Volume 25, Issue 6 pp. 489-498

ORIGINAL ARTICLE

Open Access

Association between neighborhood deprivation and mortality in patients with schizophrenia and bipolar disorder—A nationwide follow-up study

Filip Jansåker,

Corresponding Author

Filip Jansåker

[email protected]

orcid.org/0000-0003-0670-9996

Center for Primary Health Care Research, Lund University, Lund, Sweden

Department of Clinical Microbiology, Center of Diagnostic Investigations, Rigshospitalet, Copenhagen University Hospital, Copenhagen, Denmark

Correspondence

Filip Jansåker, Center for Primary Health Care Research, Lund University, Jan Waldenströms gata 35, Skåne University Hospital, 205 02 Malmö, Sweden.

Email: [email protected]

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Jan Sundquist,

Jan Sundquist

orcid.org/0000-0001-7228-5015

Center for Primary Health Care Research, Lund University, Lund, Sweden

Department of Family Medicine and Community Health, Department of Population Health Science and Policy, Icahn School of Medicine at Mount Sinai, New York City, New York, USA

Center for Community-based Healthcare Research and Education (CoHRE), Department of Functional Pathology, School of Medicine, Shimane University, Matsue, Japan

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Kristina Sundquist,

Kristina Sundquist

Center for Primary Health Care Research, Lund University, Lund, Sweden

Department of Family Medicine and Community Health, Department of Population Health Science and Policy, Icahn School of Medicine at Mount Sinai, New York City, New York, USA

Center for Community-based Healthcare Research and Education (CoHRE), Department of Functional Pathology, School of Medicine, Shimane University, Matsue, Japan

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Xinjun Li,

Xinjun Li

orcid.org/0000-0002-5559-4657

Center for Primary Health Care Research, Lund University, Lund, Sweden

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Filip Jansåker,

Corresponding Author

Filip Jansåker

[email protected]

orcid.org/0000-0003-0670-9996

Center for Primary Health Care Research, Lund University, Lund, Sweden

Department of Clinical Microbiology, Center of Diagnostic Investigations, Rigshospitalet, Copenhagen University Hospital, Copenhagen, Denmark

Correspondence

Filip Jansåker, Center for Primary Health Care Research, Lund University, Jan Waldenströms gata 35, Skåne University Hospital, 205 02 Malmö, Sweden.

Email: [email protected]

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Jan Sundquist,

Jan Sundquist

orcid.org/0000-0001-7228-5015

Center for Primary Health Care Research, Lund University, Lund, Sweden

Department of Family Medicine and Community Health, Department of Population Health Science and Policy, Icahn School of Medicine at Mount Sinai, New York City, New York, USA

Center for Community-based Healthcare Research and Education (CoHRE), Department of Functional Pathology, School of Medicine, Shimane University, Matsue, Japan

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Kristina Sundquist,

Kristina Sundquist

Center for Primary Health Care Research, Lund University, Lund, Sweden

Department of Family Medicine and Community Health, Department of Population Health Science and Policy, Icahn School of Medicine at Mount Sinai, New York City, New York, USA

Center for Community-based Healthcare Research and Education (CoHRE), Department of Functional Pathology, School of Medicine, Shimane University, Matsue, Japan

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Xinjun Li,

Xinjun Li

orcid.org/0000-0002-5559-4657

Center for Primary Health Care Research, Lund University, Lund, Sweden

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First published: 08 February 2023

https://doi.org/10.1111/bdi.13309

Citations: 1

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Abstract

Objectives

The aim was to explore the association between neighborhood deprivation and all-cause mortality and cause-specific mortalities in patients with schizophrenia and bipolar disorder. A better understanding of this potential relationship may help to identify patients with schizophrenia and bipolar disorder with an increased mortality risk.

Methods

This nationwide study included practically all adults (≥30 years) diagnosed with schizophrenia (n = 34,544) and bipolar disorder (n = 64,035) in Sweden (1997–2017). The association between neighborhood deprivation and mortality was explored using Cox regression. All models were conducted in both men and women and adjusted for individual-level sociodemographic factors and comorbidities.

Results

There was an association between level of neighborhood deprivation and all-cause mortality in both groups. The adjusted hazard ratios for all-cause mortality associated with high compared to low neighborhood deprivation were 1.18 (95% confidence interval 1.11–1.25) in patients with schizophrenia and 1.33 (1.26–1.41) in patients with bipolar disorder. The two most common mortality causes in both groups were coronary heart disease and cancer. The mortality due to coronary heart disease increased when neighborhood deprivation increased and reached 1.37 (1.18–1.60) in patients with schizophrenia and 1.70 (1.44–2.01) in patients with bipolar disorder living in the most deprived neighborhoods.

Conclusions

This study shows that neighborhood deprivation is an important risk factor for all-cause mortality and most cause-specific mortalities among patients with schizophrenia and bipolar disorder. These findings could serve as aid to policymakers when allocating healthcare resources and to clinicians who encounter patients with these conditions in deprived neighborhoods.

1 INTRODUCTION

Schizophrenia and bipolar disorder are severe chronic psychiatric disorders associated with high morbidity and mortality.^{1, 2} Patients with schizophrenia have an around 10-fold higher all-cause mortality compared with the general population.³ The leading death causes are cardiovascular disease, cancer, and suicide, but these vary across time and age groups.^3-6 In patients with bipolar disorder, the all-cause mortality is somewhat lower than in those with schizophrenia but is still two- to threefold higher than in the general population and over 10-fold higher for suicide mortality.^{7, 8} Other causes attributed to the excessive mortality among patients with bipolar disorder^{7, 8} are similar to those in patients with schizophrenia;^3-6 that is, mainly attributed to other chronic diseases frequently occurring with these severe psychiatric disorders.^{4, 7} Unfortunately, efforts to reduce the excessive mortality in patients with severe chronic psychiatric disorders have been largely ineffectual, which calls for further research on the potential association with socioeconomic risk factors that may be more common in patients with severe psychiatric disorders.

There is strong evidence showing that socioeconomic status, both at the individual and neighborhood level, shapes the burden of psychiatric morbidity in the population.^9-12 Neighborhood deprivation¹³ and low socioeconomic status¹⁴ have also been found to be related to mortality in individuals with bipolar disorder and recent research suggests that socioeconomic status and neighborhood deprivation may also affect mortality in patients with schizophrenia.¹⁵ Furthermore, socioeconomic status and neighborhood deprivation have also been found to be strongly related to several severe chronic diseases and their associated risk factors (e.g. cardiovascular diseases,^16-18 obesity and diabetes mellitus,^19-21 smoking,^{17, 22} diet,²³ and cancer^24-28), which in turn seem to be overrepresented in patients with schizophrenia and bipolar disorder.^{4, 7} However, a more comprehensive, large-scale analysis of the association between neighborhood deprivation and mortality in patients with schizophrenia and bipolar disorder is needed. There is, for example, limited knowledge about the potential neighborhood effect on specific causes of death among patients with schizophrenia and bipolar disorder. Previous studies have also had some important limitations, including an over-reliance on hospital care data, use of community-based samples, or insufficient sample sizes and short follow-up. Earlier studies have also not had access to nationwide primary healthcare data,²⁹ where many comorbidities are diagnosed.

Therefore, we sought to examine the association between neighborhood deprivation and mortality in patients diagnosed with schizophrenia and bipolar disorder in a nationwide follow-up study using comprehensive national population-based registers together with unique and practically nationwide primary healthcare data. In addition, we also aimed to investigate whether any possible associations remained after accounting for individual-level sociodemographic characteristics (age, country of origin, education level, family income level, marital status, and region of residence) as well as common comorbidities.

2 MATERIALS AND METHODS

2.1 Design and setting

A nationwide follow-up study including all individuals aged 30 years in Sweden and older with a diagnosis of bipolar disorder or schizophrenia. The outcome was mortality, and the main predictor was neighborhood deprivation. The start of the study was 1997 and the end was 2017. The STROBE statement checklist for cohort studies (Supporting information) was considered when conducting the study and writing the manuscript. The research was conducted at the Center for Primary Healthcare Research, Region Skåne/Lund University, Sweden.

2.2 Data sources

Data used in this study were retrieved from nationwide, comprehensive registers that contain individual- and neighborhood-level information on all people in Sweden. A unique dataset was constructed with data from these registers and almost nationwide primary healthcare data using the national 10-digit civic registration number, which is assigned to each person in Sweden upon birth or immigration to the country. This number was replaced by serial numbers to ensure the integrity of all individuals. The National Patient Register (In-Patient data 1964–2017 and Out-Patient data 2001–2017)³⁰ and almost nationwide primary healthcare data²⁹ (data from 20 of the 21 administrative regions in Sweden, 1997–2017) were used to collect data on medical conditions, which were identified according to specific diagnosis codes in the 10th edition of the International Classification of Diseases (ICD-10). The national Cause of Death Register³¹ was used to collect data on mortality. This register and the National Patient Register, which have almost full nationwide coverage, are managed by the Swedish National Board of Health and Welfare (in Swedish: Socialstyrelsen). The National Total Population Register (1968–2015)³² was used to collect data on sociodemographic factors, emigration, and immigration. This register is also complete for the entire population and is controlled by Statistics Sweden—the Swedish governmental bureau of statistics (in Swedish: Statistiska Centralbyrån, SCB).

2.3 Study population

All individuals aged 30 years and older with a diagnosis of schizophrenia (ICD-10 F20) and bipolar disorder (ICD-10 F30 and F31) during the time period.

2.4 Outcome

All-cause (total) mortality and the following cause-specific (ICD-10 codes) mortalities were assessed during the time period: coronary heart diseases (I20-I25); psychiatric disorders (F00-F99); cancers (C00-C97); stroke (I60-I69); chronic lower respiratory diseases (COPD; J40-J49); diabetes mellitus (E10-E14); and suicide (X60-X84).

2.5 Neighborhood deprivation (main predictor)

The home addresses of all Swedish adults have been geocoded to small geographic administrative units that have boundaries defined by homogeneous types of buildings. These neighborhood units are called small area market statistics or SAMS and have an average of 1000–2000 people per unit. SAMS units were used as proxies for neighborhoods, as has been done in previous research.¹⁸ A “Neighborhood Deprivation Index” was calculated for each SAMS. This index is a summary measure used to characterize neighborhood-level deprivation. We used deprivation indicators used by past studies to characterize neighborhood environments and then used a principal components analysis to select deprivation indicators in the Swedish national databases.³³ The following four variables were selected for those aged 25–64 years: low educational status (defined as less than 10 years of formal education); low income (from all sources, including that from interest and dividends), which was defined as less than 50% of individual median income established by the governmental institution Statistics Sweden (SCB); unemployment (defined as not employed; excluding full-time students, those completing compulsory military service, and early retirees); and social welfare assistance. The neighborhood deprivation index was calculated based on the population aged 25–64 years because this age group (i.e., the working population) was considered to be more socioeconomically active than other age groups. The study population, however, consisted of individuals aged 30 years and older. Each of the four deprivation variables loaded on the first principal component with similar loadings (+0.47 to +0.53) and explained 52% of the variation between these variables. A z-score was calculated for each SAMS neighborhood. The z-scores, weighted by the coefficients for the eigenvectors, were then summed to create the index.³⁴ The index was categorized into three groups: below one standard deviation (SD) from the mean (low deprivation), above one SD from the mean (high deprivation), and within one SD of the mean (moderate deprivation). Higher scores reflect more deprived neighborhoods.

2.6 Covariates

All individual-level variables were assessed on the year of diagnosis with bipolar disorder or schizophrenia for each individual. Comorbidities were collected and grouped into four groups: obesity (E65–E68); COPD (J40–J49); alcoholism and related liver disorders (F10 and K70); and coronary heart disease (I20–I25). Sociodemographic variables were also collected. Age was used as a continuous variable from age ≥30 years. Country of origin was divided into “born in Sweden” or “born outside Sweden”. Educational attainment was divided into three groups based on the level of schooling: completion of compulsory school or less (9 years or less), practical high school, or some theoretical high school (10–11 years), or theoretical high school and/or college (≥12 years). Employment status was divided into employed or unemployed. Family income was based on the annual family income divided by the number of people in the family, that is, individual family income per capita. This variable was provided by Statistics Sweden income parameter that also took into consideration the ages of people in the family and used a weighted system whereby small children were given lower weights than adolescents and adults. The calculation procedure was performed as follows: The sum of all family members' incomes was multiplied by the individual's consumption weight divided by the family members' total consumption weight. Marital status was divided into married/cohabitating or never married/widowed/divorced. Region of residence was divided into large cities (Stockholm, Göteborg, and Malmö), middle-sized towns, and small towns/rural areas.

2.7 Statistical analysis

Person-years were calculated from the start of follow-up (i.e., when an individual living in Sweden was ≥30 years of age and had been diagnosed with schizophrenia or bipolar disorder) until death, emigration, or the end of the study on December 31, 2017. The associations between the individual variables and mortality were analyzed by using Cox regression models. Cox proportional hazard models were used to examine the association between the predictors and covariates and mortality. The stratified Cox proportional hazards model provides a hazard ratio (HR) for mortality that is adjusted for the individual variables. First, a univariate Cox regression was performed for each variable. Next, a multivariate Cox regression model including all variables was calculated. Interaction tests were performed in order to examine whether the association between neighborhood deprivation and mortality among schizophrenia and bipolar disorder patients was affected by any of the individual variables. The proportional hazard assumptions were checked by plotting the mortality over time and calculating Schoenfeld (partial) residuals, and no substantial departures from these assumptions were found. All statistical analyses were performed using SAS 9.4.

3 RESULTS

Table 1 shows the study population comprising a total of 34,544 and 64,035 patients with schizophrenia and bipolar disorder, respectively, as well as the number of mortality events and mortality by neighborhood-level deprivation. During the follow-up (mean follow-up was 10 years for patients with schizophrenia and 8 years for patients with bipolar disorder), there were 12,182 (cumulative mortality, 35.3%) with schizophrenia and 13,067 (cumulative mortality, 20.4%) among patients with bipolar disorder. Figure 1 visualizes the cumulative mortality (%) in patients with bipolar disorder and schizophrenia during the study period by neighborhood deprivation level. More detailed study population characteristics and cumulative mortality (%) can be viewed in Table S1 and Table S2, respectively. The proportion of the most common mortalities among patients with schizophrenia and bipolar disorder are included in Table S3. CHD and cancer were the two most common causes of death in both groups of patients, followed by psychiatric disorders, COPD, and stroke in patients with schizophrenia and suicide, psychiatric disorders, and stroke in patients with bipolar disorder.

TABLE 1. Study population, number of cases, and cumulative mortality in patients with schizophrenia or bipolar disorder (1997–2017).

Schizophrenia	Population		Mortality		Cumulative mortality (%) by neighborhood deprivation level
Schizophrenia	N	%	N	%	Low (n = 4621)	Moderate (n = 17,814)	High (n = 12,109)
Total population	34,544		12,182		33.6	35.8	35.2
Sex
Males	18,896	54.7	6357	52.2	31.1	34.4	33.5
Females	15 64	45.3	5825	47.8	36.3	37.4	37.3
Age (years)
30–39	7513	21.7	844	6.9	10.2	11.0	12.0
40–49	8738	25.3	1778	14.6	19.1	20.5	20.7
50–59	7928	23.0	2844	23.3	33.2	35.9	36.7
60–69	5429	15.7	2826	23.2	46.4	51.8	54.9
≥70	4936	14.3	3890	31.9	74.7	78.4	81.5

Bipolar disorder	Population		Fatal cases		Cumulative mortality (%) by neighborhood deprivation level
Bipolar disorder	N	%	N	%	Low (n = 13,757)	Moderate (n = 36,945)	High (n = 13,333)
Total population	64,035		13,067		17.2	20.7	22.8
Sex
Males	25,465	39.8	5669	43.4	19.5	22.3	25.2
Females	38,570	60.2	7398	56.6	15.7	19.7	21.2
Age (years)
30–39	16,129	25.2	652	5.0	3.1	4.1	4.8
40–49	16,264	25.4	1281	9.8	6.3	7.7	10.1
50–59	13,883	21.7	2433	18.6	13.4	17.2	22.8
60–69	9446	14.8	3027	23.2	26.4	32.0	38.6
≥70	8313	13.0	5674	43.4	62.4	68.9	72.6

Details are in the caption following the image — **FIGURE 1**
Open in figure viewer PowerPoint

Cumulative mortality (per 100 persons) in individuals with schizophrenia or bipolar disorder by neighborhood deprivation level (low, moderate, and high).

Table 2 includes the hazard ratios (HRs) for the total mortality in patients with schizophrenia and bipolar disorder. The results indicate that the mortality seems to increase with higher neighborhood deprivation. For example, in patients with schizophrenia, the fully adjusted HRs associated with all-cause mortality were 1.02 (95% CI, 0.96–1.08) and 1.18 (1.11–1.25) for patients living in neighborhoods with moderate and high deprivation, respectively. The corresponding numbers in patients with bipolar disorder were 1.03 (0.96–1.08) and 1.33 (1.26–1.41). The HRs for all-cause mortality by neighborhood deprivation in patients with bipolar disorders and schizophrenia are also visualized in Figure 2. The sex-specific models of mortality for patients with schizophrenia can be seen in Tables S4 and S5 and Table S8; and in Tables S6 and S7, and Table S9 regarding patients with bipolar disorder.

TABLE 2. Mortality of patients with schizophrenia and bipolar disorder in relation to neighborhood deprivation, individual-level sociodemographic factors, and comorbidities.

	HR^a	95% CI		p-value	HR^a	95% CI		p-value
	Schizophrenia (N = 34,544)			p-value	Bipolar disorder (N = 64,035)			p-value
Neighborhood deprivation (ref. Low)
Moderate	1.02	0.96	1.08	0.5501	1.03	0.98	1.08	0.3070
High	1.18	1.11	1.25	<0.0001	1.33	1.26	1.41	<0.0001
Age (increasing)	1.08	1.08	1.08	<0.0001	1.09	1.08	1.09	<0.0001
Sex to men (ref. Women)	1.32	1.27	1.37	<0.0001	1.46	1.40	1.51	<0.0001
Family income (ref. Highest quartile)
Low	1.21	1.14	1.27	<0.0001	1.45	1.37	1.54	<0.0001
Middle-low	1.13	1.07	1.19	<0.0001	1.29	1.22	1.36	<0.0001
Middle-high	1.10	1.04	1.16	0.0012	1.20	1.13	1.27	<0.0001
Education attainment (ref. ≥12 years)
≤ 9	1.24	1.18	1.30	<0.0001	1.34	1.28	1.40	<0.0001
10–11	1.08	1.03	1.14	0.0027	1.12	1.07	1.17	<0.0001
Country of origin (ref. born in Sweden)	0.87	0.83	0.92	<0.0001	0.92	0.86	0.97	0.0024
Marital status (ref. Married/cohabiting)	1.01	0.96	1.07	0.7082	1.26	1.22	1.31	<0.0001
Region of residence (ref. Large cities)
Southern Sweden	0.95	0.91	0.99	0.0189	0.89	0.85	0.92	<0.0001
Northern Sweden	0.94	0.89	0.99	0.0113	0.95	0.90	1.00	0.0391
Comorbidities (ref. Non)
COPD	1.55	1.47	1.63	<0.0001	1.35	1.28	1.42	<0.0001
Alcoholism and related liver disorders	1.33	1.25	1.41	<0.0001	1.50	1.42	1.58	<0.0001
Coronary heart disease	1.19	1.12	1.25	<0.0001	1.11	1.06	1.16	<0.0001
Obesity	1.07	0.95	1.21	0.2454	1.09	0.99	1.21	0.0965

Note: Results of Cox regression models.
Abbreviations: CI, confidence interval; COPD, chronic obstructive pulmonary disease; HR, hazard ratio.
^a Fully adjusted model.

Several of the individual-level variables were significantly associated with mortality in the full models. For example, the HRs for mortality were higher for men than women and for both patients with schizophrenia and bipolar disorder. The mortality also increased by age and was increased in patients with low education, low family income, or those that had a comorbidity (Tables S8 and S9).

Figure 3 includes the HRs associated with cause-specific mortality in patients with schizophrenia. Mortality due to CHD, stroke, cancer, and COPD was significantly higher in patients living in the most deprived neighborhoods compared to those living in the most affluent neighborhoods. HRs of cause-specific mortality of patients with schizophrenia living in different levels of neighborhood deprivation are shown in Table S10. The mortality due to CHD increased when neighborhood deprivation increased and reached 1.37 (1.18–1.60) in patients from the most deprived neighborhoods.

Figure 4 includes the HRs associated with cause-specific mortality in patients with bipolar disorder. HRs of cause-specific mortality of bipolar disorder patients by different levels of neighborhood deprivation are also shown in Table S11. In general, high neighborhood deprivation was significantly associated with several cause-specific mortalities in these patients and particularly for mortality due to coronary heart disease (HR = 1.70, 95% CI = 1.44–2.01), diabetes mellitus (HR = 1.69, 95% CI 1.13–2.53), and suicide (HR = 1.34, 95% CI =1.13–1.60).

4 DISCUSSION

The main finding of this study was that all-cause mortality among patients with schizophrenia and bipolar disorder was significantly associated with neighborhood deprivation. The increased risks were attenuated but remained significant after adjustment for the individual-level sociodemographic variables and common comorbidities.^{4, 7} Neighborhood deprivation was also associated with several of the most common cause-specific mortalities in both groups of patients.

All-cause mortality has been shown to be significantly elevated in patients with severe psychiatric disorders.^{3, 7, 8} Previous studies of various designs have also indicated that socioeconomic status, both at the individual- and neighborhood-level, affects psychiatric morbidity and mortality in the population.^{9-15, 18} Our study adds new knowledge to previous research because it was based on more comprehensive, large-scale data for the analysis of the association between neighborhood deprivation and mortality in patients with schizophrenia and bipolar disorder, including the potential effect of neighborhood deprivation on cause-specific mortalities in these patients.

Patients with schizophrenia have previously been found to have an elevated mortality from cardiovascular diseases (e.g., CHD), cancers (e.g., lung and breast cancer), and suicide compared with the general population.^3-6 This study suggests that neighborhood deprivation represents a significant risk factor of overall and cause-specific mortality (e.g., CHD, stroke, lung- and breast cancer). Patients with bipolar disorder also have a higher mortality from chronic diseases and suicide compared to the general population.⁷ The present study showed that neighborhood deprivation was associated with several of these cause-specific mortalities (e.g., COPD, CHD, diabetes mellitus, and cancer in general) but not stroke and suicide.

The pathways between neighborhood deprivation and mortality among patients with schizophrenia and bipolar disorder are not fully known. Although Sweden has a universal healthcare system, it is possible that there are differences between neighborhoods in the access, continuity, and quality of primary health care.^35-39 For example, the turnover of general practitioners in England (a country which also has universal health care) has been higher in high deprivation neighborhoods over the last decades.³⁵ This seem to aggravate disease management and increase morbidity through poorer continuity of care in vulnerable patients.^36-38 Another possible mechanism is that potential differences between socioeconomic groups in knowledge, attitudes and beliefs might exist, which could lead to variations in lifestyle in patients with schizophrenia and bipolar disorder based on their neighborhood of residence. Moreover, sociocultural norms regarding physical activity,⁴⁰ diet,²³ and smoking,²² could vary between neighborhoods, which in turn can affect the mortality. For example, unsafe environments, isolation, alienation, violent crime and vandalism,⁴¹ and psychological stress⁴² are more common in socially disadvantaged neighborhoods and could lead to reduced possibilities to exercise. Previous research has also shown a higher availability of unhealthy foods in deprived neighborhoods.³⁹ For instance, a Swedish study showed that cardiovascular disease risk factors, including physical inactivity, obesity, and smoking, were more common among individuals living in deprived neighborhoods than among those living in less deprived/affluent neighborhoods.¹⁶

Some of the factors mentioned above may also lie in the potential pathways behind the associations between neighborhood deprivation, low socioeconomic status, and psychiatric disorders although other potential pathways may lie behind these associations. These pathways may include environmentally linked pathophysiologic processes such as increased risk of infections, social stress, familial factors (e.g., marital status, maternal stress), birth age, and lifestyle factors (e.g., impaired nutrition and substance abuse).^{12, 43-45}

The main limitations of this study include the possibility of residual confounding. Although we adjusted for several individual-level sociodemographic factors, it is possible that unmeasured confounders may account for the remaining part of the observed associations. Although differential access to mental health services may be a residual confounder, this is less of a caveat in Sweden than in many other countries due to the Swedish universal health care system. Moreover, some individual-level data are not possible to obtain for an entire national population. For example, we did not have data on lifestyle, such as smoking habits, type of diet, and physical activity patterns, which are important risk factors for total mortality. However, we adjusted our results for socioeconomic and demographic characteristics, which are known to be related to such risk factors^{17, 22, 23, 40} and comorbidities.^{16-21, 24-28} We also used chronic lower respiratory disease as a proxy for tobacco smoking.⁴⁶ Finally, death certificates should be interpreted with caution due to difficulties in determining the final cause of death.⁴⁷

Our study has several strengths, which balance the limitations. Firstly, in comparison to previous studies^{9, 10, 13-15} our nationwide cohort included practically all patients with schizophrenia and bipolar disorder (30 years and older) in Sweden during the study period. Secondly, this study not only used hospital data but also several other national registers as well as almost nationwide primary healthcare data.^29-32 Thirdly, the validity of the diagnosis in the National Patient Register has been found to be high for schizophrenia (94.9%)³⁰ and bipolar disorder (92.0%);⁴⁸ and the unique primary healthcare data has been proven to be useful for studies on psychiatric epidemiology.²⁹ Fourthly, the outcome data were based on clinical diagnoses, registered by physicians, rather than self-reported data, which eliminated any recall bias in the patients. Another strength is the personal identification number, replaced by a pseudonymized serial number, that is assigned to each individual in Sweden; this gave us the opportunity to follow the patients without any loss to follow-up. An additional key strength was the access to small SAMS units (in the order of 1000–2000 persons), which consisted of relatively homogenous types of buildings defined by geographic boundaries. This is a valuable strength as small neighborhoods have been shown to correspond well with how the residents define their neighborhoods.⁴⁹ Lastly, our data were highly complete, and we were able to link clinical data from individual patients to national demographic and socioeconomic data with less than 1% of missing data for each covariate.

Patients with schizophrenia and bipolar disorder are known to suffer from a very high mortality;^{1, 2} they have an around 10-fold³ and two/threefold^{7, 8} higher all-cause mortality compared to the general population, respectively. Previous efforts to reduce these disparities have been insufficent.¹¹ Our study adds to existing knowledge as it shows clear and consistent positive associations between neighborhood deprivation and mortality among patients with schizophrenia and bipolar disorder. Thus, neighborhood deprivation should be recognized as an independent risk factor for the higher mortality in patients with schizophrenia and bipolar disorder. This new evidence can be used by clinicians treating these patients in deprived neighborhoods; by policymakers for a more contextual allocation of healthcare recourses in society; and by healthcare planners for a more comprehensive approach when targeting the disparity in mortality between these patients and the general population.

5 CONCLUSIONS

The results indicate that neighborhood deprivation is an important factor to consider in order to decrease total and cause-specific mortality among patients with schizophrenia and bipolar disorder. This underscores the need for determining the possible pathways between neighborhood deprivation and mortality among patients with schizophrenia and bipolar disorder. Such research may result in more efficient preventive strategies and health policies.

AUTHOR CONTRIBUTIONS

The authors attest that all listed authors meet the authorship criteria and that no others meeting the criteria have been omitted. All authors conceptualized, visualized, developed the idea and design, and interpreted the data. KS and JS contributed to access and acquisition of data and critical revision of the manuscript for intellectual content. XL contributed to funding, analysis, and statistics. XL and FJ contributed to tables and literature search and drafting of manuscript. All authors have approved the final version of the manuscript.

ACKNOWLEDGEMENTS

The authors wish to thank science editor Patrick O'Reilly for his useful comments on the text. This work was supported by Åhlén-stiftelsens (203029 to Xinjun Li), Sparbanksstiftelsen Färs & Frosta (awarded to Xinjun Li) and the Swedish Heart Lung Foundation (awarded to Kristina Sundquist). This work was also supported by governmental funding (Alf) of clinical research, Region Skåne, Sweden (2022-0071 to Filip Jansåker) and the Swedish Society of Medicine (SLS-960562/SLS-960574 to Filip Jansåker).

CONFLICT OF INTEREST STATEMENT

The authors have nothing to disclose.

ETHICS STATEMENT

This study was a non-intervention register study on already collected and encrypted secondary data. Access to the used national registries was obtained from Swedish authorities prior to the study commencing. The study was approved by the Ethical Review Board in Lund, Sweden.

Open Research

DATA AVAILABILITY STATEMENT

This study made use of several national registers and, owing to legal concerns, data cannot be made openly available. Further information regarding the health registries is available from the Swedish National Board of Health and Welfare (https://www.socialstyrelsen.se/en/statistics-and-data/registers/) and Statistics Sweden (https://www.scb.se/en/).

Supporting Information

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Citing Literature

Volume25, Issue6

September 2023

Pages 489-498

Association between neighborhood deprivation and mortality in patients with schizophrenia and bipolar disorder—A nationwide follow-up study