Abstract
Objective
This study examined cardiovascular disease risk factors by BMI category in firefighters, the association of BMI and age with risk factor prevalence, and the prevalence of risk factors by BMI category within age groups.
Methods
Cardiovascular measures from the medical evaluations of 4,453 firefighters, performed between 2015 and 2018 at four occupational health clinics in the United States (South‐West Cohort, Mid‐Atlantic Cohort, South‐East Cohort, and Mid‐West Cohort), were analyzed cross‐sectionally by BMI and age categories.
Results
Among female firefighters with normal weight, 25% had high blood pressure, 8% had low high‐density lipoprotein cholesterol, and 0% had high glucose, whereas the prevalence in female firefighters with obesity was 57%, 45%, and 11%, respectively. Among male firefighters, there were independent and significant associations of BMI and age for the prevalence of high blood pressure, high cholesterol, high triglycerides, and high glucose. Higher BMI category was associated with a higher prevalence of high blood pressure, high triglycerides, and low high‐density lipoprotein cholesterol within all age groups and with a higher prevalence of high glucose and high cholesterol within ages 40 to 49 and 50 to 59 years.
Conclusions
An increasing prevalence of risk factors with older age and higher BMI suggests that preventive strategies should be initiated in younger firefighters and aggressively promoted or mandated throughout firefighters’ careers.
Study Importance.
What is already known?
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Sudden cardiac events are the leading cause of on‐duty death in the fire service, and higher BMI is associated with increased severity of cardiovascular disease risk factors in firefighters.
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Although both obesity prevalence and the incidence of sudden cardiac death increase with age in firefighters, the prevalence of cardiovascular disease risk factors by age and BMI in the fire service has not been reported.
What does this study add?
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A higher BMI category was significantly associated, independent from age, with a higher prevalence of high blood pressure, high cholesterol, low high‐density lipoprotein cholesterol, high triglycerides, high blood glucose, and prevalence of metabolic syndrome in firefighters.
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Within each decade of life, male firefighters with higher BMI categories were more likely to have high blood pressure, low high‐density lipoprotein cholesterol, high triglycerides, and metabolic syndrome.
How might these results change the direction of research or the focus of clinical practice?
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Health care providers who care for firefighters have a powerful opportunity to counsel firefighters on the risks of excess weight, recommend preventive strategies in younger firefighters, and aggressively promote healthy body weight throughout firefighters’ careers.
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The factors driving the high obesity prevalence in the fire service should be examined in future research for the purpose of optimizing health promotion and wellness programs.
Introduction
Health experts have repeatedly warned about an obesity epidemic in the United States (1, 2, 3), and research suggests that having a high BMI is one of the top five risk factors in the world for attributable deaths and disability‐adjusted life years (4). Obesity is associated with several negative health outcomes, including cardiovascular disease (CVD), cardiac enlargement, gallbladder disease, diabetes, several cancers, osteoarthritis, and sleeping disorders (5, 6, 7, 8, 9, 10). In addition to being a significant predictor of coronary heart disease and heart failure (5, 11), obesity is indirectly related to cardiovascular health through its association with several other CVD risk factors, including hypertension, high cholesterol, low high‐density lipoprotein (HDL) cholesterol, high triglycerides, and diabetes (3, 8, 12, 13). Therefore, obesity is a primary target for interventions to decrease overall cardiovascular risk.
Firefighters perform critical public safety work that requires substantial muscular exertion and the use of heavy personal protective equipment. Firefighting activities have been shown to induce extreme cardiovascular strain, evidenced by decreased stroke volume, impaired diastolic function, arterial stiffness, and increased coagulability (14, 15, 16, 17, 18). National statistics indicate that nearly 50% of duty‐related deaths in firefighters are due to sudden cardiac events (19). Autopsy records from firefighter fatality examinations have additionally shown that a vast majority (~80%) of firefighters who succumbed to cardiac events had evidence of atherosclerotic CVD and a structurally enlarged heart (20). Obesity has been associated with a two‐fold increased risk of left ventricular hypertrophy in firefighters (21), and other research with firefighters has found a positive relationship between BMI and both the severity of CVD risk factors (13, 22, 23, 24, 25, 26) and the risk of on‐duty cardiac fatalities (27, 28, 29). Despite the enormous implications of obesity on cardiovascular health, a high prevalence has been reported in the fire service (23, 24, 30, 31, 32), and recent studies have shown that obesity prevalence increases with advancing age (32).
Several major CVD risk factors increase with age in both the general population (33) and firefighters (12, 32, 34). This translates directly to the cardiovascular safety of firefighters, as the highest incidence of on‐duty sudden cardiac death is seen in firefighters ages 54 to 64 years (35). Given that obesity prevalence increases with age, it is necessary to consider both variables together to better understand the interaction of BMI with CVD risk factors. Such an investigation into major modifiable (obesity) and nonmodifiable (age) risk factors may help guide fire‐service health and wellness programming to improve cardiac health and reduce on‐duty cardiac fatalities. Currently, no studies to our knowledge have included a sufficient sample size to investigate CVD risk factors by BMI and age categories in firefighters. Therefore, the purpose of this paper was to describe measures of cardiovascular health and CVD risk factors based on BMI category in a large sample of firefighters, assess the association of BMI and age with CVD risk factors, and report the prevalence of CVD risk factors by BMI category within age groups.
Methods
Assessments of BMI and CVD risk factors were obtained from firefighters who participated in department‐required annual medical evaluations between the years 2015 and 2018. The medical evaluations were performed by four occupational clinics, which follow the National Fire Protection Association 1582 Standard on Occupational Medical Program for Fire Departments (36) and provide these services to fire departments on a contract basis. The four clinics served fire departments in southern Arizona (South‐West Cohort), northern Virginia (Mid‐Atlantic Cohort), central Florida (South‐East Cohort), and the capital region of Indiana (Mid‐West Cohort). Female firefighters from the South‐East and South‐West cohorts were not included in the analytical sample because of small sample sizes within BMI categories. Data on low‐density lipoprotein (LDL) cholesterol, HDL cholesterol, and triglycerides were not available from one department (n = 256), and medication usage was not available from one clinic (n = 366). For the analysis including those variables that were not available, the department or clinic was excluded. Data were combined to create a cohort of 4,453 US career firefighters (n = 4,225 males and n = 228 females). A deidentified database including descriptive characteristics and measures of cardiovascular health was shared with researchers at Skidmore College’s First Responder Health and Safety Laboratory. The study protocol was reviewed and approved by the Skidmore College Institutional Review Board.
Data collection
During the medical exams, height was assessed using a stadiometer, and weight was measured using a standard physician scale. Health care providers measured blood pressure using the auscultation technique, with firefighters in the seated position. Fasted blood glucose and cholesterol were assessed via a commercial laboratory analysis. The use of prescription medications was assessed using questionnaires.
Definitions
All participants were grouped by age according to decade of life: 20 to 29, 30 to 39, 40 to 49, and 50 to 59 years old. Additionally, participants were divided into BMI categories of having normal weight (<25 kg/m2), overweight (25‐29.9), or obesity (≥30) (37) for the main analyses, and the prevalence of obesity subclasses defined as class 1 (30‐34.9), class 2 (35‐39.9), and class 3 (≥40) were reported (37). Having high blood pressure was defined as systolic blood pressure ≥ 130 mmHg, or diastolic blood pressure ≥ 80 mmHg, or taking antihypertensive medication (38). Having high cholesterol was defined as total cholesterol ≥ 240 mg/dL and/or taking lipid‐lowering medication (39). Having high triglycerides was defined as ≥200 mg/dL (40), having high LDL cholesterol was defined as ≥160 mg/dL (40), and having low HDL cholesterol was defined as <40 mg/dL for males and <50 mg/dL for females (40). Having high fasting blood glucose was defined as >125 mg/dL and/or taking medications related to blood glucose stabilization (41).
Metabolic syndrome was determined using a modified definition of the National Cholesterol Education Panel (NCEP) guidelines (39). Firefighters were considered to have metabolic syndrome if they had three or more of the following four NCEP metabolic syndrome criteria: high blood pressure with systolic blood pressure ≥ 130 mmHg and/or diastolic blood pressure ≥85 mmHg, triglycerides ≥ 150 mg/dL, blood glucose ≥ 110 mg/dL, and HDL cholesterol < 40 mg/dL in males or < 50 mg/dL in females. The NCEP guidelines include waist circumference (>102 cm for males and >88 cm for females) as a fifth criteria measure (39), but waist circumference was not measured at all occupational health clinics. Therefore, the prevalence of metabolic syndrome, defined as having three or more out of four (rather than five) criteria, is an underestimation of true metabolic syndrome prevalence in this firefighter cohort.
Statistical analysis
Descriptive data are presented as means (SE) in Table 1. Given the large sample size differences across the geographic locations and convenient nature of the fire departments that collected and provided data, all point estimates and statistical comparisons were calculated as though there was an equal number of observations in each of the four geographical locations (i.e., each geographical location contributed equally to a point estimate or the association across locations). Unadjusted mean cardiometabolic values and risk factor prevalence were estimated for all ages combined across BMI categories for males and females separately; separate linear and logistic regression models were also conducted for each BMI category. Differences between mean cardiometabolic measures of firefighters with normal weight, overweight, and obesity in the full sample were tested using linear regression models, with a categorical variable for BMI category and geographical location. Post hoc pairwise comparisons were made between the three BMI categories. Logistic regression models were used to test for differences in the prevalence of CVD risk factors between BMI categories. The prevalence of a CVD risk factor was predicted for each BMI category and the odds ratios, which were unadjusted and adjusted for age, with 95% confidence intervals (CIs) reported using the normal‐weight BMI category as the reference group.
TABLE 1.
Descriptive characteristics and CVD risk factor values in male and female firefighters by BMI category
| BMI (kg/m2) | |||
|---|---|---|---|
| <25 | 25‐29.9 | ≥30 | |
| Male firefighters | |||
| n (%) | 498 (14) | 1,930 (49) | 1,797 (37) |
| White (%) | 84 | 86 | 82b |
| Age (y) | 37.9 ± 0.5 | 40.7 ± 0.3a | 43.4 ± 0.3ab |
| Height (m) | 1.8 ± 0.0 | 1.8 ± 0.0 | 1.8 ± 0.0 |
| Weight (kg) | 76.1 ± 0.4 | 89.0 ± 0.2a | 108.5 ± 0.5ab |
| Total cholesterol (mg/dL ) | 183.8 ± 1.6 | 192.7 ± 0.8a | 192.9 ± 0.9a |
| LDL cholesterol (mg/dL) | 109.5 ± 1.7 | 116.5 ± 1.0a | 119.6 ± 1.2a |
| HDL cholesterol (mg/dL) | 55.1 ± 0.7 | 49.4 ± 0.4a | 44.1 ± 0.4ab |
| Triglycerides (mg/dL) | 84.7 ± 2.7 | 114.1 ± 2.4a | 148.7 ± 3.3ab |
| Blood glucose (mg/dL) | 91.7 ± 0.7 | 94.8 ± 0.5a | 99.6 ± 0.6ab |
| Systolic blood pressure (mmHg) | 118.4 ± 0.5 | 121.2 ± 0.3a | 126.0 ± 0.4ab |
| Diastolic blood pressure (mmHg) | 76.2 ± 0.3 | 78.3 ± 0.2a | 81.3 ± 0.2ab |
| Female firefighters | |||
| n (%) | 75 (34) | 88 (39) | 65 (27) |
| White (%) | 93 | 76a | 87 |
| Age (y) | 39.9 ± 1.1 | 41.0 ± 0.9 | 39.9 ± 1.2 |
| Height (m) | 1.7 ± 0.0 | 1.7 ± 0.0 | 1.7 ± 0.0 |
| Weight (kg) | 64.7 ± 0.7 | 76.0 ± 0.7a | 94.8 ± 1.8ab |
| Total cholesterol (mg/dL) | 189.0 ± 3.4 | 191.3 ± 4.2 | 182.4 ± 5.1ab |
| LDL cholesterol (mg/dL) | 108.7 ± 2.7 | 114.8 ± 3.3 | 110.2 ± 4.7 |
| HDL cholesterol (mg/dL) | 65.7 ± 1.5 | 59.0 ± 1.5a | 51.8 ± 1.6ab |
| Triglycerides (mg/dL) | 73.3 ± 3.9 | 87.1 ± 9.7a | 101.7 ± 9.1ab |
| Blood glucose (mg/dL) | 86.8 ± 0.9 | 88.1 ± 1.0 | 92.2 ± 2.7ab |
| Systolic blood pressure (mmHg) | 114.9 ± 1.4 | 116.4 ± 1.1 | 123.2 ± 2.0ab |
| Diastolic blood pressure (mmHg) | 74.4 ± 0.9 | 74.8 ± 0.7 | 79.5 ± 1.2ab |
Data given as as means ± SE.
Statistical differences (P < 0.05) for post hoc pairwise comparisons are indicated by superscript “a” for comparisons between obesity or overweight BMI categories with the normal‐weight BMI category and superscript “b” for comparisons between the overweight and obesity BMI categories. Each geographical location of the fire departments was given equal weight in the point estimates and the prevalence of firefighters with normal weight, overweight, and obesity.
CVD, cardiovascular disease; HDL, high‐density lipoprotein; LDL, low‐density lipoprotein.
Owing to inadequate sample sizes among females, the analyses including both age and BMI categories were only conducted with males. Based on an a priori objective, a focus of the analysis including both age and BMI was to determine whether the likelihood of having cardiometabolic risk factors was higher among firefighters with a higher BMI and whether this was the case within each of the age groups. Descriptive estimates of risk factor prevalence were reported for each of the three BMI categories across each of the age groups. Analyses of general trends across age and BMI categories were conducted using logistic regression models that included both age group and BMI category modeled as continuous variables. A step‐down approach for modeling age was used, starting with a quadratic function based on previous findings on the relationship of age and cardiometabolic health in the same dataset. Wald tests were conducted to determine whether the quadratic relationship was significant. The male sample was also stratified by age group, and the associations of BMI with the likelihood of having a particular cardiometabolic risk factor were examined within each age group with BMI category modeled as a continuous variable and categorically with normal weight as the reference group. The level of significance for all analyses was P < 0.05 and was two‐sided for all tests. All analyses were conducted using Stata version 15.1 (StataCorp, College Station, Texas).
Results
The average age across male firefighters with normal weight, overweight, and obesity was 37.9 years, 40.7 years, and 43.4 years, respectively, and across female firefighters was 39.9 years, 41.0 years, and 39.9 years, respectively. The sample consisted predominantly of White individuals (Table 1). Among males, 82% were non‐Hispanic White individuals, 8% were non‐Hispanic African American/Black individuals, 6% were Hispanic individuals, 2% were Asian individuals, and 2% reported their race as “other” (data not shown). Among females, 84% were non‐Hispanic White individuals, 10% were non‐Hispanic African American/Black individuals, 4% were Hispanic individuals, 0.4% were Asian individuals, and 2% reported their race as “other” (data not shown). Among male firefighters, 14% had normal weight, 49% had overweight, and 37% had obesity as determined by BMI categorization, and the prevalence of obesity subclasses was 27% class 1, 7% class 2, and 2% class 3. Among female firefighters, 34% had normal weight, 39% had overweight, and 27% had obesity as determined by BMI categorization, and the prevalence of obesity subclasses was 16% class 1, 8% class 2, and 3% class 3. The unadjusted mean cardiovascular measures for all ages combined worsened significantly across BMI categories (normal weight to obesity) for both male and female firefighters. For the unadjusted and age‐adjusted estimates among all ages combined, male firefighters with overweight and obesity were more likely to have high blood pressure, high cholesterol, low HDL cholesterol, high triglycerides, and three or more of the criteria for metabolic syndrome compared with firefighters with normal weight; among females, firefighters with overweight were more likely to have low HDL cholesterol, and firefighters with obesity were more likely to have high blood pressure and low HDL cholesterol compared with firefighters with normal weight (Table 2). Among female firefighters with obesity, 58% had high blood pressure and 10% had metabolic syndrome, and among male firefighters with obesity, 80% had high blood pressure and 21% had metabolic syndrome.
TABLE 2.
Prevalence and ORs of CVD risk factors by BMI category in male and female firefighters (20‐59 years old)
| Male firefighters | Female firefighters | |||||||||
|---|---|---|---|---|---|---|---|---|---|---|
| %a | OR | 95% CI | Adjusted OR | 95% CI | %a | OR | 95% CI | Adjusted OR | 95% CI | |
| High blood pressure | ||||||||||
| Normal weight | 38 | Ref | – | – | – | 25 | Ref | – | – | – |
| Overweight | 58 | 2.3 | 1.9‐2.9 | 2.2 | 1.7‐2.7 | 32 | 1.4 | 0.7‐2.8 | 1.4 | 0.6‐3.2 |
| Obesity | 81 | 7.0 | 5.5‐8.8 | 6.2 | 4.9‐7.9 | 58 | 4.0 | 1.9‐8.6 | 5.7 | 2.3‐14.3 |
| High cholesterol | ||||||||||
| Normal | 11 | Ref | – | – | – | 4 | Ref | – | – | – |
| Overweight | 20 | 1.9 | 1.4‐2.6 | 1.7 | 1.2‐2.3 | 8 | 2.1 | 0.6‐7.2 | 2.0 | 0.6‐6.9 |
| Obesity | 26 | 2.8 | 2.0‐3.8 | 2.2 | 1.6‐3.1 | 6 | 1.5 | 0.4‐5.4 | 1.4 | 0.4‐5.2 |
| High LDL cholesterol | ||||||||||
| Normal weight | 7 | Ref | – | – | – | 0 | Ref | – | – | – |
| Overweight | 10 | 1.6 | 1.1‐2.3 | 1.5 | 1.0‐2.2 | 8 | – | – | – | – |
| Obesity | 9 | 1.4 | 0.97‐2.1 | 1.3 | 0.9‐1.9 | 3 | – | – | – | – |
| Low HDL cholesterol | ||||||||||
| Normal weight | 10 | Ref | – | – | – | 8 | Ref | – | – | – |
| Overweight | 20 | 2.2 | 1.6‐3.1 | 2.2 | 1.6‐3.0 | 26 | 4.2 | 1.6‐11.3 | 4.2 | 1.6‐11.2 |
| Obesity | 36 | 4.9 | 3.6‐6.7 | 4.8 | 3.5‐6.6 | 45 | 10.0 | 3.6‐27.7 | 10.1 | 3.6‐28.4 |
| High triglycerides | ||||||||||
| Normal weight | 2 | Ref | – | – | – | 1 | Ref | – | – | – |
| Overweight | 10 | 5.7 | 2.9‐11.2 | 5.3 | 2.7‐10.5 | 2 | 1.6 | 0.1‐18.4 | 1.4 | 0.1‐16.7 |
| Obesity | 18 | 11.3 | 5.8‐22.2 | 10.3 | 5.3‐20.2 | 4 | 3.4 | 0.4‐32.7 | 3.2 | 0.3‐32.5 |
| High blood glucose | ||||||||||
| Normal weight | 2 | Ref | – | – | – | 0 | Ref | – | – | – |
| Overweight | 3 | 1.2 | 0.6‐2.4 | 1.1 | 0.5‐2.0 | 0 | – | – | – | – |
| Obesity | 7 | 3.3 | 1.8‐6.3 | 2.6 | 1.3‐4.8 | 11 | – | – | – | – |
| Metabolic syndrome b | ||||||||||
| Normal weight | 2 | Ref | – | – | – | 0 | Ref | – | – | – |
| Overweight | 6 | 3.0 | 1.5‐6.0 | 2.7 | 1.7‐5.5 | 1 | – | – | – | – |
| Obesity | 18 | 13.4 | 5.4‐20.9 | 9.3 | 4.7‐18.2 | 10 | – | – | – | – |
Adjusted ORs were estimated using a logistic regression model that included age as a covariate.
BMI categories: normal (<25); overweight (25‐29.9); obesity (≥30).
Unadjusted prevalence of a risk factor.
Meets three or more of the four available criteria for metabolic syndrome: systolic blood pressure ≥ 130 mmHg and/or diastolic blood pressure ≥ 85 mmHg, triglycerides ≥ 150 mg/dL, blood glucose ≥ 110 mg/dL, and HDL cholesterol < 40 mg/dL in males or < 50 mg/dL in females.
CVD, cardiovascular disease; HDL, high‐density lipoprotein; LDL, low‐density lipoprotein; OR, odds ratio; Ref, reference value.
The odds ratios from the logistic regression models of BMI category with CVD risk factors stratified by age group are presented in Table 3, and the descriptive prevalence of risk factors is shown in Figure 1. Analyses of general trends in which age and BMI categories were modeled as continuous variables with respect to the likelihood of having a particular risk factor are also reported in Figure 1. Increasing age group and BMI category in male firefighters were significant and independently associated with a higher likelihood of having high blood pressure, high cholesterol, high blood glucose, and metabolic syndrome. There was a significant quadratic relationship between advancing age and a higher likelihood of having high blood pressure and high cholesterol. There was a significant quadratic relationship between age and the likelihood of having high triglycerides and high LDL cholesterol, with a predicted peak in firefighters between 40 and 49 years old; BMI was significantly associated with a higher likelihood of having high triglycerides but was not associated with a higher likelihood of having high LDL cholesterol. For low HDL cholesterol, only BMI was significantly associated with a higher likelihood of having low HDL cholesterol.
TABLE 3.
ORs for CVD risk factors in male firefighters by BMI category, stratified by age group
| Age 20‐29 | Age 30‐39 | Age 40‐49 | Age 50‐59 | |||||
|---|---|---|---|---|---|---|---|---|
| OR | 95% CI | OR | 95% CI | OR | 95% CI | OR | 95% CI | |
| High blood pressure | ||||||||
| Normal weight | Ref | – | Ref | – | Ref | – | Ref | – |
| Overweight | 2.0 | 1.1‐3.6 | 1.8 | 1.2‐2.7 | 2.7 | 1.8‐3.9 | 2.5 | 1.5‐4.2 |
| Obesity | 3.4 | 1.8‐6.5 | 6.2 | 4.0‐9.7 | 7.6 | 5.1‐11.4 | 7.2 | 4.1‐12.7 |
| High cholesterol | ||||||||
| Normal | Ref | – | Ref | – | Ref | – | Ref | – |
| Overweight | 2.0 | 0.2‐18.5 | 1.6 | 0.8‐3.4 | 2.0 | 1.2‐3.3 | 1.3 | 0.8‐2.3 |
| Obesity | 4.3 | 0.5‐38.6 | 1.9 | 0.9‐3.9 | 2.5 | 1.5‐4.1 | 2.0 | 1.2‐3.5 |
| High LDL cholesterol | ||||||||
| Normal weight | Ref | – | Ref | – | Ref | – | Ref | – |
| Overweight | 3.1 | 0.4‐26.2 | 1.6 | 0.8‐3.2 | 1.5 | 0.8‐2.7 | 0.9 | 0.4‐1.9 |
| Obesity | 6.2 | 0.7‐53.0 | 1.2 | 0.6‐2.6 | 1.1 | 0.6‐1.9 | 1.1 | 0.5‐2.4 |
| Low HDL cholesterol | ||||||||
| Normal weight | Ref | – | Ref | – | Ref | – | Ref | – |
| Overweight | 1.7 | 0.9‐3.5 | 1.8 | 1.0‐3.1 | 2.6 | 1.5‐4.7 | 3.1 | 1.3‐7.5 |
| Obesity | 4.2 | 2.0‐8.7 | 3.7 | 2.1‐6.5 | 6.0 | 3.4‐10.6 | 6.1 | 2.6‐14.4 |
| High triglycerides | ||||||||
| Normal weight | Ref | – | Ref | – | Ref | – | Ref | – |
| Overweight | 4.2 | 0.5‐34.4 | 4.5 | 1.4‐14.9 | 9.3 | 2.3‐38.5 | 3.1 | 0.9‐10.4 |
| Obesity | 15.7 | 2.0‐123.3 | 9.5 | 2.9‐30.9 | 17.6 | 4.3‐72.1 | 4.9 | 1.5‐16.1 |
| High blood glucose | ||||||||
| Normal weight | Ref | – | Ref | – | Ref | – | Ref | – |
| Overweight | 0.6 | 0.0‐9.1 | 0.7 | 0.1‐4.0 | 0.9 | 0.3‐2.8 | 1.5 | 0.5‐4.3 |
| Obesity | 0.8 | 0.0‐13.8 | 0.7 | 0.1‐4.3 | 2.5 | 0.9‐7.1 | 3.7 | 1.3‐10.6 |
| Metabolic syndrome a | ||||||||
| Normal weight | Ref | – | Ref | – | Ref | – | Ref | – |
| Overweight | 1.7 | 0.2‐17.1 | 1.3 | 0.4‐4.5 | 3.6 | 1.1‐11.8 | 3.7 | 0.9‐15.8 |
| Obesity | 10.7 | 1.3‐85.3 | 5.9 | 1.5‐16.5 | 12.6 | 3.9‐40.2 | 10.5 | 2.5‐43.7 |
ORs and 95% CIs were estimated using separate logistic regression models for each age group, with BMI modeled as a categorical variable.
Meets three or more of the four available criteria for metabolic syndrome: systolic blood pressure ≥ 130 and/or diastolic blood pressure ≥ 85 mmHg, triglycerides ≥ 150 mg/dL, blood glucose ≥ 110 mg/dL, and HDL cholesterol < 40 mg/dL.
CVD, cardiovascular disease; OR, odds ratio; HDL, high‐density lipoprotein; LDL, low‐density lipoprotein; Ref, reference value.
Figure 1.
The prevalence of cardiovascular disease risk factors in male firefighters by age and BMI. Point estimates and standard errors were predicted from a logistic regression model, with age and BMI categories modeled as categorical variables, that included terms for age, BMI, and their interaction. The sample was then stratified by age group, and the significance of BMI within each age group was tested using a logistic regression model with BMI category modeled as a continuous variable. For the analyses of general trends, a step‐down approach was taken, starting with age group modeled quadratically and including a term for BMI category. If a quadratic relationship was not statistically significant, then the model was conducted with only the lower‐level term for age group and a term for BMI category. *Indicates a significant association of BMI category with an outcome within an age group. The significant coefficients in the generaltrends models are reported in a box above the bar graph. P < 0.05 was considered statistically significant. HDL, high‐density lipoprotein; LDL, low‐density lipoprotein.
When stratified by age group, increasing BMI category was associated with a higher likelihood of having high blood pressure, low HDL cholesterol, high triglycerides, and metabolic syndrome across all age groups. Being in a higher BMI category was associated with a higher likelihood of having high cholesterol and a higher likelihood of having high blood glucose within the age groups 40 to 49 and 50 to 59 years.
Discussion
This study was the first, to our knowledge, to examine the prevalence of CVD risk factors by age and BMI category in a large cohort of US firefighters. Our sample consisted predominantly of White individuals (82%), which is consistent with broader reports in the US fire service (42). We found a high prevalence of overweight (48%) and obesity (36%) in this public safety occupational group. Furthermore, among male and female firefighters with obesity, there was an alarmingly high prevalence of cardiometabolic risk factors: 81% and 58% had high blood pressure, 36% and 45% had low HDL cholesterol, and 18% and 10% had metabolic syndrome, respectively. Being in a higher BMI category was significantly associated, independent from age, with a higher prevalence of all the examined CVD risk factors in male firefighters, including high blood pressure, high cholesterol, low HDL cholesterol, high triglycerides, high blood glucose, and prevalence of metabolic syndrome. Within each decade of life, male firefighters with higher BMI categories were more likely to have high blood pressure, low HDL cholesterol, high triglycerides, and metabolic syndrome. BMI was also significantly associated with blood glucose and high cholesterol in male firefighters aged 40 to 49 and 50 to 59 years. These results indicate that male firefighters who are older and have obesity are more likely to have CVD risk factors, and firefighters with obesity in any decade of life have a greater likelihood of developing several CVD risk factors compared with firefighters with normal weight. Given that coronary heart disease is the leading cause of on‐duty deaths in both older and younger firefighters (35), there is an urgency to better understand which firefighters are at greatest risk and to devise effective programming to mitigate that risk.
Among male firefighters in the current study, the prevalence of CVD risk factors was higher in firefighters with overweight and obesity compared with firefighters with normal weight, with the exception of high blood glucose, which was only different between those who were in the obesity and normal‐weight BMI categories. These findings are consistent with previous studies that have assessed the relationship between obesity and CVD risk factors in the fire service. There is agreement that obesity in firefighters is strongly related to high blood pressure (13, 24, 25, 26, 31), and studies have also shown associations between obesity and the prevalence of high cholesterol (25), low HDL cholesterol (24, 26), high triglycerides (25, 26), and high blood glucose (26). However, not all studies have found that obesity is associated with CVD risk factors. Poston et al. found that obesity was consistently related to high blood pressure, but not other CVD risk factors, in a cohort of 478 Missouri Valley firefighters (23).
Most previous studies reporting CVD risk factors by BMI have not included female firefighters (13, 22, 23, 24, 25, 26). The current study included a large cohort of female firefighters, and although the sample was not large enough to examine BMI within age groups, analyses among the full sample showed that female firefighters with obesity had a higher prevalence of high blood pressure and low HDL cholesterol than female firefighters with normal weight. Previous research has reported an average prevalence of 42% having high blood pressure (32), 20% having low HDL cholesterol (32), and 5% having metabolic syndrome in female firefighters (43). When assessed by weight category, the results of the current study revealed that 25% of female firefighters with normal weight and 58% of female firefighters with obesity had high blood pressure, 8% of those with normal weight and 45% of those with obesity had low HDL cholesterol, and 0% of those with normal weight and 10% of those with obesity had metabolic syndrome. Our findings support the importance of actively protecting the cardiovascular health of both male and female firefighters in order to reduce overall cardiovascular risk and subsequent cardiac events.
Although it is well understood that aging is associated with an increased prevalence of CVD risk factors in the general population (33), as well as increased incidence of cardiac events in firefighters (35), only one study with the fire service, to our knowledge, has assessed measures of cardiovascular health by age (44). In the current study of male firefighters, increasing age was associated with a higher likelihood of having high blood pressure, high cholesterol, high blood glucose, and metabolic syndrome, with an association that peaked between the ages of 45 to 50 years for the prevalence of high triglycerides and high LDL cholesterol. The nature of this quadratic relationship is likely due to an increase in lipid‐lowering medication, which is more likely to be prescribed to males ≥ 45 years old and was not used to identify high triglycerides or high LDL cholesterol as a risk factor. Importantly, across all age groups of firefighters with normal weight, the prevalence of metabolic syndrome was < 3%, and the prevalence of high blood glucose and high triglycerides was < 5%.
When assessing CVD risk factors and BMI, it is important to examine age, given the general increase in obesity prevalence with increasing age (12, 32, 45). Few studies in the general population (12), and no studies (to our knowledge) in the fire service, have examined the associations of both BMI and age with CVD risk factors using the unique stratified approach of the current study. In a general population study assessing hypertension and dyslipidemia by age and BMI, Brown et al. showed a stepwise increase in CVD risk factor prevalence with increasing age and BMI category (12), which is consistent with the findings of the current study. The average prevalence of CVD risk factors in firefighters has been previously reported, though without context to inform which firefighters were at highest risk. Hypertension is of great concern in the fire service, with a reported prevalence of 44% in 20‐ to 29‐year‐olds (Khaja SU, Mathias KC, Bode ED, et al., unpublished data, 2021). However, this prevalence conceals the important involvement of excess weight, as 64% of 20‐ to 29‐year‐old firefighters with obesity in the current study had high blood pressure. There were also large differences in young firefighters’ risk factor prevalence between BMI categories for low HDL cholesterol (12% in those with normal weight and 37% in those with obesity), high triglycerides (1% in those with normal weight and 13% in those with obesity), and metabolic syndrome (1% in those with normal weight and 14% in those with obesity). The same was true for older firefighters, particularly those with low HDL cholesterol, high triglycerides, high blood glucose, and metabolic syndrome. Ultimately, these findings reveal stunning increases in risk with being in a higher BMI category across all age groups, highlighting the importance of wellness interventions that promote healthy weight status throughout firefighters’ careers.
Obesity is an independent risk factor for CVD and is known to be associated with “risk factor clustering” (12, 24). A buildup of excess adiposity leads to several pro‐inflammatory effects in the vascular system, including adipocyte tissue dysregulation and decreased insulin sensitivity. The disruptive nature of these conditions can cause endothelial dysfunction, which is further related to atherosclerosis, hypertension, and hyperlipidemia (8, 24). The cardiac stress induced by these conditions can lead to cardiac remodeling, such as left ventricular hypertrophy and cardiomegaly, significantly increasing the risk of arrhythmia (10, 46). Obesity is a modifiable risk factor, and BMI is an easy and meaningful assessment for health management in firefighters. Although several studies have reported that the BMI of firefighters, when considered as a group, increases over time, not all firefighters gain weight. Mathias et al. reported that firefighters who lost weight over a 5‐year period had a significant reduction in BMI, total cholesterol, LDL cholesterol, and systolic and diastolic blood pressures, as well as a significant increase in HDL cholesterol, despite their advancing age (30). Occupational health care providers and primary care physicians who care for firefighters have a powerful opportunity to counsel the fire service on the risks associated with excess weight and the possibility for health improvement with lifestyle changes (nutrition and physical fitness), as well as medication use, if needed.
To our knowledge, this study is the first to report on the relationship between obesity and CVD risk factors in both female and male firefighters and the first to further assess the associations of BMI and age with CVD risk factors. Although our sample was not nationally representative, it was one of the largest firefighter cohorts to be assessed in research, and it included firefighters from four geographic regions, with racial representation similar to that of the US fire service at large. Furthermore, our results were based on data from department‐mandatory medical evaluations, eliminating potential selection bias. Although this study presents the cardiovascular health of firefighters by BMI and age, the analyses within this study are limited to observational conclusions and thus cannot determine causation and effect size of age and BMI. Future research should examine the effect of weight loss and other healthy lifestyle changes on reducing on‐duty cardiac events in firefighters. The factors driving the high prevalence of obesity in the fire service should also be examined in future studies for the purpose of optimizing health promotion and wellness programs.
Conclusion
The results of this study indicate that the majority of firefighters have overweight or obesity, and that those who are older and have obesity have the highest prevalence of CVD risk factors. There was an alarming level of risk factor prevalence among the firefighters with obesity in each age group. The combination of advancing age, excess weight, and associated risk factors is particularly concerning for firefighters, who perform arduous work under physically and psychologically stressful conditions. All firefighters should receive medical exams that include screening for CVD risk factors, including an assessment of BMI. Often, health care providers and firefighters alike are reluctant to initiate pharmaceutical treatment of CVD risk factors until firefighters are over 45 years old, as age becomes a risk factor. However, our data clearly show that increasing BMI category is associated with a higher prevalence of several CVD risk factors within all age groups, providing convincing evidence that preventive strategies should be initiated in younger firefighters and aggressively promoted or mandated throughout firefighters’ careers.
Funding agencies
This work was supported by an Assistance to Firefighters grant, which is managed by the Federal Emergency Management Agency (EMW‐2017‐FP‐PP‐00445).
Disclosure
The authors declared no conflict of interest.
Author contributions
EBD and DLS conceptualized the project and framed the manuscript. EDB drafted the manuscript, and DLS provided feedback and revisions. DFS, SMM, and KJ conducted medical evaluations, provided data, and provided input on occupational relevance of data. KCM managed data, performed statistical analyses, and contributed to the writing of the manuscript. All authors critically revised the manuscript for important intellectual content and provided final approval for the version to be published.
References
- 1.Inoue Y, Qin B, Poti J, Sokol R, Gordon‐Larsen P. Epidemiology of obesity in adults: latest trends. Curr Obes Rep 2018;7:276‐288. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 2.Jaacks LM, Vandevijvere S, Pan AN, et al. The obesity transition: stages of the global epidemic. Lancet Diabetes Endocrinol 2019;7:231‐240. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 3.James PT, Rigby N, Leach R. The obesity epidemic, metabolic syndrome and future prevention strategies. Eur J Cardiovasc Prev Rehabil 2004;11:3‐8. [DOI] [PubMed] [Google Scholar]
- 4.GBD 2017 Risk Factor Collaborators . Global, regional, and national comparative risk assessment of 84 behavioural, environmental and occupational, and metabolic risks or clusters of risks for 195 countries and territories, 1990‐2017: a systematic analysis for the Global Burden of Disease Study 2017. Lancet 2018;392:1923‐1994. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 5.Hubert HB, Feinleib M, McNamara PM, Castelli WP. Obesity as an independent risk factor for cardiovascular disease: a 26‐year follow‐up of participants in the Framingham Heart Study. Circulation 1983;67:968‐977. [DOI] [PubMed] [Google Scholar]
- 6.Guh DP, Zhang W, Bansback N, Amarsi Z, Birmingham CL, Anis AH. The incidence of co‐morbidities related to obesity and overweight: a systematic review and meta‐analysis. BMC Public Health 2009;9:88. doi: 10.1186/1471-2458-9-88 [DOI] [PMC free article] [PubMed] [Google Scholar]
- 7.Van Itallie TB. Health implications of overweight and obesity in the United States. Ann Intern Med 1985;103:983‐988. [DOI] [PubMed] [Google Scholar]
- 8.Cercato C, Fonseca FA. Cardiovascular risk and obesity. Diabetol Metab Syndr 2019;11:74. doi: 10.1186/s13098-019-0468-0 [DOI] [PMC free article] [PubMed] [Google Scholar]
- 9.Kotsis V, Tsioufis K, Antza C, et al. Obesity and cardiovascular risk: a call for action from the European Society of Hypertension Working Group of Obesity, Diabetes and the High‐risk Patient and European Association for the Study of Obesity: part B: obesity‐induced cardiovascular disease, early prevention strategies and future research directions. J Hypertens 2018;36:1441‐1455. [DOI] [PubMed] [Google Scholar]
- 10.Tavora F, Zhang Y, Zhang M, et al. Cardiomegaly is a common arrhythmogenic substrate in adult sudden cardiac deaths, and is associated with obesity. Pathology 2012;44:187‐191. [DOI] [PubMed] [Google Scholar]
- 11.Flint AJ, Hu FB, Glynn RJ, et al. Excess weight and the risk of incident coronary heart disease among men and women. Obesity (Silver Spring) 2009;18:377‐383. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 12.Brown CD, Higgins M, Donato KA, et al. Body mass index and the prevalence of hypertension and dyslipidemia. Obes Res 2000;8:605‐619. [DOI] [PubMed] [Google Scholar]
- 13.Choi BongKyoo, Steiss D, Garcia‐Rivas J, et al. Comparison of body mass index with waist circumference and skinfold‐based percent body fat in firefighters: adiposity classification and associations with cardiovascular disease risk factors. Int Arch Occup Environ Health 2016;89:435‐448. [DOI] [PubMed] [Google Scholar]
- 14.Smith DL, DeBlois JP, Kales SN, Horn GP. Cardiovascular strain of firefighting and the risk of sudden cardiac events. Exerc Sport Sci Rev 2016;44:90‐97. [DOI] [PubMed] [Google Scholar]
- 15.Fahs CA, Huimin Yan , Ranadive S, et al. Acute effects of firefighting on arterial stiffness and blood flow. Vasc Med 2011;16:113‐118. [DOI] [PubMed] [Google Scholar]
- 16.Smith DL, Horn GP, Petruzzello SJ, Fahey G, Woods J, Fernhall B. Clotting and fibrinolytic changes after firefighting activities. Med Sci Sports Exerc 2014;46:448‐454. [DOI] [PubMed] [Google Scholar]
- 17.Fernhall B, Fahs CA, Horn G, Rowland T, Smith D. Acute effects of firefighting on cardiac performance. Eur J Appl Physiol 2012;112:735‐741. [DOI] [PubMed] [Google Scholar]
- 18.Smith DL, Petruzzello SJ, Chludzinski MA, Reed JJ, Woods JA. Effect of strenuous life‐fire fire fighting drills on hematological, blood chemistry and psychological measures. J Therm Biol 2001;26:375‐379. [Google Scholar]
- 19.Fahy RF, Petrillo JT, Moliz JL. Firefighter Fatalities in the US – 2019. National Fire Protection Association; 2020. [PubMed] [Google Scholar]
- 20.Smith DL, Haller JM, Korre M, et al. Pathoanatomic findings associated with duty‐related cardiac death in US firefighters: a case‐control study. J Am Heart Assoc 2018;7:e009446. doi: 10.1161/JAHA.118.009446 [DOI] [PMC free article] [PubMed] [Google Scholar]
- 21.Soteriades ES, Targino MC, Talias MA, et al. Obesity and risk of LVH and ECG abnormalities in US firefighters. J Occup Environ Med 2011;53:867‐871. [DOI] [PubMed] [Google Scholar]
- 22.Smith DL, Fehling PC, Frisch A, Haller JM, Winke M, Dailey MW. The prevalence of cardiovascular disease risk factors and obesity in firefighters. J Obes 2012;2012:908267. doi: 10.1155/2012/908267 [DOI] [PMC free article] [PubMed] [Google Scholar]
- 23.Poston WS, Haddock C, Jahnke S, Jitnarin N, Tuley B, Kales S. The prevalence of overweight, obesity, and substandard fitness in a population‐based firefighter cohort. J Occup Environ Med 2011;53:266‐273. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 24.Soteriades ES, Hauser R, Kawachi I, Liarokapis D, Christiani DC, Kales SN. Obesity and cardiovascular disease risk factors in firefighters: a prospective cohort study. Obes Res 2005;13:1756‐1763. [DOI] [PubMed] [Google Scholar]
- 25.Clark S, Rene A, Theurer W, Marshall M. Association of body mass index and health status in firefighters. J Occup Environ Med 2002;44:940‐946. [DOI] [PubMed] [Google Scholar]
- 26.Byczek L, Walton SM, Conrad KM, Reichelt PA, Samo DG. Cardiovascular risks in firefighters: implications for occupational health nurse practice. AAOHN J 2004;52:66‐76. [PubMed] [Google Scholar]
- 27.Yang J, Teehan D, Farioli A, Baur D, Smith D, Kales S. Sudden cardiac death among firefighters ≤45 years of age in the United States. Am J Cardiol 2013;112:1962‐1967. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 28.Geibe JR, Holder J, Peeples L, Kinney AM, Burress JW, Kales SN. Predictors of on‐duty coronary events in male firefighters in the United States. Am J Cardiol 2008;101:585‐589. [DOI] [PubMed] [Google Scholar]
- 29.Kales SN, Soteriades ES, Christoudias SG, Christiani DC. Firefighters and on‐duty deaths from coronary heart disease: a case control study. Environ Health 2003;2:14. doi: 10.1186/1476-069X-2-14 [DOI] [PMC free article] [PubMed] [Google Scholar]
- 30.Mathias KC, Bode ED, Stewart DF, Smith DL. Changes in firefighter weight and cardiovascular disease risk factors over five years. Med Sci Sport Exerc 2020;52:2476‐2482. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 31.Kales S, Polyhronopoulos G, Aldrich J, Leitao E, Christiani D. Correlates of body mass index in hazardous materials firefighters. J Occup Environ Med 1999;41:589‐595. [DOI] [PubMed] [Google Scholar]
- 32.Smith DL, Graham E, Stewart D, Mathias KC. Cardiovascular disease risk factor changes over 5 years among male and female US firefighters. J Occup Environ Med 2020;62:398‐402. [DOI] [PubMed] [Google Scholar]
- 33.Virani S, Alonso A, Benjamin E, et al. Heart disease and stroke statistics – 2020 update: a report from the American Heart Association. Circulation 2020;141:e139‐e151. [DOI] [PubMed] [Google Scholar]
- 34.Glueck CJ, Kelley W, Wang P, Gartside PS, Black D, Tracy T. Risk factors for coronary heart disease among firefighters in Cincinnati. Am J Ind Med 1996;30:331‐340. [DOI] [PubMed] [Google Scholar]
- 35.Farioli A, Christophi CA, Quarta CC, Kales SN. Incidence of sudden cardiac death in a young active population. J Am Heart Assoc 2015;4:e001818. doi: 10.1161/JAHA.115.001818 [DOI] [PMC free article] [PubMed] [Google Scholar]
- 36.National Fire Protection Association . NFPA 1583: Standard on Health‐Related Fitness Programs for Fire Department Members. National Fire Protection Association; 2015. [Google Scholar]
- 37.Centers for Disease Control and Prevention . Defining adult overweight and obesity. Updated April 28, 2021. Accessed February 22, 2021. https://www.cdc.gov/obesity/adult/defining.html
- 38.Whelton PK, Carey RM, Aronow WS, et al. 2017 ACC/AHA/AAPA/ABC/ACPM/AGS/APhA/ASH/ASPC/NMA/PCNA guideline for the prevention, detection, evaluation, and management of high blood pressure in adults: a report of the American College of Cardiology/American Heart Association Task Force on clinical practice guidelines. Hypertension 2018;71:e13‐e115. [DOI] [PubMed] [Google Scholar]
- 39.National Cholesterol Education Program (NCEP) Expert Panel on Detection, Evaluation, and Treatment of High Blood Cholesterol in Adults (Adult Treatment Panel III) . Third report of the National Cholesterol Education Program (NCEP) Expert Panel on detection, evaluation, and treatment of high blood cholesterol in adults (Adult Treatment Panel III) final report. Circulation 2002;106:3143‐3421. [PubMed] [Google Scholar]
- 40.Arnett DK, Blumenthal RS, Albert MA, et al. ACC/AHA guideline on the primary prevention of cardiovascular disease: a report of the American College of Cardiology/American Heart Association Task Force on clinical practice guidelines. Circulation 2019;2019:e596‐e646. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 41.Diagnosis and treatment of diabetes. Mayo Clinic. Published October 2020. Accessed November 20, 2020. https://www.mayoclinic.org/diseases‐conditions/diabetes/diagnosis‐treatment/drc‐20371451
- 42.Evarts B, Stein GP. US Fire Department Profile – 2018: Supporting Tables. National Fire Protection Association; 2020. NFPA publication 1‐36. [Google Scholar]
- 43.Li K, Lipsey T, Leach HJ, Nelson TL. Cardiac health and fitness of Colorado male/female firefighters. Occ Med 2017;67:268‐273. [DOI] [PubMed] [Google Scholar]
- 44.Davis SC, Jankovitz KZ, Rein S. Physical fitness and cardiac risk factors of professional firefighters across the career span. Res Q Exerc Sport 2002;73:363‐370. [DOI] [PubMed] [Google Scholar]
- 45.Jousilahti P, Vartiainen E, Tuomilehto J, Puska P. Sex, age, cardiovascular risk factors, and coronary heart disease: a prospective follow‐up study of 14 786 middle‐aged men and women in Finland. Circulation 1999;99:1165‐1172. [DOI] [PubMed] [Google Scholar]
- 46.Stewart MH, Lavie CJ, Shah S, et al. Prognostic implications of left ventricular hypertrophy. Prog Cardiovasc Dis 2018;61:446‐455. [DOI] [PubMed] [Google Scholar]