Impact of Noncommunicable Diseases and Heat Stress on Estimated Glomerular Filtration Rate in Security Officers at a Tertiary Care Hospital in South India

Introduction

The job profile of security officers involves prolonged period of standing which results in complications of sedentary lifestyle. A high prevalence of diabetes, hypertension, dyslipidemia, obesity, and metabolic syndrome is reported among police personnel in India.^1-3 In contrast, agricultural workers who carry out strenuous activities in hot climates are at risk of developing heat stress nephropathy.⁴ This form of occupational renal disease is known by various terminologies such as chronic interstitial nephritis in agricultural communities (CINAC), chronic kidney disease of nontraditional origin (CKDnt), and chronic kidney disease of undetermined etiology (CKDu). There is paucity of data on the prevalence of CKDu in occupations other than agricultural workers.^5,6 Security officers from hot tropical climates are thus exposed to both traditional (diabetes, hypertension, obesity, dyslipidemia) and nontraditional (heat stress) risk factors of chronic kidney disease (CKD) However, the impact of these factors on kidney function has never been explored previously.

Vellore district in the state of Tamil Nadu has a tropical climate. The average annual temperature in Vellore is 26.9 degree Celsius (°C). The temperature is highest in the month of May [31.2 (26.2–37.4)°C] and lowest in December [22.5 (17.9–27.2)°C]. Heat stress is defined as metabolic plus environmental heat minus the heat dissipated from body to environment. There are about 165 different indices for measuring heat stress which are classified into environmental, physiological, perceptual, and perceptual-observational.⁷ Heat strain score index is a validated perceptual-observational heat stress index developed by Dehgan et al.⁸ This index has a Cronbach’s coefficient of 0.91 and all items have adequate factor loading of more than 0.40.^9,10 It has been previously studied in miners, bakers, glass manufacturers, diesel power plant operators, petrochemical workers, municipal waste collectors, copper refinery and steel plant workers.^11,12

Christian Medical College, Vellore, is a tertiary care hospital which spreads out across multiple campuses and involves around 700 security officers working under a single agency who were employed without a prior pre-employment medical checkup. The objectives of this study were

1. To estimate the prevalence of noncommunicable diseases such as diabetes, hypertension, obesity, and CKD among security officers employed at our tertiary care center.

2. To estimate prevalence of heat stress by HSSI.

3. To analyze factors affecting thermal stress.

4. To analyze the factors affecting estimated glomerular filtration rate (eGFR).

Materials and Methods

This was an observational cross-sectional study conducted at Christian Medical College, Vellore, Tamil Nadu, during the months of March to May 2020, which is the hottest period of the year. All security personnel, both men and women above 18 years of age working at various campuses were included in this study. Those who were employed for a duration of less than 6 months and those who did not consent were excluded from the study [Figure 1]. A structured questionnaire for data collection was prepared as per guidelines by World Health Organization (WHO) STEPwise approach to noncommunicable disease risk factor surveillance. This included demographic details (age, sex), co-morbidities (diabetes, hypertension, past kidney disease), working conditions (duration of employment, work-shift hours, site of work, outdoor work hours/day, water intake during work-shift), medications, addictions (smoking, alcohol intake), lifestyle, and family history [Supplemental File 1].

Close

Figure 1:

Flowchart of recruitment of security personnel. (ACR: albumin to creatinine ratio; ANA: antinuclear antibody; ANCA: antineutrophil cytoplasmic antibody; BMI: body mass index; C3: complement component 3; C4: complement component 4; CKD: chronic kidney disease; CKDu: chronic kidney disease of unknown etiology; dsDNA: double-stranded deoxyribonuclease antibody; FBSL: fasting blood sugar level; Hb: hemoglobin; HCV: hepatitis C virus antibody; HIV: human immunodeficiency virus; HSSI: heat strain score index; PTH: parathyroid hormone; SPEP: serum protein electrophoresis; USG: ultrasound); HBsAg: hepatitis B surface antigen

Export to PPT

Heat stress was assessed by an 18-item HSSI questionnaire which consisted of 12 observational and 6 perceptual questions [Supplemental File 2]. The questions were related to work-place setting, work-place ambient conditions, perceived symptoms at work, intensity of physical activity, body posture, and working attire. Scores for each item (primary score) were multiplied by effect coefficient of each question to get secondary scores. The secondary scores of each item were then summed to get a final score. Based on final HSSI scores, participants were classified into three zones:

1. Green or safe level (≤13.5) – no or low heat stress

2. Yellow or alarm level (13.6–18) – likelihood of heat stress

3. Red or danger level (>18) – definite heat stress (8)

This study was approved by institutional review board (IRB min no.12003, dated 24.04.2019).

Results

Factors affecting glomerular filtration rate

Mean eGFR was lower in men (men: 100.1 ± 14.2 versus women: 108.5 ± 11.3 mL/min/1.73 m², p = 0.001), age > 50 years (93.9 ± 12.9 versus 103.2 ± 13.9 mL/min/1.73 m², p < 0.001), hypertensives (97.4 ± 13.7 versus 100.9 ± 14.2 mL/min/1.73 m², p = 0.019), longer duration of employment (>5 years: 98.5 ± 12.8 versus <5 years: 102 ± 15.2 mL/min/1.73 m², p = 0.001), and smokers (nonsmokers: 100.1 ± 14.2 versus <10 pack-years: 103 ± 13.9 versus >10 pack-years: 93.1 ± 10.6 mL/min/1.73 m², p = 0.097). However, women security officers were younger in age (36.2 ± 8.6 years) as compared to men (45.7 ± 9.1 years, p < 0.001). eGFR was unaffected by the presence of diabetes, BMI, site of work, duration of outdoor work-shift, and HSSI [Table 3, Figure 2]. No correlation was found between eGFR and HSSI scores as continuous variables (r—0.04, p = 0.29).

Table 3: Factors affecting glomerular filtration rate

Factor	Estimated glomerular filtration rate mL/min/1.73 m2 (mean ± SD)	p-value
Sex
Men	100.1 ± 14.2	0.001
Women	108.5 ± 11.3
Age (years)
<50	103.2 ± 13.9	<0.001
>50	93.9 ± 12.9
Diabetes mellitus
No	100.5 ± 14.6	0.672
Yes	99.9 ± 12.8
Hypertension
No	100.9 ± 14.2	0.019
Yes	97.4 ± 13.7
Duration of employment
<5 years	102 ± 15.2	0.001
>5 years	98.5 ± 12.8
Site of work
Indoor	100.6 ± 12.6	0.126
Outdoor	98.2 ± 16.9
Both	101.3 ± 14.5
Heat exposure (hours per day)
<5 hours	100.5 ± 14.9	0.871
>5 hours	100.3 ± 13.5
Water intake during work shift
<1 L	102.4 ± 13.7	0.366
1–2 L	100.3 ± 14.6
>2 L	100 ± 14.1
Past H/O kidney disease
No	100.4 ± 14.1	0.511
Yes	98.5 ± 17.8
Past H/O kidney stones
No	100.4 ± 14.3	0.620
Yes	98.7 ± 10.7
Past H/O nephrotoxic medications
No	100.4 ± 14.1	0.883
Yes	100.2 ± 14.4
Nocturia
No	100.4 ± 14	0.831
Yes	100.2 ± 14.7
Smoking
No	100.1 ± 14.2	0.294
Reformed smokers	103 ± 12.8
Active smokers	99.6 ± 17.2
Pack-years of smoking
Nonsmokers	100.1 ± 14.2	0.097
<10 pack-years	103 ± 13.9
>10 pack-years	93.1 ± 10.6
Alcohol Intake
No	100.9 ± 13.6	0.189
Yes	99.4 ± 15.1
Exercise
No	100.3 ± 14.6	0.434
Yes	101.6 ± 11
Cycling to work
No	101.8 ± 13.7	0.098
Yes	99.8 ± 14.4
Family H/O kidney disease
No	100.3 ± 14.2	0.269
Yes	104.2 ± 12.5
Body mass index
Underweight	103.1 ± 17.4	0.448
Normal range	101.7 ± 14.5
Overweight	99.6 ± 12.3
Obese	99.9 ± 14.7
Abdominal obesity
No	99.7 ± 15.4	0.316
Yes	100.8 ± 13.3
HSSI category
Green zone	100.9 ± 14.5	0.762
Yellow zone	100.4 ± 15.5
Red zone	100 ± 13.3
Nonvisible hematuria
No	100.4 ± 13.9	0.884
Yes	100 ± 20.4
Proteinuria
No	100.5 ± 14.2	0.158
Yes	94.4 ± 14.8

HSSI: Heat strain score index; SD: Standard deviation, H/O: history of.

Close

Figure 2:

Factors affecting glomerular filtration rate of security personnel. (eGFR, estimated glomerular filtration rate).

Export to PPT

Discussion

Security officers in hot tropical countries form a unique occupational cohort as their job pattern exposes them to a sedentary lifestyle and heat stress. We observed a high prevalence of obesity (50.4%), diabetes (25.5%), and hypertension (15.9%) in our cohort. Data from National Health Interview Survey 2010 reported that 27.7% of US workers were obese. Among occupational categories, protective service workers had the highest incidence of obesity (40.7%).²¹ In a cross-sectional study of 963 security personnel working in six private security organizations at Istanbul, prevalence of overweight, obesity, and morbid obesity were 57, 14.4, and 0.4% respectively.²² Possible causes for such a high burden of noncommunicable diseases are long periods of physical inactivity, irregular diet and limited choice of food on duty, disrupted sleep and stress due to overtime and shift work, and high rates of alcohol and tobacco consumption as compared to the general population.^23,24

Almost half of our cohort had definite heat stress in the red zone. Similar findings have been reported in other occupational sectors in India using different heat stress indices. In a study of 442 workers from organized and nonorganized workplaces in South India, 82 and 42% were exposed to higher than recommended threshold limit values (TLVs) in summer and winter, respectively. Workers with heavy workload were exposed to higher occupational heat stress, had more heat-related health issues, and reduced productivity.¹⁸ Wet bulb globe temperature (WBGT) measurements (environmental heat strain index) were made over a 4-year period at 100 locations of automotive manufacturing units in Chennai. Measurements were made during the hottest part of the day (11am–2.30 pm) and month (May or June). Twenty-eight percent of workers had TLV above the recommended range.¹⁹

Heat stress was found to be higher in those working outdoors and with longer duration of employment in our cohort. Similar findings were observed in a cross-sectional study of 35 diesel power plant operators in an Indonesian state electricity company wherein heat stress assessed by HSSI was found to be higher in older workers, those with longer employment duration, and with poor hydration status.²⁵ In the Thai cohort study, heat stress assessed in 37,816 full-time workers with a questionnaire was found to be higher in men, those with lower education and income, those involved in physical jobs as compared to office work, workers in rural areas, and regular drinkers and smokers.²⁶ Cumulative heat exposure with longer employment duration and decrease in functional sweat glands in older individuals altering sweat rates may be the possible causes.²⁷ HSSI scores did not differ between men and women in our cohort. In a study of 261 outdoor workers in Anuradhapura district of Sri Lanka, heat stress scores were found to be higher in women. The authors postulated that even though women have a higher density of activated sweat glands as compared to men, sweat rate is lower, leading to higher core temperatures.²⁸ However, women security officers in our cohort were younger and thus having lower cumulative heat exposures. Interestingly, HSSI scores in our cohort were not affected by BMI, but those with abdominal obesity had lower scores. Theoretically, body fat has low conductivity which results in low passage of heat from surface to blood.²⁹ However, clinical trials have shown conflicting results on the effect of obesity on heat strain.^30,31 Obese individuals produce less physical work and this might have led to lower HSSI scores in officers with abdominal obesity in our cohort.

In our study, we observed that the eGFR was lower in older officers, those with longer employment duration, those who had hypertension, and those who were smokers. Hypertension is a risk factor for both development as well as rapid progression of CKD. Also, decline in eGFR can cause hypertension due to volume expansion and increase in systemic vascular resistance.³² This temporality of exposure and outcome cannot be ascertained with confidence in a cross-sectional study. The effect of smoking on eGFR is controversial with studies showing active smokers have a higher,^33,34 lower,³⁵ or no difference³⁶ in eGFR as compared to nonsmokers.

In our cohort of security officers, we did not find any correlation between HSSI scores and eGFR. The concept of heat stress nephropathy was first described among sugarcane workers in Central America and was known as “Mesoamerican Nephropathy.”³⁷ Sugarcane harvesting is done over a period of 5 months (known as “zafra”) and involves 4–12 hours of intense labor in temperatures of 34–42°C.³⁸ Physical exertion in heat causes reduction in renal blood flow which reduces oxygen delivery to renal tubules causing depletion of adenosine triphosphate (ATP) leading to acute tubular injury.³⁹ Repeated episodes of AKI can then progress to CKD.

The job profile of security officers, however, does not involve intense physical activity. The other important determinant of heat stress nephropathy is chronic dehydration. Prolonged periods of dehydration cause an increase in osmolality leading to vasopressin secretion which increases urinary concentration. Chronic dehydration also causes renal vasoconstriction and decrease in eGFR. In a study carried out at a sugar mill in Nicaragua during 2017–2018 (“harvest period 1”), Glaser et al. noted that workers involved in most strenuous work (burned cane cutters) had a greater decline in cross-harvest eGFR as compared to those carrying out less strenuous work (seed cutters, irrigation repair workers, and field support staff). Interventions like hydration, cooling techniques, and regulation of work were introduced during “harvest period 2” (2018–2019). Cross-harvest eGFR-decline and AKI rates in burned cane cutters were lower during “harvest period 2.”^40,41 Acidic urine, a marker of intravascular dehydration was more common in those working outdoors and consuming <2 L of water during the 8-hour work shift in our study.⁴² The impact of heat stress did not translate into the kidney function of our security officers probably due to lack of strenuous physical activity and good hydration habits observed in the majority of our cohort.

To the best of our knowledge, this is the first study looking into factors affecting eGFR in a large cohort of security officers. The strengths of our study are the large size of our cohort, CKD being defined as per KDIGO definition, use of validated questionnaires adapted to local population, and clinical impact of the program in treatment modifications. Our study, however, is not without limitations. We used HSSI which is an observational-perceptual tool to assess heat stress. Environmental and physiological indices were not used due to cost and invasive nature of the tests.⁴³ Being a cross-sectional study, a causal inference cannot be made due to problems of reverse causality and survivorship bias, which would need future longitudinal studies. Our institute follows occupational guidelines for heat-related preventive measures rigorously which could impact the outcomes of our study. This is evident in majority having good hydration habits. However, in spite of all these measures, almost half of the cohort had heat stress in the red zone.

Conclusion

We observed a high prevalence of obesity, diabetes, and hypertension in security personnel working at our tertiary care center. Almost half of the cohort had definite heat stress. Heat stress was higher in those working outdoors and with longer employment duration and lower in those with abdominal obesity. eGFR was lower in older officers, smokers, hypertensives, and those with longer employment duration. Less than 1% of officers developed CKDu. eGFR was unaffected by the high levels of heat stress observed in security officers. Future longitudinal occupational cohort studies are needed to understand the pathomechanisms of differential impact of heat stress on kidney function of agricultural and nonagricultural workers.