology, University of Bergen,
Bergen, Norway
b
Kings College London, Institute of Psychiatry, London, UK
c
Norwegian Institute of Public Health, Division of Mental Health, Oslo, Norway
Received 6 September 2009; received in revised form 2 March 2010; accepted 9 March 2010
Abstract
Objective: Rates of disability pension (DP) awards remain high
in most developed countries. We aimed to estimate the impact of
anxiety and depression on DPs awarded both for mental and for
physical diagnoses and to estimate the relative contribution of sub
case-level anxiety and depression compared with case-level
symptom loads. Methods: Information from a large cohort study
on mental and physical health in individuals aged 40–46
(N=15,288) was linked to a comprehensive national database of
disability benefits. Case-level and sub case-level anxiety and
depression were defined as scores on the Hospital Anxiety and
Depression Scale of ≥8 and 5–7, respectively. The outcome was
incident award of a DP (including ICD-10 diagnosis) during 1–7year follow-up. Results: DP awards for all diagnoses were
predicted both from case-level anxiety [HR 1.90 (95% CI 1.50-
2.41)], case-level depression [HR 2.44 (95% CI 1.65–3.59] and
comorbid anxiety and depression [HR 4.92 (95% CI 3.94–6.15)] at
baseline. These effects were only partly accounted for by adjusting
for baseline somatic symptoms and diagnoses. Anxiety and
depression also predicted awards for physical diagnoses [HR
3.26 (95% CI 2.46–4.32)]. The population attributable fractions
(PAF) of sub case-level anxiety and depression symptom loads
were comparable to those from case-level symptom loads (PAF
anxiety 0.07 versus 0.11, PAF depression 0.05 versus 0.06).
Conclusion: The long-term occupational impact of symptoms of
anxiety and depression is currently being underestimated. Sub
case-level symptom loads of anxiety and depression make an
important and previously unmeasured contribution to DP awards.
© 2010 Elsevier Inc. All rights reserved.
Keywords: Anxiety; Depression; Sub-clinical symptoms; Work disability
Introduction
High levels of long term sickness absence and disability
benefits are a major public health problem in most
developed countries [1,2]. Common mental disorders,
Abbreviations: CI, Confidence Intervals; DP, Disability pension; HADS,
The Hospital Anxiety Depression Scale; HR, Hazard Ratio; HUSK, The
Hordaland Health Study; ICD, International Classification of Diseases;
OECD, Organisation for Economic Co-operation and Development; PAF,
Population Attributable Fractions.
⁎ Corresponding author. Research Section of Mental Health Epidemiology, Department of Health Promotion and Development, Faculty of
Psychology, University of Bergen, Bergen, Norway Christiesgt. 13, N-5020
Bergen, Norway. Tel.: +47 55 58 83 55; fax: +47 55 58 98 87.
E-mail address: [email protected] (A.K. Knudsen).
0022-3999/10/$ – see front matter © 2010 Elsevier Inc. All rights reserved.
doi:10.1016/j.jpsychores.2010.03.007
such as anxiety and depression, make up an increasing
proportion of claims for disability benefits [2–4], and
mental disorders in general are accounting for around 35%
of all disability benefits received in the member countries
of the Organisation for Economic Co-operation and
Development (OECD) [1]. In spite of an increased
awareness of the detrimental effects of common mental
disorders [5], including their impact when co-morbid with
physical conditions [6,7], there is still evidence that mental
disorders are often under-recognized and untreated, particularly in the primary care setting [8–10]. One previous
study has suggested that depression and anxiety may
contribute more to disability pension (DP) awards than is
officially recognized [11]. However, such previous work
60
A.K. Knudsen et al. / Journal of Psychosomatic Research 69 (2010) 59–67
has tended to focus on more severe levels of mental illness.
While a dose-response association between increasing
mental symptom loads and work disability is likely,
Broadhead et al. [12] found that in population terms, the
much more prevalent condition of mild depression
accounted for more days of sick leave than more severe
states. If common mental disorders are associated with
greater risk for receipt of DP, milder symptom levels
(below the threshold for diagnosable disorders) may also
confer risk.
Most studies of DP risk factors have been conducted
on specific occupational [13,14] or patient [15,16] groups,
with limited generalizability. Research examining the
connection between common mental disorders and work
disability in the general population is scarce [17]. There is
a need for prospective, population based studies on
common mental disorders as risk factors for work
disability, with a particular focus on the role of milder
symptom levels.
In this study we have linked a large population-based
health study to longitudinal data on disability benefits
with three aims: first, to examine if symptoms of anxiety
and depression, measured in the health study, are
independent risk factors for subsequent DP award (for
any cause) during a seven year follow-up. Second, to
examine whether symptoms of anxiety and depression are
independent risk factors for DP awarded for physical
diagnoses. Finally, to examine the relative contribution of
sub case-level anxiety and depression on the distribution
of DP recipients.
Methods
The Hordaland Health Study
The Hordaland Health Study (HUSK) was an epidemiological population-based study conducted between 1997
and 1999 in the Hordaland County of western Norway. The
study was a collaboration between the Norwegian National
Health Screening Service, the University of Bergen and local
health services.
All individuals in Hordaland County born between 1953
and 1957, aged 40–46 years at the time, were invited to the
health screening (n=29,400). A total of 8598 men and 9983
women participated in some part of the HUSK study.
Individuals with incomplete responses on some of the
variables (n=2670) were excluded, giving a participation rate
of 54.1% (15911 of the 29400 invited). We further excluded
553 persons who were already receiving DP at the time of the
health screening, and 70 persons who were granted DP
award one year following the health screening to avoid
elevated symptom levels due to the pensioning process [18].
Our final study population, followed from their date
of participation until December 31, 2004, consisted of
15,288 persons.
Data collection
The target population for the health screening were
mailed personal invitations. The baseline physical examinations included blood tests (non-fasting analyses of serum
total cholesterol and high-density lipoprotein cholesterol)
and measures of blood pressure, heart rate, height, weight,
and waist and hip circumference. The participants also
received various questionnaires on other health variables.
Exposure: symptoms of anxiety and depression
Symptoms of anxiety and depression were assessed with
the Hospital Anxiety and Depression Scale (HADS), which
has seven items on anxiety (HADS-A) and seven on
depression (HADS-D) [19]. Somatic symptoms of anxiety
and depression are excluded in the scale to prevent false
positives in the context of somatic conditions [20]. The
concurrent validity of HADS as a case finding instrument for
anxiety and depression is good [21]. Using the conventional
cutoff of ≥8 on both scales, participants were grouped in
four mutually exclusive categories: anxiety (HADS-A score
of ≥8), depression (HADS-D score of ≥8), comorbid
anxiety and depression (both HADS-A and HADS-D scores
of ≥8) and no anxiety or depression (reference group, scores
below 8 on both HADS-A and HADS-D) [11]. In an
additional analysis, we also used the anxiety and depression
scores as continuous variables.
For our analysis of dose-response association between
symptoms of anxiety and depression, and subsequent DP
award, we computed ordinal variables for anxiety and
depression symptom load (range in parentheses): reference
(0–4), sub case-level (5–7), mild case-level (8–10),
moderate case-level (11–14), and severe case-level (15–
21) [21]. While these additional cut-offs are not validated,
they were defined to reflect severity, as measured by
increasing symptom load with increasing HADS scores [22].
Outcome: DP award
Within the Norwegian welfare scheme, a DP can be
awarded to individuals who have had their earning ability
permanently reduced by ≥50% due to an illness, disease,
injury, or disability accepted as a medical condition.
Awards are not to be given for social problems like
unemployment. DP in Norway is a government responsibility, and all awards are accurately documented in the
Norwegian DP registry [23]. The date (month and year) of
DP award and their warranting medico-legal diagnosis
in the period from January 1999 to December 2004
were gathered from the Norwegian National Insurance
Administration (NIA) registries, and linked to the health
screening participants by Statistics Norway, through use of
national identification numbers. The medico-legal DP
diagnoses were given in ICD-9 and ICD-10 codes. ICD-9
diagnoses were converted into corresponding ICD-10
A.K. Knudsen et al. / Journal of Psychosomatic Research 69 (2010) 59–67
61
physical activity (mean hours per week with activities
involving sweating and shortness of breath).
Body mass index (BMI) was calculated using the
participant's height and weight, while waist–hip ratio was
calculated using the individuals' waist and hip circumference. Blood pressure and resting pulse were measured
thrice, with the third measure used in our analyses. Blood
tests provided information about total cholesterol levels. All
the above-mentioned physical measures were included in the
analyses as continuous variables.
An index for number of physical conditions was
computed from self reported confirmation to questions on
the presence of myocardial infarction, stroke, asthma,
angina pectoris, diabetes or multiple scleroses. Participants
were also asked to report current use of any medication, and
for which condition it was taken. Where prescribed
medication was presented, a team of physicians appointed
appropriate diagnoses based on the International Classification of Primary Care system for the likely underlying
physical condition. This information was used as a
diagnoses, and the conditions were grouped as F00–F99
(mental and behavioral disorders), M00–M99 (musculoskeletal disorders) and other diagnosis. The 17 cases
with missing diagnosis were categorized to the 'other
diagnosis' group.
Confounders and mediators
Information about income after tax in the 2 years
preceding the health screening was gathered from NIA
registries. The health study provided self-reported information on gender, age, marital status (single, married, widow/
widower, divorced, separated), level of education (ranging
from less than seven years of schooling to more than four
years at college or university), and current work situation
(work with income, full time domestic work, studying or
military service, or unemployment or laid-off).
Measures of health related behavior included selfreported information on smoking habits (dichotomy), alcohol consumption (number of units over two weeks) and
Table 1
Population characteristics
Final study population
Age a
Gender (female)
Marital status (married)
DP award during follow-up
Follow-up time (years)
Self-reported current work for income
HADS, case-levels (≥8)
Reference group (b8)
Anxiety only
Depression only
Comorbid anxiety and depression
Body Mass Index (kg/m2)
Waist Hip Ratio
Level of total cholesterol (mmol/l)
Systolic blood pressure (mmHg)
Income after tax (EUR)
Educational level
Compulsory only
High school
Higher education (college and university)
Physical activity (h/week)
No physical activity
b1
1–2
N3
Smoking (smoker)
Alcohol consumption (units pr 2 weeks)
0
1–15
N16
Number of physical conditions (0)
Number of physical conditions under pharmacological treatments (0)
Self-reported fibromyalgia
Self-reported back pain
a
Age at participation in the health screening.
N
%
15,288
100
8315
11,541
522
54.4
75.5
3.4
13,837
90.5
12,136
1754
516
882
79.3
11.5
3.4
5.8
2671
7011
5606
17.5
45.9
36.6
4292
4394
4494
2108
5215
28.1
28.7
29.4
13.8
34.1
4284
10,187
817
14,151
14,340
857
3926
28.0
66.6
5.4
92.6
93.8
5.6
25.7
Mean
S.D.
Range
43.2
1.54
40–46
6.31
0.77
1.01–7.18
25.3
0.84
5.54
125.9
22,485
3.75
0.08
0.99
14.0
18,229
15.2–53.9
0.62–1.29
2.44–11.75
86.0–125.9
0–1.56*106
0.08
0.08
0.29
0.32
0–3
0–3
62
A.K. Knudsen et al. / Journal of Psychosomatic Research 69 (2010) 59–67
Table 2
Anxiety and depression in relation to disability pension award during 1.01 to 7.18 year follow-up. Cox regression analysis with cumulative adjustments for
potential confounding factors
Anxiety only
Adjustment variables
HR
Comorbid anxiety
depression
Depression only
95% CI
HR
All awards (predicting n=522 awards among n=15,288 participants f)
No adjustments
2.02
1.59–2.56
2.19
+Gender
1.90
1.50–2.41
2.44
+Sociodemographic factors a
1.78
1.40–2.26
2.23
+Health related behavior b
1.75
1.38–2.22
2.04
+Physical measures c
1.77
1.39–2.25
1.96
1.64
1.29–2.09
1.95
+Physical conditions d
+Back pain and fibromyalgia e
1.37
1.07–1.75
1.72
Awards for mental disorders (F00-F99) excluded (predicting n=410 awards among n=15,176 participants g)
No adjustments
1.61
1.22–2.12
1.86
+Gender
1.51
1.14–1.99
2.09
+Sociodemographic factors a
1.43
1.08–1.89
1.91
+Health-related behavior b
1.40
1.06–1.85
1.75
1.41
1.07–1.86
1.66
+Physical measures c
+Physical conditions d
1.31
0.99–1.73
1.66
+Back pain and fibromyalgia e
1.07
0.81–1.42
1.49
Fully adjusted, 1–3 years of follow-up h, i
1.21
0.79–1.85
2.69
1.48
1.10–2.00
1.28
Fully adjusted, 3–7 years of follow-up j, k
95% CI
HR
95% CI
1.49–3.23
1.65–3.59
1.51–3.28
1.39–3.02
1.32–2.89
1.32–2.88
1.16–2.55
4.90
4.92
4.22
3.83
3.79
3.59
2.60
3.92–6.13
3.94–6.15
3.36–5.29
3.05–4.80
3.02–4.77
2.85–4.50
2.06–3.28
1.19–2.90
1.34–3.26
1.23–2.99
1.12–2.73
1.06–2.60
1.06–2.60
0.95–2.33
1.52–4.77
0.74–2.21
3.24
3.26
2.85
2.56
2.52
2.38
1.73
3.04
2.44
2.44–4.29
2.46–4.32
2.14–3.78
1.93–3.41
1.89–3.35
1.79–3.17
1.30–2.32
2.10–4.40
1.80–3.30
a
Income, education and marital status.
Exercise, smoking and alcohol consumption.
c
BMI, waist hip ratio, cholesterol, blood pressure and pulse.
d
Physical conditions ticked from a list, and any physical condition currently treated pharmacologically.
e
Upper and lower back pain and fibromyalgia.
f
N=12 136 with HADSb8 as reference group.
g
N=12 101 with HADSb8 as reference group.
h
1.01–3.00 years follow-up (predicting n=192 awards among n=14,958 participants).
i
N=11,938 with HADSb8 as reference group.
j
3.01–7.18 years follow-up (predicting n=330 awards among n=15,096 participants).
k
N=12,030 with HADSb8 as reference group.
b
continuous variable reflecting the number of physical
conditions under pharmacological treatment. The participants also reported experiences of any upper or lower back
pain (yes or no) or having been diagnosed with fibromyalgia (yes or no).
Analyses
Imputation procedures were used to recode some
variables with incomplete responses. Missing responses
in health related variables (smoking habits n=528, alcohol
consumption n=32 and physical activity n=485) were
substituted with predictions based on multivariate linear
regression models built on valid responses to other
independent variables relevant for this study, while
missing data on physical measures (between n=12 and
n=29 cases) were substituted with the mean value of
the variable. Missing information in variables on physical
conditions (n=45) and physical conditions under pharmacological treatment (n=230) were coded as 0, as most
people in this age group do not have any somatic
conditions and are prescribed few, if any, medicines
(Table 1).
The independent effects of anxiety and depression on DP
award in the follow-up period were calculated with Cox
regression models (SPSS ver.15 for all analyses) (Table 2).
The regression analyses were conducted for four nested
outcomes: subsequent DP for any disorder, DP for any
disorder during short (1.01–3.00 years) and long (3.01–7.18
years) follow-up, and subsequent DP for any disorder
excluding awards for mental disorder (F00–F99 in ICD-10
codes). Results are presented as hazard ratios (HR) with 95%
confidence intervals (CI). After examining the effect of
anxiety and depression on DP award, we adjusted for
potential confounding variables by sequentially entering six
blocks in an a priori determined order. The blocks (gender,
sociodemographic factors, health related behavior, physical measures, physical conditions and back pain and
fibromyalgia) contained health and sociodemographic variables with known associations to DP award [13,15,24–28].
In an additional Cox regression analysis, we also included zscored symptom scores for anxiety and depression as
independent continuous variables, adjusted for gender
only, and then fully adjusted.
For the hypothesized dose-response associations between symptom load of anxiety and depression and
A.K. Knudsen et al. / Journal of Psychosomatic Research 69 (2010) 59–67
Fig. 1. Dose–response association of HADS anxiety and depression on disability pension award during 1.01–7.18-year follow-up.
63
64
A.K. Knudsen et al. / Journal of Psychosomatic Research 69 (2010) 59–67
subsequent DP award, gender-adjusted HRs with 95% CI
were calculated for the four groups with symptom ranges
higher than the reference group. Population attributable
fractions (PAF) were then calculated to examine the
proportion of DP awards attributable to each symptom
level [29]. The dose-response associations, including the
PAFs, are visualized as error bar graphs with 95% CI
(Fig. 1).
comorbid anxiety and depression during the short followup, while anxiety alone showed a more stable association
over the entire follow-up period (Table 2, lower sections).
Comorbid anxiety and depression remained significant
regardless of level of adjustment in both short and long
follow-up.
Aim 2: Are symptoms of anxiety and depression independent
risk factors for DP awarded for physical diagnoses?
Ethical statement
The study protocol was approved by the Regional Ethics
Committee and by the Norwegian Data Inspectorate. Written
statements of informed consent were gathered from all the
participants at the time of physical examination.
Results
DP award was more common among non-participants;
13.3% of the non-participants received DP either before
or after the health screening, versus 7.2% of the participants
(Pb.001).
Population characteristics are given in Table 1. Among
the participants, 79.3% reported no anxiety and depression,
11.5% reported case-level anxiety, 3.4% case-level depression, and 5.8% reported comorbid anxiety and depression at
the time of health screening.
Aim 1: Are symptoms of anxiety and depression independent
and longstanding risk factors for subsequent DP award?
During the 1.01–7.18-year follow-up, 522 persons, 3.4%
of the study population, were awarded DP for all
medicolegal diagnoses. Case-level anxiety, depression and
comorbid anxiety and depression were associated with
significantly elevated risk for subsequent DP award during
follow-up (anxiety: HR 1.90, depression: HR 2.44, comorbid anxiety and depression: HR 4.92, adjusted for
gender) (Table 2, upper section). The initial associations
were moderately attenuated by adjustment for the potentially
confounding variables. Both anxiety, depression, and
comorbid anxiety and depression remained statistically
significant in the fully adjusted model [anxiety: HR 1.36
(95% CI 1.07–1.74), depression: HR 1.72 (95% CI 1.16–
2.55), comorbid anxiety and depression: HR 2.60 (95% CI
2.06–3.28)]. Re-analyzing the association of interest applying continuous z-scored scale scores confirmed the
findings [anxiety: HR=1.60 (95% CI 1.49–1.71) adjusted
for gender only, HR=1.29 (95% CI 1.20–1.39] fully
adjusted; depression: HR=1.63 [95% CI 1.53–1.74) adjusted
for gender only, HR=1.33 (95% CI 1.25–1.43) fully
adjusted] (data not shown).
Examining these associations with short and long
follow-up separately (1.01–3.00 years versus 3.01–7.18
years), we found a stronger association with depression and
Among DP recipients awarded for medicolegally diagnosed mental disorder (F00–F99), 68.8% were case-positive
for anxiety and/or depression measured by HADS at baseline.
Correspondingly, 33.0% were case-positive among those
with awards for musculoskeletal disorders (M00–M99) and
36.1% were case-positive among those with awards for any
other ICD-10 diagnosis (data not shown).
Anxiety, depression, and comorbid anxiety and depression predicted awards for physical conditions (awards
for medicolegally diagnosed mental disorder excluded
from the analysis) (Table 2, middle section). The
associations were slightly weaker than in the model
including all awards (Table 2, upper section), with
anxiety HR 1.51 (95% CI 1.14–1.99), depression HR
2.09 (95% CI 1.34–3.26), and co-morbid anxiety and
depression HR 3.26 (95% CI 2.46–4.32), adjusted
for gender.
Comorbid anxiety and depression was statistically
significant in predicting awards for physical medicolegal
diagnoses regardless of level of adjustment [HR 1.73, 95%
CI (1.30–2.32)] (Table 2, middle section). The associations
between subsequent DP award and non-comorbid anxiety
and depression were robust for all adjustments except back
pain and fibromyalgia.
Aim 3: What proportion of DP awards can be attributed to
sub case-level symptom loads of anxiety and depression?
The associations between symptom load of anxiety
and depression, and subsequent DP award, followed
dose-response associations (Fig. 1). The highest symptom loads (HADS score 15-21) had associations with
hazard ratios ranging between 11 and 12. In the sub
case-level anxiety group, 140 (3.2%) were awarded DP
award during follow-up compared to 190 (7.2%) in the
combined case-level groups. In the sub case-level
depression group, 92 (3.6%) were awarded DP during
follow-up versus 131 (9.4%) in the case-level groups
combined. However, because of the higher prevalence of
sub-case level symptoms, the proportion of awards
attributable to sub case-level symptom loads of anxiety
and depression were comparable to awards attributable
to all case-level groups combined. PAF for sub caselevel anxiety was 0.07 versus case-level 0.11, and sub
case-level .05 versus case-level PAF 0.06 for depression
(Fig. 1).
A.K. Knudsen et al. / Journal of Psychosomatic Research 69 (2010) 59–67
Discussion
Key findings
This study has three main findings: First, symptoms of
anxiety and depression were independently associated with
subsequent DP award over a period of 1.01–7.18 years.
Second, comorbid anxiety and depression was independently
associated with subsequent DP award for physical conditions. Finally, in population terms, the contribution of sub
case-level symptom loads of anxiety and depression to DP
awards is comparable with symptoms reaching case-level.
To the best of our knowledge, this is the first published report
to demonstrate the long term occupational impact of subcase level mental health symptoms.
Strengths and limitations
This study has several important strengths. The number of
participants was large and drawn from a population-based
sample. Using information about DP award from national
registers allows for long follow-up with practically no
attrition. To the best of our knowledge, our study has a longer
follow-up than any other population-based study of mental
disorders and DP award. Some important biases in studies of
these associations are minimized by using discrepant data
sources for exposure and outcome measurements. Further,
the participants' responses or behaviour in the health
screening could not influence the outcome of a potential
future application for DP award, a strength compared to
studies based on information gathered in clinical settings.
The detailed nature of the HUSK allowed us to consider the
potential confounding effects of a range of sociodemographic factors, health-related behavior and physical conditions. However, except for gender, all included covariates
could act as confounding and/or mediating factors, and the
full adjustment in our analyses is likely to be an overadjustment, resulting in an underestimation of the true effect
of mental symptoms on DP award.
Our study also has some weaknesses. Case-level anxiety
and depression in HADS are not equivalent to clinical
diagnoses. We emphasize that our study demonstrates
associations between symptoms of anxiety and depression
and DP awards, rather than necessarily associations between
clinical diagnoses and the outcomes. The cutoff score of ≥8
is reported to provide an optimal balance between sensitivity
and specificity [21], while the subclassification of HADS
scores into five groups for severity (Fig. 1) rests on facevalidity only.
Second, information about physical conditions at baseline
was gathered by self-report. The list of physical conditions
was limited to six, with additional conditions derived
through information about pharmacological treatment, but
not weighed for severity. Memory bias and lack of data on
conditions neither listed nor pharmacologically treated,
might lead us to underestimate the true confounding from
65
physical conditions. Recent evidence indicates childhood
mood and temperament to be of relevance for disability
benefits in adulthood [30]. Occupational hazards and
personality, both of which could theoretically be relevant
in explaining the effect of the exposure on the outcome [31],
were not controlled for.
Third, it has been argued that the process of applying for
DP award may elevate symptom loads of anxiety and
depression [18]. Consequently, despite applying a 1-year
window before follow-up, we cannot fully exclude the
possibility of reverse causation.
Fourth, DP awards were more common among nonparticipants than participants, which fits with other studies
demonstrating that participants in health screening are
healthier than non-participants [32]. Disproportionate exclusion of individuals with poorer health might lead us to
underestimate both the effect of anxiety and depression
symptoms as risk factors for DP award and the level of
confounding from physical conditions.
Fifth, the national registry only contains information about
the primary diagnoses the DPs were awarded for. In the
analysis of the second aim, we excluded those with mental
disorders as medicolegal diagnoses. Some of these would
have had a mental disorder as a secondary or third diagnosis,
although when mental disorders appear in DP applications,
they usually do so as the primary diagnosis [11].
Finally, some might question the generalizability of the
findings. The study was conducted in a particular county and
country, and on a specific age-group. However, the increase
in disability benefit recipients in general, and for mental
disorders in particular, is similar across different OECD
countries [1], and the results from our study should be
relevant in other developed countries. The young age among
our participants may increase the importance of these results:
These individuals have many years left before scheduled
retirement age, and it is therefore of particular importance to
address the causes of work force exit in this age group.
Underestimation of the effect of symptoms of anxiety and
depression on work related disability
One interpretation of our results is that official figures
(often obtained from medicolegal diagnoses at the time of
DP award) underestimate the impact of common mental
disorders on work disability. This underestimate may also
reflect under-recognition of mental health problems at a
clinical level. Award of DP is usually the result of multiple
health problems, with anxiety and depression sometimes
comorbid with physical conditions [11,33]. When mental
and physical disorders coexist, the mental disorder may be
secondary to the physical condition [8]. In such situations,
the presence of a secondary mental disorder may cause
additional functional impairment, with award of DP being
the end result. Alternatively, somatic symptoms may reflect
an underlying primary mental disorder. In both situations,
the mental disorder may go unrecognized and untreated.
66
A.K. Knudsen et al. / Journal of Psychosomatic Research 69 (2010) 59–67
Many patients prefer somatic over mental diagnoses [34],
reducing the chances of mental disorders being reported.
An alternative interpretation of our findings is that
symptoms of distress, rather than treatable disorders, are
risk factors for DP awards. This interpretation could have
different public health implications. It would imply that
rather than being concerned with the health system's ability
to recognize treatable disorders, it is more important to
recognize that symptoms of distress are a marker of
vulnerability, possibly associated with personality characteristics [30], unhappiness in the workplace [35], interpersonal
conflict at home or at work, and so on. This interpretation
sees DP award as the end of a complex process, rather than
simply the outcome of a mental disorder.
The importance of sub case-level symptom loads
The PAF calculation combines effect sizes with frequencies. Thus the comparable PAFs between case-level and sub
case-level symptom loads of anxiety and depression are
being driven by the high prevalence of sub case-level
symptom loads [29]. Our finding is in accordance with
Broadhead's [12]: On a population level, the large group
with sub case-level symptom loads, each with a relatively
low risk, also incurs an important contribution to DP award.
The potential for preventing DP in the population is thus
comparable, with the elimination of sub case-level symptoms predicted to prevent 12% of all DPs, compared to 17%
with case-level symptoms.
Although mental disorders increasingly appear as the
warranting cause for DP awards [1], evidence from
epidemiological studies indicate that the prevalence of
mental disorders has remained unchanged between 1990
and 2003 [9]. The identified risk in the sub case-level group
is therefore probably not solely caused by sub case-level
anxiety and depression cases developing into more severe
states. Even low levels of anxiety and depression symptoms
may add weight to the burden experienced by individuals
with other conditions [6], and effectively “tip the scale” with
DP award as the outcome.
The large numbers of individuals with sub case-level
symptom load represents a major challenge to traditional
public health approaches, and makes any intervention an
economic and logistic challenge. Established treatments for
more severe depression cannot necessarily be applied to mild
or sub case-level symptom loads [36]. Individual treatment
approaches in the sub case-level group are not necessarily
the best solution. Future intervention trials may need to
focus on population or group level interventions and must
also consider the potential risks of pathologizing mild levels
of symptomatology.
Acknowledgments
The data collection for this study was conducted as part of
the Hordaland Health Study 1997-1999 (HUSK) in collab-
oration with the Norwegian National Health Screening
Service. S.H. and M.H. are supported by the NIHR
Biomedical Research Centre for Mental Health at the
South London and Maudsley NHS Foundation Trust and
Institute of Psychiatry, Kings College London. Marianne
Klokk contributed in construction of the variable “physical
conditions under pharmacological treatment,” and Jens
Christoffer Skogen helped designing the figures. We are
also grateful for contributions from Ingvard Wilhemsen and
other members of the Network for Psychiatric Epidemiology. The authors received no specific funding for this study.
References
[1] OECD. Transforming disability into ability. Policies to promote work
and income security for disabled people. Paris: OECD Publications
Service, 2003.
[2] Black C. Working for a healthier tomorrow. London: The Stationery
Office, 2008.
[3] Harvey SB, Henderson M, Lelliott P, Hotopf M. Mental health and
employment: much work still to be done. Br J Psychiatry 2009;1943:
201–3.
[4] Moncrieff J, Pomerleau J. Trends in sickness benefits in Great Britain
and the contribution of mental disorders. J Public Health Med 2000;
221:59–67.
[5] Murray CJ, Lopez AD. Global mortality, disability, and the
contribution of risk factors: global burden of disease study. Lancet
1997;3499063:1436–42.
[6] Moussavi S, Chatterji S, Verdes E, Tandon A, Patel V, Ustun B.
Depression, chronic diseases, and decrements in health: results from
the World Health Surveys. Lancet 2007;370:851–8.
[7] Harvey SB, Ismail K. Psychiatric aspects of chronic physical disease.
Medicine 2008;36:471–4.
[8] Thompson C, Kinmonth AL, Stevens L, Peveler RC, Stevens A, Ostler
KJ, et al. Effects of a clinical-practice guideline and practice-based
education on detection and outcome of depression in primary care:
hampshire depression project randomised controlled trial. Lancet 2000;
3559199:185–91.
[9] Kessler R, Demler O, Frank R, Olfson M, Pincus H, Walters E, et al.
Prevalence and treatment of mental disorders 1990 to 2003. N Engl J
Med 2005;35224:2515–23.
[10] Olsson I, Mykletun A, Dahl A. General practitioners' self-perceived
ability to recognize severity of common mental disorders: an
underestimated factor in case identification? Clin Pract Epidemiol
Ment Health 2006;2:21.
[11] Mykletun A, Overland S, Dahl AA, Krokstad S, Bjerkeset O, Glozier
N, et al. A population-based cohort study of the effect of common
mental disorders on disability pension awards. Am J Psychiatry 2006;
1638:1412–8.
[12] Broadhead WE, Blazer DG, George LK, Chiu KT. Depression,
disability days, and days lost from work in a prospective epidemiologic
survey. JAMA 1990;26419:2524–8.
[13] Holmberg S, Thelin A. Primary care consultation, hospital admission,
sick leave and disability pension owing to neck and low back pain: a
12-year prospective cohort study in a rural population. BMC
Muscloskelet Dis 2006;7:66.
[14] Manninen P, Heliovaara M, Riihimaki H, Makela P. Does psychological distress predict disability? Int J Epidemiol 1997;26:1063–70.
[15] Ericsson M, Poston W, Linder J, Taylor J, Haddock C, Foreyt J.
Depression predicts disability in long-term chronic pain patients.
Disabil Rehabil 2002;246:334–40.
[16] Sorvaniemi M, Helenius H, Salokangas R. Factors associated with
being granted a pension among psychiatric outpatients with major
depression. J Affect Disord 2003;75:43–8.
A.K. Knudsen et al. / Journal of Psychosomatic Research 69 (2010) 59–67
[17] Hensing G, Wahlstrom R. Chapter 7. Sickness absence and psychiatric
disorders. Scand J Public Health 2004;32:152–80.
[18] Øverland S, Glozier N, Henderson M, Mæland J, Hotopf M, Mykletun A.
Health status before, during and after disability pension award: the
Hordaland Health Study (HUSK). Occup Environ Med 2008;65:769–73.
[19] Zigmond A, Snaith R. The hospital anxiety and depression scale. Acta
Psychiatr Scan 1983;676:361–70.
[20] Snaith R. The concepts of mild depression. Br J Psychiatry 1987;150:
387–93.
[21] Bjelland I, Dahl A, Haug T, Neckelmann D. The validity of the
hospital anxiety and depression scale. An updated literature review.
J Psychosomat Res 2002;522:69–77.
[22] Mykletun A, Bjerkeset O, Øverland S, Prince M, Dewey M, Stewart R.
Levels of anxiety and depression as predictors of mortality: the HUNT
study. Br J Psychiatry 2009;195:118–25.
[23] Akselsen A, Lien S, Sandnes T. FD-trygd dokumentasjonsrapport.
Pensjoner. Grunn og hjelpestønader 1992-2001 [FD-trygd documentation report. Pensions. Basics and supplementary benefits]. Oslo:
Rikstrygdeverket, 2003. Report No.: 26.
[24] Eriksen H, Ihlebaek C, Jansen J, Burdorf A. The relations between
psychosocial factors at work and health status among workers in home
care organizations. J Behav Med 2006;133:183–92.
[25] Husemoen LL, Osler M, Godtfredsen NS, Prescott E. Smoking and
subsequent risk of early retirement due to permanent disability. Eur J
Pub Health 2004;141:86–92.
[26] Krokstad S, Johnsen R, Westin S. Social determinants of disability
pension: a 10-year follow-up of 62 000 people in a Norwegian county
population. Int J Epidemiol 2002;316:1183–91.
67
[27] Neovius K, Johansson K, Rössner S, Neovius M. Disability pension,
employment and obesity status: a systematic review. Obes Rev 2008;
96:572–81.
[28] Rivenes AC, Harvey SB, Mykletun A. The relationship between
abdominal fat, obesity, and common mental disorders: results from the
HUNT Study. J Psychosomat Res 2009;664:269–75.
[29] Prince M, Stewart R, Ford T, Hotopf M. Practical psychiatric
epidemiology. Oxford University Press Inc., 2003
[30] Henderson M, Hotopf M, Leon D. Childhood temperament and
long-term sickness absence in adult life. Br J Psychiatry 2009;194:
220–3.
[31] Stansfeld S. Work, personality and mental health. Br J Psychiatry
2002;181:96–8.
[32] Pietila A, Rantakallio P, Laara E. Background factors predicting
nonresponse in a health survey of northern finnish young men. Scand J
Soc Med 1995;232:129–36.
[33] Stordal E, Bjelland I, Dahl A, Mykletun A. Anxiety and depression in
individuals with somatic health problems. The Nord-Trondelag Health
Study (HUNT). Scand J Prim Health Care 2003;21:136–41.
[34] Mechanic D. Barriers to help-seeking, detection, and adequate
treatment for anxiety and mood disorders: implications for health
care policy. J Clin Psychiatry 2007;68:20–6.
[35] Stansfeld S, Candy B. Psychosocial work environment and mental
health - a meta-analytic review. Scand J Work Environ Health 2006;
326:443–62.
[36] Kirsch I, Deacon B, Huedo-Medina T, Scoboria A, Moore T, Johnso B.
Initial severity and antidepressant benefits: a meta-analysis of data
submitted to the food and drug administration. PLoS Med 2008:52.