Date of Award

1-1-2010

Document Type

Campus Access Dissertation

Department

Epidemiology and Biostatistics

Sub-Department

Epidemiology

First Advisor

Steven N. Blair

Abstract

Purpose: The purpose of this dissertation was three-fold: 1) to examine prospectively the independent and joint associations of muscular strength and cardiorespiratory fitness (CRF) with depressive symptoms in men, 2) to examine prospectively the joint associations and relative independent effects of leisure-time physical activity (LTPA) and CRF with depressive symptoms in women and men, and 3) to determine whether CRF is associated with lower risk for dementia mortality in women and men.

Methods: Participants were women and men ages 20-100 years who completed a health examination between 1970-2001 and a follow-up health survey in 1990, 1995, and/or 1999. Muscular strength was quantified by 1-repetition maximal leg and bench presses. LTPA was assessed by self-reported questionnaire and CRF by maximal exercise tests. Depressive symptoms were assessed with the 10-item Center for Epidemiologic Studies Depression Scale (CES-D). The National Death Index identified deaths through 2003. Logistic regression models were used to estimate the odds ratios (ORs) and 95% confidence intervals (CIs) of depressive symptoms across categories of muscular strength, physical activity, and CRF. Cox proportional hazards models evaluated the relationship between CRF and dementia mortality.

Results: A significant inverse association was observed between muscular strength and depressive symptoms (ptrend= 0.042) in unadjusted models; however, the adjusted association was not significant. CRF was inversely associated with odds of depressive symptoms in multivariable analyses among women (ptrend= 0.0006) and men (ptrend<0.0001). The protective effect of CRF remained even after controlling for physical activity. Compared with inactive women and men, the ORs (95% CIs) of reporting depressive symptoms were 0.87 for both women and men who were insufficiently active (CIs 0.67-1.14 and 0.73-1.03, respectively), and 0.72 (0.57-0.93) and 0.75 (0.65-0.87), respectively, for women and men who met the recommended levels of physical activity after adjusting for potential confounders. Further adjustment for CRF eliminated the association in women and attenuated the relationship in men. Analyses of the association between CRF and dementia mortality revealed that for each 1-MET increase in CRF, there was a 14% lower adjusted risk of dementia mortality (95%CI 6% 22%).

Conclusions: Muscular strength was not associated with depressive symptoms. Higher CRF was more strongly associated with lower odds of depressive symptoms than LTPA. These findings provide support for promoting physical activities that are sufficient to influence physical fitness to lower the risk of depressive symptoms. In addition, greater CRF was associated with a notably lower risk of dementia mortality.

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