Dementia and stroke comorbidity among Canadians aged 65 years and older

Organization: Public Health Agency of Canada

Published: 2020-09-18

Highlights from the Canadian Chronic Disease Surveillance System

Dementia^{Footnote i} and stroke are common and debilitating chronic conditions in Canada. They pose significant health challenges, especially among individuals aged 65 years and older. The risk of developing these conditions, either separately or together (i.e. comorbidity), increases with age.^{Footnote 1 Footnote 2 Footnote 3} Some Canadian studies have investigated comorbid dementia and stroke in specific populations;^{Footnote 4 Footnote 5} however, there are insufficient data to estimate the prevalence of this comorbidity in the general Canadian population.^{Footnote 6 Footnote 7}

This factsheet provides new estimates on dementia and stroke comorbidity among Canadians aged 65 years and older, examining the simultaneous presence of dementia and any stroke using data from the Canadian Chronic Disease Surveillance System (CCDSS). The Public Health Agency of Canada (PHAC) uses the CCDSS to conduct national surveillance of 20 chronic conditions, including diagnosed dementia and stroke.^{Footnote 8 Footnote 9}

Dementia refers to a set of symptoms and signs associated with a progressive deterioration of cognitive functions that affect daily activities.^{Footnote 8} It is caused by various diseases and injuries in the brain and vascular system. Alzheimer's disease represents the most common cause of dementia, while vascular dementia is the second most common cause of dementia. However, evidence suggests that mixed dementia, involving any combination of causes but often these two, is also common.^{Footnote 10 Footnote 11}

A stroke is a sudden loss of brain function caused by a brain blood vessel blockage (ischemic stroke) or rupture (haemorrhagic stroke).^{Footnote 9}

Validated case definitions for diagnosed dementia^{Footnote 12} in individuals aged 65 years and older, and diagnosed stroke^{Footnote 13} in individuals aged 20 years and older, were applied to CCDSS longitudinal data (i.e., April 1, 1996 to March 31, 2017). Among individuals aged 65 years and older still alive in 2016–2017, coexisting dementia and stroke cases (regardless of the order of occurrence) were identified as prevalent comorbid cases. Data are presented for fiscal year 2016–2017. Data from all Canadian provinces and territories, except Saskatchewan, were available for these analyses.

How many Canadians aged 65 years and older have both dementia and stroke (prevalence)?

According to 2016–2017 fiscal year data from the CCDSS, 6.9% (or 432,000) of individuals 65 years and older were living with dementia and 9.6% (or 602,000) had a stroke since the beginning of the surveillance period in 1996–1997. Overall, in the population aged 65 years and older:

• The prevalence of dementia was higher in women than men (8.0% vs. 5.5%);
• The prevalence of stroke was higher in men than women (10.2% vs. 9.0%).

In 2016–2017, about 1.8% (or 110,000) of individuals aged 65 years and older were living with comorbid dementia and stroke, while 5.1% (or 322,000) were living with dementia, without a stroke, and 7.8% (or 492,000) had a stroke, without dementia (Table 1).

Table 1

The prevalence of dementia and stroke comorbidity was greater in women than men (1.9% vs. 1.6%) using crude rates; however, this pattern is reversed when using age–standardized rates (1.6% vs. 1.8%) given the age distribution of the senior population.

The prevalence of dementia without stroke increased with age. Women 75 years and older had a higher prevalence of dementia without stroke than men of the same age (Table 2a). The prevalence of stroke without dementia also increased with age, although it increased less rapidly after the age of 85. Regardless of age, stroke without dementia occurred more frequently in men than women (Table 2b).

Table 2

The prevalence of dementia and stroke comorbidity among individuals aged 65 years and older markedly increased from 0.2% in individuals aged 65 to 69 years old to 8.9% in those aged 90 years and older (Table 3). The crude prevalence of dementia and stroke comorbidity was greater in males until 90 years of age, where the crude prevalence was greater in women (9.1%) than men (8.3%). This sex pattern observed in the crude rates may be explained by the greater number of women than men surviving to the oldest age groups.

Table 3

What are the mortality rates (due to any cause of death) among Canadians aged 65 years and older with dementia and stroke?

As expected, all-cause mortality rates increased with age regardless of the disease combination and were higher among older men than older women (Table 4). Overall, the age–standardized all–cause mortality rate was 6.9 times greater in individuals aged 65 years and older with both conditions compared to those without the two conditions (150.5 per 1,000 vs. 21.8 per 1,000). The age–standardized rate ratio was higher among women (7.8) than among men (6.1) (data not shown).

All–cause mortality rates were higher in persons with stroke/without dementia, persons with dementia/ without stroke and persons with both conditions when compared to persons without dementia and stroke. However, the rate ratios decreased with age, which may be explained by the increase in general mortality. As people age, they are more likely to die of any cause.

In individuals living with dementia, without stroke (Table 4a), rate ratios were similar between sexes across all age groups, except in the youngest. Rate ratios among those who had a stroke, without dementia (Table 4b) and those living with dementia and stroke comorbidity (Table 4c) were greater in women than men for all age groups, except the oldest.

Table 4

Crude all–cause mortality rates^✝ and rate ratios in individuals aged 65 years and older (a) living with dementia, without stroke, (b) who have had a stroke, without dementia and (c) living with dementia and stroke comorbidity, compared to those without dementia and stroke comorbidity, by age group and sex, Canada*, 2016–2017.

What are the risk factors associated with dementia and stroke?

Many factors are associated with the development and progression of dementia, or having a stroke. Non–modifiable risk factors for developing dementia or stroke include age, sex, family history and ethnicity.^{Footnote 10 Footnote 14 Footnote 15 Footnote 16}

Lifestyle factors, such as healthy eating, physical activity, limiting excessive alcohol intake and smoking cessation, can be protective in delaying or reducing the risk of dementia or stroke.^{Footnote 10 Footnote 14 Footnote 15 Footnote 16} Further, having a secondary school education and being socially engaged has been shown to be protective against dementia.^{Footnote 10 Footnote 16} Conditions like hypertension, elevated blood cholesterol, obesity, diabetes, depression, atrial fibrillation and other cardiac conditions are associated with a higher likelihood of developing dementia or having a stroke.^{Footnote 14 Footnote 15 Footnote 16 Footnote 17 Footnote 18}

There are multiple interactions between dementia and stroke that are not yet fully understood. Similarities in their modifiable risk factors, in particular hypertension which is highly prevalent and involved in the development of both conditions, may provide insight into potential strategies to prevent or delay the development or progression of both conditions.^{Footnote 19 Footnote 20}

Related links

• Dementia in Canada
• Stroke in Canada
• Alzheimer Society of Canada
• World Health Organization: Dementia
• Heart and Stroke Foundation of Canada
• Canadian Stroke Best Practices: Mood, cognition and fatigue following stroke

Data

• Canadian Chronic Disease Surveillance System– Data Tool

Acknowledgements

This work was made possible through collaboration between PHAC and all Canadian provincial and territorial governments and expert contributions from the CCDSS Neurological Conditions Working Group and the CCDSS Stroke Working Group. This fact sheet was developed by PHAC; no endorsement by the provinces and territories is intended or should be inferred.