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Original article
doi:10.5271/sjweh.3850
Scand J Work Environ Health
Online-first -article
Does occupational lifting affect the risk of hypertension?
Cross-sectional and prospective associations in the
Copenhagen City Heart Study
by
Korshøj M, Hannerz H, Marott JL, Schnohr P, Prescott E, Clays E,
Holtermann A
Heavy lifting acutely increases blood pressure. However, only few
inconclusive studies have investigated the prospective relation
between heavy occupational lifting and hypertension. Our exploratory
prospective analyses suggest that workers using anti-hypertensives or
aged 50 years or older may be vulnerable to increases in blood
pressure from heavy occupational lifting. However, further research is
needed to confirm these associations.
Affiliation:
National Research Centre for the Working Environment,
Lersø Parkallé 105, 2100 Copenhagen. [email protected]
Refers to the following texts of the Journal:
1989;15(3):165-179
2007;33(6):405-424 2005;31(6):409-437
Key terms:
blood pressure; blue collar; cardiovascular disease;
cohort study; Copenhagen Heart Study; heavy lifting; hypertension;
lifting; manual handling; occupational epidemiology; occupational
lifting; occupational physical activity; prospective association;
prospective study
This article in PubMed:
www.ncbi.nlm.nih.gov/pubmed/31454050
This work is licensed under a
Creative Commons Attribution 4.0 International License.
Print ISSN: 0355-3140 Electronic ISSN: 1795-990X Copyright (c) Scandinavian Journal of Work, Environment & Health
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O
riginal article
Scand J Work Environ Health – online first. doi:10.5271/sjweh.3850
Does occupational lifting affect the risk of hypertension? Cross-sectional and
prospective associations in the Copenhagen City Heart Study
by Mette Korshøj, PhD,
1
Harald Hannerz, PhD,
1
Jacob L Marott, PhD,
2
Peter Schnohr, PhD,
2
Eva Prescott, PhD,
2, 3
Els Clays, PhD,
4
Andreas Holtermann, PhD
1, 5
Korshøj M, Hannerz H, Marott JL, Schnohr P, Prescott E, Clays E, Holtermann A. Does occupational lifting affect the risk of
hypertension? Cross-sectional and prospective associations in the Copenhagen Heart Study.
Scand J Work Environ Health
–
online first. doi:10.5271/sjweh.3850
Objective
The aim of this study was to investigate cross-sectional and prospective associations between heavy
occupational lifting and hypertension.
Multivariable logistic regression models were applied to adjust for sex, age, body mass index (BMI), smoking,
education, self-rated cardiorespiratory fitness, vital exhaustion and baseline blood pressure, and were used to
estimate (i) the cross-sectional association between heavy occupational lifting and hypertension, defined as using
anti-hypertensives or having a systolic blood pressure (SBP) ≥140 mmHg or diastolic blood pressure (DBP) ≥90
mmHg, and (ii) the prospective association between heavy occupational lifting and risk of becoming a systolic
blood pressure case, defined as an above median change (from baseline to follow-up) and/or a shift from no use
of anti-hypertensives at baseline to use of anti-hypertensives at a ten-year follow-up.
Methods
Data from the third, fourth and fifth examinations of the Copenhagen City Heart Study were included.
Results
Both cross-sectional [odds ratio (OR) 1.06, 95% confidence interval (CI) 0.94–1.20] and prospective
(OR 1.10, 95% CI 0.92–1.31) analysis indicated no relations. Explorative prospective analyses suggested linear
associations between heavy occupational lifting and systolic blood pressure among participants using anti-
hypertensives. Exposure to heavy occupational lifting tended to increase the incidence of hypertension (OR 1.30,
95% CI 0.97–1.73) among participants ≥50 years.
Conclusions
No associations were seen among the general population. Positive associations were seen among
users of anti-hypertensives and participants ≥50 years, indicating these groups as vulnerable to increases in blood
pressure when exposed to occupational lifting.
Key terms
blood pressure; blue collar; cardiovascular disease; cohort study; heavy lifting; manual handling;
occupational epidemiology; occupational physical activity.
Recent surveys have concluded that heavy occupational
lifting is described as a risk for low-back pain (1), how-
ever heavy lifting also affects the cardiovascular system
through acute increases in blood pressure (BP) (2). Some
workers perform occupational lifting for several hours
per day, many days per week, and therefore may be at
risk for developing hypertension due to the frequency
and duration of acutely increased BP (3). Thus heavy
occupational lifting may act as an occupational risk factor
for hypertension (4, 5). The prevalence of hypertension
varies across occupational groups, supporting the impact
by the working environment (6). Hypertension is a major
preventable cardiovascular risk factor (7–9) and is esti-
mated to cause 14% of all annual deaths globally (10).
However, only few studies (4, 5, 11) have investigated
the relation between heavy occupational lifting and hyper-
tension, showing conflicting results. Thus, investigating
these associations could reveal a potential for prevention
of hypertension, especially among the 22% of the Danish
workforce and 32% of European workers estimated to be
1
2
3
4
5
National Research Centre for the Working Environment, Copenhagen, Denmark.
Copenhagen City Heart Study, Bispebjerg Frederiksberg Hospital, University of Copenhagen, Copenhagen, Denmark.
Department of Cardiology, Bispebjerg Frederiksberg Hospital, University of Copenhagen, Copenhagen, Denmark.
Department of Public Health and Primary Care, Ghent University, Ghent, Belgium.
Department of Sports Science and Clinical Biomechanics, University of Southern Denmark, Odense, Denmark.
Correspondence to: Mette Korshøj, National Research Centre for the Working Environment, Lersø Parkallé 105, 2100 Copenhagen. [E-mail
[email protected]]
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Occupational lifting and risk for hypertension
exposed to heavy occupational lifting on a regular basis
(12) (6
th
survey in Eurofound).
This study’s objective was to explore associations
between heavy occupational lifting and hypertension
in the Copenhagen City Heart Study, with the hypoth-
esis that heavy occupational lifting is associated with
a higher prevalence of hypertension and an increased
incidence of new-onset hypertension in normotensives.
Methods
A detailed protocol for this study has been reported
elsewhere (13). Briefly, randomly selected Copenhagen
citizens, aged ≥20 years, were examined in the Copen-
hagen City Heart Study, containing person-based infor-
mation on health as well as a large variety of biological,
environmental and lifestyle-related factors (14). Data
from the third (1991–94, response rate 61.2%), fourth
(2001–03, response rate 49.5%) and fifth (2011–15,
response rate 46.6%) examination were included in this
study. Thus, the cross-sectional analysis had a possibility
of three observations per participant, and the prospec-
tive analysis had possibility of two observations per
participant.
Inclusion criteria
All participants with data on BP, level of occupational
physical activity (OPA) (including heavy lifting) and
antihypertensive drug usage were included in the cross-
sectional analysis.
All normotensive participants with data on level of
OPA at the third and/or fourth examination n, and data
on BP and antihypertensive
drug usage in examination
n and n+1 were included
in the prospective analysis.
Assessment of heavy lifting
Self-reported level of OPA was obtained by use of
the same question in all three examinations: “Please
describe your level of occupational physical activ-
ity within the past year” with the following response
categories:” (i) predominantly sedentary; (ii) sitting or
standing, some walking; (iii) walking, some handling of
material; (iv) heavy manual work”. If answering iii or
iv, an additional question regarding heavy occupational
lifting was applied: “Do you lift heavy burdens?” with
the response categories: yes or no. In the analysis, the
participants were classified as exposed to heavy occu-
pational lifting by answering “yes” to the question con-
cerning heavy burdens, and those participants answering
i, ii and iii or iv in combination with not lifting heavy
burdens were set as the reference group.
No information was collected in between exami-
nations. In the prospective analysis, the stability of
exposure was accounted for by cross-tabulating the
self-reported exposure at examination three by exposure
at examination four, and also the self-reported expo-
sure at examination four by exposure at examination
five. An evaluation of the agreement (Cohen’s kappa)
between exposures to heavy occupational lifting across
the examinations showed fair agreement (13), and thus
the baseline exposure were regarded as valid and used
throughout.
Definition of hypertension
Hypertension, the primary outcome measure, was
defined as self-reported use of any antihypertensive
drugs or a measured systolic blood pressure (SBP) ≥140
mmHg or diastolic blood pressure (DBP) ≥90 mmHg
(15) in the cross-sectional analysis. In the prospective
analysis, hypertension was defined as the shift from not
using antihypertensive drugs in examination n to use of
antihypertensive drugs in examination n+1 or an above
median delta value of SBP (SBP in examination n+1 –
SBP in examination n). Additionally, pulse pressure (PP)
(PP = SBP – DBP), mean arterial pressure (MAP) (MAP
= (2×DBP + SBP)/3)) and mid BP (�½ SBP + �½ DBP)
were investigated as secondary outcomes.
BP was measured according to the WHO guidelines
recommended by Rose & Blackburn (16). Using a Lon-
don School of Hygiene sphygmomanometer (17), BP
was measured one time on the non-dominant arm after
5-minute sitting rest. The fall of the mercury column was
set to 2 mm/s. The specially trained technicians were
instructed in the same way, and all conditions during
the measurements were identical at all examinations.
Assessment of covariates
A number of factors have previously been shown to be
associated both with exposure to OPA, such as occupa-
tional lifting, and BP. Thus, the following factors were
included as covariates: sex (male/female) (18); age
(<40, 40–49, 50–59, 60–69, 70–79, >80 years) (19);
body mass index (BMI) (<18.5, 18.5–24.9, 25.0–29.9,
≥30 kg/m
2
) (20) calculated from measured body height
and weight; smoking (non-smoking; currently smok-
ing) (21); length of education (no formal education;
low educated up to 3 years; vocationally educated
1–3 years; higher educated; academically educated)
(22); and, for the prospective analysis only, additional
adjustment for vital exhaustion, split in four categories
defined elsewhere (0, 1–4, 5–9, 10–17) (23); self-rated
cardiorespiratory fitness (lower, similar, higher cardio-
respiratory fitness compared to peers of same sex and
age) (24); SBP at baseline (80–89, 90–99, 100–109,
2
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Korshøj et al
110–119, 120–129, 130–139, ≥140 mmHg) (25), and
DBP at baseline (40–49, 50–59, 60–69, 70–79, 80–89,
≥90 mmHg).
Statistical analyses
The primary null-hypothesis for the cross-sectional
analysis was that heavy occupational lifting is not asso-
ciated to hypertension, defined as using antihypertensive
drugs or having a measured SBP ≥140 mmHg or DBP
≥90 mmHg. In the prospective analysis, the primary
null-hypothesis was that heavy occupational lifting at
baseline does not increase the incidence of new-onset
hypertension in normotensives.
The overall significance level was set at 0.05. How-
ever, Bonferroni corrections were applied meaning that
the two primary hypotheses were tested at a significance
level of 0.025 (13). The exploratory secondary analyses
were not tested for statistical significance but reported
by 95% confidence interval (CI).
Primary analyses
In the cross-sectional and prospective analyses, as a
function of heavy occupational lifting, the odds of being
hypertensive and becoming a SBP case, respectively,
were estimated using logistic regression in a generalized
estimating equation (GEE) model, with no exposure to
heavy occupational lifting were reference. Observa-
tions from the same person were treated as repeated
measurements. A first order autoregressive correlation
structure was assumed. The cross-sectional analysis was
controlled for sex, age, BMI, smoking and education.
In addition, the prospective analysis was controlled for
self-rated cardiorespiratory fitness, vital exhaustion, and
BP at baseline.
Secondary analyses
Linear regressions.
The associations between heavy occupa-
tional lifting and SBP, DBP,
PP and MAP
(mmHg) were
Figure 1.
Flow of the observations
and participants in the third, fourth
and fifth examination of the Copen-
hagen City Heart Study.
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Occupational lifting and risk for hypertension
investigated, first cross-sectionally and then prospectively
(change in mmHg from examination n to examination
n + 1), by use of linear regression models. These linear
regressions were applied to both the entire included popu-
lation as well as a population excluding those participants
who reported to use antihypertensive drugs.
Sensitivity to choice of comparison group.
To investigate
how sensitive the adjusted primary analyses were to
the choice of comparison group, we performed an addi-
tional linear regression with SBP as outcome only. Here
the comparison group was split into three different
subgroups according to the self-reported categories of
OPA, thus an exposure variable with four instead of two
categories was created.
Sensitivity to the definition of hypertension.
Due to the vari-
ety in cut-points for defining hypertension [SBP ≥160
mmHg or DBP ≥100 mmHg (14); SBP ≥180 mmHg or
DBP ≥110 mmHg (15, 26) or SBP ≥130 mmHg or DBP
≥80 mmHg (25)], we investigated whether the OR for
hypertension as a function of heavy occupational lifting
was sensitive to the cut-point for defining hypertension.
Thus, two additional cross-sectional logistic regression
analyses were conducted using alternative cut-points:
SBP ≥160 mmHg or DBP ≥100 mmHg and SBP ≥130
mmHg or DBP ≥80 mmHg.
Stratification by age.
Due to the lack of occupational
exposures as a result of old age pension (65 years) and/
or early retirement (60 years) at the follow-up examina-
tion, analysis similar to the primary analysis stratified
by age at baseline (≥ versus <50 years) were performed.
Results
From examination three, 5106 observations were
excluded: 2717 from examination four and 1689 from
examination five. Hence, 7052 and 4014 participants
were included in the cross-sectional and prospective
analyses, respectively (figure 1 and table 1).
Primary analysis
The crude primary cross-sectional analysis showed
that those performing heavy occupational lifting had
Table 1.
Baseline characteristics of the included participants for the cross-sectional analysis; 11 410 observations on 7052 participants, and for
the prospective analysis; 3890 observations on 2821 participants. [MVPA=moderate-to-vigorous physical activity; SD=standard deviation
Cross-sectional analysis
Age (years)
Sex (female)
BMI (kg/m
2
)
Smoking (current smokers)
Systolic blood pressure (mmHg)
Diastolic blood pressure (mmHg)
Blood pressure ≥90/≥140 mmHg
Using anti-hypertensive medication
Using diuretic medication
Hypertensive ( ≥90/≥140 mmHg or using
anti-hypertensive medication)
Hypertensive (≥80/≥130 mmHg or using
anti-Hypertensive medication)
Hypertensive (≥100/≥160 mmHg or using
anti-hypertensive medication)
Education (years)
No formal education
Low educated (<3)
Vocational education (1 – 3)
Higher education (>3)
Academic education
Occupational physical activity
Predominantly sedentary
Sitting or standing, some walking
Walking, some handling of material
Heavy manual work
Occupational heavy lifting (yes)
Leisure time physical activity (hours/week)
Inactive/light physical active (<2)
Light physical active (2-4)
Light physical active (>4) or MVPA (2-4)
MVPA (>4)
Vital exhaustion (sum, 0-17)
Cardiorespiratory fitness (similar to peers)
Observation per participant
Mean
48.9
25.2
131.1
80.4
SD
13.7
4.2
19.6
11.9
N (%)
6201 (54.3)
4211 (36.9)
4018 (35.2)
1117 (9.8)
477 (4.2)
4309 (37.8)
7211 (63.2)
2131 (18.7)
1577 (13.8)
1767 (15.5)
3069 (26.9)
2051 (18.0)
2770 (24.3)
4294 (37.6)
3992 (35.0)
2683 (23.5)
441 (3.9)
1795 (15.7)
983 (8.6)
5319 (46.6)
4378 (38.4)
699 (6.1)
6272 (55.0)
461 (11.8)
1490 (38.3)
1194 (30.7)
260 (6.7)
402 (10.3)
1445 (37.1)
1329 (34.2)
990 (25.4)
126 (3.2)
664 (17.1)
281 (7.2)
1899 (48.8)
1499 (38.5)
205 (5.3)
2235 (57.5)
Range
20.3–93.4
12.8–56.6
77.0–240.0
33.0–154.0
Mean
45.4
24.2
119.2
74.9
Prospective analysis
SD
11.7
3.6
10.6
8.3
N (%)
2341 (60.2)
1520 (39.1)
Range
20.3–81.9
16.0–48.4
82.0–139.0
42.0–89.0
86 (2.2)
68 (1.7)
3.0
1.6
3.5
0-17
1-3
2.9
1.4
3.3
0.0–17.0
1–2
4
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Korshøj et al
Table 2.
Crude and adjusted odd ratios (OR) of prevalence of being hypertensive (in the cross-sectional model) and for becoming a systolic blood
pressure (BP) case (in the prospective model) by self-rated exposure to heavy occupational lifting. No exposure to heavy occupational lifting was
reference. All models include a repeated statement. [CI=confidence interval.]
Heavy occupational lifting
N
Cross-sectional hypertensive
Prospective systolic case
b
Prospective diastolic case
b
a
b
a
Crude model
OR
1.12
1.11
1.11
95% CI
1.01–1.24
0.95–1.30
0.95–1.31
P-value
0.04
0.19
0.18
N
11 039
3668
3668
11 410
3890
3890
Adjusted model
OR
1.06
1.10
1.06
95% CI
0.94–1.20
0.92–1.31
0.88–1.27
P-value
0.34
0.29
0.54
The cross-sectional model is adjusted for sex, age, BMI, smoking and education.
The prospective model is adjusted for sex, age, body mass index, smoking, education, self-rated cardiorespiratory fitness, vital exhaustion and BP at baseline.
Table 3.
Adjusted associations between self-reported heavy occu-
pational lifting and systolic blood pressure (BP) (mmHg), diastolic BP
(mmHg), pulse pressure (mmHg) and mean arterial pressure (mmHg),
stratified on use of anti-hypertensive. Occupational physical activity
groups are clustered by answering “yes” or “no” to exposure to heavy
occupational lifting; “yes” are in the heavy lifting category and “no”
are divided in the other categories set by their self-reported level of
occupational physical activity where the categories of walking, some
handling of material AND heavy manual work, but no heavy lifting are
collapsed. [CI=confidence interval]
Heavy occupational
lifting
NOT using
anti-hypertensives
Systolic BP
Diastolic BP
Pulse pressure
Mean arterial pressure
USING anti-hypertensives
Cross-sectional
a
β
(mmHg)
95% CI
9945 observations
6574 participants
0.45
-0.45–1.35
0.34
-0.25–0.94
0.12
-0.59–0.83
0.36
-0.26–0.99
Prospective
b
β
(mmHg)
95% CI
3589 observations
2752 participants
-0.08
-1.29–1.14
-0.02
-0.84–0.81
0.01
-1.04–1.07
-0.03
-0.87–0.80
outcomes either in the cross-sectional or in the prospec-
tive analyses (supplementary material,
www.sjweh.fi/
show_abstract.php?abstract_id=3850,
table S1). The
linear regressions relating heavy occupational lifting to
BP, stratified on use of anti-hypertensives, showed that,
among participants not using anti-hypertensives, no sig-
nificant associations between heavy occupational lifting
and any of the BP outcomes neither cross-sectionally
nor prospectively were seen (table 3). Also among
users of anti-hypertensives no significant associations
were seen cross-sectionally (table 3). However, positive
associations between heavy occupational lifting and SBP
and MAP were seen prospectively among users of anti-
hypertensives (table 3).
Sensitivity to choice of comparison group
By stratifying the participants by their self-reported
level of OPA the sensitivity to choice of comparison
group of the secondary linear regression was tested.
However, this analysis did not show any significant
associations neither in the cross-sectional nor the pro-
spective analysis (supplementary file, table S2).
Sensitivity to definition of hypertension
1096 observations
84 observations
967 participants
79 participants
Systolic BP
-1.98
-5.22–1.26
15.91
5.30–26.52
Diastolic BP
-0.38
-2.43–1.67
4.02
-2.21–10.27
Pulse pressure
-1.59
-4.44–1.27
7.87
-0.06–15.80
Mean arterial pressure
-0.94
-3.05–1.18
7.46
0.67–14.24
a
Adjusted for sex, age, body mass index, smoking and education.
b
Adjusted for sex, age, body mass index, smoking, education, self-rated car-
diorespiratory fitness, vital exhaustion and BP at baseline.
a 12% higher prevalence for hypertension than the
non-exposed. However, when adjusting for relevant
confounders, heavy occupational lifting did not affect
the prevalence of hypertension (table 2). The prospective
models did not show significantly increased risks for
becoming a SBP or DBP case when exposed to heavy
occupational lifting (table 2).
Secondary analyses
Linear regressions.
Secondary analyses were performed
by linear regressions to investigate the differences in
SBP, DBP, PP, and MAP between participants exposed,
or not, to heavy occupational lifting (13). The linear
regressions relating heavy occupational lifting to BP
showed no significant associations with any of the BP
The sensitivity analyses applying cut-points for the defi-
nition of hypertension being higher (SBP ≥160 mmHg or
DBP ≥100 mmHg) and lower (SBP ≥130 mmHg or DBP
≥80 mmHg) than the cut-point used in the primary anal-
ysis (SBP ≥140 mmHg or DBP ≥90 mmHg), showed that
the OR for being hypertensive as a function of heavy
occupational lifting was sensitive to the cut-points for
definition of hypertension. By application of the higher
cut-points, no relation between risk for hypertension and
heavy occupational lifting was seen (OR 0.96, 95% CI
0.82–1.11), whereas the lower cut-points showed a ten-
dency towards an increased OR for being hypertensive
when exposed to heavy occupational lifting (OR 1.13,
95% CI 0.99–1.28).
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Occupational lifting and risk for hypertension
Table 4.
Adjusted odd ratios (OR) for being hypertensive, in the cross-sectional model, and for becoming a systolic blood pressure (BP) case, in the
prospective model, stratified on age at baseline (≥ vs. < 50 years). No exposure to heavy occupational lifting was reference. All models include a
repeated statement. [CI=confidence interval]
Heavy occupational lifting
N
a
Age ≥50 years
OR
95% CI
P-value
N
Age <50 years
OR
95% CI
P-value
0.36
0.77
0.59
Cross-sectional hypertensive
5670
1.06
0.90–1.24
0.50
5371
1.09
0.90–1.32
Prospective systolic case
b
1435
1.22
0.90–1.66
0.20
2233
1.03
0.83–1.30
Prospective diastolic case
b
1435
1.30
0.97–1.73
0.08
2233
0.94
0.74–1.19
a
Adjusted for sex, age, body mass index, smoking and education.
b
Adjusted for sex, age, body mass index, smoking, education, self-rated cardiorespiratory fitness, vital exhaustion and BP at baseline.
Age stratified analysis
The cross-sectional and prospective analyses among both
participants
<50 and ≥50 years old showed that heavy
occupational lifting did not affect the odds for being
hypertensive or
becoming a SBP or DBP case (table 4).
However, a tendency of an increased risk for becoming
a DBP case was seen among participants ≥50 years old.
Discussion
This study aimed to investigate cross-sectional and
prospective relations between heavy occupational lift-
ing and hypertension. Neither the cross-sectional nor
the prospective analysis could reject the primary null-
hypothesis of no effect of heavy occupational lifting
on the prevalence nor incidence of hypertension since
non-significant increases in the prevalence and incidence
of hypertension by 6% and 10%, were seen (table 2).
The secondary analyses showed large rises in BP (ΔSBP
16 mmHg, 95% CI 5–27 mmHg, and ΔMAP 7 mmHg,
95% CI 1–14 mmHg, table 3) among participants using
anti-hypertensives when exposed to heavy occupational
lifting. Another sensitivity analysis indicated that par-
ticipants aged ≥50 years were at 30% increased risk (OR
1.30, 95% CI 0.97–1.73) for becoming a DBP case when
exposed to heavy occupational lifting. Further investiga-
tions of these associations are therefore warranted for
prevention of hypertension, particularly across older
workers and workers using anti-hypertensives.
These indications of increases in BP can be explained
by the acutely increasing effect on BP from lifting, due
to the acute increases in total peripheral resistance from
the occlusion of vessels by the static muscle activity (2,
28). However, longitudinal studies show that leisure
time resistance training lowers BP (29, 30), which
may be explained by the physiologic adaptations in the
cardiorespiratory system, taking place during restitu-
tion, leading to beneficial effects as increased cardio-
respiratory fitness (28). Yet, the lack of these beneficial
effects from OPA could be explained by the insufficient
recovery due to the high frequency (5 days a week) and
long duration (7–9 hours per day) (31, 32). Across some
occupations, heavy occupational lifting is a part of OPA,
and could therefore prospectively raise BP due to the
high frequency and duration of lifting combined with an
insufficient recovery (3). However, studies investigating
the relation between heavy occupational lifting and BP
are few and conflicting (4, 5, 33).
One major challenge in this research field is the
healthy worker selection, described as workers migrat-
ing away from occupations with high OPA into more
sedentary occupations (34). This selection could be
based on symptoms of deteriorated health, eg, angina
pectoris. Hypertension could be seen as non-symptom-
atic, however high SBP are thought to impact risk for
angina (35). Future analysis should therefore investigate
relations between heavy occupational lifting and risk
factors for cardiovascular disease (CVD) by use of non-
symptomatic outcomes or precursors of hypertension to
bypass the healthy worker selection.
The secondary analyses revealed two sub-groups:
users of anti-hypertensives and participants aged ≥50
years as being particularly vulnerable for exposure to
heavy occupational lifting.
The prospective linear associations relating heavy
occupational lifting to BP, stratified on use of anti-
hypertensives, showed large rises in BP (ΔSBP 16
mmHg, 95% CI 5–27 mmHg, and ΔMAP 7 mmHg, 95%
CI 1–14 mmHg, table 3) among users of these medica-
tions. Additionally, the 95% CI for the prospective linear
relations between heavy occupational lifting and ΔDBP
and ΔPP likewise indicated clinically relevant hazardous
increases (25). These increases in BP may be explained
by these participants being more susceptible to having a
low compliance in the arteries due to decreased elastic-
ity caused by the endothelia damage from the increased
level of mean arterial pressure (36) initially causing
the use of anti-hypertensives. Low arterial compliance
decreases the ability of the arteries to dilate sufficiently
when the blood are being pumped from the heart, this
combined with occlusion of the vessels during static
activities, such as lifting, will lead to major increases
of the BP (28).
6
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Korshøj et al
The estimated OR from the analysis stratified by
age (</≥ 50 years) showed tendencies of stronger asso-
ciations between heavy lifting and hypertension among
participants aged ≥50 years (OR of becoming a SBP case
of 1.22 and a DBP case of 1.30) compared to among
participants aged <50 years (1.03 and 0.94) (table 4).
This can be explained by the age and health-dependent
decreases in aerobic capacity, leading to increased car-
diorespiratory load from performing heavy occupational
lifting (37). Also, the age-dependent loss of compliance
in the arteries
contributes to increases in BP due to the
increased total peripheral resistance (28, 38).
The literature proposes differences in cut-points
for being classified as hypertensive (15, 26, 27), and
therefore two additional cut-points of hypertension [SBP
≥160 mmHg or DBP ≥100 mmHg (15, 26) and SBP
≥130 mmHg or DBP ≥80 mmHg (27)] were applied
to
the cross-sectional analyses. These sensitivity analyses
showed that the OR for being hypertensive as a func-
tion of heavy occupational lifting seemed to be sensitive
to the choice of cut-point; the cut-point of SBP ≥130
mmHg or DBP ≥80 mmHg yielded an OR of 1.13,
whereas the cut-point of SBP ≥160 mmHg or DBP ≥100
mmHg yielded an OR of 0.96, and the cut-point of SBP
≥140 mmHg or DBP ≥90 mmHg yielded an OR of 1.06.
Taken together, this paper contributes to the knowl-
edge of risk for hypertension from heavy occupational
lifting and sheds light on the need for specific attention
among those performing heavy occupational lifting
while using anti-hypertensives (25). These results could
therefore feed into prevention initiatives of hypertension
specifically targeted workers exposed to heavy occupa-
tional lifting.
Methodological challenges
These analyses should be interpreted in light of the
present limitations: the self-reported exposure to heavy
occupational lifting and level of cardiorespiratory fitness
might be affected by recall bias (39, 40); self-reported
data are only collected from participants at the examina-
tions, which could add a selection bias to the collected
data. To collect exposures of heavy lifting independently
of participation, future studies could consider receiving
the exposure data from job exposure matrices, addition-
ally could the recall bias be bypassed by use of technical
measures of exposure to heavy occupational lifting. The
collection of BP only in consultation during rest gives
a lower prognostic value than obtained by monitoring
of 24 hours BP or BP during sleep (41, 42); and the
lowered odds for having prolonged working hours when
exposed to heavy occupational lifting (33), which was
not possible to adjust for in the present analysis due to
the lacking information of amount of weekly working
hours. Future studies investigating these relations could
consider collecting the exposure information by use of a
job exposure matrix or technical measures, not holding
the limitations of being self-reported.
However, the analysis also holds some strengths; the
follow-up time of 8–10 years and the determination of
hypertension based both on use of prescription medicine
and the resting BP in mmHg, limiting the risk of clas-
sifying participant as false negative. Also the randomly
selected study population is a strength as well as the
inclusion criteria of no use of antihypertensive medicine,
as these medications potentially may conceal, reverse
or otherwise distort effects of heavy occupational lift-
ing on BP. In line with this, participants diagnosed
with hypertension at baseline were excluded from the
prospective analysis because they were likely to receive
antihypertensive medication in the time period between
examinations. On the other hand, exclusion of those par-
ticipants being diagnosed as hypertensive and/or using
anti-hypertensives decreases variability of the analyzed
population towards a more healthy population and
thereby lacks the potential of investigating the effects of
heavy occupational lifting among a population propos-
edly at higher risk for cardiovascular endpoints (31).
Implications of the results
Heavy lifting acutely increases BP (2). Approximately
22% of Danish workers and 32% of European workers
are regularly exposed to heavy occupational lifting (12)
(6
th
survey in Eurofound), and due to the frequency
and duration of the occupational lifting, it is likely that
increases in BP and hypertension will occur (3). Hyper-
tension is a major risk factor for CVD and mortality (7,
8, 10). In spite of this, the Danish Working Environment
Authority guideline for occupational lifting from 2005
(arbejdstilsynet.dk/da/regler/at-vejledninger/l/d-3-
1-loft-traek-og-skub)
only concerns risk factors for
musculoskeletal disorders. Therefore we conducted this
study to feed into the discussion on cardiovascular risk
factors from heavy occupational lifting. This study finds
that the prevalence and incidence of hypertension, to
some extent, may increase by exposure to heavy occu-
pational lifting. Although these OR are uncertain, the
indications of rises in risk for hypertension up to 10%
might still be of preventive importance for the general
working population.
Secondly, the results showed that workers using
anti-hypertensives would be expected to experience
rises in SBP – from exposure to heavy occupational
lifting – by 16 mmHg, which indicates a major increase
in CVD risk (7, 9, 25). Also older workers (aged ≥50
years old at baseline) seemed to be more vulnerable to
developing hypertension from exposure to heavy occu-
pational lifting than younger workers (aged <50 years
old at baseline). Hence, exposure to heavy occupational
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2081317_0009.png
Occupational lifting and risk for hypertension
lifting could impact the workability as well as employ-
ability among workers aged ≥50 years old or those who
use anti-hypertensives due to the fact that high SBP
are thought to impact risk for angina (35), and thereby
migration from occupations exposed to heavy occupa-
tional lifting to occupations with more light physical
activity levels. Thus, it could be considered that tailor-
ing the exposure to heavy occupational lifting to the age
and general health of the worker would impact risk for
hypertension and work sustainability beneficially.
These results suggest that the risk for hypertension
might be lowered by reducing the exposure to heavy
occupational lifting, especially among workers using
anti-hypertensives and aged ≥50 years. These results are
drawn among participants who showed up at examina-
tions in a randomly selected adult Danish population
and since the work environmental laws and regulations
of occupational lifting are the same in the entire nation,
we believe that the result of the study to some extent
may be generalized to the entire Danish workforce. Yet,
these conclusions are solely based on those who partici-
pated in examinations and, thus, a future investigation
of this association might benefit from a study design
not dependent on participation, such as a job exposure
matrix. Nonetheless, knowledge is still needed to verify
these findings and also to investigate the effect of accu-
mulation of exposure from heavy occupational lifting on
hypertension. Future studies investigating these relations
could consider collecting the exposure information by
use of job exposure matrices or technical measures,
without the limitations of being self-reported.
Concluding remarks
No associations between heavy occupational lifting and
prevalence and incidence of hypertension were seen
among the general population. The secondary analyses
showed positive associations between heavy occupa-
tional lifting and risk of hypertension among two vul-
nerable sub-groups, ie, (i) users of anti-hypertensives,
and (ii) workers aged ≥50 years. Yet, these conclusions
should be interpreted with the methodological limita-
tions of this study in mind, and therefore further research
is needed to confirm these associations.
Conflicts of interest
None declared.
number 20150067515. We would also like to thank
Niklas Krause for valuable discussions.
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Received for publication: 12 April 2019
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