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Previous studies of neighborhood deprivation and mental disorders have yielded mixed results, possibly because they were based on different substrata of the population. We conducted a national multilevel study to determine whether neighborhood deprivation is independently associated with psychiatric medication prescription in a national population.
Nationwide outpatient and inpatient psychiatric medication data were analyzed for all Swedish adults (N=6,998,075) after 2.5 years of follow-up. Multilevel logistic regression was used to estimate the association between neighborhood deprivation (index of education, income, unemployment, and welfare assistance) and prescription of psychiatric medications (antipsychotics, antidepressants, anxiolytics, or hypnotics/sedatives), after adjusting for broadly measured individual-level sociodemographic characteristics.
For each psychiatric medication class, a monotonic trend of increasing prescription was observed by increasing level of neighborhood deprivation. The strongest associations were found for antipsychotics and anxiolytics, with adjusted odds ratios of 1.40 (95% CI, 1.36–1.44) and 1.24 (95% CI, 1.22–1.27), respectively, comparing the highest- to the lowest-deprivation neighborhood quintiles.
These findings suggest that neighborhood deprivation is associated with psychiatric medication prescription independent of individual-level sociodemographic characteristics. Further research is needed to elucidate the mechanisms by which neighborhood deprivation may affect mental health and to identify the most susceptible groups in the population.
In recent years interest has rapidly increased in the contextual effects of neighborhood deprivation on mental health,(1–2) and the use of multilevel modeling to disentangle these effects from individual-level risk factors.(3–4) Previous smaller studies have been based on different population substrata and have yielded mixed results, but most have reported associations between at least one neighborhood characteristic and psychiatric disorders after adjusting for individual-level characteristics.(1, 5–7) The objective of our national multilevel study is to evaluate whether adults living in higher-deprivation neighborhoods are more likely to be prescribed and dispensed psychiatric medications than adults living in lower-deprivation neighborhoods, after adjusting for individual-level sociodemographic characteristics. This study extends previous research through the use of nationwide outpatient and inpatient pharmacy data which enabled us to include all medically treated mental disorders from all health care settings in a national population.
This study is based on anonymous census and pharmacy data for the entire Swedish adult population, ages 18 years and older. Individual-level sociodemographic characteristics were identified using national census data from 2005. Neighborhoods were identified using small area market statistics (SAMS), which are small geographic units with boundaries defined by homogeneous types of buildings and with 1000 to 2000 residents on average.(8) Using 2005 census data, the home addresses of all Swedish adults were geocoded to one of 8,293 SAMS throughout Sweden. These small geographic units were used as proxies for neighborhoods, as has been done in previous research.(8–9)
Psychiatric medication prescription data were obtained using the national pharmacy register maintained by the National Board of Health and Welfare in Sweden. This register contains a record of each medication that is prescribed by a health care provider and dispensed by any outpatient or inpatient pharmacy in Sweden, starting July 1, 2005. To any extent that individuals in higher-deprivation neighborhoods are less likely to pick up psychiatric medications from their pharmacy when prescribed, the association between neighborhood deprivation and psychiatric medications would be underestimated using these data.
The medication data are classified according to the Anatomical Therapeutic Chemical (ATC) System developed by the WHO Collaborating Centre for Drug Statistics Methodology. We obtained data for medications prescribed for conditions of the nervous system (code N), subclassified as antipsychotics (N05A), anxiolytics (N05B), hypnotics and sedatives (N05C), and antidepressants (N06A). These data were linked to census data using an anonymous, serial number version of each individual's unique personal identification number (similar to the U.S. social security number).
A total of 7,036,095 women and men, ages 18 years and older, were identified who were living in Sweden as of July 1, 2005. We excluded 15,908 (0.2%) individuals who had missing data for neighborhood, and 22,112 (0.3%) who had missing data for family income. A total of 6,998,075 individuals (99.5% of the original cohort) remained for inclusion in the analysis.
The study cohort was followed from July 1, 2005 through December 31, 2007, the first 2.5 years that the pharmacy register was kept.
The primary outcome of interest was one or more prescriptions of a psychiatric medication dispensed at any outpatient or inpatient pharmacy in Sweden during the follow-up period. This outcome was evaluated separately for antipsychotics, antidepressants, anxiolytics, and hypnotics/sedatives. We also evaluated for one or more prescriptions in “any of the above” categories.
Neighborhood deprivation was measured using an index comprised of important deprivation indicators (education, income, unemployment, and welfare assistance) identified in the Swedish population by principal components analysis (8) and used in previous research. (8, 10) Using deprivation indicators identified in past studies to characterize neighborhood environments, the principal components analysis was performed to select the most important deprivation indicators based on individuals aged 25 to 64 years using Swedish national census data from 2005. The following four variables were identified and selected by the analysis: low educational level (<10 years of formal education); low income (defined as income from all sources, including interest and dividends, less than 50% of the median individual income);(11) unemployment (excluding full-time students, those completing compulsory military service, and early retirees); and social welfare assistance (in 2005). Each of these variables loaded on the first principal component with similar loadings and explained 52% of the variation among the variables included. Z scores, calculated for each SAMS neighborhood, were weighted by the coefficients for the eigenvectors and summed to create the index,(8, 12) with higher scores indicating more deprived neighborhoods. Neighborhood deprivation index scores were categorized in quintiles for the current analysis.
Female or male.
Age ranged from 18 years and above at the beginning of the study period and was modeled as a continuous variable.
Married/cohabiting, never married, or divorced/widowed.
Employed or unemployed.
Completion of compulsory school or less (≤9 years), practical high school or some theoretical high school (10–11 years), or theoretical high school and/or college (≥12 years).
Provided by Statistics Sweden and derived by dividing annual family income by the number of people in the family, using a weighting system whereby small children were given lower weights than adolescents or adults. The final variable was categorized in quartiles.
Large cities, medium-sized towns, or small towns/rural areas.
<1 year, 1–5 years, or ≥5 years. This was alternatively modeled as a continuous variable but its association with psychiatric medication prescription was constant across the middle portion of this range (1–5 years), and the odds ratios for the main associations of interest (neighborhood deprivation and psychiatric medications) were unchanged.
Multilevel logistic regression was used to estimate odds ratios (ORs) and 95% confidence intervals (CIs) for the association between neighborhood deprivation quintile and prescription of each psychiatric medication (one or more vs. none), using the lowest-deprivation neighborhood quintile as the reference category. Analyses were conducted unadjusted, and then were adjusted for individual-level sociodemographic characteristics (gender, age, marital status, employment status, education, family income, urban/rural status, and time lived at current residence). We explored for interaction effects between neighborhood deprivation and each of these individual-level characteristics with respect to psychiatric medication prescription, using a likelihood ratio test to evaluate for statistical significance.
To explore the effect of residential mobility on these results, sensitivity analyses were conducted after excluding individuals who had lived at their current address for less than one year (n=804,728; or 11.4% of the cohort), or alternatively for less than five years (n=2,387,987; or 33.9% of the cohort). These results did not differ substantially from those of the primary analysis performed without these exclusions.
All analyses were performed using Stata statistical software, version 11.0.(13)
Individual-level sociodemographic characteristics are presented by neighborhood deprivation quintile in Table 1 (N=6,998,075). The proportion of women and men was similar across all neighborhood deprivation quintiles. Higher-deprivation neighborhoods had a slightly higher percentage of young adults (18–39 years), and a lower percentage of middle-aged adults (40–64 years), compared to lower-deprivation neighborhoods. Individuals in the highest-deprivation neighborhoods also tended to have lower educational attainment and family income; and were less likely to be married, employed, and/or to have lived at their current residence for five or more years.
For each psychiatric medication class (antipsychotics, antidepressants, anxiolytics, and hypnotics/sedatives), a monotonic trend of increasing prescription rates was observed by increasing level of neighborhood deprivation (Table 2). A total of 376,722 (27.0%) individuals in the highest-deprivation neighborhood quintile were prescribed at least one of these medications, compared to 298,207 (21.3%) in the lowest-deprivation neighborhood quintile.
Table 3 presents odds ratios and 95% confidence intervals from multilevel logistic regression, unadjusted and adjusted, for the association between neighborhood deprivation and psychiatric medication prescription. Higher neighborhood deprivation was associated with a monotonic increasing relative rate of antipsychotic, antidepressant, anxiolytic, and hypnotic/sedative prescription. A substantial part of these associations remained after adjusting for individual-level sociodemographic characteristics. After adjusting for these characteristics, individuals in the highest-deprivation neighborhood quintile were 1.15 times more likely to be prescribed at least one of the medications studied (95% CI 1.13–1.17), compared to individuals in the lowest-deprivation neighborhood quintile. The strongest associations were found for antipsychotics and anxiolytics (adjusted ORs 1.40 [95% CI, 1.36–1.44] and 1.24 [95% CI, 1.22–1.27], respectively, comparing the highest-deprivation quintile to the lowest). Weaker associations were found for antidepressants and hypnotics/sedatives, but a monotonic trend was still present across neighborhood deprivation quintile.
Table 4 provides further details for the relationship between neighborhood deprivation and antipsychotic prescription, for which the strongest association was found. Adjusted odds ratios and 95% confidence intervals are presented for all covariates included in the multilevel logistic regression model. Women were slightly more likely to be prescribed an antipsychotic medication than men after adjusting for the other covariates included in the model (adjusted OR 1.09; p<0.001). Individuals 40–64 years or ≥65 years old were more than twice as likely to be prescribed an antipsychotic than younger individuals. Other factors positively associated with antipsychotic medication prescription included never married marital status, unemployment (which had the largest adjusted OR, 3.85), lower educational attainment, lower family income, residence in a large city, and increased residential mobility (<5 years at current residence). Interestingly, individuals in the second-lowest income quartile were more likely to be prescribed antipsychotics than those in the other income quartiles, a relationship that was not well explained in these data. The second-lowest income quartile had the highest percentage of older adults (≥65 years) and divorced or widowed adults, but the increased risk of antipsychotic prescription in this quartile persisted after adjustment for these and all other individual-level characteristics included in Table 4.
Exploratory analyses were performed to evaluate for interactions between neighborhood deprivation and individual-level characteristics with respect to psychiatric medication prescription. Each of the individual-level characteristics included in Table 1 had an interaction with neighborhood deprivation that was significant at the P=0.0001 level, after adjusting for all other individual-level characteristics in Table 1, but the effect sizes were generally small and did not appear clinically meaningful (data not shown). In particular, the association between neighborhood deprivation and psychiatric medication prescription tended to be stronger among younger adults (<40 years) than adults older than 65 years; and among adults who had never married than among those who had married, divorced, or widowed.
This study is the largest to date of neighborhood deprivation and medically treated mental disorders, which were identified on the basis of psychiatric medication prescriptions from all outpatient and inpatient pharmacies in Sweden. We found a monotonic trend of increasing prescription of antipsychotics, antidepressants, anxiolytics, and hypnotics/sedatives associated with increasing neighborhood deprivation. A substantial part of this association persisted after adjusting for broadly measured individual-level sociodemographic characteristics, suggesting that neighborhood deprivation may be an independent risk factor for these mental disorders.
We also found that neighborhood deprivation was more strongly associated with antipsychotic medications than with other classes of psychiatric medications. It has previously been assumed that depression and anxiety are more strongly related to social factors than are psychotic disorders,(14) although comparative data for different mental disorders are still relatively sparse and inconclusive. It is possible that the effect sizes for antidepressants or anxiolytics in the current study are underestimated relative to those for antipsychotics. If a smaller percentage of individuals with depression or anxiety are treated with prescription medications compared to individuals with psychotic disorders, this would have resulted in greater misclassification of individuals with depression or anxiety in the current study which may have biased these results toward the null hypothesis. Additional studies are clearly warranted to examine the differential effect of neighborhood deprivation on different mental disorders, and to evaluate these effects in other populations. If it were possible to replicate the current study in the U.S., larger effect sizes may be expected given larger socioeconomic and neighborhood disparities in the U.S. relative to Sweden.(15–16)
These findings from a national population extend those of previous smaller studies. In a review of 45 studies of neighborhood-level factors and depression, 37 found an association of at least one neighborhood deprivation characteristic and depression after adjustment for individual-level factors.(1) Other studies,(17–24) but not all,(25–26) have reported that neighborhood deprivation characteristics are independently associated with schizophrenia. The mixed results from previous studies may be due in part to their use of different population substrata, as well as the variability across studies in individual-level adjustment variables, neighborhood definitions, and outcome measurement.
The process by which neighborhood deprivation may affect mental health is still not well established. Social capital, characterized by high levels of interpersonal trust and social cohesion, has been hypothesized to serve as a buffer against the psychological effects of stress or dopamine regulation in the development of psychotic disorders.(5, 27) Other neighborhood contextual factors such as poor social networks, perceived alienation, and crime are hypothesized to be independent risk factors for the development of mental disorders through psychological mechanisms in susceptible individuals.(5, 10, 28–29) Further research is needed to clarify these potential mechanisms.
It is also possible that individuals with mental disorders are more likely to migrate to higher-deprivation neighborhoods, thus increasing the prevalence of mental disorders in such neighborhoods by “reverse causation.” Longitudinal or quasi-experimental studies with a lengthy period of follow-up are needed in order to evaluate the issue of reverse causation, with multilevel modeling to separate neighborhood from individual effects.
Limitations of the current study include the possibility of residual confounding. Although we adjusted for broadly measured sociodemographic factors at the individual level, it is possible that unmeasured confounders may account for the remaining associations that were found. Second, as noted previously, it was not possible to assess for reverse causation in these data. A third limitation is the use of psychiatric medication prescriptions as a proxy for mental disorders. This approach fails to identify mental disorders that are treated without prescription medications or are untreated. We are unable to exclude the possibility of therapeutic bias resulting in differential use of prescription medications in high deprivation neighborhoods, or differential use of alternative therapies in low deprivation neighborhoods.
This study also has several important strengths. It is the largest study to date of neighborhood deprivation and mental disorders. The use of nationwide medication prescription data from all outpatient and inpatient pharmacies in Sweden allowed us to include all medically treated mental disorders from all health care settings in this national population, and to evaluate several different classes of psychiatric medications. The availability and use of these data for all Swedish adult residents prevents bias that may result either from self-reporting or from the sole use of hospital-based data. These pharmacy data were linked to sociodemographic census data that are remarkably complete. Family income data, for example, which are often missing in large numbers in U.S. studies, were 99.7% complete allowing us to minimize potential bias from differential missing data. Neighborhoods were defined on the basis of small geographic units with ~1000 to 2000 people which, in general, are consistent with how residents define their neighborhoods.(30) Neighborhood deprivation was determined using a well-specified principal components analysis based upon Swedish national census data. Multilevel modeling was used to separate individual-level from neighborhood-level effects.
In summary, these findings study suggest that neighborhood deprivation is associated with psychiatric medications and that this relationship is independent of individual-level sociodemographic characteristics. Further research is needed to clarify the mechanisms by which neighborhood deprivation may affect mental health and to identify the most susceptible groups in the population.
This work was supported by grants from the National Institute of Child Health and Human Development [1R01HD052848-01], the National Institute of Drug Abuse [1 R01 DA030005-01A1], the Swedish Research Council [2008-3110 and 2008-2638], the Swedish Council for Working Life and Social Research [2006-0386, 2007-1754, and 2007-1962], and ALF project grant, Lund, Sweden. The funding agencies had no role in the design and conduct of the study; in the collection, analysis, and interpretation of the data; or in the preparation, review, or approval of the manuscript. There were no conflicts of interest for any authors.
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