American Journal of Epidemiology
Copyright C 1996 by The Johns Hopkins University School of Hygiene and Public Health
All rights reserved
Vol. 143, No. 1
Printed In USA.
Physical Activity Levels and Changes in Relation to Longevity
A Prospective Study of Swedish Women
Lauren LJssner,1 Calle Bengtsson,1 Cecilia Bjorkelund,1 and Hans Wedel2
In 1968-1969, a population-based sample of Swedish women aged 38-60 years was recruited for a health
survey, and 20-year survival was later ascertained from national registries. Occupational and leisure-time
physical activity data from the baseline and 6-year follow-up examinations were evaJuated in relation to
all-cause mortality among 1,405 women who were initially free of major diseases. In comparison with being
inactive, the mortality relative risk associated with being somewhat active was 0.28 (95% confidence interval
0.17-0.46) for occupational activity and 0.56 (95% confidence interval 0.39-0.82) for leisure-time activity.
Being in the most active occupational or leisure activity category further decreased mortality risk to a minor
extent. A within-subject decrease in leisure activity over 6 years was also a significant risk factor for all-cause
mortality (relative risk = 2.07, relative to no change), although there was no evidence of a benefit from
increasing physical activity levels. Since exclusion of early endpoints did not affect the associations in any
significant way, underlying illness Is unlikely to have played a major role in these analyses. It is concluded that
decreases in physical activity as well as low initial levels are strong risk factors for mortality in women, and that
their predictive value persists for many years. Am J Epidemiol 1996;143:54-62.
exercise; longevity; mortality; physical fitness; women
Inverse associations between physical activity and
total mortality and coronary heart disease have been
reported in a large number of prospective, populationbased studies. One noticeable characteristic of the
earlier literature (reviewed by Powell et al. (1)) is that
this relation has been far less frequently studied in
women than in men. Another feature of previous prospective studies is the fact that physical activity has
been modeled as a static risk factor at baseline; withinsubject changes in physical activity have, with rare
exceptions (2, 3), not been studied. However, the main
limitation of these and all observational studies is that
it is difficult to distinguish between cause and effect;
in the case of physical activity, a compelling argument
may be made that certain individuals are inactive
because of poor health and not vice versa. If this were
the case, one might expect to observe stronger associations between physical activity and deaths observed
during short-term follow-up compared with long-term
follow-up.
The purpose of this paper is to address the above
issues by studying changes in as well as initial levels
of physical activity as risk factors for all-cause mortality in a prospective study of Swedish women. Previous analyses based on the first 12 years of mortality
in this cohort have suggested that physical activity
measured at the baseline examination had strong protective effects (4). In the present analysis of 20-year
mortality, we followed up on this observation with
special attention to the chronology of events. Specifically, sequential exclusion of earlier endpoints was
conducted, and the magnitude of the association was
compared over varying follow-up intervals. Because
of probable confounding between physical activity and
other behavioral and biologic health indicators, covarying factors were considered in the predictive models. Furthermore, subgroup analyses were conducted
to examine the possibility that physical activity might
convey a greater benefit in certain groups. Finally,
6-year changes in activity were examined as predictors
of subsequent mortality.
Received for publication October 20, 1994, and in final form
October 10, 1995.
Abbreviations: Cl, confidence interval; RR, relative risk.
1
Department of Primary Health Care, Institute of Community
Medicine, Gflteborg University, G6teborg, Sweden.
2
Nordic School of Public Health, Gflteborg, Sweden.
Reprint requests to Dr. Lauren LJssner, Department of Primary
Health Care, Vasa Hospital, 411 33 Gateborg, Sweden.
MATERIALS AND METHODS
Population studied
In 1968-1969, a sample of women aged 38, 46, 50,
54, or 60 years was randomly selected from the local
population registry of Gothenburg, Sweden. A total of
54
Physical Activity and Longevity in Women
1,622 female residents born on selected days were
initially contacted and invited to participate in a health
survey; 1,462 of them agreed to undergo the baseline
examinations in 1968-1969, and all survivors were
invited to a second examination in 1974-1975. Relative to the initial recruitment list, the participation rate
at the first examination was 90.1 percent; 89.1 percent
of these women were alive and returned for a
follow-up examination after 6 years. Twenty-year
mortality follow-up was conducted with the assistance
of the Swedish National Death Registry and the State
Person and Address Registry. Ninety-nine percent of
the original sample was accounted for in this search.
Details on recruitment, participation, and follow-up
have been presented previously (5-7).
Women with a history of stroke, myocardial infarction, diabetes mellitus, or cancer at the baseline
examination in 1968-1969 were excluded from the
analyses, along with subjects who had been lost to
follow-up. This reduced the sample size from 1,462 to
1,405. For the analysis of changes in physical activity,
an additional 37 women were excluded because of
incident cancer, myocardial infarction, stroke, or diabetes between their baseline and 6-year follow-up
examinations. These latter exclusions, plus dropouts
and deaths during the first 6-year interval, resulted in
a maximum sample size of 1,267 for the analysis of
physical activity changes.
Physical activity indicators
A physical activity questionnaire originally developed and used in male subjects (8, 9) was adapted in
the present study to include examples more characteristic of women's usual activity patterns. Although the
questionnaire has not been formally validated in
women, the men's version has been shown to discriminate sedentary former athletes from their still-active
counterparts with respect to maximal oxygen uptake
(8).
The modified questionnaire used in the present
study (see figure 1) was administered verbally by a
physician during a general health examination. As in
the original version, two 4-point scales were used,
describing physical activity at work and during leisure
time, respectively, in which a 1 indicates least active
and a 4 signifies most active. Physical activity levels at
work and (separately) at leisure were thereby estimated for the following periods of subjects' lives: ages
20-38 years (all women), age 39 to the present (women aged 46-60 years), and during the past 12 months
(all women).
Figure 2 shows the distributions of the physical
activity scores used in this analysis. The occupational
index gave higher values than the leisure-time index.
Am J Epidemiol
Vol. 143, No. 1, 1996
55
This difference may reflect the fact that the occupation
of housewife, reported by one third of the women, was
graded according to the amount of domestic help a
woman had and the number of children being cared for
in the home, and thus was often coded as a physically
demanding job.
In addition to the physical activity categories shown
in figure 2, a crude index of total adulthood activity
("adulthood activity index") was calculated for each
woman by averaging all of her responses, which resulted in a continuous version of the original 4-point
scale. This index is a convenient way to summarize
previous adulthood activity in a mixed group of older
and younger women. Finally, 6-year changes in leisure
and work activity were assessed separately, based on
the reported level during the 12 months prior to the
second examination minus the level 12 months before
the original examination. These group mean activity
values are shown in table 1.
Covariates
The multivariate regression models included a series
of potentially confounding variables, measured by
methods that have been previously described (5, 6, 10,
11). Group-level statistics describing these variables at
baseline are given in table 1. Serum triglyceride and
cholesterol levels were measured in the fasting state;
systolic and diastolic blood pressures were taken in the
sitting position after 5 minutes' rest; body mass index
was calculated as weight (kg)/height (m) ; and standing waist and hip circumferences were converted into
a waist:hip ratio. Smoking habits were categorized
according to whether or not the subject was a current
smoker. Habitual alcohol consumption was summarized as none versus once per month or more. Educational level was defined as having continued in school
after primary school or not. Dietary intake was measured by means of a 24-hour recall, on the basis of
which energy-percentage of fat was calculated. Pulmonary function was measured with a peak expiratory
flow meter. Some of these variables were measured
again at the 6-year follow-up visit and were included
in a separate model focusing on time-dependent covariates.
Endpoints
Person-years of follow-up were calculated for 20year all-cause mortality (7). When baseline physical
activity was studied as a risk factor, the first analysis
retained all deaths occurring at any time after the
initial examination. In subsequent analyses, all deaths
occurring during the first 6 and 12 years after the
initial examination were sequentially excluded in sep-
56
LJssner et al.
Occupational Activity
Group 1:
Mostly sedentary
work
Group II:
Sittino. or standing.
Group III:
Walkinq and some
lifting
Group IV:
Heaw physical labor
EXAMPLESHousewife without
children at home, with
household help; desk
work without much
work in the home
EXAMPLESShopkeeper, teacher,
light factory work;
sedentary at work but
some additional work
at home; housewife
who cleans house by
herself with one or no
children
EXAMPLESHealth care
worker, mail carrier,
heavy factory work,
housewife with 2-3
children without
houshold help; Group I
or II plus two or more
children at home
EXAMPLESHeavy manual labor at
work plus cleaning at
home; Group III
occupations
plus two or more
children at home
(1)
Period
At ages
20-38 years
(2)
At ages
39-60 years
(3)
During the past
12 months
Group I
Group II
Group III
Group IV
Leisure Activity
Activity Group I:
Almost completely
inactive
Activity Group II:
Some physical activity
at least 4 hours per
week
Activity Group III:
Regular physical
activity
Activity Group IV:
Regular heavy
physical training and
competition
EXAMPLESReading, watching TV
or movies
EXAMPLESBiking or walking
to work or at leisure;
family walks
EXAMPLESGardening, golf,
jogging, aerobic
exercise, tennis,
dancing
EXAMPLESSwimming or
jogging several times
per week; competitive
sports
(4)
Period
At ages
20-38 years
(5)
At ages
39-60 years
(6)
During the past
12 months
Group I
Group II
Group III
Group IV
FIGURE 1. Translation of the physical activity questionnaire used at the baseline examination (questions 1-6) and at the 6-year follow-up
examination (questions 3 and 6) in the Gothenburg Prospective Study of Women, 1968-1969 and 1974-1975. An adulthood physical activity
index was constructed as a composite indicator of occupational activity plus leisure-time activity and was calculated as an average of six
responses (questions 1-6) for subjects aged 46-60 years and the mean of four responses (questions 1,3,4, and 6) for subjects aged 38 years.
Am J Epidemiol
Vol. 143, No. 1, 1996
Physical Activity and Longevity in Women
1 2
(low)
3
4
1 2
(high) (low)
Occupational
3
57
4
(high)
Leisure
FIGURE 2. Distribution (percentage of sample) of baseline responses to six questions on occupational and leisure-time physical activity
levels in the Gothenburg Prospective Study of Women, 1968-1969. Separate answers were given for the following periods: ages 20-38 years,
ages 39-60 years, and the 12 months preceding the first examination.
arate regressions. For the analysis of changes in physical activity as a risk factor for total mortality, all
deaths occurring at any time after the second measurement were included in the initial analysis, and those
occurring 0-2 and then 0 - 6 years after the second
examination were subsequently excluded. Thus, in the
analyses of physical activity changes and initial levels,
there was a maximum time interval of 12 years between the initial examination and the first death.
Statistical methods
Associations between physical activity and the
covariates were based on nonparametric methods
(Spearman correlations and Wilcoxon and MannWhitney tests). Proportional hazards regression analysis was used for the analysis of mortality. Estimated
relative risks are presented with 95 percent confidence
intervals. For the analysis of physical activity at baseline, two approaches were used. The first considered
the physical activity indicators categorically, and ageadjusted relative risks are presented for the increasingly active categories compared with the most sedentary group. Because of small cell sizes, it was
necessary to collapse physical activity levels 3 and 4
into a single category. The second analysis considered
the predictive value of the adulthood activity index
before and after controlling for additional risk factors
(described in "Covariates" above). For the analysis of
physical activity changes, the adulthood activity index
was included as an additional independent variable in
all models, to account for covariation between total
adulthood activity at baseline and subsequent changes
Aw J Epidemiol
Vol. 143, No. 1, 1996
in physical activity. Time-dependent covariates were
also added to the analysis of physical activity changes,
where all changes reflect measurements made at 6
years minus those made at baseline.
RESULTS
Physical activity in relation to other baseline
characteristics
Correlations between physical activity indicators
and selected health indicators at the baseline examination are shown in table 2. The strongest correlate of
adulthood activity index was peak expiratory flow
(positive). When the previous 12 months of occupational activity were considered, age and blood pressures showed the strongest correlations (negative).
Leisure-time activity during the past 12 months was
positively associated with alcohol consumption and
was negatively correlated with serum triglyceride,
with both obesity indices, and with smoking. In comparing women who completed more than primary
school with those who did not, the more educated
group reported significantly more leisure-time activity
and less occupational activity. There was no correlation between leisure-time and occupational activity
(r = 0.02, p = 0.4; data not shown).
Analysis of physical activity categories and
20-year mortality
Table 3 gives the risk estimates for all-cause mortality in relation to physical activity during different
periods in adulthood. Activity category 1 is the refer-
58
LJssner et al.
TABLE 1. Descriptive data on participants In the
Gothenburg Prospective Study of Women at baseline
(1968/1969) and 6-year changes in physical activity levels
in
TABLE 2. Nonparametrlc correlations between physical
activity Indicators and covarlates at the baseline examination,
Gothenburg Prospective Study of Women, 1968-1969
lSf/4/19'3
Variable
Adulthood activity index
Occupational activity in the
past 12 months
Leisure activity in the past 12
months
Dietary tat (energy-%)
Body mass indext
Waisthip ratio
Peak expiratory flow
(liters/minute)
Serum triglycerides
(mmol/liter)
Serum cholesterol (mmol/liter)
Systolic blood pressure
(mmHg)
Diastolic blood pressure
(mmHg)
Current smoking (yes/no)
More than a primary education
(yes/no)
Alcohol drinking (yes/no)
fi-uAflr rhanos IIIn1 \s\*\*\4}JClli\Jl
occuDfltional
IQI
activity}:
6-year change in leisure
activity*
No.
Mean
Adulthood
activity
tnosx
SD«
1,405
2.22
0.33
1,404
2.27
0.54
1,405
1,311
1,405
1,353
1.95
39.0
24.1
0.74
0.55
7.75
3.81
0.05
Serum triglycerides
1,393
38.0
6.12
Serum cholesterol
1,401
1,400
1.2
6.8
0.6
1.2
Body mass index
1,405
133.0
21.7
83.1
10.8
Age group
Smoker (yes/no)
Peak expiratory flow
Waisthip ratio
Systolic blood pressure
1,405
576/828
(41.0%)
Diastolic blood pressure
Dietary fat (energy-%)
426/979
(30.3%)
1,060/342
(75.6%)
Alcohol drinking (yes/no)
Education (more than
primary vs. not)
U^VsQI I/I KU IMO
1,267
-0.13
0.65
1,266
-0.02
0.70
• SD, standard deviation,
t Weight (kg)/height (m)2.
t During the first 6 years of follow-up (1968/1969-1974/1975).
ence level ("low"); level 2 is "medium"; and levels 3
and 4 are grouped together as "high." The results
presented in table 3 show that medium levels of leisure
and occupational activity during the 12 months preceding the baseline examination (1968-1969) were
associated with lower all-cause mortality in comparison with the least active (reference) category (for
occupational activity, relative risk (RR) = 0.28, 95
percent confidence interval (CI) 0.17-0.46; for
leisure-time activity, RR = 0.56, 95 percent CI 0.390.82). Some further risk reductions associated with
being in the high activity categories were observed.
Physical activity patterns earlier in life displayed similar but statistically weak trends. Sequential exclusion
of endpoints at 6 and 12 years did not affect the
associations in a significant or consistent way.
Adulthood activity index and 20-year mortality
after covariate adjustment
We next considered the predictive value of the composite adulthood activity index, with attention to sta-
-0.03
(0.3)*
-0.05
(0.04)
0.10
(0.0002)
-0.02
(0.5)
0.01
(0.6)
0.02
(0.4)
0.02
(0.5)
-0.05
(0.07)
-0.05
(0.08)
-0.2
(0.5)
0.05
(0.05)
-0.01
(0.7)
Activity level during trie
past 12 months
WorkLeisurerelated
time
-0.15
(0.0001)
0.01
(0.6)
0.08
(0.003)
0.01
(0.6)
-0.03
(0.3)
0.05
(0.07)
0.04
(0.2)
-0.09
(0.0007)
-0.09
(0.0007)
0.04
(0.2)
-0.01
(0.8)
-0.08
(0.003)
-0.01
(0.8)
-0.08
(0.003)
0.07
(0.007)
-0.10
(0.0001)
-O.03
(0.4)
-0.08
(0.002)
-0.11
(0.0001)
-0.02
(0.7)
-0.01
(0.7)
-0.05
(0.05)
0.12
(0.0001)
0.08
(0.003)
* Numbers In parentheses,p value.
bility after covariate adjustment and exclusion of early
endpoints. The age-adjusted association between
adulthood activity and mortality was largely unaffected by individual inclusion of the following covariates: smoking, alcohol consumption, educational level,
body mass index, waist: hip ratio, dietary fat intake,
systolic and diastolic blood pressure, serum cholesterol and triglyceride, and peak expiratory flow. After
these further adjustments, no relative risk deviated
from the age-adjusted point estimate by more than 0.1
(data not shown). Simultaneous inclusion of all covariates that were independently predictive of mortality
(age, smoking, waist: hip ratio, peak expiratory flow,
systolic and diastolic blood pressure, and serum triglyceride—all associated with increased mortality)
again did not modify the conclusions, as shown in
table 4. After removal of early endpoints, the risk
estimate was stable and even tended to become stronger with exclusion of the first 12 years of deaths, in
spite of the diminished numbers. Similar inverse associations were seen after exclusion of all myocardial
infarction deaths from the results. Myocardial infarction deaths alone showed statistically weak trends that
were consistent in direction with the non-myocardial
infarction associations.
Am J Epidemiol
Vol. 143, No. 1, 1996
Physical Activity and Longevity in Women
59
TABLE 3. Relative risk estimates for all-cause mortality associated with medium and high physical
activity levels* at different ages (as reported In 1968/1969), before and after sequential exclusion of
deaths occurring after 6 and 12 years of follow-up: The Gothenburg Prospective Study of Women
No.
rrf
OT
deaths
Medium vs. low
Total
no.
High vs. low
RRt
95%Clt
RR
95% Cl
Years 1-20t
Work-related
Past 12 months
Age 39-60 years
Age 20-38 years
147
130
147
1,405
1,036
1,405
0.28
0.66
0.59
0.17-0.46
0.21-2.08
0.18-1.87
0.24
0.47
0.50
0.14-0.43
0.14-1.52
0.16-1.58
Leisure-time
Past 12 months
Age 39-60 years
Age 20-38 years
147
130
147
1,404
1,036
1,405
0.56
0.56
0.66
0.39-0.82
0.35-0.90
0.34-1.26
0.45
0.44
0.46
0.24-0.86
0.22-0.91
0.21-1.01
Years 7-20
Work-related
Past 12 months
Age 39-60 years
Age 20-38 years
134
119
134
1,392
1,025
1,392
0.26
0.56
0.51
0.15-0.43
0.18-1.79
0.16-1.63
0.24
0.43
0.44
0.13-0.43
0.13-1.39
0.14-1.42
Leisure-time
Past 12 months
Age 39-60 years
Age 20-38 years
134
119
134
1,391
1,025
1,392
0.53
0.49
0.57
0.36-0.77
0.30-0.80
0.30-1.10
0.43
0.40
0.42
0.22-0.85
0.19-0.84
0.19-0.94
0.16-0.70
0.08-0.48
0.10-1.67
0.16-0.95
0.08-0.79
0.14-1.33
Years 13-20
Work-related
Past 12 months
Age 39-60 years
Age 20-38 years
85
73
85
1,341
979
1,341
0.34
NAt,§
0.59
0.14-2.47
0.20
NA
0.40
Leisure-time
Past 12 months
Age 39-60 years
Age 20-38 years
85
73
85
1,340
979
1,341
0.59
0.57
0.80
0.36-0.96
0.30-1.09
0.32-1.98
0.39
0.25
0.43
* Activity category 1 was defined as Tow," category 2 as "medium," and categories 3 and 4 as "high" (see figure
1).
t RR, relative risk; Cl, confidence interval; NA, not applicable.
$ Years of follow-up.
§ There were no deaths in the low occupational activity group during follow-up years 13-20. When death rates
in the high activity group were compared with those In the low group plus the medium group, the estimated relative
risk was 0.61 (95% Cl 0.37-1.02).
Subgroup analyses by body mass index and
smoking
No statistically significant interactions were seen
between adulthood activity index and either baseline
body mass index or smoking in the prediction of
mortality (data not shown). However, in a stratified
analysis comparing the associations among women
with body mass indices above and below 27, the
relative risk was 0.49 (95 percent Cl 0.27-0.92) in the
leaner group and 0.18 (95 percent Cl 0.07-0.45) in the
heavier group. Stratification by smoking revealed significant associations among nonsmokers (RR = 0.34,
95 percent Cl 0.17-0.66) and somewhat weaker associations among smokers (RR = 0.47, 95 percent Cl
0.21-1.05).
Am J Epidemiol
Vol. 143, No. 1, 1996
6-year activity changes
Changes in physical activity, particularly during leisure time, were also inversely associated with allcause mortality. In this analysis, the relative risks of
mortality after the second examination were initially
calculated as a function of prior 6-year changes in
physical activity. The risks associated with a 1-point
within-individual change were 0.78 (95 percent Cl
0.58-1.06) for occupational activity and 0.65 (95
percent Cl 0.49-0.87) for leisure activity. The
multivariate-adjusted results were almost unchanged,
although occupational changes reached statistical significance. After removal of those endpoints appearing
during the first 2 and 6 years after the second examination, respectively, the results were stable. The re-
60
LJssner et al.
TABLE 4. Age-adjusted relative risk estimates associated with adulthood activity index* (as reported
in 1968/1969) for mortality from all causes, from myocardial infarction (Ml), and from non-MI causes:
Gothenburg Prospective Study of Women
Endpolnt and
adulthood activity
Index adjustment
No early
exclusions
Follow-up years
7-20
Follow-up years
13-20
RRt
95%Clt
RR
95% Cl
RR
95% Cl
Total mortality {n = 147):):
Age-adjusted
Multivariate§
0.37
0.42
0.22-0.63
0.24-0.74
0.36
0.42
0.21-0.63
0.23-0.74
0.25
0.24
0.13-0.50
0.11-0.50
Non-MI mortality (n= 125)
Age-adjusted
Multivariate§
0.37
0.43
0.21-0.64
0.23-0.78
0.35
0.42
0.20-0.63
0.22-0.79
0.23
0.23
0.11-0.49
0.10-0.52
Ml mortality only {n = 22)
Age-adjusted
Mufti variate§
0.41
0.36
0.10-1.61
0.08-1.59
0.43
0.35
0.10-1.76
0.07-1.65
0.38
0.28
0.08-1.81
0.05-1.55
• Results are presented before and after sequential exclusion of all deaths occurring 6 and 12 years after the
baseline examination.
t RR, relative risk; Cl, confidence Interval.
t Number of deaths with no early exclusions.
§ The following variables were added because they were significantly associated with increased mortality In
the age + single covariate model: smoking, waisthip ratio, peak expiratory flow, systolic and diastolic blood
pressure, and serum triglycerides.
suits were also similar after we controlled for selected
time-dependent covariates that were measured again in
1974-1975. These results are shown in table 5.
Increases vs. decreases
To better understand the implications of the negative associations between changes in leisure activity
and mortality, we stratified the sample into three
groups: those reporting increases (n = 251), those
reporting decreases (n = 265), and those reporting no
changes (n = 713) in leisure activity between the two
examinations. Analyses with and without exclusion of
early deaths at 2 and 6 years gave consistent results;
the data with no early exclusions are presented here.
Specifically, there was no evidence of decreased mor-
TABLE 5. Relative risk estimates for all-cause mortality associated with 6-year changes in
occupational and leisure activity levels (1968/1969-1974/1975), with and without exclusion of deaths
occurring 2 or 6 years after the 6-year follow-up examination: Gothenburg Prospective Study of Women
Observation years and
type of physical
activity change
Model 1: adjusted (or
age and adulthood
activity Index
Model 2: baseline
multivarlate modelf
Model 3: time-dependent
covartateaj:
RR*
95% Cl*
RR
95% Cl
RR
95% Cl
Follow-up years 7-20 (110
deaths, no exclusions)
Work-related
Leisure-time
0.78
0.65
0.58-1.06
0.49-0.87
0.72
0.63
0.53-0.97
0.46-0.85
0.77
0.67
0.56-1.06
0.49-0.92
Follow-up years 9-20
(105 deaths)
Work-related
Leisure-time
0.79
0.66
0.58-1.08
0.49-0.86
0.73
0.63
0.53-1.01
0.46-0.85
0.78
0.67
0.56-1.09
0.49-0.92
Follow-up years 13-20
(72 deaths)
Work-related
Leisure-time
0.82
0.61
0.57-1.20
0.42-0.88
0.74
0.63
0.50-1.08
0.43-0.93
0.82
0.66
0.55-1.22
0.45-0.97
* RR, relative risk; Cl, confidence interval.
t Includes baseline covariates only: age, adulthood activity index, dietary fat, alcohol intake, peak expiratory
flow, serum cholesterol and triglycerides, body mass index, smoking, waist:hip ratio, education, and systolic and
diastolic blood pressure.
t Includes the following covariates: adulthood activity index, initial age, and baseline levels of and 6-year
changes in smoking, serum triglycerides, body mass index, waisthip ratio, and diastolic blood pressure.
Am J Epidemiol
Vol. 143, No. 1, 1996
Physical Activity and Longevity in Women
tality in association with increasing leisure-time activity, compared with no changes (RR = 1.11, 95 percent
CI 0.67-1.86). In contrast, mortality was significantly
increased in subjects who decreased their leisure-time
activity levels (RR = 2.07, 95 percent CI 1.39-3.09).
DISCUSSION
In the present study of women who were initially
free of major diseases, moderate levels of physical
activity appeared to exert a protective effect with
respect to all-cause mortality, and a slight additional
risk reduction was observed at the higher activity
levels. Furthermore, we have shown that the inverse
association is not dependent on inclusion of earlier
endpoints. Although it is possible that women who
were less active at the time of their first visit were
already experiencing the effects of the condition that
caused their death 12 or more years later, it is remarkable that the association was not attenuated after exclusion of the first 12 years of endpoints. Rather than
diminishing with exclusion of the deaths observed at 6
and 12 years, the association was stable and sometimes strengthened, an observation upon which we
will comment below.
Several previous studies of women have reported
associations between physical inactivity or low fitness
on the one hand and mortality or cardiovascular
disease on the other (4, 12-14). Although early
follow-up of the Framingham Study population gave
no evidence of an association in women (15), longerterm follow-up recently revealed inverse associations
between physical activity levels and total mortality in
both middle-aged (16) and elderly (17) Framingham
women. However, in the middle-aged Framingham
women, who are those most comparable to this Swedish sample, physical activity did not relate to cardiovascular morbidity or mortality. This is consistent with
our observation that none of the baseline physical
activity indices was a significant predictor of 20-year
death from myocardial infarction, in spite of risk estimates that were suggestive of a protective influence.
Regarding all-site cancer, it has previously been reported that physical activity at baseline was not a
significant risk factor for 19-year incidence in these
women (18), although again the direction appeared to
be negative. Forthcoming analyses from the 24-year
follow-up may enable us to examine these associations
in a cause- and site- specific manner. Note, however,
that the present analysis independently confirms the
results of the 12-year follow-up of this cohort (4),
since a negative association between physical activity
and deaths occurring between follow-up years 13 and
Am J Epidemiol
Vol. 143, No. 1, 1996
61
20 is shown here. It is further clarified in this 20-year
follow-up that these associations are not explained by
lifestyle factors or other covarying health indicators.
Regarding the multivariate analysis, it may be noted
that a number of traditional cardiovascular disease risk
factors were included in the full model. It is generally
considered inappropriate to include these factors in models predicting cardiovascular mortality, because these
variables could be considered intermediate endpoints. In
the case of the present analysis of all-cause mortality, we
included these variables with the expectation that their
inclusion might diminish the association. For instance, it
has been previously shown that lung function is a strong
indicator of cardiovascular disease and mortality in these
women (10). However, even adjustment for.peak expiratory flow, which weakened the mortality risk estimate
from 0.37 to 0.47, did not negate the significance of the
adulthood activity index in the prediction of all-cause
mortality. Individual adjustment for the other covariates
had even less impact On this basis, we conclude that
these results are not explainable by covarying factors
indicating either a healthier lifestyle or better cardiovascular health.
We acknowledge that the indices of physical activity used here are crude and self-reported, and that their
reliability and validity were not ascertained. In this
context, however, it may be noted that significant
correlations were observed between physical activity
levels and measurements of lung function in these
women. Furthermore, supplementary questions which
asked the subjects to specify the number of hours per
week they spent outdoors and engaged in sports gave
correlations of 0.41 and 0.40, respectively (bothp's <
0.0001), with the 4-point leisure activity scale, which
provides some additional indication of the method's
relative validity.
The negligible effect of removing earlier endpoints on
the relative risks was somewhat unexpected and thus
requires further consideration. Specifically, table 4 suggests that the association is not attenuated when only the
later deaths are studied, providing evidence that preexisting illness is not driving these results. However, the
fact that the later endpoints seem more strongly related to
baseline activity is difficult to interpret. The confidence
intervals surrounding the relative risks with and without
early exclusions display substantial overlap; thus, the
following discussion regarding this apparent difference
must be considered tentative. We first speculated that
exercise-induced myocardial infarctions among extremely active individuals during the first 12 years of
follow-up might explain the somewhat strengthened association during the remaining 8 years; however, the
tendency toward a stronger result when only later deaths
62
LJssner et al.
were used remained even after the removal of all
myocardial infarction deaths. A remaining possibility is
that "unnatural causes"—i.e., suicides, accidents, and
alcohol-related deaths—may be overrepresented during
the first 12 years, before the onset of many chronic
diseases. If such individuals were more physically active
(note the positive correlation between physical activity
and alcohol use in table 2), their inclusion would weaken
the result However, the number of deaths of this type
was not large enough for testing this hypothesis.
Although moderate levels of physical activity have
been shown in other female cohorts to be an inverse
risk factor for mortality, this is the first study, to our
knowledge, to report that intraindividual changes in
leisure-time activity also predict total mortality in
women. It has recently been observed that initiation of
moderately vigorous sporting activity (2) was associated with decreased mortality in men, and it may be
tempting on the basis of the present findings to make
similar inferences for women. However, our findings
appear to have the most relevance to the importance of
maintaining (and not decreasing) one's physical activity levels during the aging process. The mortality risks
associated with increasing as opposed to maintaining
one's leisure-time activity level were in fact suggestive of a slight excess risk, although not significantly
so. This is consistent with trends that have been reported in elderly Danish men (3), on which basis the
investigators concluded that a thorough medical
checkup is desirable before an increase in physical
activity can be recommended to an elderly man.
Whether inactive men and women who are no longer
young should be advised to increase their activity
levels is thus a critical question that requires further
investigation.
In conclusion, this study underscores the importance
of including longitudinal measurements of physical
activity in future prospective studies. It confirms that
physical inactivity is one of the strongest epidemiologic predictors of mortality and suggests that maintenance of leisure-time activity levels is an important
health promotor in aging populations.
ACKNOWLEDGMENTS
This study was supported by grants 27X-4578 and
K92-27P-10146-01A from the Swedish Medical Research
Council.
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