A case-control study was conducted at the Department of Biochemistry, BLDE (DU) Shri BM Patil Medical College, Vijayapura, Karnataka, from June 2014 to March 2015 after obtaining the Institutional Ethical Committee approval for the protocol as per the revised Helsinki declaration. All the participants were pre-intimated about the purpose of the study and their consent was taken.

Inclusion criteria: This study comprised 90 professional, male bus drivers aged 27-60 years, who expressed job-related complaints, as the study group.

Age-matched 110 male subjects from the general population who visited our hospital Outpatient Department for various other purposes were included as the control group.

Exclusion criteria: The bus drivers with existing ailments like rheumatoid arthritis, tuberculosis, and other infective conditions were excluded from the study.

Sample size calculation: It was was done by using the formula:

Where, n=sample size. The ‘Z’ value is 1.96. In this study, the results are presented with 95% confidence intervals (CI), P=35%; Prevalence rate, metabolic syndrome [9]; d=Precision, 0.1, Keeping all the values, n came to be 87.4 (Rounded to 90).

Blood samples were collected from the subjects with overnight fasting for estimation of biochemical parameters. Detailed information about their physical activity [10] and habits such as smoking and alcohol consumption and their previous medical history was recorded. Physiological measurements were recorded, including the subjects’ height, weight, WC, and hip circumference. Systolic and diastolic blood pressures were measured in the supine position after the participant was settled for at least 10 minutes.

Perceived Stress Scale (PSS) criteria: The self-perception of stress was measured in the bus drivers with the PSS-14. It has a set of 14 items (questions). PSS is a psychological instrument used to measure the extent to which situations were perceived as stressful in one’s life. The fourteen questions cover both negative and positive elements. Each question was scored on a five-point scale from 0=‘Never’ to 4=‘Very often,’ covering the past month. The PSS ratings were obtained by reversing the responses (e.g., 0=4, 1=3, 2=2, 3=1 and 4=0) to the four positively stated items (items 4, 5, 7, and 8) and then computing across all the scale items. The scores ranged from 0 to 56. The set of questions translated within the local language was provided to the participants. The score 28, was set as the upper bound’s operational cut-off value and identified as the ‘stressed’ and ‘non stressed’ those who scored less than 28 [11].

Framingham risk score: (Assessment of cardiovascular risk.) American College of Cardiology suggests utilising the Framingham model in predicting the 10-year possible risk of developing CVD in subjects with metabolic syndrome [12]. The coronary risk factors, including age, sex, total, and High Density Lipoprotein (HDL). Cholesterol, triglyceride, systolic blood pressure, smoking habit, and the subjects being diabetics were considered for the FRS calculation. Points determined a Ten-year chance of CVD risk in rate. (point 1=1.9%), (point 2=2.3%), (5=3.9%), (10=9.4%), (15=21.6%), (point 17=29.4%), (point 18=≥30%) and so on. The CVD risk percentage over ten years was classified as low risk (<10%), intermediate-risk (10-20%), and high risk (>20%) [13].

Metabolic syndrome: The subjects from control group and bus drivers were classified as per modified NCEP ATP III Guidelines. Accordingly, the presence of any three of the subsequent five factors is required for a diagnosis of Metabolic Syndrome: (1) abdominal obesity (WC ≥90 cm for Asian men or ≥80 cm for Asian women); (2) TG ≥150 mg/dL; (3) HDL cholesterol ≤40 mg/dL for men or ≤50 mg/dL for women; (4) systolic/diastolic blood pressure ≥130/85 mmHg or receiving drug treatment; and (5) fasting plasma glucose ≥100 mg/dL [14].

All characteristics were summarised descriptively. The data for the continuous variables were presented as mean±SD. An independent t-test was used to find the significance between the two groups. Statistical significance was established at p<0.05. Bivariate correlation analysis was applied using Pearson’s correlation coefficient (r) to test the strength and direction of relationships between the interval levels of variables. For categorical data, numbers and percentages was used in the data summaries. Statistical analysis was done by using Statistical Package for the Social Sciences (SPSS) version 16.

In total, 200 subjects were involved in this present study. As there was no substantial difference in age between the two groups, it implied an equal distribution of participants. More participants belonged to the 41-50 years age group (58.9%), followed by the 51-60 years age group (18.9%). The bus drivers had a higher mean BMI, waist to hip ratio, and both systolic and diastolic blood pressure compared to control subjects. (p<0.001). Except for FBS, total cholesterol, and LDL cholesterol rest of all parameters were significantly raised amongst bus drivers (p<0.001) [Table/Fig-1].

[Table/Fig-2] shows the percentage distribution of smoking, tobacco chewing, alcohol consumption, and the categorised physical activity as a low, average, regular activity in both control and bus drivers.

A significant difference in the values for WC, FBS, and HbA1c, triglyceride, and VLDL Cholesterol, serum Cortisol, and PSS have been recorded (p<0.05) [Table/Fig-3].

About 40% of bus drivers with a score of more than 28 were categorised as stressed. A significant increase in cortisol and PSS score levels was observed in bus drivers classified as ‘stressed’ (p<0.001) [Table/Fig-4].

The WC was found to correlate significantly with diastolic blood pressure (r=0.329, p<0.001), triglyceride (r=0.215, p<0.05), Gly. HbA1c (r=0.409, p<0.001). Such observations were not found in both the BMI and waist to hip ratio [Table/Fig-5].

As seen in [Table/Fig-6], we tabulated the values in a two-set of variances, expressed in (%) distribution, regarding CVD risk indicators in control subjects, bus drivers with and without metabolic syndrome. To define the metabolic syndrome, the values for the first set indicate ranges set as the cut off value. The second set of observations was clinically demonstrative of abnormalities and suggestive of components of CVD threat.

In the bus drivers with metabolic syndrome, we observed that 39.4% of the subjects had FBS greater than 125 mg/dL. Furthermore, 66.7% had HDL cholesterol of 31-40 mg/dL, and 36.4% had blood pressure higher than 140/90 mm/Hg. The values for age, systolic and diastolic blood pressure, triglyceride, and FBS differed significantly. (p<0.001). WC, total cholesterol, and serum cortisol values were also significantly differed (p<0.05) from each other [Table/Fig-7]. The [Table/Fig-8] shows, the prevalence of metabolic syndrome in both bus drivers and control subjects by age group. Bus drivers over the age of 50 were found to have a higher rate. Metabolic syndrome was evaluated among the control subjects using the same modified NCEP ATP III guidelines. A total of 13 (11.8 %) of the 110 control subjects were found to have metabolic syndrome. However, none of the studied parameters showed any substantial difference with non-metabolic syndrome subjects.

This study’s outcome implies the strategy for the bus driver’s health condition and its existing association with the risk factors involved in their occupation. There was a higher prevalence of risk factors for them than for the general population (controls), and many of them were unaware of their risk status. During the interaction, the bus drivers expressed concern over prevailing working conditions, low social support, and occupational stress. Only a few studies have adopted the validated questionnaires to assess stress at work [15]. In the present study, the PSS-14 questionnaire was implemented to evaluate the self-perception of stress. Cortisol level in the blood has been identified as a stress index. It secretes more when the body is subjected to chronic stress. According to the studies, there is a correlation between serum cortisol and CVD [6], and serum cortisol and the PSS-14 score show the potential role of the occupation’s stress factor [16]. It was observed that the ‘stressed group’ levels for serum cortisol and PSS differed significantly from the’ non-stressed group. (p<0.001). Earlier studies have linked metabolic syndrome with occupational stress as a clinical tool to find the risk of CVD [17,12].

The prolonged exposure to stress at work will lead to metabolic syndrome and induce more cortisol production [18]. In line with this study’s observations, Park SB et al., reported the rise in risk for the metabolic syndrome associated with increased cortisol levels after adjusting for age and BMI [19]. The authors in this study found that subjects with metabolic syndrome had higher serum cortisol and PSS score levels than non-metabolic syndrome (p-value <0.0001). These findings of serum cortisol and PSS indicate the current role played by the stress among the bus drivers. Additionally, other selected variables such as lipid profile, blood glucose, HbA1c, and other anthropometric parameters varied significantly from each other in participants with the metabolic and non-metabolic syndrome (p-value <0.001). A statistically substantial disparity in cortisol levels was also seen in the three FRS classification classes (p<0.05).

FRS classification demonstrated that the high-risk group subjects had an age of mean of 51.50±5.37 years. These reports suggest that the bus driver’s job, which involves occupational stress, posed a risk of cardiovascular disease only in their late middle years.

During their duty hours, many bus drivers remain in a sitting position for a long and extended period and are more prone to becoming obese. Obesity adds further to the development of metabolic syndrome and plays a significant role in developing health-related complications like CVD [20]. A meta-analysis report found that for those who exhibited work stress, the association between work stress and elevated cardiovascular risks was attributable to physical inactivity rather than smoking [21]. One of the significant predictors of obesity is WC, which is identified as the primary risk factor for metabolic syndrome.

Likewise, hyperglycaemia is considered a key risk factor for the development of CVD [22]. It was observed that 23.3% of bus drivers with a WC >90.0 cm had a blood glucose level of more than 126.0 mg/dL. Thus, both the WC and elevated blood glucose components of metabolic syndrome demonstrated a significant inter-relationship among them (p<0.001) and exhibited a higher risk for CVD. In the FRS classification, the subjects with high-risk groups were shown to have higher WC (p<0.05).

WC played a major role in identifying other existing risk factors, and a positive correlation of WC was found with triglyceride (r=0.215, p-value <0.05), diastolic blood pressure (r=0.329, p<0.01), and gly. HbA1c (r=0.409, p<0.01). However, no such kind of association could be found between BMI and any other variables studied. Similarly, in one Vietnam study, it was noted that CVD was linked with WC and was more explanatory than BMI [23]. Studies have investigated the current association between high mortality risk and physical inactivity with higher WC [24]. For either case, the American Heart Association (AHA) recommends 150 minutes of moderate-intensity aerobic exercise or, if nothing else, 75 minutes of aerobic activity per week to have good cardiovascular health [10]. The present study showed that 52.2% of bus drivers had low physical activity, and daily physical activity was only 12.2%. Another important finding in this study was that 42.4% of bus drivers had their BMI with a metabolic syndrome between 25-29.9 kg/m² and 18.2% with a BMI above 30.0 kg/m². These results indicate the presence of pre-obesity or obesity in bus drivers. Besides, as an individual component, BMI signifies its role as one of the risk factors for CVD.

In addition to obesity, hypertension is a significant risk factor for CVD [25]. It is a silent disease that remains undetected for a long time. Because of persistent stress exposure over time, individuals are at a higher risk of developing hypertension [26]. Continuous driving and prolonged sitting can cause stress, and this type of repeated exposure can increase blood pressure [7]. The bus drivers revealed that they are used to being on the road for 11-12 hours a day, almost every day and that a large portion of the street condition is below average and not smooth-riding.

Along with obesity, bus drivers’ irregular eating habits and lack of physical activity can serve as a combination of factors to raise blood pressure, demonstrating a deep connection between hypertension and obesity. In the current study, the prevalence of hypertension (blood pressure higher than 140/90 mm Hg) was 36.4% in bus drivers with metabolic syndrome. This observation was analogous to the studies carried out at other places. In a study on bus drivers from North Kerala, India, the prevalence of hypertension was 41.3% [27] and 33.5% in Sokoto, Nigeria [28]. The lack of awareness, the asymptomatic nature of hypertension, and ignorance were a few reasons that contributed to the rise in the number of hypertensive subjects in the present study.

Bus drivers have revealed that they have developed tendencies towards unhealthy habits such as smoking and consuming alcohol. They attribute it to the nature of occupation and an endeavor to get relieved from the perceived stress they experience. High rates of smoking and alcohol intake each have their impact on mortality risk. When combined, however, they have a stimulating effect [29], and some studies have confirmed their strong link with CVD [30]. In this study, the prevalence of smoking among the bus drivers was 23.3%, the habit of regularly chewing tobacco was 32.2%, and the rate of alcohol consumption was 47.7%. With the FRS classification, the smoking habit was around 58 % among the high-risk group bus drivers. These characteristic observations provided precise data on potential risk factors contributing to CVD development in them. Similarly, alcohol consumption was prevalent in a Nigerian study conducted on long-distance bus drivers, and the prevalence rate was 71.1%, and the smoking rate was 19.5% [31].

Dyslipidemia is considered a significant metabolic syndrome component and is predicted to be a risk factor for CVD [32]. The studies have identified lipid disorders with job stress in bus drivers and found the impact of stress on dyslipidemia [33]. In the present study, predominantly, the HDL-C between the ranges of 31-40 mg/dL was 66.7% and below 30.0 mg/dL was 15.2%, followed by triglyceride level more than 200 mg/dL was 30.3% in the subjects identified with metabolic syndrome. The authors found many bus drivers had low HDL-C levels, which pose a potential risk for CVD. Kajani S et al., have reported that low HDL-C is a risk factor for CVD development [34]. One of the instruments used to describe metabolic syndrome is impaired blood glucose. Hyperglycaemia initiates a complex chain of events that damages blood vessels and will cause CVD [35]. The stress at work was found to play an influential role in raising the number of hyperglycaemia incidences among bus drivers. It was found that 24.2% of study subjects had their blood glucose between 100-125.0 mg/dL, and 39.4% of participants had their blood glucose level of more than 125.0 mg/dL, who were identified with metabolic syndrome. Similar findings were observed in the study done in Brazil on truck drivers [36]. The prevalence rate of metabolic syndrome of bus drivers was 33 (36.7%) and 13 (11.8%) in control subjects.

It is relevant to note from this study that the prevalence of metabolic syndrome, co-existing of CVD risk factors among the bus drivers, emphasises the impact of work stress on their health. The risk factors of metabolic syndrome represent the major threat of CVD among them. Each component of metabolic syndrome, in its capacity, has a contribution to the advancement towards the risk of CVD, which can be observed from FRS classification. It was also noted that the bus drivers who were classified as high-risk groups as per FRS classification were found to have a higher percentage of family history of diabetes mellitus and hypertension. The stress being the underlying cause at work, it has been tended very precisely with PSS and serum cortisol in this study.

The study subjects were bus drivers and males by gender. Even though the useful questionnaires was incorporated to collect the work-related psychosocial hazards, few could have remained unnoticed and may significantly impact CVD outcomes.

The bus drivers are at higher risk for CVD. The prevalence of risk factors for metabolic syndrome and CVD among them was evaluated and found that the rate of hypertension, diabetes, obesity, and stress was significantly higher. It is necessary to make them understand the benefits of regular physical activity, reducing the pace of smoking, and consumption of alcohol. Besides, steps such as reducing long driving hours and routine health check-ups are ultimately required. Moreover, it is proposed that more longitudinal studies should be carried out to improve the validity of the results of this report.