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Reference: Podewils, 2005
Cohort: Cardiovascular Health Cognition Study/Cardiovascular Health Study Cognition Study
Risk Factor: Physical Activity


Average Follow-up Time Detail
These figures pertain to the analysis of total dementia, but are expected to be reasonably similar for the analysis of AD. Participation was between 1992 and 2000.

Exposure Detail
"Information on physical activity was collected by trained interviewers at CHS baseline (1989–1990) and at CHCS baseline (1992–1994). A modified Minnesota Leisure Time Activity Questionnaire (30, 31) asked participants about the frequency and duration of 15 different types of activities over the previous 2 weeks. These activities were selected because they were previously shown to be the most common among older adults (32). Included were walking, household chores, mowing, raking, gardening, hiking, jogging, biking, exercise cycling, dancing, aerobics, bowling, golfing, general exercise, and swimming.

"Activities were assigned metabolic equivalents (ml O2/minute: METs) according to intensity (30), and leisure-time energy expenditure (kilocalories/week) was estimated for each person. Kilocalorie expenditure at CHS baseline and CHCS baseline were averaged to obtain an estimate of habitual physical activity levels in older adulthood used for the current analysis. Only a single measure of physical activity was used for participants for whom values were missing at one of the testing periods (n = 416)."

Screening and Diagnosis Detail
Screening Method:
IQ-CODEInformant Questionnaire for Cognitive Decline in the Elderly (Jorm 1989)
3MSEModified Mini-Mental State Examination (Teng 1987)
Other
TICSTelephone Interview of Cognitive Status

AD Diagnosis:
NINCDS ADRDA National Institute of Neurological and Communicative Diseases and Stroke/Alzheimer's Disease and Related Disorders Association Criteria (McKhann 1984)

Total dementia definition: Dementia was diagnosed with a multistage process and was either AD, vascular AD or other dementia. Vascular dementia via Alzheimer Disease Diagnostic and Treatment Center criteria (43).

"Dementia status and type in CHCS were classified in 1999–2000 by using a multistage process (25–27). Initially, participants were classified at their local study site into a dementia risk stratum (high or low). Persons were deemed high risk if they 1) had a 3MS score of <80 within the last two study visits, 2) had a decline of ≥5 points on the 3MS within their follow-up period, 3) had a Telephone Interview for Cognitive Status score of <28 or an Informant Questionnaire for Cognitive Decline in the Elderly score of >3.6, 4) had an incident stroke, 5) had a diagnosis of dementia that was documented in medical records, or 6) resided in a nursing home during the study period.
At the Pittsburgh site, all participants who were alive and could be traced were invited to the center in 1999–2000 for a full neuropsychiatric examination, regardless of dementia risk. At the three remaining sites, high-risk participants (as described above), all minority participants, and participants for whom cognitive data were incomplete were invited for a comprehensive evaluation. For those who did not attend the clinic visit, medical records and proxy or previous telephone interviews were used for diagnosis. The diagnosis was based on a deficit in performance in two or more cognitive domains sufficiently severe to affect the subjects' activities of daily living for those with a history of normal intellectual function. The dementia criteria were designed to identify subjects with syndromes that could include relatively preserved memory functions (e.g., frontotemporal dementia), and thus memory deficit was not required for the diagnosis of dementia (26).
All participants identified as having dementia were reviewed by the Adjudication Committee, made up of neurology and psychiatry experts. The diagnosis of Alzheimer's disease was based on National Institute of Neurological and Communicative Disorders and Stroke–Alzheimer's Disease and Related Disorders Association (NINCDS-ADRDA) (42) criteria, and the diagnosis of vascular dementia was based on Alzheimer's Disease Diagnostic and Treatment Centers criteria (43). Time of dementia onset was established by the first diagnosis if recorded in medical records and otherwise as the midpoint between two annual CHS follow-up interviews with a marked change in cognition leading to the final dementia diagnosis."

Covariates & Analysis Detail
Analysis Type:
Cox proportional hazards regression

In the fully adjusted models, as reported here, the number of participants is 3,041. The crude and age-adjusted models have N=3,373.

"When analyses were stratified by APOE {varepsilon}4 carrier state, the inverse association of energy expenditure and activity index with dementia risk was limited to APOE {varepsilon}4 noncarriers (table 6 and figure 2). The multivariate-adjusted hazard ratios for all-type dementia comparing the highest with the lowest quartile of energy expenditure in APOE {varepsilon}4 noncarriers was 0.68 (p-trend = 0.01), and the hazard ratio comparing the highest with the lowest quartile of activity index was 0.44 (p-trend < 0.001). The corresponding hazard ratios for energy expenditure and activity index for APOE {varepsilon}4 carriers were 1.29 (p-trend = 0.53) and 1.20 (p-trend = 0.68). The p values for the interaction of energy expenditure or activity index with APOE {varepsilon}4 carrier status were 0.06 and 0.003, respectively. The same pattern was observed for Alzheimer's disease [p-trend in noncarriers=0.01] and vascular dementia (figure 2). Persons may be less active because they are less physically able to be active. Therefore, we repeated the analysis by excluding subjects with one or more instrumental activities of daily living impairments and with one or more activities of daily living impairments, but the associations of energy expenditure and the activity index with dementia risk and the effect modification with APOE carrier status were similar."

AD Covariates:
Aage
Eeducation
Ggender
ADLIactivities of daily living impairment
APOE4APOE e4 genotype
MMSEbaseline MMSE
IADLIinstrumental activities of daily living impairment
MRImagnetic resonance imaging white-matter-grade score
RErace/ethnicity
SNSsocial network score
SSSsocial support score

TD Covariates:
Aage
Eeducation
Ggender
ADLIactivities of daily living impairment
APOE4APOE e4 genotype
MMSEbaseline MMSE
IADLIinstrumental activities of daily living impairment
MRImagnetic resonance imaging white-matter-grade score
RErace/ethnicity
SNSsocial network score
SSSsocial support score