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April 9 th, 2013 Journal Club University of Southern California José L González, MD
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Prevalence o 1/8 Americans > 65yoa o $200b/yr Why this study? o Prevention of cognitive disability o Lifestyle modification = most cost-effective o Current evidence insufficient o No public health recommendation
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Increased fitness protects against o All-cause mortality o Stroke o Diabetes o HTN Other studies linked to dementia o Only associated dancing o Only vascular dementia o Only Alzheimers
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Intermediate outcomes o Brain atrophy – med. Temporal lobe vol. o MMSE NIH consensus statement “physical activity may prevent dementia” o Self-reported physical activity Canadian study of health and aging o 5-yr f/u, n= 4615
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Assess association between objectively measured fitness and all-cause dementia w/ long-duration of follow-up. Hypothesized: pts w/ greater midlife fitness = lower risk for dementia later in life o Independent of antecedent cerebrovascular disease
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Study Design: Prospective, observational cohort study Cooper Longitudinal Study o Non-profit, independent research organization o Assessing lifestyle behavior on health outcomes o Observational database of 28,968 community-dwelling participants o Dallas, TX
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Generally healthy self-referred/employee referred for preventative health (midlife) exam. Midlife exam: o H&P (HTN, DM, smoker, level of education) o Physical Exam o Fasting labs (blood glucose, lipids) o Anthropomorphic measurements (Ht, Wt, BMI) o ETT between 1971 - 2001 Cooper database: n = 28,968 and matched w/ indivdiuals w/ Medicare claims = 25,995
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w/ the following exclusions @ time of midlife exam: o MI or stroke o Chronic illness leading to disability o On renal dialysis o >65yoa o Prior dx of dementia before 1999 Final cohort, N = 19,458
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Fitness level = Max time on treadmill METs Adjusted for age and sex, classified into quintiles o 1 = lowest level o 5= highest level No categorization or definition of fitness
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Diagnosis from Chronic Condition Data Warehouse o Data from Medicare beneficiaries for research purposes o Used to identify chronic diseases Primary Outcome of Interest: diagnosis of all-cause dementia defined by claim filed from o SNF, home health, hospital outpatient or inpatient, physician or supplier claim o 24 different ICD-9 codes for types of dementia: Alzheimers Senile Pre-senile Vascular
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Hazard Ratios = (chance of an event occuring)tx group (chance of an event occuring)control group Resolution depicted on Kaplan-Meir curve o Proportion of each group where end-point has not been reached o End-point = dx of dementia Cox-proportional hazards model: estimate of tx effect on survival after adjustment for other explanatory variables
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disease-free survival vs 5-level categorical covariate corresponding to age and sex-adjusted quintiles of fitness Adjusted for demographic and study variables o Sex, exam age, exam year Adjusted for clinical variables o HTN, fasting glucose level, current tobacco use, BMI, total cholesterol, SBP, DM) Repeated analysis w/ midlife fitness as a continuous variable (METs) rather than by category (quintile)
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Mean follow-up from CCLS data = 24 years Mean 7.2 years on Medicare data 1659 cases of all-cause dementia Prevalence of dementia increased w/ age Age (years)70758085 Dementia Prevalence0.8%2.9%8.3%14.8%
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Incidence of different variables amongst the 5 quintiles o Raw numbers sorted by clinical variables (HTN, DM, smoker, level of education, FLP, glucose level) o Sorted by quintiles (1 lowest, 5 highest) o Decreased incidence of all variables in higher quintiles Except etoh intake and education Quintile12345All METs8.19.410.411.313.310.6
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Higher fitness levels = lower risk for incident dementia Similar findings when fitness was modeled on a continuous scale (i.e. by METs) Figure 1: Kaplan-Meier curve o y-axis: probability of dementia-free survival (%) o x-axis: Age
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Derived hazard ratio for each quintile, reference = 1 o Lowest HR in quintile 5 o Statistical significance reached in quintile 3 (CI and P-value) Adjusted for sex, age and listed RFs o Statistical significance reached in quintile 3 Adjusted for individual RFs o Only HTN was statistically significant
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Association similar among pts w/ & w/o hx of previous stroke o HR w/o stroke 0.74 [CI 0.61-0.90] o HR w/ stroke 0.74 [CI 0.53-1.04]
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Generally healthy community-dwelling pts + association between o Midlife fitness levels (as measured by ETT) o Independent of other RFs Association present w/ and w/o stroke suggesting a non- vascular MOA No statistical significance between dementia and education o Homogenous group (see table 1)
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Previous studies confirm: ↑fitness = ↓risk DM, HTN o Established RFs for dementia Previous studies o Brain atrophy o ↑ # small caliber vessels, ↓ tortuosity = ? ↑ blood flow o ↓ prod. Neurotoxins o Enhanced neuroplasticity w/ exercise
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Strengths o Large cohort study size o Long duration of f/u Weaknesses o Not randomized: unmeasured cofounder, such as lifestyle factors could lead to ↑ exercise & ↓ dementia o Based on Medicare claims data 85% sens, 89% spec
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Homogenous population (Medicare, non-Hispanic, mid to upper-mid class) Initial exclusion criteria limits applicability Can’t give specific recommendations about activity level due to breakdown into quintiles Future studies should focus on dose-specific relationship to give recs
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Defina LF, Willis BL, Radford NB, Gao, A, Leonard, D, Haskell, WL et al. The Association Between Midlife Cardiorespiratory Fitness Levels and Later Life Dementia: A Cohort Study. Ann Intern Med. 2013;158:162-168
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