Journal of Gerontology: MEDICAL SCIENCES
2008, Vol. 63A, No. 12, 1389–1392
Copyright 2008 by The Gerontological Society of America
Brief Report
Fatigue and Function Over 3 Years
Among Older Adults
Susan E. Hardy1 and Stephanie A. Studenski1,2
1
2
University of Pittsburgh School of Medicine, Pennsylvania.
GRECC, Pittsburgh Veterans Affairs Health Care System, Pennsylvania.
Background. Fatigue is a common complaint among older adults, but the association of fatigue with subsequent
function is not well known.
Methods. This 3-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.
Results. After adjustment for multiple potential confounders, participants who were tired at baseline had worse Short
Form-36 Physical Performance Index scores, activity of daily living scores, and gait speeds. These functional deficits
persisted throughout the follow-up period.
Conclusions. 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.
Key Words: Fatigue—Gait speed—Functional status—Longitudinal studies.
A
LTHOUGH 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 (8–11), 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 3 years in older
primary care patients. We operationalized fatigue as tiredness because it is a commonly used synonym for fatigue in
published fatigue scales (16,18–20), and we did not have
data available directly assessing ‘‘fatigue.’’
METHODS
Overview
Participants 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 3 years. The study
was approved by the relevant institutional review boards.
Study methods, described in detail elsewhere (21), are
summarized below.
Participants
Community-dwelling patients 65 years old or older were
eligible if they were cognitively intact [Mini-Mental State
Examination (MMSE) (22) score 24] or mildly impaired
(MMSE score 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 selfreport and performance-based measures at each assessment:
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HARDY AND STUDENSKI
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Table 1. Participant Characteristics by Baseline Tiredness
Tired Most of the Time in Past Month
Characteristics
Age, y
Female
White
No. of chronic conditions (of 8)*
Cardiovascular
Neurological
Musculoskeletal
Pulmonary
Diabetes
Cancer
Visual
General
Cognitive function (MMSE)y
Depressive symptoms (GDS)z
Depressive symptoms (mood items)z
Body mass index, kg/ms2
NHIS ADL§
SF-36 PFIk
Gait speed, m/s
Total
(N ¼ 496)
Yes
(N ¼ 212)
No
(N ¼ 284)
p Value
74.0 6 5.7
279 (44)
397 (80)
74.3 6 5.6
105 (49)
179 (84)
73.8 6 5.8
113 (40)
218 (77)
.34
.03
.05
2.2 6 1.3
2.6 6 1.2
1.9 6 1.2
,.0001
113
53
352
119
87
115
263
105
27.5
2.3
0.3
27.5
14
64
.88
(23)
(11)
(71)
(24)
(18)
(23)
(53)
(21)
6
6
6
6
6
6
6
2.3
2.8
0.8
5.1
2
30
.24
56
30
168
70
52
56
129
70
(26)
(14)
(79)
(33)
(24)
(26)
(61)
(32)
57
23
184
49
35
59
134
35
(20)
(8)
(65)
(17)
(12)
(21)
(47)
(12)
.10
.03
,.001
,.001
,.001
.15
.003
,.001
27.5
3.6
0.5
28.0
13
50
.82
6
6
6
6
6
6
6
27.4
1.4
0.2
27.2
15
74
.92
6
6
6
6
6
6
6
.72
,.0001
,.0001
.11
,.0001
,.0001
,.0001
2.3
3.1
0.9
5.5
2.5
28
.24
2.4
2.0
0.6
4.8
1.6
26
.23
Notes: Values represent N (%) for dichotomous variables and mean 6 standard deviation for continuous variables.
*Chronic condition categories include: cardiovascular (angina, heart failure, or heart attack), neurological (stroke or Parkinson’s disease), pulmonary (lung disease,
emphysema, asthma, or bronchitis), musculoskeletal (arthritis, osteoporosis, broken bone, amputation, or joint replacement), diabetes, cancer, visual (cataracts or
glaucoma), and general (depression, anxiety, emotional problem, sleep problem, or chronic pain).
y
MMSE (Mini-Mental State Examination): range 0–30, with higher scores representing better cognition.
z
GDS (Geriatric Depression Scale): range 0–15, with higher scores representing more depressive symptoms; we also present a four-item scale using only mood
items (life is empty, downhearted and blue, good spirits, happy most of the time), with a range of 0–4.
§
NHIS ADL (National Health Interview Survey Activities of Daily Living): range 0–16, with higher scores representing better function.
k
SF-36 PFI (Medical Outcomes Survey Physical Function Index): range 0–100, with higher scores representing better function.
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 4meter course.
Covariates
All covariates were measured at baseline and included
demographic characteristics, cognition (22), and selfreported 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. Interrater and test–retest reliability for our measures
was excellent with intra-class correlations generally
.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
3 years. Models were adjusted for age, gender, race,
education, cognition, BMI, comorbidity, and depressive
symptoms. SAS (version 8.2; SAS Institute, Cary, NC) was
used for all analyses.
RESULTS
Of the 572 individuals screened, 496 (87%) entered the
study. Participants had a mean age of 74 years, and 44.4%
were women (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 non-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 participants who were and were not tired at baseline (p ¼ .39).
For all three outcomes, tiredness at baseline was
associated with worse baseline function (Table 2). Persons
who were tired had persistently worse function throughout
the follow-up period, although the rate of decline did not
differ from that of participants without tiredness.
DISCUSSION
This study demonstrated that fatigue, operationalized as
feeling tired most of the time, is associated with functional
FATIGUE AND SUBSEQUENT FUNCTION
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Table 2. Difference (95% Confidence Interval) in Baseline Function, Annual Change in Function, and Function at
3 Years Between Participants Who Did and Did Not Report Tiredness
Functional Parameter
NHIS ADL
SF-36 PFI
Gait Speed, m/s
1.6 (1.9, 1.3)
1.2 (1.5, 0.8)
23 (28, 19)
16 (21, 12)
.10 (.14, .06)
.05 (.09, .01)
1.9 (2.4, .40)
1.0 (2.4, .38)
.004 (.015, .007)
.004 (.015, .007)
25 (32, 19)
17 (23, 11)
0.11 (0.17, 0.05)
0.05 (0.10, 0.01)
Baseline Function
Unadjusted
Adjusted*
Annual Change in Function
Unadjusted
Adjusted*
.005 (.12, .11)
.01 (.12, .10)
Function at 3 y
Unadjusted
Adjusted*
1.6 (2.1, 1.1)
1.1 (1.7, 0.6)
Notes: Values for baseline function and annual change in function represent coefficients from hierarchical linear models, and values for function at 3 years represent
coefficients from multiple linear regression models.
*Adjusted for age, gender, race, education, cognition, body mass index, comorbidity, and depressive symptoms.
NHIS ADL ¼ National Health Interview Survey Activities of Daily Living; SF-36 PFI ¼ Medical Outcomes Survey Physical Function Index.
deficits that persist for years. Although 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 3 years).
These findings, together with the examination of taskspecific tiredness by Avlund et al. (16,17), indicate that
fatigue or tiredness is not just an unpleasant symptom, but
that it has implications for subsequent function. Although
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.
ACKNOWLEDGMENTS
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).
CORRESPONDENCE
Address correspondence to Susan Hardy, MD, PhD, Division of Geriatric
Medicine, University of Pittsburgh, 3471 Fifth Ave., Suite 500, Pittsburgh,
PA 15213. E-mail: [email protected]
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Received February 27, 2008
Accepted March 5, 2008
Decision Editor: Luigi Ferrucci, MD, PhD