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Logo of nihpaAbout Author manuscriptsSubmit a manuscriptNIH Public Access; Author Manuscript; Accepted for publication in peer reviewed journal;
J Gerontol A Biol Sci Med Sci. Author manuscript; available in PMC Dec 1, 2009.
Published in final edited form as:
PMCID: PMC2713931

Fatigue and Function over Three Years among Older Adults

Susan E. Hardy, MD, PhD* and Stephanie A Studenski, MD, MPH*



Fatigue is a common complaint among older adults, but the association of fatigue with subsequent function is not well known.


This three-year longitudinal study of older primary care patients evaluates the association of fatigue, operationalized as feeling tired most of the time, with functional status at baseline and over time.


After adjustment for multiple potential confounders, participants who were tired at baseline had worse SF-36 Physical Performance Index scores, activity of daily living scores, and gait speeds. These functional deficits persisted throughout the follow-up period.


Fatigue in older adults is associated with functional deficits that persist for years. Further research is needed to understand the causes of fatigue and to develop specific treatments for this serious symptom.


Although fatigue is a normal response to exertion, it is abnormal when it is distressing and persistent, is not proportional to recent activity, and interferes with usual function.(1) Fatigue is highly prevalent; approximately 20–25% of adults report fatigue.(2) Among 199 ambulatory assisted living residents, 98% reported at least mild fatigue, with 40% reporting moderate and 7% severe fatigue.(3) Fatigue is the most common reason given by community-dwelling older adults for restricted activity,(4) and is commonly reported as a cause of disability by older women.(5) Fatigue is highly prevalent among both the chronically ill and the acutely hospitalized.(6,7) It has been associated with a wide array of chronic diseases,(811) and has been identified as a key component of the frailty syndrome.(12)

The association of fatigue with decreased daily function makes clinical sense, but relatively little research has examined the relationship between fatigue and function. Fatigue has been associated cross-sectionally with limitations in daily activities in a general population of older adults,(13) and in several chronic diseases.(10,14,15) Tiredness with daily activities predicts the subsequent development of disability in those activities,(16,17) but the predictive ability of general fatigue has not been evaluated.

Our objective was to determine the association of general fatigue with functional trajectories over three years in older primary care patients. We operationalized fatigue as tiredness because it is a commonly used synonym for fatigue in published fatigue scales,(16,1820) and we did not have data available directly assessing “fatigue.”



Subjects were recruited from two primary care clinics (a Medicare Health Maintenance Organization and a Veterans Affairs clinic) in 1996. The original study evaluated the use of physical performance measures as predictors of health and function in the primary care setting. Participants were evaluated in person 10 times over three years. The study was approved by the relevant Institutional Review Boards. Study methods, described in detail elsewhere,(21) are summarized below.


Community-dwelling patients aged 65 years or older were eligible if they were cognitively intact (Mini Mental State Examination (MMSE)(22) score ≥24) or mildly impaired (MMSE 16–23) with a caregiver, were able to walk 4 meters, and had a gait speed between 0.2 and 1.3 meters per second.

Assessment of Tiredness

As part of a baseline symptom assessment, participants were asked if, during the past month, they had been “feeling tired most of the time.” Participants who reported tiredness were asked how much it affected their function.

Functional Measures

Functional status was evaluated with the following self-report and performance-based measures at each assessment: the Medical Outcomes Study Physical Function Index,(18) the National Health Interview Survey Activities of Daily Living (NHIS) scale,(23) and usual gait speed over a four-meter course.


All covariates were measured at baseline and included demographic characteristics, cognition,(22) and self-reported physician-diagnosed chronic conditions.(24) Depressive symptoms were assessed with the Geriatric Depression Scale.(25) Because fatigue is a symptom of depression, we also created a scale using four items assessing mood (life is empty, downhearted and blue, good spirits, happy most of the time). Body Mass Index (BMI) was calculated from height and weight from the medical record. Inter-rater and test-retest reliability for our measures was excellent with intra-class correlations generally over 0.9.(21)

Statistical analysis

We used hierarchical linear models to determine the effect of baseline tiredness on function at baseline and on change in function over time, and multiple linear regression to determine the effect of baseline tiredness on function at three years. Models were adjusted for age, gender, race, education, cognition, BMI, comorbidity, and depressive symptoms. SAS® version 8.2 (SAS Institute, Cary, North Carolina) was used for all analyses.


Of the 572 individuals screened, 496 (87%) entered the study. Participants had a mean age of 74 years and 44.4% were female (Table 1, first column). Men were overrepresented because of recruitment from a Veterans Affairs clinic. At baseline, 212 participants (43%) reported feeling tired most of the time. Among participants who reported tiredness, 33 (16%) said their function was affected not at all, 62 (29%) a little, 61 (29%) moderately, and 56 (26%) quite a lot. Participants who reported tiredness were more likely to be female and white (Table 1). Tiredness was associated with higher rates of specific conditions, more concurrent conditions, and more depressive symptoms. There was no significant difference in loss to follow-up between those who were and were not tired at baseline (p=0.39).

Table 1
Participant Characteristics by Baseline Tiredness*

For all three outcomes, tiredness at baseline was associated with worse baseline function (Table2). Persons who were tired had persistently worse function throughout the follow-up period, although the rate of decline did not differ from those without tiredness.

Table 2
Difference (95% confidence interval) in baseline function, annual change in function, and function at three years between participants who did and did not report tiredness


This study demonstrated that fatigue, operationalized as feeling tired most of the time, is associated with functional deficits that persist for years. While tiredness was associated with many chronic conditions, including sleep problems, emotional problems, and chronic pain, the association of fatigue with functional status persisted despite adjustment for these conditions (except for gait speed at three years).

These findings, together with Avlund’s examination of task-specific tiredness,(16,17) indicate that fatigue or tiredness is not just an unpleasant symptom, but that it has implications for subsequent function. While the current study cannot address the mechanisms by which fatigue affects function, the association of fatigue with multiple markers of mental and physical health suggests that it may represent a general state of altered physiology. Fatigue could be the symptomatic presentation of subclinical disease(12), increased inflammation,(12,26,27) physiologic dysregulation,(28) or increased work in maintaining homeostasis.(29) More research is needed to understand the pathophysiologic origins of fatigue.

Several aspects of the current study deserve comment. Tiredness, although a synonym for fatigue, may not encompass all aspects of fatigue (e.g. weakness or cognitive fatigue). Longitudinal studies of older adults are at risk of disproportionate loss to follow-up of the most vulnerable participants. However, tiredness was not significantly associated with loss to follow-up and our repeated measures design allows us to use all available data on each participant.

Fatigue is common, is associated with functional limitations that persist for years, and should be taken seriously. Further research is needed to identify underlying mechanisms and to develop specific treatments for fatigue.


The original study was funded by Merck Research Laboratories. This study was supported by the Pittsburgh Claude D. Pepper Older Americans Independence Center (P30AG-024827), the Hartford Foundation, and the National Institute on Aging (K07AG023641).


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