Study sampling in the Canadian Study of Health and Aging

Estimating the lifetime risk of dementia in the Canadian elderly population using cross-sectional cohort survival data

Dementia is one of the world's major public health challenges. The lifetime risk of dementia is the proportion of individuals who ever develop dementia during their lifetime. Despite its importance to epidemiologists and policy-makers, this measure does not seem to have been estimated in the Canadian population. Data from a birth cohort study of dementia are not available. Instead, we must rely on data from the Canadian Study of Heath and Aging, a large cross-sectional study of dementia with follow-up for survival. These data present challenges because they include substantial loss to follow-up and are not representatively drawn from the target population because of structural sampling biases. A first bias is imparted by the cross-sectional sampling scheme, while a second bias is a result of stratified sampling. Estimation of the lifetime risk and related quantities in the presence of these biases has not been previously addressed in the literature. We develop and study nonparametric estimators of the lifetime risk, the remaining lifetime risk and cumulative risk at specific ages, accounting for these complexities. In particular, we reveal the fact that estimation of the lifetime risk is invariant to stratification by current age at sampling. We present simulation results validating our methodology, and provide novel facts about the epidemiology of dementia in Canada using data from the Canadian Study of Health and Aging.

Digestive symptoms in older adults: prevalence and associations with institutionalization and mortality

BACKGROUND

Digestive symptoms are common in adults. However, little is known about their prevalence in older adults and the association of digestive symptoms with institutionalization and mortality in community-dwelling older adults.

OBJECTIVE

To determine the prevalence of digestive symptoms among older adults in Canada and whether they are associated with increased risk of institutionalization and mortality, independent of the effect of potential confounders.

METHODS

The present study was a secondary analysis of data collected from community-dwelling participants 65 years of age and older in the Canadian Study of Health and Aging. Measures incuded age, sex, presence of digestive symptoms, cognition, impairment in activities of daily living (ADL) and self-reported health. Outcome measures included death or institutionalization over the 10 years of follow-up.

RESULTS

Digestive symptoms were found in 2288 (25.6%) of the 8949 subjects. Those with digestive symptoms were older, with a mean difference in age of six months (P=0.007). Digestive symptoms were more common among women (28.4%) than men (20.3%), among individuals with poor self-reported health and those with an increased number of impairments in their ADLs (P<0.001). The presence of digestive symptoms was associated with higher mortality (HR 1.15 [95% CI 1.05 to 1.25] adjusted for age, sex, cognitive function and ADL impairment); however, this association was not statistically significant after adjusting for self-reported health.

CONCLUSION

Although digestive symptoms were associated with increased mortality independent of age and sex, cognition and function, this association was largely explained by poor self-assessed health. Digestive symptoms were not associated with institutionalization.

Executive function and survival in the context of chronic illness

BACKGROUND

Individual differences in executive function (EF) have been shown to predict risk factors for chronic illness. It is not currently known whether EFs also predict survival time following a diagnosis of a chronic illness.

PURPOSE

The objective of this investigation was to examine the association between individual differences in EF and survival time among individuals suffering from one or more chronic illness.

METHODS

A sample of 162 community-dwelling older adults who suffered from a chronic illness at baseline underwent thorough medical and neurological examinations to ensure freedom from actual or probable dementia. Participants completed cognitive testing and were subsequently followed for 10 years; survival was assessed as survival time over the follow-up interval.

RESULTS

Findings indicated that individual differences in EF predicted survival time, and this association held when adjustments were made for demographic variables (age, sex), education, and body mass index.

CONCLUSION

Individual differences in EF may be important determinants of survival in the context of chronic illness.

The Canadian Longitudinal Study on Aging (CLSA)

Les Canadiens vivent plus longtemps et les personnes plus âgées composent une part croissante de la population (14% en 2006, projeté d’atteindre 20% d’ici 2021). L’Étude longitudinale canadienne sur le vieillissement (ÉLCV) est une étude longitudinale nationale portant sur le développement adulte et le vieillissement qui recrutera 50 000 Canadien(ne)s âgé(e)s de 45 à 85 ans et qui les suivra pendant au moins 20 ans. Tous les participants fourniront un ensemble d’informations communes sur plusieurs aspects de la santé et du vieillissement, et 30 000 passeront un examen approfondi couplé au don de spécimens biologiques (sang et urine). L’ÉLCV deviendra une source de données riches pour l’étude d’inter-relations complexes entre les facteurs biologiques, physiques, psychosociaux et sociaux qui affectent le vieillissement en santé.

Does executive function explain the IQ-mortality association? Evidence from the Canadian study on health and aging

OBJECTIVE

To assess the robustness of the association between intelligence quotient (IQ) and mortality in older adults and to examine whether or not the association can be explained by more specific cognitive processes, including individual differences in executive functioning.

METHODS

We examined the associations among Full Scale IQ, individual IQ subtest scores, and 10-year mortality among older community-dwelling, adult participants in the Canadian Study of Health and Aging, who were verified as disease and cognitive-impairment free at baseline via comprehensive medical and neurological evaluation (n = 516). Survival analysis including Cox proportional hazards regression models were used to examine mortality risk as a function of Full Scale IQ and its specific subcomponents.

RESULTS

An inverse association was found between IQ and mortality, but this did not survive adjustment for demographics and education. The association between IQ and mortality seemed to be predominantly accounted for by performance on one specific IQ subtest that taps executive processes (i.e., Digit Symbol (DS)). Performance on this subtest uniquely and robustly predicted mortality in both unadjusted and adjusted models, such that a 1-standard deviation difference in performance was associated with a 28% change in risk of mortality over the 10-year follow-up interval in adjusted models.

CONCLUSIONS

The association between IQ and mortality in older adults may be predominantly attributable to individual differences in DS performance.

Changes in cognition and mortality in relation to exercise in late life: a population based study

Background

On average, cognition declines with age but this average hides considerable variability, including the chance of improvement. Here, we investigate how exercise is associated with cognitive change and mortality in older people and, particularly, whether exercise might paradoxically increase the risk of dementia by allowing people to live longer.

Methods and Principal Findings

In the Canadian Study of Health and Aging (CSHA), of 8403 people who had baseline cognition measured and exercise reported at CSHA-1, 2219 had died and 5376 were re-examined at CSHA-2. We used a parametric Markov chain model to estimate the probabilities of cognitive improvement, decline, and death, adjusted for age and education, from any cognitive state as measured by the Modified Mini-Mental State Examination. High exercisers (at least three times per week, at least as intense as walking, n = 3264) had more frequent stable or improved cognition (42.3%, 95% confidence interval: 40.6–44.0) over 5 years than did low/no exercisers (all other exercisers and non exercisers, n = 4331) (27.8% (95% CI 26.4–29.2)). The difference widened as baseline cognition worsened. The proportion whose cognition declined was higher amongst the high exercisers but was more similar between exercise groups (39.4% (95% CI 37.7–41.1) for high exercisers versus 34.8% (95% CI 33.4–36.2) otherwise). People who did not exercise were also more likely to die (37.5% (95% CI 36.0–39.0) versus 18.3% (95% CI 16.9–19.7)). Even so, exercise conferred its greatest mortality benefit to people with the highest baseline cognition.

Conclusions

Exercise is strongly associated with improving cognition. As the majority of mortality benefit of exercise is at the highest level of cognition, and declines as cognition declines, the net effect of exercise should be to improve cognition at the population level, even with more people living longer.

Prevention of CIND by physical activity: different impact on VCI-ND compared with MCI

BACKGROUND

Cognitive impairment that does not meet the criteria for dementia ("Cognitive Impairment, No Dementia" -- CIND) is a heterogeneous category with an increased risk of dementia. While greater physical activity is generally associated with a lower odds of both dementia and CIND, whether this effect applies across subgroups is not known.

OBJECTIVES

To investigate the association between physical activity and the risk of vascular CIND (VCI-ND) or mild cognitive impairment (MCI).

METHODS

In the Canadian Study of Health and Aging community-dwelling cohort, of 4683 people who were not impaired at baseline, 3945 remained without cognitive impairment at 5 years, 454 were diagnosed with CIND, and 284 with dementia. Incident CIND and VCI-ND (n=163) and MCI (n=100) subtypes were investigated in relation to baseline physical activity, stratified by sex.

RESULTS

In women, moderate-high exercise was associated with a lower odds of CIND (OR=0.62, 95% CI=0.46-0.84) and VCI-ND (0.34, 0.18-0.63) relative to low exercise. There was no association for men or for MCI.

CONCLUSION

Exercise appears to reduce the risk of VCI-ND in women. Whether the lack of an effect of exercise on the odds of MCI reflects that 'prevented AD' is indistinguishable from MCI is an intriguing possibility that merits further study.

Mapping the connections between education and dementia

Explanations for the association between educational attainment and the risk of dementia fall into three main categories. It may arise as an artefact of study methods; education may predict broader socioeconomic circumstances and exposures, or education may reflect brain reserve or cognitive capacity that protect against dementia. Data from the Canadian Study of Health and Aging (N=6646, giving 44,676 person-years of follow-up) are analyzed to test a series of hypotheses reflecting these explanations. Years of education showed a strong association with the risk of dementia (relative risk [RR] 2.1 for those with less than 6 years of education compared to those with 13 or more years; RR=2.9 among survivors). Possible artefactual factors were detected, but were insufficient to invalidate the association. Adjustments for a range of other socioeconomic indicators, health problems and lifestyle factors reduced, but did not remove, the association. Adjustments for intelligence and for an indicator of lifetime mental activity also appeared to account for some but not all of the association. The conclusion is that there appears to be a real association between educational attainment and the risk of dementia 50 to 60 years later; this influence appears to run through a number of different, and sometimes complementary, pathways.

Cognitive-impairment-free life expectancy for Canadian seniors

BACKGROUND/AIMS

While cognitive impairment (CI) and dementia are among the most common morbid conditions in later life, life expectancies free from CI or dementia have been the object of much less investigation than life expectancy based on measures of physical functioning.

METHODS

We estimated sex-specific CI-free life expectancy in Canada for people aged 65 and older using data from a nationwide, multicenter Canadian study on the epidemiology of dementia.

RESULTS

The absolute number of years with CI remains virtually constant with increasing age. Whatever the current age, senior men can expect to live 2.5-3 years of their remaining life with some form of CI and about 1.5 years of those with dementia. For women, these figures rise to 3-4 years with CI, of which 2-2.5 years are spent with dementia.

CONCLUSION

Surviving to an older age does not result in a longer average absolute period of CI. This period is associated with a significant reduction in quality of life, the use of home and institutional services, as well as psychological and physical distress for formal and informal caregivers. Results are compared to findings reported in other countries.

APOE genotype, vascular risk factors, memory test performance and the five-year risk of vascular cognitive impairment or Alzheimer's disease

The APOE epsilon4 gene and poor memory test performance have each been associated with an increased risk of developing dementia, but the relationship between these risk factors in predicting dementia is unclear. We examined the multivariate effects of APOE genotype, memory test performance and vascular risk factors in predicting incident Alzheimer's disease (AD) and vascular cognitive impairment (VCI) in the Canadian Study of Health and Aging. Delayed free recall was measured by the Buschke Cued Recall Test (BCRT). The study sample included 223 people who were identified as having no cognitive impairment (NCI) and either APOE epsilon3/epsilon3 or epsilon3/epsilon4 genotypes at the baseline clinical assessment. After 5 years, 182 (82%) still had NCI, 21 developed VCI (9%) and 20 AD (9%). Multivariate analyses demonstrated that APOE epsilon4 increased the risk of AD (OR, 3.48; CI, 1.15-10.48) but not VCI (OR, 0.89; CI, 0.24-3.27). Vascular risk factors increased the risk of VCI (OR, 2.18; CI, 1.36-3.51) but not AD (OR, 0.68; CI, 0.38-1.20). Lower BCRT scores conferred an increased risk of both VCI (OR, 1.75; CI, 1.27-2.42) and AD (OR, 1.86; CI, 1.29-2.67) but attenuated the APOE epsilon4 effect in AD. VCI and AD have different risk profiles and outcomes, but subtle memory difficulties may be an early feature of both.

Prevalence, Attributes, and Outcomes of Fitness and Frailty in Community-Dwelling Older Adults: Report From the Canadian Study of Health and Aging

BACKGROUND

Frailty and fitness are important attributes of older persons, but population samples of their prevalence, attributes, and outcomes are limited.

METHODS

The authors report data from the community-dwelling sample (n = 9008) of the Canadian Study of Health and Aging, a representative, 5-year prospective cohort study. Fitness and frailty were determined by self-reported exercise and function level and testing of cognition.

RESULTS

Among the community-dwelling elderly population, 171 per 1000 were very fit and 12 per 1000 were very frail. Frailty increased with age, so that by age 85 years and older, 44 per 1000 were very frail. The risk for adverse health outcomes increased markedly with frailty: Compared with older adults who exercise, those who were moderately or severely frail had a relative risk for institutionalization of 8.6 (95% confidence interval, 4.9 to 15.2) and for death of 7.3 (95% confidence interval, 4.7 to 11.4). These risks persist after adjustments for age, sex, comorbid conditions, and poor self-rated health. At all ages, men reported higher levels of exercise and less frailty compared with women. Decreased fitness and increased frailty were also associated with poor self-ratings of health (42% in the most frail vs 7% in the most fit), more comorbid illnesses (6 vs 3), and more social isolation (34% vs 29%).

CONCLUSIONS

Fitness and frailty form a continuum and predict survival. Exercise influences survival, even in old age. Relative fitness and frailty can be determined quickly in a clinical setting, are potentially useful markers of the risk for adverse health outcomes, and add value to traditional medical assessments that focus on diagnoses.

Does Self-Rated Health Predict Survival in Older Persons with Cognitive Impairment?

OBJECTIVES

To determine whether baseline self-rated health (SRH) independently predicted survival in an older Canadian population and to investigate the role of cognition on the SRH-mortality relationship.

DESIGN

Population-based prospective cohort study.

SETTING

Ten Canadian provinces, community-based.

PARTICIPANTS

A total of 8,697 community-dwelling participants aged 65 and older.

MEASUREMENTS

Self-reported measures of overall health, physical function, comorbidities, and demographic characteristics were obtained by interview. Cognitive ability was ascertained using the Modified Mini-Mental State Examination (3MS). Participants were followed for their survival status from the initial interview in 1991 until October 31, 1996.

RESULTS

Subjects with reports of poor SRH were significantly more likely to die during follow-up than those reporting good SRH, after adjusting for relevant covariates (adjusted hazard ratio (AHR)=1.38, 95% confidence interval (CI)=1.24-1.53). SRH was also related to other measures of health status across levels of cognitive impairment. SRH remained a significant predictor of mortality in subjects with mild to moderate cognitive impairment (AHR=1.26, 95% CI=1.01-1.59) but not in those with severe cognitive impairment (AHR=1.00, 95% CI=0.76-1.31).

CONCLUSION

This study supports the utility of SRH assessments in predicting survival of individuals with mild to moderate cognitive impairment. The findings highlight the potential role of complex cognitive processes underlying the SRH-mortality relationship.

Canadian Outcomes Study in Dementia: study methods and patient characteristics

OBJECTIVE

To describe the methods and patient characteristics of the Canadian Outcomes Study in Dementia (COSID).

METHODS

COSID is a 3-year prospective study of dementia patients living in the community at the time of study registration. We assessed patients' cognition, behaviour, and functioning every 6 months, using the Modified Mini-Mental State Examination (3MS), the Neuropsychiatric Inventory (NPI), and the Functional Autonomy Measurement System (SMAF), respectively. We assessed caregivers, using the Zarit Burden Interview (ZBI). Additional information included the Global Deterioration Scale (GDS), patients' driving status, and clinical information including family history, dementia type, concomitant medications, and comorbid conditions. From the patient or caregiver, we collected details of inpatient and outpatient resources used by the patient and (or) caregiver.

RESULTS

We enrolled 766 patients from 31 Canadian sites. Overall mean age was 76.8 years, and mean age of onset was 73.1 years. Of the total patients, 98% were white, 54% were women, and 84% were diagnosed with Alzheimer's disease. Mean baseline 3MS was 66.5, NPI was 9.5, and SMAF was 18.30. Of these patients, 48% reported a GDS score of 3 (that is, moderate), 16% reported a GDS score of 4 (that is, moderately severe), and the remaining 36% reported a GDS score of 1 or 2 (that is, mild or very mild). At baseline, 83% of patients received cholinesterase inhibitors, 46% received nonsteroidal antiinflammatory drugs, 39% received vitamin E, and 25% received antidepressants. Adult day care and home help were the largest cost factors in this population, with mean monthly costs of $65 and $64, respectively. We found interesting differences in the resources used among geographic regions and care settings.

CONCLUSIONS

COSID is already generating valuable information about treatment patterns, outcomes, and resource use in Canadian patients with dementia. As the data mature, it will be possible to build robust models on treatment effectiveness and costs of care.

Patterns and health effects of caring for people with dementia: the impact of changing cognitive and residential status

PURPOSE

To link changes over 5 years in the health, vital and residential status of very elderly people to changes in their family caregivers' health.

DESIGN AND METHODS

Canadian population-based, longitudinal study including community and institutional residents. From interviews and clinical examinations, 948 people (mean age = 86 years) were classified as demented, frail, or healthy at two points in time. Caregivers reported on the care they provided and their health outcomes.

RESULTS

Diagnostic and residential groups of care recipients differed significantly in their level of activity of daily living/instrumental activity of daily living disability (range = 0.2 problems for the healthy group, 10-12 in the dementia groups) and in the amount of assistance received; caregiver burden scores were higher for people with dementia in the community than for those in institutions (p <.001). However, these differences did not translate directly into contrasts in caregiver health. Caregivers of healthy elders reported fewer health problems than did caregivers for people with dementia or frailty, but the latter groups did not differ significantly. Death of the care recipient and admission to institutional care did not have a consistent impact on caregiver health.

IMPLICATIONS

The relationship between caregiver load and health outcomes is complex and dynamic; treatments that slow the progression of dementia will not necessarily relieve caregiver strain.