Prevalence of and risk factors for obstructive sleep apnea
syndrome in Brazilian railroad workers
Renata G. Koyamaa, Andrea M. Estevesa,b,⇑, Luciana Oliveira e Silvaa, Fabio S. Lirab,
Lia R.A. Bittencourtb, Sergio Tufikb, Marco Tulio de Melloa,b,⇑
aCentro de Estudo Multidisciplinar em Sonolência e Acidentes, São Paulo, Brazil
bUniversidade Federal de São Paulo, São Paulo, Brazil
a r t i c l e i n f o
Received 9 September 2011
Received in revised form 16 April 2012
Accepted 14 June 2012
Available online 26 July 2012
Obstructive sleep apnea syndrome
a b s t r a c t
Objective: This study evaluated the prevalence of, and the risk factors for, obstructive sleep apnea syn-
drome (OSAS) among Brazilian railroad workers.
Methods: Male railroad workers (745) from a railway company in Brazil were analyzed after responding
to questionnaires about their demographics, sleep habits, excessive daytime sleepiness (Epworth), and
the likelihood of having apnea (Berlin). We also performed polysomnography and measured anthropo-
metric data for all of the railroad workers.
Results: The results showed that 261 (35.03%) of the railroad workers presented with OSAS. These rail-
road workers were older (OSAS: 38.53 ± 10.08 versus non-OSAS: 33.99 ± 8.92 years), more obese accord-
ing to body mass index (27.70 ± 4.38 versus 26.22 ± 3.92 kg/m2), and employed for a longer period of time
(14.32 ± 9.13 years) compared with those without OSAS (10.96 ± 7.66 years). Among those with OSAS,
9.5% were smokers and 54.7% reported alcohol use. The associated risk factors were age (OR = 2.51,
95% CI = 1.76–3.57), BMI (OR = 1.56, 95% CI = 1.04–2.34), alcohol use (OR = 1.28, 95% CI = 0.90–1.81),
and a high chance of having sleep apnea, as assessed by the Berlin questionnaire (OR = 2.19, 95%
CI = 1.49–3.21).
Conclusion: The prevalence of OSAS in Brazilian railroad workers was higher than that observed in the
general population but similar to that found in the population of the city of São Paulo, Brazil. These
results suggest that age, BMI, a high risk of developing apnea through subjective self-reporting (Berlin),
and alcohol use are associated with a higher risk of developing OSAS. These data reinforce the need to be
more attentive to this population because they have a higher propensity for accidents.
? 2012 Elsevier B.V. All rights reserved.
Studies have indicated that excessive sleepiness is a risk factor
for accidents, and it can be inferred that patients with obstructive
sleep apnea syndrome (OSAS) have an increased risk of transport-
related accidents compared with the general population . OSAS
is characterized by repeated episodes of upper airway obstruction
during sleep, which is associated with intermittent hypoxemia, in-
creased respiratory effort, and arousals. The most frequent clinical
symptom is excessive sleepiness [2,3].
Sleepiness and fatigue are frequent problems for workers in the
transportation sector [4,5], particularly in night and shift workers
because they have inverted sleep-wake cycles that lead to a
significant reduction in the duration and effectiveness of sleep
. Excessive sleepiness is considered a problem because it affects
quality of life and has negative effects on productivity and work
safety. Excessive sleepiness may also result from sleep deprivation
and may be associated with sleep-disordered breathing .
The prevalence of OSAS is variable and depends on an individ-
ual’s age, gender, and nationality, as well as on the methodology
of the criteria used for diagnosis. The prevalence of OSAS in the
general population ranges from 2% to 32.8% [3,8–12]. In studies
on transportation workers, most of which have focused on profes-
sional automotive drivers, such as bus and truck drivers, the prev-
alence ranges from 15.8% to 78% [13–17]. However, there are few
studies on the prevalence of sleep-disordered breathing in railroad
workers, among whom there is a very high risk for accidents.
Increases in body mass index (BMI), neck circumference, and
the waist-hip ratio in non-obese persons are associated with a
gradual increase in the prevalence of OSAS . Additionally, other
factors have been correlated with the apnea–hypopnea index
(AHI), such as gender, age, tobacco use, and alcohol consumption
1389-9457/$ - see front matter ? 2012 Elsevier B.V. All rights reserved.
⇑Corresponding authors. Address: Departamento de Psicobiologia, Universidade
Federal de São Paulo, Rua Professor Francisco de Castro, 93 Vila Clementino, São
Paulo 04020-050, Brazil. Tel./fax: +55 11 5572 0177.
E-mail addresses: firstname.lastname@example.org (A.M. Esteves), email@example.com
(M.T. de Mello).
Sleep Medicine 13 (2012) 1028–1032
Contents lists available at SciVerse ScienceDirect
journal homepage: www.elsevier.com/locate/sleep
[19–21]. However, little is known about OSAS or the risk factors for
its onset in railroad workers. Therefore, the aim of this study was
to evaluate the prevalence of and possible risk factors associated
with OSAS in railroad workers employed by a Brazilian company.
This study was conducted on a sample of 745 railroad workers
employed by a railroad company in Brazil who were evaluated be-
tween January 2008 and November 2010. All of the railroad work-
ers in the sample were male. The participants were informed about
the study procedures prior to signing consent forms. The protocol
was approved by the Ethics Committee at the Universidade Federal
de São Paulo (REC 0547/08).
Of the 745 railroad workers, 715 were train conductors (486
were long-distance railroad conductors and 229 were rail yard
conductors) and 30 were rail yard and terminal controllers. There
were no exclusion criteria; all railroad workers were invited to par-
ticipate in the study.
2.2. Experimental design
The railroad workers were invited to complete anthropometric
assessments (weight, height, waist, hip, and neck measurements)
to determine their BMI, obesity, and risk for cardiovascular disease.
BMI calculations were determined using the criteria established by
the World Health Organization . After responding to the
general questionnaire (to assess demographics, lifestyle, and daily
routine) the Epworth Sleepiness Scale (ESS) and the Berlin ques-
tionnaire, the participants then underwent polysomnography to
evaluate their sleep patterns and verify the presence or absence
of OSAS. For the sleep record, railroad workers were invited to a
hotel that was usually used for rest between work-related travel
2.2.1. General questionnaire
To assess demographics (age, years of schooling, and time em-
ployed as shift workers), lifestyle (alcohol and tobacco use), and
daily routine (commute time from home to work and work respon-
sibilities), the participants were asked to self-report using a general
2.2.2. Berlin Questionnaire
The Berlin questionnaire was used to evaluate the risk of OSAS,
which has been previously described by Netzer et al.  and val-
idated for use in Portuguese . The questionnaire includes 10
items organized into three categories related to snoring and wit-
nessed apneas (five items), daytime sleepiness (four items), and
hypertension/obesity (one item). Information on gender, age,
height, weight, neck circumference, and race is also requested.
The determination of high or low risk for OSAS is based on the re-
sponses for each category of items.
2.2.3. Epworth sleepiness scale
The ESS is the most widely used subjective scale for assessing
daytime sleepiness because it is able to distinguish people with
and without sleepiness from those with excessive sleepiness. The
ESS consists of eight questions that describe everyday situations
that can induce sleepiness. Each question is graded from 0 to 3; to-
tal scores above 10 indicate significant daytime sleepiness, and
scores above 15 are associated with pathological sleepiness pres-
ent in specific conditions, such as sleep apnea and narcolepsy .
2.2.4. Polysomnography examination (PSG)
An all-night PSG was performed using a digital EMBLA
Titanium™ system (Embla, Broomfield, USA). The room used for
the recordings had a large comfortable bed, acoustic isolation,
and controlled temperature and light. The following physiological
characteristics were monitored simultaneously and continuously:
electroencephalogram (3 canals F4-M1, C4-M1, O2-M1), electrooc-
ulogram, chin and side tibial electromyograms, electrocardiogram,
airflow (thermal sensor), thoracic-abdominal movements, snoring
as detected by a microphone placed on the lateral neck, pulse
oximetry, and body position. Polysomnographic recordings were
performed according to the criteria established by the AASM Man-
ual for Scoring Sleep and Associated Events . Electrode place-
ment was performed according to the international 10–20
system . Thirty-second epochs were staged according to stan-
dard criteria and were visually inspected by a sleep specialist.
The following parameters were analyzed: (a) total sleep time
(TST, in min), defined as the actual time spent asleep; (b) sleep la-
tency (SL, in min), defined as the time from lights out until the on-
set of three consecutive epochs of stage 1 or deeper sleep; (c) sleep
efficiency (SE), defined as the percentage of total recording time
spent asleep; (d) wakefulness after sleep onset (WASO, in min), de-
fined as the total time scored as wakefulness between sleep onset
and final awakening; (e) stages 1, 2, 3, and REM sleep, as percent-
ages of total sleep time; and (f) latency to REM, defined as the time
from sleep onset until the first epoch of REM sleep.
OSAS was diagnosed according to the American Academy of
Sleep Medicine  based on the following criteria: an AHI P five
events per hour and a daytime sleepiness score over 11 points, as
diagnosed by the ESS or the presence of snoring or reports of ap-
nea. An AHI > 15, regardless of the presence or absence of symp-
toms, was also used as a criterion for OSAS. The severity of OSAS
was classified according to the AHI scale as follows: mild, 5–15;
moderate, 15–30; and severe, >30 .
2.3. Statistical analyses
Statistical analyses were performed using the statistical soft-
ware package PASW Statistics for Windows, version 18.0 (SPSS
Inc., Chicago, IL).
The Kolmogorov–Smirnov test was used to test for normal dis-
tribution. Variables with non-normal distribution were trans-
formed using a Z-score to normalize their distribution prior to
statistical analyses. Descriptive statistics were used. The data were
presented as the mean ± SD. Differences between groups referring
to continuous variables were assessed using the analysis of vari-
ance (ANOVA). Levene’s test was used in ANOVA to evaluate homo-
geneity. The categorical variables were assessed using the Pearson
v2test. An a value < 0.05 was considered to be statistically
The risk factors for OSAS in railroad workers were categorized
and explored by employing the Receiver Operating Characteristic
(ROC) curve for the continuous variables of age, waist circumfer-
ence, and time employed as a shift worker. The area under the
curve (AUC) was reported as well as its asymptotic p value. Individ-
uals with a BMI P 25 kg/m2were classified as having excess
weight (overweight and obese). The Berlin questionnaire was used
to assess the risk of OSAS. The risk factors associated with lifestyle
variables were dichotomized into ‘‘yes’’ and ‘‘no’’ responses, and
alcohol consumption and cigarette smoking (either socially or reg-
ularly) were considered as a pair when considering the risk for
OSAS. Odds ratios (OR) and 95% confidence intervals (CI) were
determined. Variables showing association with an a value of
<0.05 in univariate analysis were considered candidate risk factors
for use in multivariate analysis. The analysis was performed with
logistic regression to identify significant independent risk factors
R.G. Koyama et al./Sleep Medicine 13 (2012) 1028–1032
for OSAS. In multivariate analysis, the variables that had high asso-
ciations were excluded from the regression model. Two log-likeli-
hood, Cox and Snell R Squared, and the Hosmer and Lemeshow
tests were used to examine the fitness of the model.
In the overall sample of railroad workers, the average age was
35.63 ± 9.59 years and the mean BMI was 26.74 ± 4.14 kg/m2. The
alcohol consumption rate was 59.6% and the tobacco use rate
was 10.2%. The average length of time employed as shift workers
was 13.9 ± 14.32 years. With regard to obesity, 69.5% of all railroad
workers studied had above average weight (BMI P 25 kg/m2);
47.6% of railroad workers were overweight and 21.9% were obese.
Of the 745 railroad workers, 261 (35.03%) were diagnosed with
OSAS; of these, 54.4% were diagnosed with mild OSAS, 25.3% with
moderate OSAS, and 20.3% with severe OSAS. Descriptive data for
the sample pool are shown in Table 1 and divided into OSAS and
non-OSAS groups. Railroad workers who were diagnosed with
OSAS were more obese, older, had worked for the company longer,
and had consumed more alcohol compared with non-OSAS railroad
workers. The variables associated with a risk for OSAS were age
(AUC = 0.628, p < 0.001, cut-off: 37 years), waist circumference
(AUC = 0.677, p < 0.001, cut-off: 98 cm), and time employed as a
shift worker (AUC = 0.606, p < 0.001, cut-off: 12 years).
Table 2 depicts the risk factors for OSAS according to the univar-
iate analysis. The variables showing association (a value of <0.05)
according to univariate analysis were considered candidate risk
factors for use in multivariate analysis. In the multivariate analysis
shown in Table 3, the variables selected for the model were age,
BMI, and symptoms related to the risk for OSAS, as evaluated using
the Berlin questionnaire.
The results of this study indicate that Brazilian railroad workers
exhibit a high incidence of OSAS and that the risk factors most clo-
sely related to having the syndrome include age, BMI, and alcohol
This is the first study describing the prevalence and risk factors
for OSAS in a group of Brazilian railroad workers; most of the cur-
rent studies in the literature were performed on professional driv-
ers who drove trucks, automobiles, and buses [1,29,30]. Among the
745 Brazilian railroad workers who participated in our study, the
prevalence of OSAS was 35.03% (261 railroad workers). The diagno-
sis of OSAS was based on AHI scores between five and 15 events
per hour and associated with excessive sleepiness, the presence
of snoring or self-reporting of apnea, or AHI P 15 events per hour.
In addition, individuals over the age of 37 years who had a BMI
above 25 kg/m2, a subjective self-report for a high risk of develop-
ing apnea (Berlin), and who reported alcohol use showed a higher
risk of developing OSAS.
When only subjective parameters and AHI were evaluated in
professional drivers, the prevalence of obstructive sleep apnea
(OSA) ranged from 11.5% to 78% [7,13–16,31,32]. In studies
conducted with professional drivers in Philadelphia (truckers),
Australia (automotive), and Spain (automotive), the prevalence of
OSAS was shown to be lower (28.2%, 15.8% and 8.6%, respectively)
when compared with the railroad workers in our study (35.03%)
[13,14,31]. However, in a study of train engineers in Greece,
Demographic characteristics of the study population (n = 745).
(n = 484)
(n = 261)
Body mass index (kg/m2)
(BMI P 25 kg/m2) (%)
Neck circumference (cm)
Waist circumference (cm)
Epworth P 10 (%)
Shift work time (years)
Alcohol use (%)
33.99 ± 8.92
26.22 ± 3.92
38.48 ± 3.37
89.37 ± 9.14
7.49 ± 3.46
10.96 ± 7.66
38.53 ± 10.08
27.70 ± 4.38
39.57 ± 3.06
95.36 ± 10.06
8.79 ± 3.62
14.32 ± 9.13
Data presented as the mean and SD (±), comparison made using ANOVA.
Data presented as the absolute frequency (relative frequency %), comparison performed using v2test.
Variables analyzed for the chance of OSAS (univariate analysis).
n = 484
n = 261
OR (95% IC)#
Age < 37 years
Age > 37 years
Shift work time
Risk of sleep apnea (Berlin)
BMI: body mass index.
*Data represented as the absolute frequency (n) and relative frequency (%).
#Odds ratio represent the chance of OSAS in case group.
Logistic regression model of factors associated with the risk of OSAS.
VariablesAdjusted OR (95% IC)
Age (>37 years)
BMI (P25 kg/m2)
High risk of sleep apnea
Hosmer and Lemeshow test (v2= 4.99, p = 0.66), Cox and Snell = 0.096.
BMI: body mass index.
R.G. Koyama et al./Sleep Medicine 13 (2012) 1028–1032
the prevalence of sleep-disordered breathing (OSA) was 62% .
Regarding the severity of apnea, professional automotive drivers
in Australia and railroad drivers in Greece had a lower prevalence
of mild OSA (34.8% and 40%, respectively) compared with our study
sample (54.4%). However, this large variation in prevalence in the
literature may be due to the definitions used for diagnosis, the
selected study population, or to other criteria including age,
Despite the diversity of prevalence rates in the literature, we
found that the prevalence of OSAS in Brazilian railroad workers
was higher when compared with the rates in the American and
Italian general adult population [2,9]. However, the prevalence in
our study sample is similar to that of the population of the city
of São Paulo, Brazil , perhaps because the two studies had sim-
ilar criteria for diagnosing OSAS and a population with a similar ge-
Several factors have been associated with an increased risk of
OSAS, including age, male gender, obesity, alcohol abuse, otorhino-
laryngological changes, inherited traits, and aging [2,33]. Our study
results corroborate previous findings that obesity is a major mod-
ifiable risk factor for OSAS . Longitudinal studies, such as the
Sleep Heart Health Study, the Wisconsin Sleep Cohort Study, and
the Cleveland Family Study, have shown that increased levels of
BMI over time can accelerate the progression of obstructive sleep
apnea or lead to the development and increased severity of apnea
The accumulation of fat in the neck (leading to the obstruction
of airways) is one of the primary reasons for the onset of OSAS .
The accumulation of abdominal fat and the presence of metabolic
syndromes can also lead to the onset and development of OSAS
due to declining respiratory function (e.g., a reduction in pulmon-
ary volume) [37,38]. Our sample of individuals over the age of
37 years had a higher chance of developing OSAS. These data are
supported by other studies reporting that difficulties in sleeping
normally increase with advancing age . In a sample of the gen-
eral population, the prevalence of sleep apnea (AHI P 10) in men
from Pennsylvania increased progressively with age; the group be-
tween 65–100 years in age had an OR of 6.6 (95% CI = 2.6–16.7)
compared with those 20–44 years in age. This is also observed in
epidemiological data from Brazil, where people between 60–
80 years in age had an OR of 34.5 (95% CI = 18.5–64.2) compared
with those between 20–29 years in age .
alter the functionality of different systems, including the nervous
and endocrine systems . The hypothalamic–pituitary–adrenal
lated to the sleep-wake cycle. This axis plays a central role in inte-
grating the responses of both the endocrine and nervous systems
to external and internal stimuli. With aging, there is a decline in
the amplitude of markers for the sleep-wake cycle, such as body
temperature, melatonin, and cortisol. Such changes are closely re-
lated to the deterioration of sleep quality during aging . These
reports corroborate our data because age was a determining factor
for the decline in sleep quality for Brazilian railroad workers.
Risk factors, such as alcohol consumption, appear to decrease
professional performance . In our sample population, alcohol
had an OR of 1.28 (95% IC 0.90–1.81) for OSAS. Even though this
factor was not statistically significant, we kept it as a risk factor
in multivariate analysis because it was a significant variable in uni-
variate analysis together with other parameters (e.g. age, BMI, etc.).
Other studies have demonstrated that alcohol use is associated
with increased OSAS severity [43,44]. Proposed mechanisms for
side effects of alcohol upon OSAS include selective reduction upper
airway obstruction via reduced dilatory muscle tone, or by blunted
ventilator response to hypoxia [43,44].
durationof sleep during
OSAS has been associated with a myriad of symptoms, such as
trouble sleeping, memory loss, impaired concentration, and loss
of attention span. These effects arise from the sleep architecture
assessed in this study. Although polysomnography is considered
the gold standard for diagnosing OSAS, it is an expensive examina-
tion, and many population studies have used other subjective
instruments to identify individuals at higher risk of developing ap-
nea [23,32]. According to our results, the subjective evaluation
(based on the Berlin questionnaire) showed an OR of 2.19 (95%
CI = 1.49–3.21) for developing OSAS, which is consistent with that
reported in the literature.
Previous studies have reported that in the general population,
despite the scientific and clinical advances in relation to obstruc-
tive sleep apnea, the vast majority (70–80%) of those affected re-
main undiagnosed . It is very likely that, as in the general
population, train conductors are similarly under diagnosed. One
reason that diagnosis may be missed is because patients remain
unaware of the associated symptoms, which are often identified
by a spouse or another family member. Compounding the lack of
awareness on the part of the patient , few health professionals
have the knowledge and training necessary to make the diagnosis
and then recommend treatment . Therefore, detecting the risk
factors associated with obstructive sleep apnea is very important
in making the appropriate diagnosis in high-risk populations.
Many studies have correlated OSAS with automotive accidents,
showing an increased risk for individuals with OSAS compared
with the general population . This often occurs because the
majority of professional drivers, such as truck drivers, bus drivers
and train drivers, may also have irregular sleeping habits, sleep
deprivation, or sleep disorders such as OSAS. These factors or their
cumulative effects may increase the predisposition toward exces-
sive sleepiness and alter circadian rhythms [48,49]. In the case of
railroad workers, working conditions may exacerbate these symp-
toms because of the irregular shift system and the automation and
monotony of the journey .
Self-reporting of excessive sleepiness, alcohol use, and smoking
through questionnaires was one of the limitations of this study be-
cause workers usually omitted information even when they were
informed that all data were highly confidential. The failure to
quantify alcohol consumption may have been a further limitation
to the study. However, these limitations are not a mitigating factor
because even with the potential omission of information, we found
a high prevalence of OSAS in the study population.
In conclusion, we found a high prevalence of OSAS in Brazilian
railroad workers that was similar to the rates found in the general
population of the city of São Paulo, Brazil . Our results further
suggest that age, BMI, a self-reported higher risk of developing ap-
nea (Berlin), and alcohol use increase the risk of developing OSAS.
These data reinforce the need to be attentive to the population be-
cause they may be at a higher risk for having accidents as well as
experiencing loss of productivity and work-related injuries.
Conflicts of interest
The ICMJE Uniform Disclosure Form for Potential Conflicts of
Interest associated with this article can be viewed by clicking on
the following link: http://dx.doi.org/10.1016/j.sleep.2012.06.017.
This work was supported by grants from the Universidade
Federal de São Paulo (UNIFESP), Associação de Fundo e Incentivo
à Pesquisa (AFIP), FAPESP (CEPID No. 98/14303-3 to ST), CEPE
(Psychobiology and Exercise Study Center), CNPq (National Council
for Scientific and Technological Development), and the Center for
Multidisciplinary Studies on Sleepiness and Accidents (CEMSA).
R.G. Koyama et al./Sleep Medicine 13 (2012) 1028–1032
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