How does occupational physical activity influence health? An umbrella review of 23 health outcomes across 158 observational studies

Abstract

Objective: Physical activity (PA) has substantial benefits across a range of health outcomes. There is uncertainty about the PA-specific health effects, and in particular, the occupational domain. In this umbrella review, we synthesised available evidence on the associations between occupational PA (OPA) and health-related outcomes (including cancer, all-cause mortality and cardiovascular disease). This work informed the development of WHO's guidelines on PA and sedentary behaviour (2020).

Design: Umbrella review of systematic reviews.

Data source: We performed a literature search in PubMed, Web of Science, Embase, CINAHL and Sportdiscuss from database inception to 2 December 2019.

Eligibility criteria for selecting studies: We included systematic reviews if they contained a quantitative assessment of OPA and its relationship with at least one health-related outcome.

Results: We summarised the evidence of 17 reviews covering 23 unique health-related outcomes. We graded most evidence as low or very low, or moderate quality. We found health benefits for those engaging in high versus low OPA for multiple cancer outcomes (including colon and prostate), ischaemic stroke, coronary heart disease and mental health (ie, mental well-being and life satisfaction). High OPA was associated with unfavourable health outcomes for all-cause mortality in men, mental ill health (ie, depression and anxiety), osteoarthritis, and sleep quality and duration.

Conclusions: We found favourable associations for most health-related outcomes with high OPA levels, but we also found some evidence for unfavourable associations due to high OPA levels. At this point, there is a need for better quality evidence to provide a unequivocal statement on the health effects of OPA.

Full text

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CillekensB, etal. Br J Sports Med 2020;54:1474–1481. doi:10.1136/bjsports-2020-102587
How does occupational physical activity influence
health? An umbrella review of 23 health outcomes
across 158 observationalstudies
Bart Cillekens,1 Matthias Lang,1 Willem van Mechelen,1 Evert Verhagen ,1
Maaike A Huysmans,1 Andreas Holtermann ,2,3 Allard J van der Beek,1
Pieter Coenen 1
Review
To cite: CillekensB,
LangM, van MechelenW,
etal. Br J Sports Med
2020;54:1474–1481.
►Additional material is
published online only. To view,
please visit the journal online
(http:// dx. doi. org/ 10. 1136/
bjsports- 2020- 102587).
1Department of Public
and Occupational Health,
Amsterdam UMC, Vrije
Universiteit Amsterdam,
Amsterdam Public Health
Research Institute, Amsterdam,
The Netherlands
2National Research Centre
for the Working Environment,
Copenhagen, Denmark
3Department of Sport Science
and Clinical Biomechanics,
University of Southern Denmark,
Odense, Denmark
Correspondence to
Dr Pieter Coenen, Department
of Public and Occupational
Health, Amsterdam Public
Health Research Institute,
VU University Medical Centre
(VUmc) Van der Boechorststraat
7, 1081 BT Amsterdam, The
Netherlands;
p. coenen@ amsterdamumc. nl
Accepted 13 September 2020
© Author(s) (or their
employer(s)) 2020. No
commercial re- use. See rights
and permissions. Published
by BMJ.
ABSTRACT
Objective Physical activity (PA) has substantial benefits
across a range of health outcomes. There is uncertainty
about the PA- specific health effects, and in particular,
the occupational domain. In this umbrella review, we
synthesised available evidence on the associations
between occupational PA (OPA) and health- related
outcomes (including cancer, all- cause mortality and
cardiovascular disease). This work informed the
development of WHO’s guidelines on PA and sedentary
behaviour (2020).
Design Umbrella review of systematic reviews.
Data source We performed a literature search
in PubMed, Web of Science, Embase, CINAHL and
Sportdiscuss from database inception to 2 December
2019.
Eligibility criteria for selecting studies We
included systematic reviews if they contained a
quantitative assessment of OPA and its relationship with
at least one health- related outcome.
Results We summarised the evidence of 17 reviews
covering 23 unique health- related outcomes. We graded
most evidence as low or very low, or moderate quality.
We found health benefits for those engaging in high
versus low OPA for multiple cancer outcomes (including
colon and prostate), ischaemic stroke, coronary heart
disease and mental health (ie, mental well- being and life
satisfaction). High OPA was associated with unfavourable
health outcomes for all- cause mortality in men, mental
ill health (ie, depression and anxiety), osteoarthritis, and
sleep quality and duration.
Conclusions We found favourable associations for
most health- related outcomes with high OPA levels,
but we also found some evidence for unfavourable
associations due to high OPA levels. At this point,
there is a need for better quality evidence to provide a
unequivocal statement on the health effects of OPA.
INTRODUCTION
Physical activity (PA) has significant health bene-
fits and contributes to the prevention of a range
of lifestyle- related, non- communicable diseases.1 2
Physical inactivity is one of the global leading risk
factors for all- cause mortality.3 Both national and
international PA guidelines for adults, including
the 2010 guidelines by WHO, recommend at least
150 min per week of moderate- intensity PA.1 2 The
Global Action Plan on PA highlighted the need to
update the 2010 WHO Global recommendations
on PA for Health.4 WHO published the guidelines
on PA and sedentary behaviour in 2020, further
details of which can be found in the current issue
of BJSM.4
The 2010 WHO PA guidelines did not differen-
tiate between domains of PA (work, commuting,
household and leisure), suggesting comparable
health benefits for all these PA domains.2 Most
studies reviewed by the 2010 guidelines were
restricted to leisure- time PA (LTPA) domain,2 and
evidence on domain specific health benefits was
largely inconclusive. Differential health effects
have been reported for LTPA and occupational
PA (OPA),5–7 a phenomenon which is referred to
as the PA paradox.8 For example, a prospective
cohort study showed that LTPA was associated
with reduced risk of all- cause mortality, while OPA
was associated with an increased risk of all- cause
mortality.6 It is not clear whether these differential
associations are due to domain- specific PA charac-
teristics (eg, differences in posture, intensity level,
frequency, duration and/or recovery time between
OPA and LTPA8) or down to methodological
reasons.9 10
As the amount of systematic reviews and meta-
analyses accumulates,11 more advanced evidence
synthesis methods such as umbrella reviews can
be employed.12 An umbrella review provides a
broader picture of findings for a particular question
or phenomenon, and is therefore useful to inform
guidelines.12 PA- related umbrella reviews are mostly
restricted to LTPA only,13–15 with no umbrella
review on the health effects of OPA currently.
In this umbrella review, we aimed to provide
an overview on the relationships between OPA
and a range of health- related outcomes, including
cancer, cardiovascular disease (CVD) and all- cause
mortality. We also aimed to assess dose–response
relationships and whether the relationship between
OPA and health differs from that of LTPA.
This review builds on a report on OPA commis-
sioned by WHO to inform the guidelines on PA and
sedentary behaviour (2020).
METHODS
Literature search
This protocol was registered in PROSPERO (id:
163090).16 We searched in PubMed, CINAHL, Web
of Science, Embase and Sportdiscuss from database
inception up to 2 December 2019 for systematic
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reviews assessing the relationship between OPA and health-
related outcomes. Searches contained keywords covering OPA,
systematic reviews and meta- analyses. See online supplemental
material table 1 for a detailed outline of the search strategy. We
identified additional reviews by screening the reference list of
included reviews and by consulting experts. Two reviewers (BC
and ML) independently screened title, abstract and full text
of identified references using the online Rayyan application (
rayyan. qcri. org).17 Discrepancies between the two reviewers
were resolved in a consensus meeting, or by consulting a third
reviewer (PC).
Review inclusion and data extraction
We included full- text systematic reviews of observational (eg,
cohort, case–control, cross- sectional) and experimental studies
(eg, (randomised) controlled trials) written in English. Reviews
had to contain a quantitative assessment of OPA and an associ-
ation with at least one health- related outcome considered rele-
vant by WHO PA guideline advisory committee. See the full list
of outcomes considered in online supplemental material table
2. We excluded articles if the OPA domain was not specifically
assessed. We also excluded reviews if they focused on sedentary
behaviour only or on biomechanical exposures only (ie, lifting
or prolonged postures such as standing or kneeling), without
considering energetic components of OPA. We excluded reviews
focused on specific (clinical) populations, such as pregnant
women or cohorts with an disease.
One reviewer (BC) extracted data from included reviews,
which was checked by a second reviewer (ML). Potential conflicts
were discussed until consensus was reached. We extracted first
author, title, year of publication, outcome, study design, number
of included studies, comparison group and effect sizes. If avail-
able, effect sizes of LTPA were also extracted.
Methodological quality and certainty of evidence
We rated included systematic reviews using A MeaSurement
Tool to Assess systematic Reviews2 (AMSTAR2),18 a 16- point
tool for assessment of the methodological quality of systematic
reviews, with good inter- rater agreement, test–retest reliability
and content validity.19 Review quality could be high, moderate,
low or critically low, with cut- off values of 100%, ≥75%, ≥50%
and <50%, respectively. One reviewer (BC) assessed method-
ological quality; the second reviewer (ML) checked these assess-
ments. If reviews were rated critically low, they were excluded
from further analyses.
We used the Grading of Recommendations Assessment, Devel-
opment and Evaluation (GRADE) method20 to rate the quality of
evidence for each of the health- related outcomes. The GRADE
system rates the quality of evidence as:
►High quality: further research is very unlikely to change our
confidence in the estimate of effect.
►Moderate quality: further research is likely to have an
important impact on our confidence in the estimate of effect
and may change the estimate.
►Low quality: further research is very likely to have an
important impact on our confidence in the estimate of effect
and is likely to change the estimate.
►Very low quality: any estimate of effect is very uncertain.20
The starting point for the quality of the evidence was
‘high’.21 22 We decreased this grading if the reviews showed:
risk of bias (ie, selection, performance, detection, attrition and/
or reporting bias), inconsistency of results (ie, unexplained
heterogeneity or I²-statistics ≥50%), indirectness of evidence
(ie, differences in populations, intervention, outcome measures
or indirect comparisons), imprecision (ie, 95% CI includes 1.0)
or publication bias (asymmetry in funnel plot). We increased the
rating by one level if there was a large magnitude of the effect
(eg, RR or OR ≥2.0 or ≤0.5), in case of plausible confounding
(which may have reduced an observed effect), or in case of a
dose–response gradient.23
Data analysis
If more than one review reported on a certain outcome, we
only used the most recently published review (typically with
the highest number of included studies) for further analyses;
unless a less recent review reported higher certainty of evidence
(GRADE). Online supplemental material table 3 enumerates the
included studies for main and sensitivity analyses. If subgroup
analyses (eg, regarding higher quality evidence or different study
designs) were provided with different GRADE scores, then
evidence from the highest GRADE score was synthesised. We
constructed forest plots to display the relationship of high vs
low OPA with health- related outcomes. We conducted sensitivity
analyses to assess consistency of the synthesised evidence if there
was more than one review for the same outcome.
If the original review had estimated the I² statistics, we synthe-
sised this information to assess heterogeneity.24 If reviews did
not publish the I² statistics, we calculated this where possible.
We synthesised small- study bias or publication bias (when
referring to OPA studies). Whenever a review did not provide
this information, and included more than ten OPA studies we
reanalysed the data and provided funnel plots to assess publi-
cation bias on visual inspection. In case no information was
provided and less than 10 studies were available, we considered
the review at stake to be ‘at risk of bias’ since a funnel plot would
be inaccurate with fewer than 10 studies.25
If available, we provided dose–response relationships from
reviews that had reported on more than two categories of OPA
or on a continuous OPA scale. For the comparison of the rela-
tionships of OPA and LTPA with health, we only used already
included reviews that reported on both OPA and LTPA. Differ-
ences between the effect sizes of OPA and LTPA were statistically
tested26 using a test of interaction. All analyses were conducted
using Revman V.3.5.3.
RESULTS
The literature search generated 573 references. After removing
duplicates and adding seven reviews from snowball searching, we
screened 312 references by title and abstract (figure 1). Full texts
of 73 reviews were screened, of which we excluded 37 reviews
for various reasons (online supplemental material table 4).
We identified 36 reviews that examined the associations
between OPA and 23 unique health- related outcomes.27–62 The
most frequently reported outcome was cancer, with 11 different
cancer types (24 reviews). Other reviews evaluated CVD (n=3),
osteoarthritis (n=3), all- cause mortality (n=2), hypertension
(n=1), diabetes mellitus type 2 (n=1), insomnia (n=1) and
mental health (n=1) (online supplemental material table 3). We
did not detect any reviews on adiposity, cognitive outcomes or
health- related quality of life.
Quality assessment
AMSTAR2 scores for methodological quality of the 36 included
reviews are shown in online supplemental material table 5.
Six reviews scored (17%) critically low which we did not use
for further analyses.30 32 35 49 55 59 Eight reviews (22%) scored
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moderate, and 22 (61%) scored low methodological quality.
None of the included reviews scored high on the AMSTAR2
scale, with common methodological issues for example being
lack of a priori protocol registration (only done in four reviews),
not reporting a comprehensive search strategy (only performed
in ten reviews) and not providing a list of excluded studies (only
done in five reviews).
Evidence synthesis
Online supplemental material table 6 presents extracted data.
Seventeen reviews (on 23 unique outcomes) were synthesised.
These reviews reported on 158 studies: 96 (61%) longitudinal
cohort studies, 60 (38%) case–control studies and 2 (<1%)
cross- sectional studies, while no reviews on experimental studies
met the inclusion criteria. Reviews described between three and
27 individual studies, with a median of 7.5 studies per review.
We did not synthesise thirteen reviews because there was a more
recent published review, or a review with a higher certainty of
evidence (online supplemental material table 3).
Grading of Recommendations Assessment, Development and
Evaluation
We graded none of the included reviews as high quality; overall
the evidence was of moderate quality at best (online supple-
mental material table 6). Four reviews (17%) on colon cancer,
rectal cancer, endometrial cancer and prostate cancer provided
moderate quality evidence. Reviews of nine (39%) outcomes
provided low quality evidence (all- cause mortality, ischaemic
stroke, coronary heart disease (CHD), proximal and distal colon
cancer, breast cancer, gastric cancer and renal cancer) and ten
other reviews (43%) offered very low- quality evidence.
PA measurement methods varied across reviewed studies,
and included self- administered questionnaires, interviews or
job titles. Because PA was mostly self- reported, misclassification
was reported in almost all included reviews. In some reviews
PA was assessed at baseline, but a change in PA over time was
not considered. Over half of the reviews reported that there
was confounding bias, that the adjustment of variables widely
varied between studies, or that important confounding variables
were not addressed in reviewed studies. Some review reported
language bias; typically only one or two languages were included
in the reviews.
Of the 23 health outcomes, 14 (61%) reported an I² statistics
<50% and seven (30%) reported an I² statistics ≥50% (hyperten-
sion, mental health, mental ill health, stroke, all- cause mortality,
poor sleep duration and/or quality and osteoarthritis). For two
outcomes (oesophageal and endometrial cancer) the reviews did
not provide I² statitics. Re analysis showed a low heterogeneity
(I²=0%) for endometrial cancer and considerable heterogeneity
for oesophageal cancer (I²=89%) (online supplemental mate-
rial figure 7). Most reviews were precise; the risk estimates of
only seven (30%) outcomes had 1.0 included in their 95% CI.
Although all 17 reviews used the Eggers asymmetry test to detect
publication bias, in most reviews, the association between OPA
and a health- related outcome was investigated in a subgroup
analysis on OPA only, with the Egger test conducted for ‘total
PA’ (including OPA). Only for four outcomes (17%) (in three
reviews) a test for publication bias was conducted, addressing
the OPA domain. Only one of these three reviews found a small
risk for publication bias. It is likely that reviews did not conduct
separate analyses because there were not enough unique OPA
studies included: fourteen (61%) outcomes included less than 10
studies on OPA. We reanalysed the data of four outcomes and
did not detect publication bias in these reviews (online supple-
mental material figure 8). One review included more than ten
studies, but did not report individual study effect sizes, hence we
could not perform an assessment of publication bias.47
Evidence
All synthesised reviews are summarised in figure 2, with quality
of the evidence ranging from moderate to very low.
Moderate quality evidence
A meta- analysis of Mahmood et al33 including five cohort and ten
case- control studies showed a statistically significant reduction
in risk of colon cancer among those with high compared with
low OPA (RR 0.74, 95% CI 0.67 to 0.82). This association was
comparable for men (RR 0.74, 95% CI 0.66 to 0.82) and women
(RR 0.78, 95% CI 0.65 to 0.93). In the same review, authors
presented pooled estimates regarding the association between
OPA and rectal cancer from five cohort and seven case–control
Figure 1 Flow chart depicting the review search and selection procedure. OPA, occupational physical activity.
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studies, showing a reduced risk in those with high compared with
low OPA (RR 0.88, 95% CI 0.79 to 0.98). Another systematic
review that investigated colon cancer subtypes, found compa-
rable effects for proximal (RR 0.72, 95% CI 0.61 to 0.85) and
distal colon cancer (RR 0.75, 95% CI 0.63 to 0.88).36 In our
sensitivity analysis, comparable associations were found for both
colon cancer (and subtypes) and rectal cancer.34
A review on seven cohort and twelve case–control studies
found a statistically significant risk reduction of endometrial
cancer for women with high compared with low OPA (RR 0.81,
95% CI 0.75 to 0.87).41 Another review showed comparable
results.40
A review by Liu et al52 showed that OPA was significantly
related with a reduced risk of prostate cancer (RR 0.81, 95% CI
0.73 to 0.91). The reduction in risk was statistically signifi-
cantly lower for nine cohort studies (RR 0.91, 95% CI 0.87 to
0.95) compared with eighteen case–control studies (RR 0.73,
95% CI 0.62 to 0.87). When stratified for study quality, the
higher quality studies showed a lower reduced risk (RR 0.86,
95% CI 0.78 to 0.94) compared with lower quality studies (RR
0.75, 95% CI 0.89 to 1.00). A statistically significant protective
effect of OPA only existed in those studies in which the median
follow- up duration was >10 years. Comparable results were
found in other systematic reviews.50 51
Low-quality evidence
In the most recent systematic review,28 men with high level OPA
experienced a statistically significant increased risk of all- cause
mortality (HR 1.18, 95% CI 1.05 to 1.34), even after adjusting
for possible confounders, such as LTPA. A non- significant
reduced risk was observed among women (HR 0.90, 95% CI
0.80 to 1.01). Authors reported considerable heterogeneity in
the pooled study findings for men (I² statistic=76%), but not
for women (I² statistic=0%), and some risk of publication bias
was discussed by the authors. An earlier review, with a lower
number of included studies, showed a reduction in mortality risk
for both genders27 (RR 0.66, 95% CI 0.49 to 0.89 and RR 0.94,
95% CI 0.75 to 1.19, for females and males, respectively). In the
this review, high heterogeneity was reported.
A higher level OPA was related to a lower risk of stroke;
although, this association was not statistically significant for
total stroke (RR 0.74, 95% CI 0.49 to 1.12).29 In the associa-
tion between OPA and ischaemic stroke, statistically significant
protective effects were found for high vs low OPA (RR 0.57,
95% CI 0.43 to 0.77).
Sattelmair et al showed, based on evidence from four studies
with low heterogeneity, that high versus low OPA was related to
a statistically significant reduced risk of CHD (RR 0.84, 95% CI
0.79 to 0.90).31 Three out of four studies were based on male
samples only (RR 0.87, 95% CI 0.81 to 0.99).
Pizot et al observed that high OPA versus low OPA was related
to a statistically significantly reduced risk of breast cancer in a
female population (RR 0.88, 95% CI 0.82 to 0.95).38 These
results were based on eleven cohort studies with low heteroge-
neity. Two other reviews showed comparable results.37 39
Chen et al showed that high versus low OPA had a statistically
significantly lower risk of gastric cancer (RR 0.79, 95% CI 0.65
to 0.95).45 Behrens et al observed a statistically non- significant
association between OPA and oesophageal cancer (RR 0.91,
95% CI 0.46 to 1.81).46 Two other reviews found comparable
results.43 44
Behrens et al found that high versus low OPA was related
to a statistically non- significant reduction in renal cancer (RR
0.91, 95% CI 0.79 to 1.04). The authors estimated these results
Figure 2 Forest plot depicting the evidence for the association of occupational physical activity and health. (1) (F)= Female population only,
(M)=Male population only, all other studies included both genders. (2) Only results from 13 high- quality studies were presented. (3) Not published
in the original review, but reanalysed (online supplemental files 7 and 8). (4) Unable to reanalyse because no separate risk estimates were provided
in the original review. An arrow indicates that the effect size is larger than the range of the figure. CHD, coronary heart dsease; GRADE, Grading of
Recommendations Assessment, Development and Evaluation; TD2, diabetes mellitus type 2.
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from data of six cohort and five case–control studies47 with low
heterogeneity. Another review showed comparable results.48
OPA showed no association with lymphoma (OR 0.98,
95% CI 0.80 to 1.02) from a review with one cohort and four
case–control studies.42
One review reported on the association between OPA and
pancreatic cancer.54 Three cohort studies showed a statistically
significant reduction (RR 0.75, 95% CI 0.58 to 0.96). There was
low heterogeneity between the included studies.
Three cohort studies with over 9000 diabetes mellitus type
2 cases showed a lower risk on this outcome (RR 0.85, 95% CI
0.79 to 0.92) for people with high versus low OPA.56
Pooled results from two cohort, three cross- sectional and
three case–control studies showed that high OPA was related
with a statistically significant higher risk of knee osteoarthritis
(OR 1.45, 95% CI 1.20 to 1.76).57 Authors of this review
reported high heterogeneity and a high likelihood of publication
bias. Cohort studies showed lower risks compared with cross-
sectional and case–control studies. Another review showed that
cumulative physical workloads were associated with hip osteo-
arthritis in men; this review showed mixed evidence for physical
demands and knee osteoarthritis, hip osteoarthritis and osteoar-
thritis in multiple other joints.58
For high versus low OPA, there was an statistically significant
increased risk of insomnia (OR 2.76, 95% CI 1.71 to 4.45),61
with pooled results from four cross- sectional and three cohort
studies, and high heterogeneity.
In comparison with low OPA, high OPA was related with a
decreased, but statistically non- significant, risk of hypertension
(RR 0.93, 95% CI 0.81 to 1.08).62 The heterogeneity among six
studies was high.
OPA had a weak positive association with mental ill- health (ie,
depression and anxiety) (r 0.10, 95% CI 0.04 to 0.16), but also
a weak positive association with mental health (ie, mental well-
being and life satisfaction) (r 0.02, 95% CI −0.09 to 0.12).60
Both effects showed high heterogeneity.
Health effects of occupational versus LTPA
In the included reviews, effect sizes of seventeen outcomes were
available for both OPA and LTPA (figure 3). Effect sizes of both
OPA and LTPA generally pointed into the same direction, with
some differences in estimates provided for OPA and LTPA. The
association between OPA and LTPA was statistically significant
different for CHD, distal colon cancer and diabetes mellitus type
2. We could not compare OPA and LTPA for all- cause mortality,
sleep quality and/or duration, osteoarthritis and mental (ill)
health, because LTPA was not included in the reviews for these
outcomes.
Dose–response associations
Only five outcomes, presented in three reviews, reported on
dose–response associations (figure 4). Three outcomes (stroke,
ischaemic stroke and hypertension) showed a gradual risk
increase across three groups of OPA (high, moderate, low levels
of OPA). For total stroke, the lowest risk reduction was shown
for the moderately active vs inactive workers (RR 0.64, 95% CI
0.48 to 0.87). For ischaemic stroke, the most active workers
Figure 3 Forest plot depicting the evidence for the association of physical activity and health. Association for occupational and leisure- time physical
activity are depicted. *Effect of LTPA and OPA is statistically significantly different (p≤0.05). An arrow indicates effect sizes that were out of range of
our figure. CHD, coronary heart disease; LTPA, leisure- time physical activity; OPA, occupational physical activity; T2D, diabetes mellitus type 2.
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category was found to have the highest reduced risk.29 The
results also showed that there was no evidence for an association
between high- level or moderate- level OPA and hypertension.62
Mahmood reported the pooled RR for colon cancer with an
OPA level per 210 metabolic equivalent of task (MET) hour/
week (RR 0.86, 95% CI 0.80 to 0.91). This effect was stronger
for men (RR 0.82, 95% CI 0.76 to 0.88) than for women (RR
0.96, 95% CI 0.86 to 1.08). In the same review, the pooled RR
with OPA level per 210 MET our/week for rectal cancer was (RR
0.94, 95% CI 0.87 to 1.01).33
DISCUSSION
Main findings
In this umbrella review, we summarised the evidence on the
associations between OPA and 23 health- related outcomes based
on 17 systematic reviews that included 158 individual studies.
Engaging in high versus low OPA showed beneficial health
effects for multiple cancer outcomes, stroke, CHD and mental
health. In contrast, high versus low OPA showed unfavourable
health outcomes regarding all- cause mortality in men, mental
ill health, osteoarthritis and sleep duration and/or quality. For
some outcomes, our results are inconclusive (ie, for several
cancer outcomes, hypertension, all- cause mortality in females).
We identified no reviews on adiposity, cognitive outcomes or
health- related quality of life. The associations between OPA and
health- related outcomes, for most outcomes, were not differen-
tial from that of LTPA in direction and/or magnitude. Although
for three health outcomes we found a significant difference in
magnitude (figure 3), LTPA showed a higher protective effect in
distal colon cancer, CHD and diabetes type 2 than OPA. Reviews
that reported unfavourable health outcomes for OPA (ie, all-
cause mortality in men, osteoarthritis and sleep duration and/
or sleep quality) did not report on LTPA, as a result of which we
could not make a comparison between OPA and LTPA.
Only three reviews, addressing five outcomes, reported dose–
response associations of OPA and health. We can, therefore, only
make limited inferences on the health effects of the full OPA
continuum. Higher OPA- specific energy expenditure was asso-
ciated with a gradually reduced risk of colon cancer and to a
lesser extent a reduced risk for rectal cancer. For hypertension
and ischaemic stroke, the highest OPA groups were associated
with the lowest risk (although non- significant for hypertension).
Interpretation of the results
In this umbrella review, we applied the GRADE method. Other
criteria to evaluate the quality of evidence have been proposed
in other reviews13–15 and by other organisations.63 Using such
criteria could have possibly led to other results in the interpre-
tation of the reviews identified in our umbrella review. None of
the relationships we identified were supported by strong evidence
(with moderate GRADE scores at best) and therefore results
should be interpreted with caution. We only detected evidence
from systematic reviews of observational studies, which bears
a higher risk of selection bias and confounding.64 All identified
evidence suffers from risk of bias (eg, misclassification, publi-
cation bias and confounding bias) and reviews showed high
heterogeneity and/or inconsistent results. Studies varied widely
regarding the confounding variables that were considered and
relevant variables such as socioeconomic status, body mass index
and lifestyle factors (eg, smoking, alcohol and diet) were not
addressed in every study. All reviews reported issues with the
measurements of PA, specifically with the use of self- reported
methods to assess OPA in all reviews and studies. Measuring
OPA can be challenging as the occupational dose and intensity
can fluctuate over time (eg, between days, weeks or seasons) and
a general shift in OPA from physically demanding jobs to more
sedentary occupations has been seen over the last decades.65 As
most studies of the current evidence base assessed OPA only at
a single instance, changes over time were not considered, which
could have led to misclassification. On the other hand, OPA
could be less subjected to recall bias than LTPA because of the
routine nature of OPA and relatively long (ie, sometimes livelong)
exposure to OPA.66 Self- reported PA may suffer from several
biases67 68 induced by socially desirable or culturally influenced
answers; for example, variation across socioeconomic and demo-
graphic groups,69 participants’ inability to assess PA at different
intensities and recall bias.70 Arbitrary cut- off points (with hetero-
geneous definitions) to operationalise OPA categories were used
and precision was reduced by using dichotomous OPA categories.
Most reviews were able to include a substantial number of
studies on LTPA since reviews often had their main focus on
either LTPA or total PA (ie, OPA and LTPA combined). Only
limited evidence was available for OPA, sometimes from
subgroup analyses only. In addition, reviews could or did not
detect heterogeneity/publication bias for OPA. Some reviews did
not draw any conclusions on OPA or stated that more evidence
was needed on this topic. In contrast, reviews with a relatively
high number of included studies on OPA showed the importance
of subgroup analyses to provide more profound insight. The
review about prostate cancer showed, for example, that higher
quality studies had a lower reduced risk in comparison with lower
quality studies; cohort studies showed a lower reduced risk in
comparison with case–control studies.52 In this review, a statisti-
cally significant beneficial health effect of OPA was only evident
in studies with a long follow- up (median >10 years).52 Coenen
et al showed that high OPA was related to an increased risk of
all- cause mortality for men, but a non- significant decreased risk
for women.28
Figure 4 Dose–response associations for occupational physical activity and health. MET, metabolic equivalent of task; OPA, occupational physical
activity.
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Sensitivity analyses were used to assess the consistency of
the evidence when multiple reviews were available per health
outcome. These analyses showed that almost all reviews provided
comparable direction and magnitude of effect sizes. The two
reviews on all- cause mortality, however, showed opposite
effects. Coenen et al reported that the risk of all- cause mortality
was higher for male workers,28 while Samitz et al reported in an
earlier review with fewer studies that men with higher OPA had
a reduced risk of all- cause mortality.27 While both reviews had
a low GRADE- score, we synthesised the findings from the most
recent review, which also included more studies.28 The evidence
was therefore considered to be more up to date. Nevertheless,
while in the male population high level OPA was associated
with all- cause mortality, other included reviews on the leading
causes of death,71 such as CVD and cancer outcomes, showed
favourable health outcomes for high versus low OPA. The afore-
mentioned and other methodological issues could partly explain
these contradictory findings.9 10 There are also several plausible
physiological explanations as to why OPA might not confer the
cardiovascular health benefits of LTPA.8 For example, LTPA
entails dynamic movements which is mostly performed volun-
tarily over short time periods with sufficient recovery time,
while OPA is most often of too low intensity or of too long dura-
tion to be health beneficial.
Methodological strengths and limitations
We followed a systematic methodology including search strategy
in electronic databases and independent study selection and
extraction by two researchers. We also used standard approaches
to assess the quality of methods (AMSTAR2) and to rate the
quality of the evidence (GRADE). GRADE has increasingly
been adopted by organisations worldwide for grading evidence
and for guideline development.20 Moreover, if a review did not
report on heterogeneity (in terms of I² statistics) or publication
bias (eg, using funnel plots), we reanalysed the available data,
leading to more accurate GRADE scores.
A limitation of our umbrella review is that with the rapidly
evolving body of evidence on the health effects of OPA, evidence
may have only recently been published and as a consequence
has not been summarised in reviews yet. For example, since the
review by Coenen et al (with literature search until September
2017) at least six new studies reporting on all- cause mortality
and OPA would have met the inclusion criteria for systematic
reviews included in our umbrella review.10 None of the system-
atic reviews included experimental studies, although some indi-
vidual experimental studies addressed the relationship between
OPA and health- related outcomes.72 73 Experimental studies
provide more insight into causality and deal with issues such as
selection bias and confounding.
We included reviews that addressed OPA with at least an
aerobic component and excluded reviews with only biome-
chanical (eg, lifting, kneeling) OPA components. We only
included health- related outcomes prioritised by WHO (online
supplemental material table 2); thereby excluding evidence on
outcomes such as musculoskeletal and neurological disorders.
The limitation of the exclusion of neurological outcomes seems
to have hardly any influence on our findings. For example,
Morgan et al could not provide any convincing evidence on the
associations between OPA and dementia in later life.74 Stephen
et al showed that there was inconclusive evidence regarding the
associations between OPA and Alzheimer’s disease.75 However,
it is known that high biomechanical demands at work, such as
lifting and heavy manual work, are associated with increased risk
of musculoskeletal disorders such as low back, neck/shoulder and
lower extremity pain.76–78 We also reported on outcomes that
are closely related (eg, colon cancer and rectal cancer) because
they were addressed in separate systematic reviews.33 34 36
Implications for future research
WHO guidelines on PA and sedentary behaviour (2020) state
that more evidence is needed on the health effects of occupa-
tional OPA.79 We recommend that further research addressing
OPA should be based on more sophisticated OPA assessments
(eg, using a combination of device measured PA and a diary to
distinguish domains of PA). This will help to address biases due
to self- reports and can additionally measure PA metrics, such as
intensity, duration and frequency.10 Second, we recommend that
reviews and prospective cohort studies examine health effects by
PA domains, so that possible differential health effects of LTPA
and OPA can further be explored. Third, to get a better under-
standing of the health- related outcomes of OPA, it is important
to consider biomechanical demands at work and musculoskel-
etal disorders. Particularly since musculoskeletal disorders, such
as (low) back and neck pain, result in considerable healthcare
spending,80 as well as substantial indirect cost due to presen-
teeism and absenteeism,81 and are among the leading causes of
disability worldwide.82 83 To increase the quality of evidence,
more experimental studies comparing OPA with health- related
outcomes should be conducted and included in systematic
reviews. Lastly, we urge researchers to conduct subgroup anal-
yses, if possible (such as for gender), since these seem to provide
a more thorough understanding of the health effects of OPA.
Implications for practice
High- quality evidence on the relationship between LTPA and
the prevention of non- communicable diseases is available and
has been incorporated in national and global guidelines.3 WHO
guidelines advise that some PA is better than none and recom-
mend working age adults to engage in at least 150–300 min of
moderate- intensity PA per week. The recommended amounts
of PA can be done as part of leisure, transportation, work and
household activities.79
There is inconclusive evidence of very low to moderate quality
for OPA to provide comparable beneficial health effects to
LTPA. At this point, there is a need for better quality evidence to
provide a unequivocal statement on the health effects of OPA.
As the evidence base develops, a more nuanced message
concerning the health effects of OPA may be possible. Such a
nuanced message will be relevant to large parts of the working
population, in particular, those from low socioeconomic groups
and people in low- income and middle- income countries who do
most of their daily PA at work.84 85 Although more high- quality
evidence is still needed on health effects of OPA, OPA holds
many workers back from engaging in sufficient LTPA due to
fatigue and exertion from work, and therefore, it may limit the
beneficial health effects of engaging in LTPA for a large fraction
of the adult population.86
CONCLUSION
We found that high OPA has favourable health associations with
most health- related outcomes (multiple cancer outcomes, stroke,
CHD and mental health). Other reviews showed unfavourable
health associations with high OPA levels (all- cause mortality in
men, mental ill health, osteoarthritis and poor sleep duration
and/or quality).
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Review
Included reviews were of very low to moderate quality. To
increase the quality, future research should focus on sophisti-
cated PA measurements, include relevant confounders such as
socioeconomic status, lifestyle factors and other types of PA
and regular updating of existing systematic reviews. Improved
research will lead to a better understanding of the associations
between OPA and health- related outcomes.
What is already known
►Adequate physical activity (PA) prevents a range of lifestyle-
related, non- communicable diseases.
►It is uncertain if all domains of PA have comparable health
effects, with some evidence suggesting that leisure time
PA (LTPA) and occupational PA (OPA) may have differential
health effects.
►Methodological issues or differences posture, intensity level,
frequency, duration and/or recovery time between OPA
and LTPA could explain these differential health effects of
different PA domains.
What are the new findings
►This umbrella review, which is the first of its kind, suggests
that high occupational physical activity (OPA) was beneficial
for most health outcomes including coronary heart disease
and several cancers.
►High OPA showed unfavourable associations with all- cause
mortality in men, mental ill health, osteoarthritis and sleep
duration and/or quality.
►This review synthesised a heterogeneous evidence base of
very low to moderate quality, highlighting the need for better
quality research in this area.
Twitter Evert Verhagen @Evertverhagen and Andreas Holtermann
@profHoltermann
Acknowledgements This review was prepared for and funded by the WHO, to
contribute to the development of the Guidelines on physical activity and sedentary
behaviour (2020). It was submitted to the Guideline Development Group and
considered as they formulated their recommendations. The views expressed in this
article do not necessarily represent the decisions, policy or views of the World Health
Organization.
Contributors BC and ML conducted the literature screening and data extraction of
all included reviews. All authors (BC, ML, WvM, EV, MH, AH, AJvdB, PC) reviewed the
manuscript for important intellectual content. PC was the study guarantor.
Funding This paper was based on a report that was commissioned and funded by
WHO. This research was furthermore funded by The Netherlands Organisation for
Health Research and Development; ZonMw (grant #: 531-00141-3).
Competing interests For the avoidance of doubt, WvM wishes to declare that he
is a non- executive board member of Arbo Unie B.V. WvM and AJvdB are director and
advisor, respectively, of Evalua Nederland B.V. Both Arbo Unie and Evalua Nederland
operate in the Dutch occupational healthcare market.
Patient consent for publication Not required.
Provenance and peer review Not commissioned; externally peer reviewed.
Supplemental material This content has been supplied by the author(s). It
has not been vetted by BMJ Publishing Group Limited (BMJ) and may not have
been peer- reviewed. Any opinions or recommendations discussed are solely those
of the author(s) and are not endorsed by BMJ. BMJ disclaims all liability and
responsibility arising from any reliance placed on the content. Where the content
includes any translated material, BMJ does not warrant the accuracy and reliability
of the translations (including but not limited to local regulations, clinical guidelines,
terminology, drug names and drug dosages), and is not responsible for any error
and/or omissions arising from translation and adaptation or otherwise.
ORCID iDs
EvertVerhagen http:// orcid. org/ 0000- 0001- 9227- 8234
AndreasHoltermann http:// orcid. org/ 0000- 0003- 4825- 5697
PieterCoenen http:// orcid. org/ 0000- 0002- 4034- 7063
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