Common mental disorders and disability pension award: Seven year follow-up of the HUSK study

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1 Journal of Psychosomatic Research 69 (2010) 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 (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 7- year follow-up. Results: DP awards for all diagnoses were predicted both from case-level anxiety [HR 1.90 (95% CI Keywords: Anxiety; Depression; Sub-clinical symptoms; Work disability 2.41)], case-level depression [HR 2.44 (95% CI ] and comorbid anxiety and depression [HR 4.92 (95% CI )] 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 )]. 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 Elsevier Inc. All rights reserved. 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.: ; fax: address: Ann.Knudsen@psych.uib.no (A.K. Knudsen). 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 /10/$ see front matter 2010 Elsevier Inc. All rights reserved. doi: /j.jpsychores

2 60 A.K. Knudsen et al. / Journal of Psychosomatic Research 69 (2010) 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 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 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,andlinkedtothehealth 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

3 A.K. Knudsen et al. / Journal of Psychosomatic Research 69 (2010) 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 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 Table 1 Population characteristics N % Mean S.D. Range Final study population 15, Age a Gender (female) Marital status (married) 11, DP award during follow-up Follow-up time (years) Self-reported current work for income 13, HADS, case-levels ( 8) Reference group (b8) 12, Anxiety only Depression only Comorbid anxiety and depression Body Mass Index (kg/m 2 ) Waist Hip Ratio Level of total cholesterol (mmol/l) Systolic blood pressure (mmhg) Income after tax (EUR) 22,485 18, *10 6 Educational level Compulsory only High school Higher education (college and university) Physical activity (h/week) No physical activity b N Smoking (smoker) Alcohol consumption (units pr 2 weeks) , N Number of physical conditions (0) 14, Number of physical conditions under pharmacological treatments (0) 14, Self-reported fibromyalgia Self-reported back pain a Age at participation in the health screening.

4 62 A.K. Knudsen et al. / Journal of Psychosomatic Research 69 (2010) 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 Depression only Comorbid anxiety depression Adjustment variables HR 95% CI HR 95% CI HR 95% CI All awards (predicting n=522 awards among n=15,288 participants f ) No adjustments Gender Sociodemographic factors a Health related behavior b Physical measures c Physical conditions d Back pain and fibromyalgia e Awards for mental disorders (F00-F99) excluded (predicting n=410 awards among n=15,176 participants g ) No adjustments Gender Sociodemographic factors a Health-related behavior b Physical measures c Physical conditions d Back pain and fibromyalgia e Fully adjusted, 1 3 years of follow-up h, i Fully adjusted, 3 7 years of follow-up j, k a Income, education and marital status. b 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= with HADSb8 as reference group. g N= with HADSb8 as reference group. h years follow-up (predicting n=192 awards among n=14,958 participants). i N=11,938 with HADSb8 as reference group. j years follow-up (predicting n=330 awards among n=15,096 participants). k N=12,030 with HADSb8 as reference group. 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 ( years) and long ( 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 z- scored 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

5 A.K. Knudsen et al. / Journal of Psychosomatic Research 69 (2010) Fig. 1. Dose response association of HADS anxiety and depression on disability pension award during year follow-up. 63

6 64 A.K. Knudsen et al. / Journal of Psychosomatic Research 69 (2010) 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). 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 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 ), depression: HR 1.72 (95% CI ), comorbid anxiety and depression: HR 2.60 (95% CI )]. Re-analyzing the association of interest applying continuous z-scored scale scores confirmed the findings [anxiety: HR=1.60 (95% CI ) adjusted for gender only, HR=1.29 (95% CI ] fully adjusted; depression: HR=1.63 [95% CI ) adjusted for gender only, HR=1.33 (95% CI ) fully adjusted] (data not shown). Examining these associations with short and long follow-up separately ( years versus years), we found a stronger association with depression and 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? 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 ), depression HR 2.09 (95% CI ), and co-morbid anxiety and depression HR 3.26 (95% CI ), 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 ( )] (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).

7 A.K. Knudsen et al. / Journal of Psychosomatic Research 69 (2010) 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 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 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.

8 66 A.K. Knudsen et al. / Journal of Psychosomatic Research 69 (2010) 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 (HUSK) in collaboration with the Norwegian National Health Screening Service. 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