The Effect of Economic Assets on Mortality in Patients with Dementia: A Population-Based Cohort Study

Abstract

Background:

We investigated the effect of economic assets on mortality in patients with dementia in a national cohort of elderly individuals aged 65 or older.

Objective:

To examine the effect of economic assets on mortality in patients with dementia.

Methods:

Incidence of dementia and all-cause mortality was analyzed with incidence rate ratios (IRR) in three different categories of economic assets by means of Cox regression models.

Results:

A total of 874,246 individuals aged 65+ were included. The risk of receiving a dementia diagnosis was highest in the low economic asset group (IRR 1.19). Patients with dementia had a higher mortality compared to those without a diagnosis (IRR 2.85). The mortality in the dementia group was lowest in the high economic asset group (IRR 3.31). However, the increase associated with dementia was lowest within the low economic assets group (IRR 2.57).

Conclusion:

Mortality is increased with a dementia diagnosis and highest for the low economic asset group. However, the increase in mortality attributable to dementia was higher in the high economic assets group.

Keywords

Comorbidity dementia economic assets epidemiology mortality socio economy

INTRODUCTION

Dementia is a common chronic condition among the elderly [1, 2]. It is a progressive and often irreversible cognitive dysfunction [1 , 4] leading to functional decline and high dependency on caregivers [5, 6]. Due to the demographic developments leading to an increasing elderly population, the prevalence of patients with dementia is expected to increase [1 , 7] and challenge healthcare systems worldwide [8]. Furthermore, it is well established that receiving a dementia diagnosis increases mortality [9 –12], and that comorbidity also increases mortality in patients with dementia (Bebe et al. unpublished results). Increased mortality for patients with dementia is linked to several factors, such as age, low functional status [13], history of falls [14], and age [15]. It should also be noted that patients with dementia are more vulnerable to factors which do not normally affect mortality, such as infections [16], and that dementia has a larger effect on mortality among the youngest of the elderly, since the oldest of the elderly have a shorter survival time [17].

In general, it is well known that low socioeconomic status (SEP) increases both morbidity and mortality for many diseases [18 –21] and this may also include mental diseases [22]. However, this association is less clear for people with dementia [23 –31]. However, the concept of SEP can be measured by multiple markers, none of which are relevant for all study outcomes and in all settings and at all periods in an individual’s life [32]. SEP is used to refer to both social and economic factors that have an influence on an individual’s or a group’s position in a society [22]. We chose economic assets as an indicator of SEP because our target population is an elderly population with many retired individuals. Economic assets are believed to be a good indicator of SEP when studying an elderly population [21, 32] since this measure can reveal differences between individuals that might otherwise be diminished when using other factors to describe SEP [33].

We hypothesized that economic assets have an effect on mortality in patients with dementia. Higher levels of economic assets may partly compensate for the effects of dementia due to the ability of the affluent to pay for more personal help and healthcare as well as for an overall healthier lifestyle.

The objective of this study was to examine the effect of economic assets on mortality in patients with dementia.

METHODS

Study design and population

This study is a register-based cohort study comprising all residents of Denmark aged 65 years or older on 1 January 2009 (baseline) (Table 1). The follow-up period was five years, from baseline through 31 December 2013.

Table 1

Numbers of individuals in the different groups of economic assets at baseline and in follow up period, with and without dementia

	Baseline population N = 874,426	Dementia N = 34,783	Non-Dementia N = 839,643
Economic Assets	N (%)	N (%)	N (%)
Low: <8,000 Euro	274,292	12,941	261,351
	(31.37)	(37.20)	(31.13)
Middle: 8,000–	317,168	13,817	303,351
134,400 Euro	(36.27)	(39.72)	(26.13)
High: >134,400 Euro	282,966	8,025	274,941
	(32.36)	(23.07)	(32.74)
	Follow-up period 2009–2013 N = 839,643 *	Dementia N = 40,815	Non-Dementia N = 798,828
Economic Assets	N (%)	N (%)	N (%)
Low: <8,000 Euro	261,351	13,572	247,779
	(31.13)	(33.25)	(31.02)
Middle: 8,000–	303,351	15,327	288,024
134,400 Euro	(26.13)	(37.55)	(36.06)
High: >134,400 Euro	274,941	11,916	263,025
	(32.74)	(29.20)	(32.93)
	Died in follow-up period 2009–2013 N = 204,489	Dementia N = 41,017 **	Non-Dementia N = 163,472
Economic Assets	N (%)	N (%)	N (%)
Low: <8,000 Euro	72,881	14,787	58,094
	(35.64)	(36.05)	(35.54)
Middle: 8,000–	76,777	16,198	60,579
134,400 Euro	(37.55)	(39.49)	(37.06)
High: >134,400 Euro	54,831 (26.81)	10,032 (26.46)	44,799 (27.40)

^*Including those without dementia at baseline. Shows the incidence of dementia in the follow-up period. ^**Including those both with and without dementia at baseline.

Setting

In Denmark, access to the health care system is free for everyone with legal residency [34, 35]. The health care system is provided by the state and financed by taxes [34, 35].

Furthermore, the municipalities of Denmark provide social services for elderly citizens, also financed by taxes. Additionally, the municipalities provide elderly people unable to manage everyday life with home care services. Finally, for elderly people experiencing loss of physical and/or mental functions, there are nursing homes. Residence in such facilities is partly paid by the residents, depending on their assets [34, 35].

Sources of data

For nearly five decades, the Danish national registers have recorded information on the Danish population, including health, demographic and socioeconomic data [36].

The Central Personal Registration (CPR) number, a unique identification number given at birth or residence upon immigration by the Danish Civil Registration System (CRS) and used in every Danish register [37], provides the opportunity to link registers together at the individual level and study different factors from birth to late stages in life. The CPR number also ensures that the individual-linked information is accurate [38].

Identifying individuals with dementia

Indications of a dementia diagnosis for the people in our cohort at various time points were obtained from the National Patient Register (NPR), the Danish Psychiatric Central Research Register (PCRR), and the Danish National Prescription Register (DNPR). In the NPR and PCRR, dates of dementia-related contacts with secondary care providers are listed using the registered ICD-10 codes (see Supplementary Table 1) [39 –41]. In the DNPR, the dates of the prescriptions redeemed for dementia are also listed using the ATC codes (N06DA01-N06DA04, N06DX1) whereby dementia treated in primary care is tracked and captured.

Individuals in our cohort with an indication of a dementia diagnosis in the ten-year period prior to baseline (1 January 1999 – 31 December 2008) were classified as having dementia at baseline. For individuals without dementia at baseline, the time of first indication of a dementia diagnosis in the follow-up period is taken as the date of the dementia diagnosis.

Defining economic assets

Economic assets included savings, pension, stocks, real estate, bonds, and also debts up to just before the beginning of the follow-up period (the end of 2008). Three categories of economic assets were defined:Low (including individuals with negative economic assets): <8,000 Euro; Middle: 8,000–134,400 Euro; High: >134,400 Euro.

This division was primarily chosen because it creates almost equally large asset groups. The groups are, however, not entirely arbitrary. In Denmark many age-pensioners with a defined set of free assets below approximately 8,000 Euro are entitled to a small extra state pension because they are considered economic vulnerable [42]. The group with assets above 134,400 Euro are millionaires in Danish Kroner and more likely to have economic freedom.

Outcome

Dementia incidence and mortality over the five-year period: 1 January 2009 – 31 December 2013.

Potential confounders

The following information, collected from Statistics Denmark’s registers at baseline, was included in the analyses to adjust for confounding: sex, age, geographical location (defined by Denmark’s five regions), co-habitation status (yes/no), education (none registered, primary school, secondary school, or higher education), retirement status (yes/no), and comorbidity (measured by the Charlson Comorbidity Index (CCI) status, looking at all diseases included in the CCI individually [43]).

Data analyses

Incidence of dementia

The incidence of dementia over the follow-up period was analyzed using Cox regression models on time to first occurrence of dementia. This time was censored at death or emigration or at end-of-follow-up (31 December 2013). Subjects who were already diagnosed with dementia at the study’s start date (1 January 2009) were omitted from these analyses. The difference in dementia incidence between two groups is presented as an incidence rate ratio (IRR), i.e., how many times higher the dementia incidence rate is in one group compared to a reference group. The specific focus here is on the association between economic assets and a dementia incidence. This association is analyzed unadjusted and in multivariable models, first adjusted for the potential confounders except CCI, and secondly adjusted for the potential confounders including CCI. All the presented IRRs in the results section are adjusted values unless otherwise specified.

Mortality

The incidence of all-cause mortality over the follow-up period was also analyzed using Cox regression models on time to death. This time was censored at emigration or at end-of-follow-up. The progression to dementia in the follow-up period was included in these analyses as a time-dependent variable, i.e., individuals contributed with risk-time as long as they belonged to either the group having dementia or the one without dementia. The mortality difference between two groups is also here presented as incidence rate ratio (IRR), i.e., how many times higher the mortality rate is in the dementia group compared to the group without dementia.

Dementia, economic assets, and mortality

We analyzed the associations between economic assets and mortality, and dementia and mortality individually, and economic assets and dementia interaction and mortality, i.e., the differences in the effect of a dementia diagnosis on mortality between the categories of economic assets.

All statistical analyses were performed with SAS version 9.4 (SAS Institute, Cary, NC, USA).

RESULTS

This study included 874,246 individuals at the age of 65 years and over. Out of these, 31.4% were allocated to the low economic asset group, 36.3% to the middle, and 32.4% in the high economic asset group. A total of 34,783 were identified with dementia at the start of the study and 40,815 at the end of the follow-up period. In total, 204,489 individuals died in the follow-up-period (Table 1).

The incidence of dementia per 100 person-years was highest in the group of people with low assets (IRR 1.22, 95% CI 1.20–1.24) and lowest among the high economic asset group (IRR 0.97, 95% CI 0.95–0.99) (Fig. 1 and Table 2). After adjustment for potential confounders, the incidence for receiving a dementia diagnosis was still highest in the low economic asset group (IRR 1.19, 95% CI 1.16–1.22) (Table 2).

Fig.1

This figure shows the incidence of dementia in the different economic assets groups.

Table 2

Incidence of dementia and the incidence rate ratio of incidence in the different groups of economic assets

	N (%)	Dementia N	Person years	Incidence * (95% CI)	IRR unadjusted (95% CI)	IRR adjusted ** (95% CI)	IRR adjusted *** (95% CI)
Economic
Assets
Low	261351	13572	1113699	1.22	1.26	1.24	1.19
	(31.13)			(1.20–1.24)	(1.23–1.29)	(1.20–1.27)	(1.16–1.22)
Middle	303351	15327	1316739	1.16	1.20	1.13	1.11
	(36.13)			(1.15–1.18)	(1.17–1.23)	(1.10–1.16)	(1.09–1.14)
High	274941	11916	1230899	0.97	reference	reference	reference
	(32.74)			(0.95–0.99)

^*per 100 person years. ^**adjusted for sex, age, region, family type, education, and retirement. ^***adjusted for sex, age, region, family type, education, retirement, and the presence of either of 13 co-morbidities at baseline.

The mortality was highest in the low economic asset group (IRR 6.20, 95% CI 6.16–6.25) as compared to the middle (IRR 5.55, 95% CI 6.51–5.59) and high economic asset groups (IRR 4.29, 95% CI 4.26–4.33). Patients with dementia had a higher mortality compared to those without a diagnosis, with an IRR of 2.85 (95% CI 2.82–2.88). In the group of patients with dementia, mortality was lowest in the high economic asset group (IRR 3.31, 95% CI 3.23–3.38). However, the increase associated with dementia was lowest within the low economic asset group (IRR 2.57, 95%, CI 2.52–2.62) compared to the middle economic asset group (IRR 2.88, 95% CI 2.83–2.93) and high economic asset group (IRR 3.31, 95% CI 3.23–3.38) (Table 3).

Table 3

Incidence Rate ratio of mortality in the different groups of economic assets, with or without dementia

		Deaths N	Person years	Mortality * (95% CI)	IRR unadjusted (95% CI)	IRR adjusted ** (95% CI)	IRR adjusted^*** (95% CI)	IRR unadjusted (95% CI)	IRR adjusted ** (95% CI)	IRR adjusted *** (95% CI)
Dementia
No		163472	3661337	4.47	reference	reference	reference
				(4.44–4.49)
Yes		41017	175113	23.42	5.25	2.94	2.85
				(23.20–23.65)	(5.19–5.30)	(2.91–2.98)	(2.82–2.88)
Economic
Assets
Low		72881	287864	6.20	1.44	1.43	1.28
				(6.16–6.25)	(1.43–1.46)	(1.42–1.45)	(1.27–1.30)
Middle		76777	332495	5.55	1.29	1.23	1.18
				(5.51–5.59)	(1.28–1.31)	(1.22–1.25)	(1.17–1.20)
High		54831	294882	4.29	reference	reference	reference
				(4.26–4.33)
Economic	Dementia				IRR relative to high EA without dementia			IRR relative to without dementia within each EA group
Assets (EA)
Low	No	58094	1113699	5.22	1.43	1.51	1.35	reference	reference	reference
				(5.17–5.26)	(1.42–1.45)	(1.49–1.53)	(1.33–1.35)
	Yes	14787	61824	23.92	6.57	4.00	3.46	4.59	2.66	2.57
				(23.54–24.31)	(6.45–6.69)	(3.92–4.08)	(3.39–3.53)	(4.50–4.67)	(2.61–2.70)	(2.52–2.62)
Middle	No	60579	1316739	4.60	1.26	1.27	1.21	reference	reference	reference
				(4.56–4.64)	(1.25–1.28)	(1.25–1.28)	(1.20–1.23)
	Yes	16198	67315	24.06	6.61	3.73	3.49	5.23	2.94	2.88
				(23.70–24.44)	(6.49–6.73)	(3.66–3.80)	(3.42–3.55)	(5.14–5.32)	(2.89–3.00)	(2.83–2.93)
High	No	44799	1230899	3.64	reference	reference	reference	reference	reference	reference
				(3.61–3.67)
	Yes	10032	45974	21.82	6.00	3.45	3.31	6.00	3.45	3.31
				(21.40–22.25)	(5.87–6.13)	(3.38–3.53)	(3.23–3.38)	(5.87–6.13)	(3.38–3.53)	(3.23–3.38)

^*per 100 person years, ^**adjusted for sex, age, region, family type, education, and retirement, ^***adjusted for sex, age, region, family type, education, retirement, and the presence of either of 13 co-morbidities at baseline.

We followed a large, unselected population of almost 900,000 individuals for five years using data from national Danish registers. The cohort included the entire Danish population over the age of 65. The use of national registers ensured complete data on our outcomes—mortality and dementia— and the exposures of economic assets and other baseline socioeconomic factors [36]. Furthermore, the use of the national registers made selection bias negligible [44] due to the fact that all individuals over the age of 65 in Denmark were included. Finally, registration in the Central Registration System is required by Danish law and the register is updated on a daily basis. The information is therefore assumed to be high in quality and complete [37].

We have a large data set where both the exposure and the outcome are prevalent; we did not have information about functioning status, quality of life, body mass index, as well as lifestyle factors, such as smoking and could therefore not adjust for these potential confounders. We cannot exclude the possibility that including some of these confounders may weaken the associations found. However, these confounders could include “intermediate variables” that falsely take away part of the effect since they are on the causal pathway between the exposure, economic assets, and the outcome, death. Many of these factors may also be associated with low SEP, e.g., low SEP might reflect an unhealthy way of living, therefore an adjustment for these confounders may underestimate the associations with SEP [45].

There is an under-diagnosis of dementia internationally in healthcare systems [7, 46], a problem also found in Danish settings [47]. Hence, we cannot exclude the possibility that our results are biased due to a potential risk of the presence of individuals with undiagnosed dementia in the population. Some patients could have been misclassified, either undiagnosed or referred even though they do not have dementia. This could have an impact on the results, leading to a false, higher mortality rate of dementia. However, in order to minimize this possibility, we identified patients with dementia using three different national registers, which enhances our chances of finding additional individuals, even though under-diagnosis likely remains an issue. Additionally, the diagnosis of dementia in the NPR has been found to be of high validity and suitable for epidemiological studies concerning dementia [48].

We only used the NPR in our definition of diseases included in the CCI, and not information from the DNPR. This means that individuals diagnosed and treated in general practice are not included. If and when the diseases are critical they will appear in the NPR. This fact combined with the five-year follow-up period may potentially have impacted our results. Five years could potentially be too short a time period, meaning that a lot could happen beyond the follow-up period, especially for individuals only 65 years old at baseline. However, the survival time after a dementia diagnosis has been estimated to be between three and ten [11, 49], which indicates that a five-year long follow-up period time is sufficient.

The markers or elements defining SEP in studies differ substantially and proxies such as annual income, educational level, adequate financial resources, and geographical residency (income level for the neighborhood) have been used. Furthermore, there are more studies that have used not one but several combined markers for SEP [23 , 51], but few of them include financial adequacy [50] or wealth [28]; wealth in particular is closely related to economic assets. The studies that do examine wealth find that it is significantly associated with cognitive function [4].

There are conflicting results regarding the impact of SEP on both the incidence and prevalence of dementia: some have found that low SEP was associated with both an increase in the incidence and prevalence of dementia compared to those with high SEP [23–31 , 51] whereas others did not find this association [52]. Our result demonstrates a clear association between low SEP and high incidence and prevalence of dementia. Our study population is by far the largest and therefore we believe that the association is valid. The increased mortality in patients with dementia found in our study is in accordance with previous studies [16, 53]. The survival time after receiving a dementia diagnosis varies between three and ten years [11] and the IRR varies from 1.9 to 3.0. The noted variation in IRR may be explained by study characteristics such as individuals’ age at onset, severity of dementia included in the study, length of study period, or the age of the included population [4, 17].

DISCUSSION

We found a higher mortality among individuals diagnosed with dementia when compared to those without a dementia diagnosis. Among patients with dementia, the mortality was lowest in the high economic asset group and highest in the group with low economic assets. However, within the group with low economic assets, the increase in mortality associated with dementia was not as high as for the other economic groups.

To our knowledge, this is the first time that the effect of economic assets on mortality in patients with dementia has been investigated. A dementia diagnosis increased mortality regardless of economic assets. The mortality was lowest in the high economic asset group but the increase in mortality attributable to dementia was highest for this group. In contrast, mortality was highest among patients with dementia in the low economic asset group, but the increase attributable to dementia was lower. People with low economic assets may face a number of competing risks affecting mortality, including an increased risk of multimorbidity [54]. We have previously reported that patients with dementia have a higher prevalence of chronic obstructive pulmonary disease as well as diabetes (Bebe et al., unpublished results), which leads to higher mortality. We hypothesize that the effect of dementia on mortality in the low economic asset group may be less visible due to a ceiling effect produced by the competing risks. Differences in time of diagnosis (early versus late) could also produce differences in survival between groups. We found that the prevalence of the diagnosis was lower in the high asset group, but found no indication that the time of detection was different. The low asset group is, however, consulting primary care doctors more frequently due to, e.g., multimorbidity [55]. Frequent contacts with healthcare providers may furthermore increase the probability of an early dementia diagnosis [56] and hence result in a higher proportion of mild dementia in the low economic asset group.

Conclusion

Low economic assets were associated with increased general mortality for the total population. Mortality was increased with a dementia diagnosis and was highest for the low economic asset group. However, the increase in mortality attributable to dementia was higher in the high economic assets group. The mechanisms behind the unexpected interaction effect between dementia and low economic assets should be investigated further. Authors’ disclosures available online (https://www.j-alz.com/manuscript-disclosures/18-1107r1).

Footnotes

ACKNOWLEDGMENTS

This study was supported by the Research Board of the Sector for General Practice, the Research Fund for General Medicine, and the Alzheimer Fund.

The supplementary material is available in the electronic version of this article: .

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