Introduction: Depression disorders are common and debilitating conditions which can affect older individuals, especially those with cardiovascular disease (CVD). The association of midlife cardiorespiratory fitness (fitness), an objective measure of habitual physical activity, with later-life depression is not fully understood. Furthermore, although depression is associated with incident CVD, little is known about the long term association of midlife fitness with CVD death following the onset of depression decades later.
Hypothesis: Fitness measured in midlife will be inversely associated with depression in later life and risk of CVD death with or without intercurrent depression.
Methods: Linking participant data from the Cooper Center Longitudinal Study with Medicare claims files, we studied 16,728 participants (19% women, mean age 51) without prior history of depression or CVD, who received Medicare coverage from 1999-2009. Midlife fitness was estimated by Balke protocol treadmill time in metabolic equivalents and grouped into age and sex-specific categories: low, moderate, and high fitness. Other midlife risk factors were measured using standard protocols. Depression diagnosis was defined from Medicare claims files according to established algorithms and CVD mortality was determined from National Death Index records. Multivariate survival modeling was used to assess the associations between midlife fitness and time to any of three later life events: incident depression, CVD death without incident depression, and CVD death following incident depression. The model was adjusted for midlife age, gender, year of examination, smoking, systolic blood pressure, cholesterol, BMI, and fasting glucose.
Results: After 109,143 person years of Medicare follow-up, we observed 2379 cases of incident depression, 570 CVD deaths without incident depression and 218 CVD deaths following incident depression. High fitness in midlife was associated with a 24% lower risk of depression (hazards ratio [HR] 0.76, 95% CI 0.67-0.86 compared to low fit). High fitness was also associated with a 63% lower risk of CVD death without incident depression (HR 0.37, 95% CI 0.30-0.47 compared to low fit) and 50% lower risk of CVD death (HR 0.50, 95% CI 0.34-0.72 compared to low fit) following incident depression.
Conclusion: Midlife fitness, a modifiable CVD risk factor, is associated with lower risk of depression in later life, lower risk of CVD death without incident depression, and lower risk of CVD death following incident depression decades later. These findings suggest the importance of fitness in primary prevention of depression and mortality in older age.