Mortality in elderly Canadians with and without dementia: a 5-year follow-up

Abstract

Objectives: Based on the national Canadian Study of Health and Aging (CSHA), to compare 5-year overall mortality and causes of death in elderly with and without dementia. To determine how frequently dementia was mentioned on the death certificate.

Methods: For people who underwent a clinical examination in 1991 (n = 2,923), overall and cause-specific mortality rate ratios were calculated by dementia status (AD; vascular dementia; other dementias/other cognitive impairment; and normal cognition), age group (65 to 74, 75 to 84, 85+ years), and sex, using the Canadian general population as the reference. Similar rate ratios were calculated for people in the community who screened negative for cognitive impairment and who did not undergo a clinical examination (n = 7,340). Among elderly diagnosed as having AD or vascular dementia through the CSHA and who later died, it was determined how frequently dementia was recorded on the death certificate.

Results: The subgroup without cognitive dysfunction had a survival rate similar to that of the overall Canadian population except in the oldest age group, where the survival rate was better than that of the general population, which includes people with dementia. People in the three groups with cognitive impairment had a poorer survival in all age/sex groups than those without cognitive impairment and the general Canadian population. The most common causes of death in all groups were from vascular diseases. People with vascular dementia had the highest relative mortality rates for heart and cerebrovascular disease. Most of the AD groups also had high relative vascular system mortality rates. Among patients clinically diagnosed with AD, only 14.3% had any dementing illness recorded as the underlying cause of death; 41.8% had any dementing illness recorded anywhere on the death certificate. For vascular dementia, the corresponding numbers were 5.8% and 23.3%.

Conclusion: Elderly with dementia have clearly increased mortality rates relative to elderly without cognitive impairment in all age/sex categories. People with vascular dementia have a particularly poor prognosis. Studies of AD and vascular dementia using death certificate data will grossly underestimate the proportions of elderly with these diseases.