Socioeconomic Position and Major Mental Disorders

Abstract

Psychiatric epidemiologists were among the first to use the term “social epidemiology” (1), and the role of the social environment in the etiology and course of major mental disorders continues to be investigated (2–5). A number of reviews published in the late 1990s documented the associations between socioeconomic position (SEP) and specific mental disorders (6–9); in 2003, a comprehensive meta-analysis of the research on SEP and depression (10) concluded that both prevalence and incidence studies show that persons of low SEP (i.e., low educational and low income levels) are at a higher risk of depression. Here, we examine innovative developments in the study of the associations between SEP and major mental disorders. We use the term “socioeconomic position” for pragmatic and conceptual reasons: 1) it allows us to follow the convention in the first textbook of social epidemiology (i.e., Berkman and Kawachi’s Social Epidemiology (8)), and 2) socioeconomic “position” is neutral with respect to the relational/ordinal distinction that sets social class apart from socioeconomic status. Thus, the term “socioeconomic position” encompasses both social class (referring to social relations of ownership and control over productive assets) and socioeconomic status (referring to the ordering of persons along a continuum of some valued socioeconomic attribute such as income or education). We focus on the life-course approach (11) taken in studies of the selection-causation issue, using data on ethnic stratification, immigration and schizophrenia, and the long-term impact of early life-course exposures such as fetal stress and childhood poverty. We also highlight new developments in social class concepts and measures that have led to new findings on the effects of SEP, the relative contributions of neomaterial and psychosocial pathways, evidence on multilevel associations between geographic area SEP and mental disorders, and gender-specific hypotheses. Contrary to the idea that the research on the relation between SEP and mental disorders has been exhausted, these recent innovations are generating promising hypotheses to be tested in future research in upcoming years. Using multidisciplinary (Current Contents; Thomson ISI, Philadelphia, Pennsylvania) and biomedical (PubMed; National Library of Medicine, Bethesda, Maryland) databases, our review is based primarily on English-language cross-sectional and longitudinal studies published between 1999 and August 2003 that included “social class” or “socioeconomic status” and selected major psychiatric disorders (i.e., schizophrenia, major depression, and anxiety disorders). The period covered was chosen to minimize overlap with previous reviews (6, 7, 9, 12). Disorders were selected on the basis of their prevalence in the population (depression and anxiety) or their centrality to the literature on SEP (schizophrenia, bipolar disorder, and depression). Evidence on the relation of anxiety disorders to SEP is more limited because the diagnosis has been subject to more fluctuation than that for depression, bipolar disorder, or schizophrenia. For example, the current diagnostic concepts of panic disorder, phobic disorder, and generalized anxiety disorder are new with the 1980 revision of the diagnostic manual of the American Psychiatric Association (13). As a result, few longitudinal studies are available. Prevalence data from the Epidemiologic Catchment Area Study (14–16) consistently suggest that lower socioeconomic status groups have a higher prevalence of panic, all types of phobias, and generalized anxiety disorder. The evidence is less conclusive for obsessive-compulsive disorder. These general findings about socioeconomic status and prevalence were confirmed in the National Comorbidity Study for generalized anxiety disorder (17), panic (18), and agoraphobia, simple phobia, and social phobia (19). Incidence data from the Epidemiologic Catchment Area Study show that low occupational prestige is a risk factor for panic attacks and panic disorder (20) and that low educational level is a risk factor for agoraphobia (21), social phobia (22), and obsessive-compulsive disorder (23). To our knowledge, there are no population-based incidence data for generalized anxiety disorder. Since we did not find much innovation in the literature on SEP and anxiety disorders or bipolar disorder, our review focuses on schizophrenia and depression. Because of the breadth of the SEP literature, we have omitted associated work on community integration and the role of access to and utilization of health services in explaining the relation between SEP and the course of major psychiatric disorders (24). Schizophrenia is considered the most severe and debilitating mental illness. It is characterized by delusions, hallucinations, disorganized behavior, negative symptoms (e.g., flat affect), and social/occupational dysfunction. The relation of SEP to severe mental disorders was the subject of inquiry even a hundred years ago, before the diagnostic distinction between schizophrenia and manic-depressive illness was made (25); research in this area has continued (26–29). Over the years, the literature on schizophrenia has been rich but woefully inadequate on bipolar disorder. Scattered findings show no relation between risk of bipolar disorder and socioeconomic disadvantage as indexed by measures such as income, education, occupation, or area of residence (or a random distribution, as Faris and Dunham (26) concluded). A recent review noted the paucity of research (30). A 1974 review (31) included 17 studies, and all but two (in rural areas) showed a higher risk of schizophrenia for those of lower SEP. A review through 1998, with 13 additional studies, also showed a higher risk (32). Methodological progress has occurred over these years: the early studies were of prevalence data, later studies used administrative incidence data, and some recent studies have been conducted with large registry systems with data on the SEP of parents or at birth. The theoretical issue has always been whether stresses associated with low SEP increase the risk or whether the occurrence of frank or occult psychosis, or its insidious onset, leads to less-effective performance in the socioeconomic arena and lower SEP—the so-called selection-causation issue (5). Nevertheless, there is no consistent pattern in the literature with regard to the direction and magnitude of socioeconomic differences in schizophrenia. The latest review (32) was able to determine whether indices of SEP focused on the respondent’s SEP or that of the respondent’s parents. Studies using the respondent’s SEP all reported that schizophrenics had a lower SEP than expected. Of the five studies that used the parents’ SEP, three reported a higher risk for those whose parents had a higher SEP, one reported no difference, and the fifth reported an increased risk for those whose parents’ SEP was lower than expected. Since that review was published, three studies have appeared: one showed a higher risk for those whose parents were in a disadvantaged position (33); in two, the findings depended on the measure of SEP used (34, 35). It may be that the finding of high SEP for parents of schizophrenics is explained by earlier treatment (34), but some data suggest that low-SEP schizophrenics are more likely to have positive symptoms, which logically would be expected to be associated with early treatment (36). A recent longitudinal study from the Danish registry helps sort out these complex findings (37). That study found that as many as 19 years prior to treatment, the odds of lower SEP were greater for those who eventually were diagnosed as schizophrenic than for a control population. This study was drawn from the same Danish population as the study by Byrne et al. (35) (albeit with slightly different sample requirements), which found a weak relation of schizophrenia risk to the SEP of parents. Most of the SEP data are consistent with little or no effect of SEP at birth but a gradual onset of subtle educational and occupational disabilities associated with an eventual diagnosis of schizophrenia. Ethnicity is often defined by a set of cultural patterns (values, beliefs, roles, affective and cognitive styles, and norms), heritage, or ancestry shared by a social group of common national or geographic origin. In many countries, processes of ethnic stratification place disproportionate numbers of persons from some ethnic groups at a substantial social disadvantage. Religion, language, and country of origin, which are ethnic indicators, thus serve as markers for deprived ethnic groups in many national settings (38). Unlike socioeconomic indicators such as education, occupation, and income, there is no possibility that ethnic status could be determined by schizophrenia or its insidious onset. Seventeen studies conducted prior to 1997 (38) and at least one performed since then (39) have shown a higher risk for deprived ethnic groups in England and the Netherlands, with odds ratios comparing them with the general population ranging from 1.7 to 13.2 (none of the 17 studies adjusted for SEP). Rates of schizophrenia are low in the countries of origin in which these rates have been studied, suggesting that a genetic explanation is unlikely. Rates are high in second-generation immigrants in the ethnically deprived groups, suggesting that the stress of immigration is not the culprit. The possibility of stress to the fetus through cephalopelvic disproportion has been suggested as an explanation, since, compared with the fetus, these mothers tend to have been raised in nutritionally less advantaged environments in their country of origin (40). However, studies show little or no difference between groups in terms of fetal stress (41). It thus appears that something connected to the disadvantaged placement of the group in the society of destination increases the risk of schizophrenia. Building on Murphy’s notions of the schizophrenia-evoking role of complex social tasks (42) and work on frontal lobe disturbances in schizophrenia (43), Eaton and Harrison (32) have suggested that the cognitive challenge of formulating a life plan is more difficult for those of a disadvantaged ethnic status, and the difficulty of this task interacts with genetic vulnerability to schizophrenia in some persons, increasing the risk of schizophrenia for those who are ethnically disadvantaged. This view is consistent with the evidence that persons belonging to deprived ethnic groups are at a greater risk of schizophrenia if they live in neighborhoods with proportionately fewer persons of the same ethnic group (44). The contrast between SEP results as indexed by typical indicators of socioeconomic status and indicators based on ethnic status is informative. It has sometimes been assumed that the stresses associated with socioeconomic deprivation are equivalent to the stresses associated with ethnic stratification (4). However, apparently the causal factors operate differently for these two aspects of social stratification, because ethnic stratification increases the risk of schizophrenia and SEP does not. The clinical syndrome of depression (i.e., major depressive disorder) includes alterations of mood such as sadness, irritability, despair or loss of motivation or pleasure, and psychophysiologic symptoms involving appetite, sleep, libido, energy level, and psychomotor activity. For persons in the lower social strata, the odds of reporting depression are about 1.81 times higher than for those in the higher social strata, according to a recent meta-analysis focusing on socioeconomic status and depression (10). Analyses that use a life-course approach to examine the higher odds of depression in the lower social strata primarily emphasize the association of SEP with depression over long periods of time, decades, or even generations. This topic is difficult to analyze with cross-sectional research because any differences in the association of SEP with depression across age groups are subject to at least three different interpretations. That is, a change could represent 1) an aging effect that reflects differences to age or life 2) a effect that reflects the of a or a period effect that all who a A for these effects is a longitudinal that includes measures of SEP and depression. Here, we review selected studies based on such data sets a of the most longitudinal data sets that would be for life-course of SEP and mental to Eaton et al. To two have much of the research on SEP and depression over the life The first is the causal direction between SEP and depression. association represent an of SEP on depression, to the that the greater prevalence of and stress in the lower social strata or an to the that depressive illness leads to or this is in whether studies of the association between SEP and depression are to risk factors for depression in of lower SEP as of a or or to factors that SEP. the is in whether SEP be as an and depression as a or In terms of the is in whether and based that depression (e.g., or focus on persons with mental illness from social (e.g., by increasing access to treatment and and social and community Most longitudinal focusing on this suggest a causal direction from SEP to depression of the first longitudinal studies to social was the by longitudinal studies that of data from and the to the using have to and by using cross-sectional that to their mental many years before the of but the results from these studies are in of the finding that are subject to substantial A in recent life-course studies is whether the higher rates of depression anxiety) in the lower social strata that place earlier in the life in or in earlier of or whether they This is of theoretical in to determine whether SEP an role in the of depression. the to this determine whether studies to factors that to an association of SEP with depression and anxiety use a cross-sectional research would be if the association reflects longitudinal studies with on In terms of this is in whether at the negative of socioeconomic on health its earlier in the life evidence that the association of socioeconomic status with depression and anxiety reflects both in and long-term in previous life of the studies to this used the birth which on more than at birth and at 7, and years. Using these data, et al. showed that factors at age years the association of SEP with depression and anxiety symptoms at age years by as much as These factors included the and in the the same time, the study found that the association of SEP with depression also factors such as and have also shown that the association of SEP with depression anxiety) reflects factors that from previous life as as in social epidemiology has to the of the and measures of SEP the conceptual and of social as a social relation to the of and services (e.g., from socioeconomic status, as the of persons along a continuum of or cultural (e.g., income, educational occupational recent studies have tested the of social class measures and to mental health findings have from this 1) social class and socioeconomic status to different hypotheses the relation between SEP and mental disorders, and 2) measures of social class and socioeconomic status are not study for example, found a overlap between socioeconomic status and social class but the association between social class and depression, as by the could not be for by socioeconomic status (i.e., and occupational This set of specific diagnostic was for a selected group of psychiatric disorders and is to a major in psychiatric the low of psychiatric studies found evidence of a relation between social class and mental as would be by social class but not by socioeconomic status a class et al. found that not have but and have higher rates of depression and anxiety than both have control over and and have The class from of class relations that includes control and relations in the that is, control over over is determined by the possibility of (i.e., the number of or services of work and of and by over in the or or or The of control at work would most mood and anxiety disorders. on the are to a the of to the and the of little over This class may place at greater risk of depression and anxiety disorders than or the a socioeconomic status would have a lower of mental disorders among because they have higher and prestige than Nevertheless, the literature on social class and major psychiatric disorders evidence of class position to depression and anxiety disorders. of the relative of or risk or and (e.g., of relative in the income of SEP in health in countries indicators of SEP (e.g., a a indices of have been in the social epidemiology of mental disorders, in the For example, in a national of in the et al. found an association between access to a and disorder some of anxiety and depression. In an of the found that a low of in a and no access to a or was associated with a risk of depression and anxiety disorders A geographic area (i.e., an in the deprivation and has been associated with the prevalence of depression. deprivation indicators suggest that of increases the risk of psychiatric disorders, the research has to the specific factors to depression or the a number of studies have cross-sectional and evidence of the association of psychosocial factors (e.g., with depression, symptoms of depression, and anxiety disorders A common of both and studies is on measures of depression and anxiety and use of diagnostic to mental disorders. In of this the that (i.e., or exposures are more than in explaining the association between SEP and most mental disorders (e.g., less than for exposures to such as on by could the association between SEP and schizophrenia, mood disorders such as depression are by risk factors that among persons of low SEP (e.g., life The study of the associations between SEP (e.g., the or income of a respondent’s area of or and mental health is a area of social epidemiology These studies as a across all of have since the and have to contributions to our about the association of SEP with health for as as the for SEP to the association between and health status for to et al. studies to in the area of mental health have been or findings on associations between (e.g., indices of disadvantage or and mental health are consistent across of level of and in two studies have been longitudinal and of the and et study studies have less consistent with two out of five studies reporting no association between income and depression or anxiety Rates of major mental disorders have been by with have been shown to be at two times or more the risk of depression and disorders Most of the research on mental disorders among or that comparing with has focused on few studies have at SEP, as in a of has been consistently to be to the risk of anxiety and depressive disorders among However, studies of SEP and depression among have focused on status occupational or no studies have the associations of social class with depression and anxiety among studies of mental disorders among have previous on SEP, stress and the role of social in explaining the higher prevalence of depression among compared with The studies of to find that low SEP low increases the risk of depression of to show higher rates of depression than of with higher or the general population of studies of of of socioeconomic have reported that factors such as and level of are associated with higher rates of depression among SEP has been shown to be associated with a higher risk of depression among studies of SEP and also compared with are at a higher risk of depression and depression in because of their lower socioeconomic and higher to (e.g., higher relative of the of and work stress or negative The most recent studies of depression and have in the by which SEP is to mental disorders among both and reported that and the relation bet