The association between long-term night shift work and metabolic syndrome: a cross-sectional study of male railway workers in southwest China

Abstract

Objectives
Metabolic syndrome (MetS) increases the risk of new diabetes and cardiovascular disease. Night shift work (NSW) may influence metabolic disturbance and lead to MetS. This study aims to investigate the association between long-term NSW (≥ 10 years) and MetS combined with its components in male railway workers in southwest China.

Methods
11,023 male railway workers with long-term NSW of more than 10 years in the Physical Examination Center of the Affiliated Hospital of Chengdu University were enrolled. The basic data were collected by investigators and blood test results were collected. The primary outcome was the prevalence of metabolic syndrome. The results were analyzed using statistical software SPSS 22.0.

Results
In total, 11,023 people over the age of 40 with more than 10 years of working experience were enrolled, and 4759 (43.2%) participants had a diagnosis of MetS. The basic data indicated that night shift workers tended to be younger, shorter working years, but with higher body mass index and longer hip circumference (p < 0.05). The adjusted analysis revealed that there was no significant association between NSW and metabolic syndrome (OR 1.03, 95% CI 0.94–1.12, p = 0.543). NSW was associated with SBP ≥ 130 mmHg (OR 1.11, 95% CI 1.02–1.21, p < 0.001) and waist circumference ≥ 90 cm (OR 1.11, 95% CI 1.02–1.21, p < 0.001).

Conclusions
Long-term night shift workers had a higher prevalence of MetS. However, long-term NSW is not associated with a significantly increased risk of metabolic syndrome in male railway workers in southwest China. Long-term NSW is associated with elevated SBP, and waist circumference increase.

Full text

Dongetal. BMC Cardiovascular Disorders (2022) 22:263
https://doi.org/10.1186/s12872-022-02705-7
RESEARCH
The association betweenlong-term
night shift work andmetabolic syndrome:
across-sectional study ofmale railway workers
insouthwest China
Chaohui Dong1, Honglian Zeng1*, Bo Yang1, Yi Zhang1 and Zhitao Li2
Abstract
Objectives: Metabolic syndrome (MetS) increases the risk of new diabetes and cardiovascular disease. Night shift
work (NSW) may influence metabolic disturbance and lead to MetS. This study aims to investigate the association
between long-term NSW (≥ 10 years) and MetS combined with its components in male railway workers in southwest
China.
Methods: 11,023 male railway workers with long-term NSW of more than 10 years in the Physical Examination
Center of the Affiliated Hospital of Chengdu University were enrolled. The basic data were collected by investigators
and blood test results were collected. The primary outcome was the prevalence of metabolic syndrome. The results
were analyzed using statistical software SPSS 22.0.
Results: In total, 11,023 people over the age of 40 with more than 10 years of working experience were enrolled,
and 4759 (43.2%) participants had a diagnosis of MetS. The basic data indicated that night shift workers tended to
be younger, shorter working years, but with higher body mass index and longer hip circumference (p < 0.05). The
adjusted analysis revealed that there was no significant association between NSW and metabolic syndrome (OR 1.03,
95% CI 0.94–1.12, p = 0.543). NSW was associated with SBP ≥ 130 mmHg (OR 1.11, 95% CI 1.02–1.21, p < 0.001) and
waist circumference ≥ 90 cm (OR 1.11, 95% CI 1.02–1.21, p < 0.001).
Conclusions: Long-term night shift workers had a higher prevalence of MetS. However, long-term NSW is not associ-
ated with a significantly increased risk of metabolic syndrome in male railway workers in southwest China. Long-term
NSW is associated with elevated SBP, and waist circumference increase.
Keywords: Metabolic syndrome, Night shift work, Occupational health
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Introduction
Metabolic syndrome (MetS) is a disease syndrome char-
acterized by abdominal obesity, hypertension, hyper-
glycemia, high triglyceride (TG), and low high-density
lipoprotein (HDL), which increased the risk of new dia-
betes and cardiovascular disease [1, 2]. With the develop-
ment of the social economy and the improvement of per
capita living standards, the incidence of metabolic syn-
drome is on the rise [3, 4]. Precious studies indicated that
Open Access
*Correspondence: zenghonglianhl@163.com
1 Department of Health Management Center, Clinical Medical College
and Affiliated Hospital of Chengdu University, Chengdu University, Sichuan
Province, Jinniu District, Chengdu City 610081, China
Full list of author information is available at the end of the article
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Dongetal. BMC Cardiovascular Disorders (2022) 22:263
people with MetS were at increased risk of cardiovascu-
lar events [5], however, there may be gender differences
[6, 7]. MetS evaluated BP, plasma glucose, apo B-contain-
ing lipoprotein, and inflammatory cytokines, which leads
to atherosclerotic plaque development and rupture [8, 9].
Rotating NSW refers to work day and night because
of the nature of the jobs, which can lead to sleep rhythm
inversion and disturbance [10, 11]. e prevalence of
NSW ranged from 20.88%to 45.5% according to different
types of work and were higher in women [12–14]. Previ-
ous studies showed that occupations such as nursing may
require long night shifts, which may associate with a sta-
tistically significant but small absolute increase in CHD
risk [15, 16]. Other studies concentrated on the associa-
tion between NSW and MetS, however, the results were
inconsistent [6, 7, 12, 14]. Some studies have suggested
that NSW and sleep quality may be associated with an
increased risk of MetS [12, 14], while others have sug-
gested the opposite, especially in male patients [6, 7].
NSW also influenced the hepatorenal function of night
shift workers, studies on Japanese workers showed that
shift work and awaking in the night increased the risk of
chronic kidney diseases [17, 18], while a 4-year cohort
study of 15,871 workers indicated that shift work is asso-
ciated with hyperuricemia [19]. e previous study has
shown that liver function is also affected by NSW [20].
However, previous systematic reviewed retrieved origi-
nal reviews and found some methodological problems
presented in these studies, such as waist circumference
being replaced by body mass index [21]. On the other
hand, study indicated that the short time of NSW do not
increase the risk of CVD [15].
Since most of the previous studies focused on female
nurses, there was no accurate description of the length
of NSW. We therefor do the study aims to investigate
the association between long-term NSW (more than
10years) and MetS combine with its components in male
railway workers in southwest China.
Methods
Study population
A cross-sectional survey was conducted in the Physical
Examination Center of the Affiliated Hospital of Chengdu
University from January 2020 to December 2020. Railway
workers from Sichuan, Chongqing, and Guizhou prov-
inces were enrolled in our study.
Patient andpublic involvement
All included participants voluntarily participated in this
study and signed the informed consent form. is study
was approved by the Affiliated Hospital of Chengdu
University.
Inclusion andexclusion criteria
Inclusion criteria: People over 40 years of age and 10
working years were included in this study. Exclusion cri-
teria are as follows: severe hepatic and renal insufficiency;
malignant tumor; incomplete basic information or blood
test data.
Data collection
Basic data are collected by the health train, which
passes along the railway and conducts health check-ups
for employees. e investigators used questionnaires
designed by professionals to collect the data, includ-
ing basic demographic information (age, sex), health
behaviors (alcohol consumption, smoking), and history
of chronic diseases (hypertension and diabetes, cardio-
vascular diseases). e body mass index (BMI) was cal-
culated as weight in kilograms (measured to the nearest
0.1kg by a uniform scale)divided by the square of height
in meters (measured to the nearest 0.1 cm by uniform
height ruler). Waist circumference was measured to the
nearest 0.1cm at the end of normal expiration on bare
skin, midway between the lower rib margin and iliac crest
by a uniform flexible rule. Blood pressure readings were
taken from the participants’ resting blood pressure in the
morning. Blood samples were obtained in the morning,
including blood lipid, creatinine (Cr), uric acid (UA), liver
function, fasting blood glucose (FBG). e biochemical
parameters were measured at the laboratory of the Affili-
ated Hospital of Chengdu University. All control values
were consistent with the standards recommended by
the medical laboratory of the China Center for Disease
Control and Prevention. All laboratory technicians were
trained in formal laboratory biosafety and biosecurity
procedures.
Denitions
e definition of MetS has been updated over time [2],
and we used the following definitions according to the
American Heart Association [1] (at least 3 of the follow-
ing 5 risk factors are present): abdominal obesity: waist
circumference ≥ 90cm for men and ≥ 80cm for women;
hypertension: systolic blood pressure (SBP) ≥ 130 mm
Hg or diastolic blood pressure (DBP) ≥ 85 mm Hg or
current use of antihypertensive medication; hyper-
glycemia: fasting plasma glucose (FBG) ≥ 100 mg/dl
(5.6mmol/l) or current use of antidiabetic medication;
low HDL: HDL < 40mg/dl (1.04mmol/l) or current use
medication treatment; and hypertriglyceridemia: triglyc-
eride ≥ 150 mg/dl (1.7 mmol/l) or current use of medi-
cation treatment for elevated triglyceride. Overweight
was defined as a BMI ≥ 24.0 kg/m2, according to the
cut-off points for Chinese adults. Smoking status was
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Dongetal. BMC Cardiovascular Disorders (2022) 22:263
categorized according to 1year of smoking at least one
cigarette per day. Alcohol consumption was considered
in terms of whether the participant consumed alcohol
at least 12 times in 1year. Based on previous literature
[10, 11], NSW was defined as working during the even-
ing and overnight hours (6 P.M.–8 A.M). e working
rhythms were provided by the Chengdu Railway Bureau,
the working rhythms varies from different types of job.
Statistical analysis
All data were analyzed using SPSS statistical software
(version 22.0). e means and standard deviations of
the continuous variables were provided. Student’s t-test
was used to test the differences in the means of the con-
tinuous variables, and the chi-square test was used to
test the differences in the categorical variables. We did
stratified analysis by age and working years. We applied
univariate logistic regression models to assess the asso-
ciation of NSW and covariates with MetS, and their odds
ratios (OR) and 95% confidence intervals (CI) were esti-
mated. We employed multivariable logistic regression
models (model 1) to analyze the association between the
independent variable (NSW) and the dependent vari-
able (MetS).Model 2 was adjusted for age, model 3 was
adjusted for age and working years, model 4 was adjusted
for age, working years, smoking status, alcohol consump-
tion, and previous CAD. We also analyzed the association
between NSW and the components of MetS. Bonferroni
adjustment was used as post hoc comparisons to adjust
for type I error, p value below 0.05 (p < 0.05) was consid-
ered as statistically significant.
Results
Baseline characteristics ofthestudy population
In total, 11,023 participants including 3008 night shift
workers were enrolled in the study (Fig.1). Because of the
special nature of the job, all night shift workers enrolled
were male. e basic data indicated that night shift work-
ers tended to be younger, shorter working years, but
with higher BMI and longer hip circumference (p < 0.05).
Night shift workers accompanied with a lower propor-
tion of hypertension (HBP), diabetes (DM), and coronary
artery disease (CAD) when compared with day work-
ers (p < 0.05). We found night shift workers had a higher
level of ALT, Cr, and UA as well (31.1 ± 17.1 mmol/L vs
30.2 ± 17.4 mmol/L, p = 0.019; 75.0 ± 13.2 mmol/L vs
73.8 ± 13.6 mmol/L, p < 0.001; 394.8 ± 81.1 mmol/L vs
391.0 ± 83.5 mmol/L, p = 0.032). e baseline character-
istics of the participants were shown in Table1.
Mean value andprevalence ofeach criterion forMetS
e study indicated that night shift workers had a
lower level of SBP and FBG (126.7 ± 15.0 mmHg
vs 127.7 ± 16.5 mmHg, p < 0.001; 5.9 ± 1.7 mmol/L
vs 6.0 ± 1.0 mmol/L, p < 0.001). e level of DBP
was higher in night shift workers than day workers
(85.1 ± 11.9 mmHg vs 83.8 ± 8.3 mmHg , p < 0.001,
Table1). A total of 4759 participants had a diagnosis of
MetS, the overall crude prevalence of MetS was 43.2%.
4979 participants had 1 or 2 components of MetS, while
only 11.7% participants had none. Day workers seemed
to have a higher proportion of abnormal blood pres-
sure and blood sugar (61.9% vs 58.6%, 45.5% vs 40.8,
p < 0.05). Night shift workers tended to have a higher
proportion of low HDL (24.9% vs 22.6, p = 0.013). How-
ever, there was no significant difference in the preva-
lence of MetS between the two groups (42.6% vs 43.4%,
p = 0.472, Table2).
Age andworking years stratied analysis ofMetS
Due to the difference in age and length of service
between night shift workers and day workers, we con-
ducted a subgroup analysis by age and length of ser-
vice stratification. e resulted indicated that the
overall prevalence of MetS in 40–45, 45–50, 50–55
and ≥ 55 years old were 40.5%, 41.3%, 45.2%, 47.5%.
e overall prevalence of MetS in 10–20, 20–25, 25–30,
30–35, and ≥ 35working years were 43.1%, 40.1%,
41.6%, 43.3% and 47.6%. However, no significant dif-
ference was found between night shift workers and
day workers in all age groups and all working year sub-
groups (p ˃0.05, Additional file1: Fig. S1).
Fig. 1 Flow chart of sample inclusion and exclusion
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Dongetal. BMC Cardiovascular Disorders (2022) 22:263
Associations betweennight shift workers andmetabolic
syndrome
We conducted an analysis of the association between
NSW and MetS with its components. e univariate
analysis revealed that there was no significant associa-
tion between NSW and MetS (OR 0.97, 95% CI 0.89–
1.06, p = 0.472, Table3). is result was also confirmed
after adjusting for age, working years, smoking status,
alcohol consumption, and previous CAD (OR 1.03, 95%
CI 0.94–1.12, p = 0.543). However, the adjusted model
found that NSW was associated with SBP ≥ 130 mmHg
(OR 1.11, 95% CI 1.02–1.21, p < 0.001) and Waist cir-
cumference ≥ 90 cm (OR 1.11, 95% CI 1.02–1.21,
p < 0.001).
Table 1 Basic characteristics of the study population
BMI, body mass index; HBP, hypertension; DM, diabetes mellitus; CAD, coronary atherosclerotic heart disease; SBP, systolic blood pressure; DBP, diastolic blood
pressure; TC, total cholesterol; TG, triglyceride; LDL, low density lipoprotein cholesterol; HDL, high-density lipoprotein cholesterol; hsCRP, hypersensitive C-reactive
protein; FBG, fasting blood glucose
Characteristics Night shift workers
(n = 3008) Day workers (n = 8015) Overall p value
Age (mean ± SD, y) 47.5 ± 3.5 49.4 ± 4.9 48.9 ± 4.7 < 0.001
Working years(mean ± SD, y) 28.6 ± 4.2 30.5 ± 5.7 30.0 ± 5.4 < 0.001
BMI (mean ± SD, kg/m2) 25.2 ± 3.1 24.8 ± 3.1 24.9 ± 3.1 < 0.001
Hip circumference (mean ± SD, cm) 96.1 ± 6.3 95.6 ± 6.1 95.7 ± 6.1 0.024
Smoking status (n, %) 0.599
Current smoker 1973 (65.6) 5250 (65.5) 7223 (65.5)
Former smoker 263 (8.7) 659 (8.2) 922 (8.4)
Never-smoker 772 (25.7) 2106 (26.3) 2878 (26.1)
Alcohol consumption (n, %) < 0.001
Current drinker 542 (18.0) 1980 (24.7) 2522 (22.9)
Former drinker 46 (1.5) 191 (2.4) 237 (2.2)
Never-drinker 2420 (80.5) 5844 (72.9) 8264 (75.0)
HBP (n, %) 579 (19.2) 1728 (21.6) 2307 (20.9) 0.008
DM (n, %) 205 (6.8) 710 (8.9) 915 (8.3) 0.001
CAD (n, %) 12 (0.4) 98 (1.2) 110 (1.0) < 0.001
SBP (mmHg) 126.7 ± 15.0 127.7 ± 16.5 127.4 ± 16.1 < 0.001
DBP (mmHg) 85.1 ± 11.9 83.8 ± 8.3 84.7 ± 11.7 < 0.001
TC (mmol/L) 5.1 ± 0.9 5.1 ± 0.9 5.1 ± 1.0 0.051
TG (mmol/L) 2.3 ± 2.1 2.3 ± 2.0 2.3 ± 2.1 0.693
LDL (mmol/L) 3.1 ± 0.7 3.1 ± 0.7 3.1 ± 0.7 0.478
HDL (mmol/L) 1.2 ± 0.3 1.3 ± 0.3 1.3 ± 0.3 < 0.001
hsCRP (mg/l) 2.4 ± 3.4 2.6 ± 4.3 2.5 ± 4.1 0.095
FBG (mmol/L) 5.9 ± 1.7 6.0 ± 1.0 6.0 ± 1.9 < 0.001
ALT (U/L) 31.1 ± 17.1 30.2 ± 17.4 30.5 ± 17.4 0.019
Cr (μmol/L) 75.0 ± 13.2 73.8 ± 13.6 74.1 ± 13.5 < 0.001
UA (mmol/L) 394.8 ± 81.1 391.0 ± 83.5 392.0 ± 82.9 0.032
Table 2 Prevalence of each criterion for metabolic syndrome (n, %)
Characteristics Nitht shift workers
(n = 3008) Day workers
(n = 8015) Overall (n = 11,023) p value
Waist circumference (≥ 90 cm for men) 1304 (43.4) 3313 (41.3) 4617 (41.9) 0.056
Blood pressure (≥ 130/85 mm Hg or under medications) 1763 (58.6) 4963 (61.9) 6726 (61.0) 0.001
Fasting blood sugar (≥ 5.6 mmol/L or under medications) 1228 (40.8) 3646 (45.5) 4874 (44.2) < 0.001
Triglycerides (≥ 1.7 mmol/L or under medications) 1612 (53.6) 4173 (52.1) 5785 (52.5) 0.153
High-density lipoprotein (< 1.04 mmol/L) 748 (24.9) 1813 (22.6) 2561 (23.2) 0.013
Metabolic syndrome (≥ 3 fac tors) 1282 (42.6) 3477 (43.4) 4759 (43.2) 0.472
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Dongetal. BMC Cardiovascular Disorders (2022) 22:263
Discussion
is cross-sectional study examined the association
between long-term NSW and metabolic syndrome and
found that long-term NSW was not associated with an
significantly increased risk of MetS. Night shift workers
tended to have a higher proportion of low HDL when
compared with day workers. No significant difference
was found between night shift workers and day workers
in all age groups and all working year subgroups.
Pervious study concentrated on nurses indicated that
a longer duration of rotating NSW was associated with
an increased risk in CHD [15], our study focuses on
another special character, train drivers, who work the
same round-the-clock shifts. Our present study showed
the overall crude prevalence of metabolic syndrome was
43.2%, which was higher than previous studies [7, 22].
is result may be related to the high incidence of hyper-
tension and diabetes in China, which is currently in the
third to the fourth stage of epidemiology [23, 24]. Our
study suggested that shift workers had a higher level of
BMI and hip circumference, which was consistent with
previous studies [25, 26]. However, night shift workers
had a lower proportion of history of chorionic diseases
such as hypertension, DM, and coronary heart dis-
eases. So the influence of NSW on MetS could be quite
important.
e association between NSW and MetS can be
explained by the following reasons. First, it is reported
that NSW leads to sleep loss and increases the risk of
obesity and diabetes [27]. On the other hand, irregular
food intake influence energy balance and weight regula-
tion, which lead to metabolic disturbance [28, 29]. Sec-
ond, circadian disruption and eating meals irregularly
disturb the natural rhythmicity of insulin action and
lead to insulin resistance and obesity [30–32]. ird, it is
reported that the gene REV-ERBα, which regulates circa-
dian rhythms, is associated with liver lipid metabolism,
which influence metabolic disturbance [33, 34]. ere-
fore, NSW are key regulators of metabolic disturbance,
which can affect metabolic syndrome.
NSW may result in a higher risk of liver disfunction
and non-alcoholic fatty liver disease [20, 35], our pre-
sent study consisted of the previous results. Shift work
also has a confluence on renal function according to
our study, shift workers showed a higher level of creati-
nine and uric acid. Animal study suggest that circadian
rhythm reversals may affect renal metabolic rhythms,
which may result in impaired kidney function [36]. How-
ever, no significant differences in TC, TG, and LDL-C
were found between groups. Previous studies found that
NSW may lead to higher risk of dyslipidemia and related
to a higher risk of cardiovascular diseases [37, 38]. e
association between shift work and lipid may need fur-
ther studies.
Our study indicated that railway workers had a high
prevalence of waist circumference increase, hypergly-
cemia, and high triglycerides over 40%, while the preva-
lence of hypertension was 60%. e railway workers are
in poor health. Night shift workers had a higher preva-
lence of waist circumference increase and low LDL-C
when compared with day workers, which was consistent
with the previous study [15]. Hypertension and hyper-
glycemia were more common among day workers, which
may be related to different lifestyles. However, the overall
prevalence of metabolic syndrome of night shift workers
and day workers showed no significant difference.
Table 3 Associations between NSW and METS with its components
Model 1 No adjusted
Model 2 Adjusted for age
Model 3 Adjusted for age and working years
Model 4 Adjusted for age, working years, smoking status, alcohol consumption, and previous CAD
SBP, systolic blood pressure; DBP, diastolic blood pressure; BMI, body mass index; TG, triglyceride; HDL- C, high-density lipoprotein cholesterol; DM, diabetes mellitus;
FBG, fasting blood glucose; METS, Metabolic syndrome
Factors Model 1 Model 2 Model 3 Model 4
OR (95% CI) p value OR (95% CI) p value OR (95% CI) p value OR (95% CI) p value
SBP ≥ 130 mmHg 0.97 (0.89, 1.05) 0.446 1.08 (0.99, 1.18) 0.082 1.08 (0.99, 1.18) 0.082 1.11 (1.02, 1.21) 0.022
DBP ≥ 85 mmHg 0.88 (0.81, 0.96) 0.004 0.93 (0.85, 1.01) 0.078 0.93 (0.85, 1.01) 0.078 0.95 (0.87, 1.04) 0.262
SBP ≥ 130 mmHg and DBP ≥ 85 mmHg 0.98 (0.89, 1.07) 0.577 1.06 (0.97, 1.16) 0.192 1.06 (0.97, 1.16) 0.193 1.09 (1.00, 1.20) 0.05
Waist circumference ≥ 90 cm 1.09 (1.00, 1.18) 0.056 1.10 (1.01, 1.20) 0.037 1.10 (1.01, 1,19) 0.038 1.11 (1.02, 1.21) 0.017
TG ≥ 1.7 mmol/L 1.06 (0.98, 1.16) 0.153 1.02 (0.94, 1.11) 0.682 1.02 (0.93, 1.11) 0.694 1.02 (0.94, 1.11) 0.653
HDL-C < 1.04 mmol/L 1.13 (1.03, 1.25) 0.013 1.09 (1.00, 1.21) 0.084 1.09 (0.99, 1.21) 0.084 1.06 (0.96, 1.18) 0.227
DM or FBG > 5.6 mmol/L 0.83 (0.76, 0.90) < 0.001 0.94 (0.86, 1.02) 0.136 0.94 (0.86, 1.02) 0.135 0.96 (0.88, 1.04) 0.304
METS 0.97 (0.89, 1.06) 0.472 1.01 (0.93, 1.10) 0.826 1.01 (0.93, 1.10) 0.833 1.03 (0.94, 1.12) 0.543
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Dongetal. BMC Cardiovascular Disorders (2022) 22:263
As for the difference of age and working years between
shift workers and day workers, we did a subgroup analy-
sis of the study. e finding suggested that no significant
difference was found between night shift workers and day
workers in all age groups and all working year subgroups.
e prevalence of metabolic syndrome was increased by
age and working years, which was consistent with pre-
vious studies [6, 39]. We did the analysis between night
shift workers and metabolic syndrome and its compo-
nents, the result insisted that NSW was not associated
with a higher risk of metabolic syndrome. We reviewed
the studies and found that the previous results were
inconsistent. Some studies have suggested that shift work
and sleep quality may be associated with an increased
risk of metabolic syndrome [6, 12, 15], while others were
not [14, 40]. e results of the study by Vetter C etal. sug-
gested that recent night shift work may be more related
to the onset of cardiovascular diseases [15]. It is not clear
whether the results were affected by years of work, our
study indicated that long-term shift work was not associ-
ated with the increased risk of metabolic syndrome. Fur-
ther study may concentrate on recent shift work. After
adjusting for age, working years, smoking status, alcohol
consumption, and history of chronic diseases, our analy-
sis showed that NSW was associated with elevated sys-
tolic blood pressure, and waist circumference increase.
e treatment of metabolic syndrome was based on the
diseases, studies showed exercise training, mediterranean
diets, and supervised lifestyle intervention may improve
outcomes and reduce individual risk factors of metabolic
syndrome [41–43]. Our study insisted that railway work-
ers need long-term and effective interventions to reduce
the incidence of metabolic syndrome.
Strengths andlimitations
is study investigates the relationship between long-
term night shift workers and MetS and has some limi-
tations. First, since there are more men working along
railway lines, our study lacks data on women. Secondly,
the data on physical activity, sleep quality and duration,
nutritional status, and exposure to noise were absent,
which may have effect on the results of analysis. ird,
because we are an observational study and based on phys-
ical examination data, we lack data on the treatment of the
disease. However, despite the above limitations, we still
believe that this study can reflect the association between
long-term night shift workers and metabolic syndrome.
Although there is no significant difference between shift
work and the incidence of metabolic syndrome, the pre-
vention and treatment of metabolic syndrome and its fac-
tors still need to be carried out in all railway workers.
Conclusion
Long-term night shift workers had a higher prevalence of
MetS. However, long-term NSW is not associated with a
significantly increased risk of metabolic syndrome in male
railway workers in southwest China. Long-term NSW is
associated with elevated SBP, and waist circumference
increase. All the railway workers need long-term and
effective interventions to reduce the incidence of MetS.
Supplementary Information
The online version contains supplementary material available at https:// doi.
org/ 10. 1186/ s12872- 022- 02705-7.
Additional le1: Fig. S1. Age and working years stratified analysis of
MetS.
Acknowledgements
We appreciated the cooperation of the Chengdu Railway Bureau.
Author contributions
DC and ZH put forward the design and conception of this study. DC, YB, LZ,
and ZY completed data collection, DC completed manuscript writing. YB
and LZ participated in part of the data analysis, ZY participated in the part of
manuscript preparation. ZH and LZ gave some important suggestions on arti-
cle revision. All authors read and approved the final version of the manuscript.
Funding
The study is funded by Clinical Medical College & Affiliated Hospital of
Chengdu University (2020YYZ30), Special Talent Plan. The funders had no role
in the design and conduct of the study; collection, management, analysis, and
interpretation of the data; preparation, review, or approval of the manuscript;
and decision to submit the manuscript for publication.
Availability of data materials
The data that support the findings of this study are available from the
Affiliated Hospital of Chengdu Medical University, but restrictions apply to
the availability of these data, which were used under license for the current
study, and so are not publicly available. Data are however available from the
authors upon reasonable request and with permission of Affiliated Hospital of
Chengdu Medical University.
Declarations
Ethics approval and consent to participate
All included participants voluntarily participated in this study and signed the
informed consent form. This study was approved by the Affiliated Hospital of
Chengdu University.
Consent for publication
Not applicable.
Competing interests
The authors declared no conflicts of interest.
Author details
1 Department of Health Management Center, Clinical Medical College
and Affiliated Hospital of Chengdu University, Chengdu University, Sichuan
Province, Jinniu District, Chengdu City 610081, China. 2 China Railway Chengdu
Group Co., Ltd., Jinniu District, Chengdu City 610081, Sichuan Province, China.
Received: 15 February 2022 Accepted: 3 June 2022
Content courtesy of Springer Nature, terms of use apply. Rights reserved.

Page 7 of 7
Dongetal. BMC Cardiovascular Disorders (2022) 22:263
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