Independent and joint associations of cardiorespiratory fitness and BMI with dementia risk: the Cooper Center Longitudinal Study.

OBJECTIVE: This study aimed to examine the association of midlife fitness and body mass index (BMI) with incident dementia later in life. DESIGN AND PARTICIPANTS: A cohort study of 6428 individuals (mean age 50.9±7.6 years) from the Cooper Center Longitudinal Study. MEASURES: Cardiorespiratory fitness and BMI were assessed twice (1970-1999) during visits to the Cooper Clinic, a preventive medicine clinic in Dallas, Texas. These measures were examined as continuous and categorical variables. As continuous variables, fitness and BMI were examined at baseline (averaged of two examinations) and as absolute change between exams (mean time 2.1±1.8 years). Variables were categorised: unfit versus fit and normal versus overweight/obese. Medicare claims data were used to obtain all-cause dementia incidence (1999-2009). Mean follow-up between midlife examinations and Medicare surveillance was 15.7 ((SD=6.2) years. Multivariable models were used to assess the associations between fitness, BMI and dementia. RESULTS: During 40 773 person years of Medicare surveillance, 632 cases of dementia were identified. After controlling for BMI and covariates, each 1-metabolic equivalent increment in fitness was associated with 5% lower (HR 0.95; 95% CI 0.90 to 0.99) dementia risk. In comparison, after controlling for fitness and covariates, each 1 kg/m2 increment in BMI was associated with a 3.0% (HR 1.03; 95% CI 1.00 to 1.07) higher risk for dementia, yet without significance (p=0.051). Similar findings were observed when the exposures were categorised. Changes in fitness and BMI between examinations were not related to dementia. Jointly, participants who were unfit and overweight/obese had the highest (HR 2.28 95% CI 1.57 to 3.32) dementia risk compared with their fit and normal weight counterparts. CONCLUSION: Lower midlife fitness is a risk marker for dementia irrespective of weight status. Being unfit coupled with overweight/obese status might increase one's risk for dementia even further.

Physical activity trajectories, autonomic balance and cognitive function: The Coronary Artery Risk Development in Young Adults (CARDIA) study.

Physical activity (PA) plays an important role in cognitive health. However, the underlying mechanisms are not fully understood. Cardiac autonomic balance is influenced by PA and implicated in dementia pathogenesis. We examined whether autonomic balance mediates the association between PA and cognitive function. The sample included 1939 participants from the Coronary Artery Risk Development in Young Adults study who completed cognitive testing after 30-year follow-up (baseline: mean age 25.2 ± 3.5y; 58% women; 43% Black). Moderate to vigorous intensity PA (MVPA) was obtained in 7 consecutive examinations over 20 years (Year 0-Year 20). Cardiac autonomic balance was assessed at Year 20 via resting heart rate (RHR), standard deviation normal to normal (SDNN) and root mean square of successive differences (RMSSD). We used group-based trajectory modeling to identify homogenous MVPA trajectory groups, and formal mediation analysis to test whether autonomic function indices mediate the association between MVPA trajectories and cognition. We identified three distinct PA trajectory patterns: (1) Below MVPA guidelines (n = 1122; 57.9%); (2) Meeting MVPA guidelines (n = 652; 33.6%); and (3) Exceeding MVPA guidelines (n = 165; 8.5%). Meeting and exceeding MVPA guidelines were related to better autonomic balance overall, and to improved semantic fluency performance. Statistically, the association between higher MVPA level and verbal ability was mediated by SDNN and RMSSD, but not by RHR. In our sample of young and middle-aged adults, higher MVPA levels over time were associated with better cardiac autonomic function, which explained some of the associations between PA trajectories and better cognition.

Sitting Time, Physical Activity, and Cognitive Impairment in Midlife and Older Adults.

This study cross-sectionally examines the relations of sitting and physical activity (PA) with cognitive impairment in community-dwelling adults aged 55-87 years (n = 3,780). Multivariable logistic regression assessed independent and joint relations of sitting and PA with Montreal Cognitive Assessment scores adjusting for covariates. Sitting ≥75% of the time and not meeting PA guidelines were related to 60% (95% confidence interval [CI] [1.19, 2.17]) and 27% (95% CI [1.06, 1.53]) higher odds for cognitive impairment, respectively. Stratification by age showed that sitting ≥75% of the time was associated with higher cognitive impairment odds in midlife (odds ratio [OR] = 1.86; 95% CI [1.31, 2.65]), but not older adults (OR = 1.06; 95% CI [0.57, 1.95]). Joint association analysis revealed that, overall, the highest odds for cognitive impairment were in those sitting ≥75% of the time while meeting or not meeting PA guidelines (OR = 1.69, 95% CI [1.13, 2.53]; and OR = 1.66, 95% CI [1.19, 2.32], respectively). In conclusion, prolonged sitting and insufficient PA are independent risk markers for cognitive impairment.