Perceived Fatigability, Fatigue, and Mortality in Mid-to-Late Life in the Baltimore Longitudinal Study of Aging

Fatigue is an established prognostic indicator of mortality risk. It remains unknown whether fatigability anchored to a physical task is a more sensitive prognostic indicator and whether sensitivity differs by prevalent chronic conditions.

A total of 1076 physically well-functioning participants 50 yr or older in the Baltimore Longitudinal Study of Aging self-reported fatigue (unusual tiredness or low energy) and had perceived fatigability assessed after a standardized treadmill walk. All-cause mortality was ascertained by proxy contact and National Death Index linkage. Cox proportional hazards models estimated associations of perceived fatigability and fatigue with all-cause mortality, adjusting for demographic and clinical covariates. Interactions by chronic conditions were also examined.

Each 1 SD higher in perceived fatigability, unusual tiredness, or low energy was associated with a higher relative hazard of all-cause mortality after covariate adjustment (fatigability: hazard ratio (HR), 1.18 (95% confidence interval (CI), 1.03-1.36); unusual tiredness: HR, 1.25 (95% CI, 1.08-1.44); low energy: HR, 1.27 (95% CI, 1.10-1.46)). Models had similar discrimination ( P > 0.14 for all). Perceived fatigability was associated with mortality risk among participants free of arthritis or osteoarthritis who otherwise appeared healthy (no arthritis: HR, 1.45 (95% CI, 1.15-1.84); arthritis: HR, 1.09 (95% CI, 0.92-1.30); P -interaction = 0.031). Unusual tiredness was associated with mortality among those with a history of diabetes (no diabetes: HR, 1.16 (95% CI, 0.97-1.38); diabetes: HR, 1.65 (95% CI, 1.22-2.23); P -interaction = 0.045) or pulmonary disease (no pulmonary disease: HR, 1.22 (95% CI, 1.05-1.43); pulmonary disease: HR, 2.15 (95% CI, 1.15-4.03); P -interaction = 0.034).

Higher perceived fatigability and fatigue symptoms were similarly associated with higher all-cause mortality, but utility differed by chronic condition. Perceived fatigability might be useful for health screening and long-term mortality risk assessment for well-functioning adults. Alternatively, self-reported fatigue seems more disease-specific with regard to mortality risk.