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AlzRisk Paper Detail

Reference: Scarmeas, 2009
Cohort: Washington Heights-Inwood Columbia Aging Project
Risk Factor: Physical Activity

Average Follow-up Time Detail
The study includes 2 cohorts recruited through the WHICAP in 1992 and 1999. Neurological evaluations were repeated every 1.5 years from 1992 through 2006.

Exposure Detail
"Two slightly different versions of the Godin leisure time exercise questionnaire were used (18). Most participants (n = 1133) were queried about a 2-week period. The number of times participating and the number of minutes per time participating were recorded for 3 different categories of activities: vigorous (aerobic dancing, jogging, playing handball), moderate (bicycling, swimming, hiking, playing tennis), and light (walking, dancing, calisthenics, golfing, bowling, gardening, horseback riding).

We constructed a summary physical activity score for each individual using the following formula: number of minutes x number of times x coefficient (9 for vigorous, 5 for moderate, and 3 for light activities corresponding to the metabolic equivalent [MET](18)). The MET expresses the energy cost consumption during specific physical activities as multiples of resting metabolic rate (obtained during quiet sitting and set by convention to 1 kcal x kg–1 x hr–1 or 1 MET). Physical activities can therefore be classified in terms of intensity based on corresponding METs. In this case, vigorous activities were considered to correspond to 9 METs (or 9 kcal x kg–1 x hr–1), moderate activities to 5 METs (or 5 kcal x kg–1 x hr–1), and light activities to 3 METs (or 3 kcal x kg–1 x hr–1).

Because of skewed distribution, the summary physical activity score was again categorized into tertiles with a similar number of individuals in each group and the following median weekly physical activity values in each group: no physical activity, 0 hours; some physical activity, 0.1 hours of vigorous, 0.8 hours of moderate, or 1.3 hours of light, or a combination thereof; much physical activity, 1.3 hours of vigorous, 2.3 hours of moderate, or 3.8 hours of light, or a combination thereof. Dichotomizing the summary physical activity score resulted in 2 groups with the following median weekly levels: low physical activity, 0 hours; high physical activity, 1.3 hours of vigorous, 2.4 hours of moderate, or 4 hours of light physical activity, or a combination thereof.

A subset of individuals who were recruited earlier in the study (n = 747) were queried regarding their physical activity in a different way (number of hours during the most recent month in which they engaged in their typical number of activities). Using procedures similar to the ones described above, a physical activity score was calculated and categorized into tertiles of no physical activity, some physical activity, and much physical activity. Although categorization of individuals in physical activity categories was performed within each version of the questionnaire, in supplementary analyses we additionally explored inclusion of a term representing the period of physical activity assessment in the analyses and considered only the most recent version of the questionnaire.

Test-retest (2 weeks to 1 month) reliability correlation coefficients of the Godin Leisure Time Exercise Questionnaire18 have ranged between 0.62 and 0.81 (18-20). Validity of the instrument has been demonstrated in relation to multiple measures including body fat(18-19), maximum oxygen consumption(18-19,) Caltrac actometer(19, 21), treadmill time(19), and other similar physical activity questionnaires(20-21). Because the questionnaire has not been validated in individuals older than 65 years, we explored its validity in our cohort comparing it with available measures of physical performance: time to complete 5 chair stands (available for 716 individuals), time to walk 1 meter (measured twice and averaged; available for 924 individuals), and time to walk 4 meters (measured twice and averaged; available for 924 individuals). The correlation (Spearman {rho} correlation coefficient) of the sum physical activity score was –0.10 with time for chair stands (P = .009), –0.10 with mean time for the 1-meter walk (P = .002), and –0.28 with mean time for the 4-meter walk (P < .001)."

Screening and Diagnosis Detail
Screening Method:

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 diagnosed via DSM III-R.

"At entry, each individual's medical and neurological history was recorded and a standardized physical and neurological examination was conducted by physicians. All available ancillary information (medical charts, computed tomography scans or magnetic resonance imaging scans) was considered in the evaluation. Additional evaluation instruments included a structured in-person interview including an assessment of health and function and a neuropsychological battery that contained tests of memory (short- and long-term verbal and nonverbal), orientation, abstract reasoning (verbal and nonverbal), language (naming, verbal fluency, comprehension, and repetition), and visual-spatial abilities (copying and matching)(16). Using previously described methods (17), data on 15 neuropsychological test variables from the initial visit were grouped into 4 cognitive factors (memory, language, processing speed, and visual-spatial ability), converted into z scores and then averaged to create a composite cognitive z score. A Clinical Dementia Rating (CDR) score also was assigned.

A consensus diagnosis for the presence or absence of dementia was made at a diagnostic conference of neurologists and neuropsychologists based on criteria from the Diagnostic and Statistical Manual of Mental Disorders (Third Edition Revised). Standard diagnostic criteria were used for determination of the type of dementia. The diagnosis of probable or possible AD was based on the criteria of the National Institute of Neurological Disorders and Stroke and the Alzheimer's Disease and Related Disorders Association."

Covariates & Analysis Detail
Analysis Type:
Cox proportional hazards regression

The results from the adjusted models include a lower number of individuals (N=1252 vs. N=1880) because of missing data on some of the covariates.

This study examined physical activity as both a dichotomous and a trichotomous variable (trichotomous reported here).

In addition to examining the association between physical activity and risk of AD, this study investigated the extent to which physical activity and adherence to a Mediterranean-type diet had independent association with AD.

"Using physical activity and diet adherence in their tertile forms, we constructed an additional combined variable classifying individuals as (1) no physical activity plus low diet score; (2) some physical activity plus low diet score or no physical activity plus middle diet score; (3) some physical activity plus middle diet score, or no physical activity plus high diet score, or much physical activity plus low diet score; (4) some physical activity plus high diet score or much physical activity plus middle diet score; and (5) much physical activity plus high diet score. The variable was entered as a predictor in the Cox models in a dummy form using no physical activity plus low diet score as the reference group. For the trend test calculation, a continuous variable (range, 1-5) was used. This study had 80% power to detect a significant (type I error of .05) joint (much physical activity plus high diet score vs other) HR as high as 0.67."

AD Covariates:
APOE4APOE e4 genotype
bsln BMIbaseline BMI
Kcalcaloric intake
CFcognitive function
CIcomorbidity index
LAleisure activities
SMsmoking status
SPstudy population

The comorbidity index (CI) covariate here is a modified version of the Charlson Index of Morbidity, which includes items for myocardial infarction, congestive heart failure, peripheral vascular disease, hypertension, chronic obstrucitve pulmonary disease, arthritis, gastrointestinal tract disease, mild liver disease, diabetes, chronic renal disease, and systemic malignancy from baseline visit. All items received a weight of 1, expect chronic renal disease and systemic malignancy which received weights of 2.

The cognitive function (CF) covariate was based on a Clinical Dementia Rating score (0 vs. 0.5).

The other (O) covariate refers to time between first dietary and first physical activity assessment.

"If the omnibus test was significant in the analysis of variance models examining the association between age, education, caloric intake, BMI, comorbidity index, leisure activities, or diet score (dependent variable) and physical activity tertiles (independent variable), post hoc Bonferroni and Tukey tests were used."