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ORIGINAL ARTICLES

Cardiovascular Disease Risk Factor Changes Over 5 Years Among Male and Female US Firefighters

Smith, Denise L. PhD; Graham, Elliot BS; Stewart, Donald MD; Mathias, Kevin C. PhD

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Journal of Occupational and Environmental Medicine: June 2020 - Volume 62 - Issue 6 - p 398-402
doi: 10.1097/JOM.0000000000001846
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Abstract

Learning Objectives

  • Discuss previous findings on cardiovascular disease (CVD) risk in firefighters, including studies of CVD risk factors in female firefighters.
  • Summarize the new findings on prevalence of CVD risk factors in firefighters, including changes over a five-year follow-up period.
  • Discuss the study implications for ongoing efforts to address the cardiovascular health of US firefighters.

There were approximately one million firefighters in the United States in 2017, and 7% of the firefighters were women.1 Firefighters perform important public safety duties and it is essential that they are healthy enough to perform their work without becoming a risk to themselves or to the completion of their mission. Firefighting involves many potential hazards; however, sudden cardiac events are the leading cause of on-duty death among firefighters.2,3 Several cross-sectional studies have evaluated measures of obesity and other cardiovascular disease (CVD) risk factors in male firefighters.4,5 To date, limited research has examined changes in measures of cardiovascular health over time and the authors know of no studies that have examined changes in CVD risk factors in female firefighters.

Learning Objectives

Discuss previous findings on cardiovascular disease (CVD) risk in firefighters, including studies of CVD risk factors in female firefighters. Summarize the new findings on prevalence of CVD risk factors in firefighters, including changes over a five-year follow-up period. Discuss the study implications for ongoing efforts to address the cardiovascular health of US firefighters.

Previous evaluations of CVD risk factors in female firefighters have reported prevalence estimates of elevated blood pressure,6,7 obesity,7–9 metabolic syndrome,7 hyperglycemia,7 smoking,7,9 and cardiorespiratory fitness levels.6,7 Research suggests that in comparison to their male counterparts, the prevalence of CVD risk factors is lower among female firefighters.6–8 Large percentages of male firefighters have been shown to have one or more of the following conditions: obesity, hypertension, smoker, dyslipidemia, and/or low physical fitness.4,5 Since the 1980s, the average body mass index (BMI) of veteran firefighters and recruits has increased.4 Prospective cohorts from 1996/1997 to 2000/2001 have also shown increases in weight and BMI,10 decreases in cholesterol levels,11 and relatively stable percentages with hypertension over a 4-year period.12 While treatment rates increased as firefighters aged, a significant proportion of firefighters with elevated cholesterol or hypertension were not receiving treatment.11,12

Firefighters work as members of a team, and an on-duty injury or death can jeopardize the work of the entire crew and place fellow firefighters at greater risk of adverse outcomes. The fire service recognizes the burden of CVD and has instituted several national strategies to help improve the cardiovascular health of firefighters.13–15 The objective of this study was to evaluate how the prevalence of CVD risk factors that were measured as part of an occupational medical evaluation changed in both males and females over 5 years in a large cohort of career firefighters.

METHODS

Study Population

A cohort of career firefighters from a county in Northern Virginia was examined based on records from occupational medical exams that were performed between 2009 and 2016. A total of 672 firefighters (603 males and 69 females) out of 1498 firefighters in the cohort had medical exam records at two time points that were separated by 5 years (range of 4 to 6 years).

Data Collection

Data from medical evaluations were collected by an occupational health clinic that performs annual medical evaluations on a contract basis to a large county-wide fire department. The medical evaluations are consistent with the National Fire Protection Association's 1582 Standard on Comprehensive Occupational Medical Program for Fire Departments and includes assessment of modifiable CVD risk factors.15 To examine changes in cardiovascular health over time within firefighters, the medical records of firefighters who had two exams separated by 5 years (4 to 6 year range) were examined.

During the occupational exam, height and weight were recorded using a digital physician's scale and stadiometer. Percent body fat was assessed via bioelectrical impedance (Tanita TBF-410) and waist circumference was assessed by a medical provider at the level of the umbilicus. Smoking history and medication use were recorded by questionnaire. Current smoking status was not reported due to a smoking ban policy initiated prior to baseline in this cohort. Blood pressure was measured in the seated position by a nurse via auscultation. A fasting venous blood draw was obtained and sent to a commercial laboratory for the determination of blood lipids and blood glucose levels. Data from the questionnaire, medical exam, and blood lab report were entered into a database by the clinic staff and a de-identified dataset was transferred by the occupational clinic to researchers in the First Responder Health and Safety Laboratory at Skidmore College. The study protocol was reviewed and approved by the Institutional Review Board at Skidmore College.

Definitions

Subjects were classified as obese if their BMI was ≥30 kg·m−2;16 excessive waist circumference was defined as >40 inches for males and >35 inches for females;17 elevated cholesterol levels were defined by two definitions, hypercholesterolemia (total cholesterol ≥200 mg·dL−1) and primary hypercholesterolemia (low-density lipoprotein [LDL] cholesterol ≥160 mg·dL−1 or non-high-density lipoprotein [HDL] cholesterol ≥190 mg·dL−1);18 low HDL cholesterol was defined as <40 mg·dL−1 for males and <50 mg·dL−1 for females;18 high blood pressure was defined as systolic blood pressure ≥130 mm Hg or diastolic blood pressure ≥80 mm Hg;19 high fasting blood glucose levels was defined as >125 mg·dL−1.20

Statistical Analyses

Descriptive statistics were expressed as mean ± standard deviation in Table 1. Continuous baseline measurements were compared between males and females using t-tests and Fisher exact tests were used to compare proportions. Linear and logistic regression models including a coefficient for age were conducted to determine if differences between males and females remained significant after controlling for age. For changes over time within males or females, paired t-tests were utilized for continuous measurements, and McNemar's tests of differences were conducted for proportions. The level of significance for all analyses was considered at P < 0.05 and was two sided for all tests. All analyses were conducted using Stata 15.1 (StataCorp, College Station, TX, USA).

TABLE 1
TABLE 1:
Cohort Baseline Descriptive Statistics by Male and Female Firefighters

RESULTS

The mean age was not significantly different between males (38.2 years, SD = 7.8) and females (37.2 years, SD = 7.5) (Table 1). The cohort identified primarily as white/other with 20% of males and 17% of females identifying as African American. The mean duration between baseline and follow-up was not significantly different between men (4.8 years, SD = 0.5) and women (4.7 years, SD = 0.6). At baseline, BMI was significantly higher (P < 0.001) among males (28.4 kg·m–2, SD = 3.7) versus females (25.0 kg·m–2, SD = 3.7); LDL cholesterol was significantly higher (P < 0.01) among males (118.0 mg·dL−1, SD = 30.7) versus females (103.6 mg·dL−1, SD = 28.1); HDL cholesterol was significantly lower (P < 0.001) among males (46.2 mg·dL−1, SD = 10.3) versus females (58.8 mg·dL−1, SD = 13.0); blood glucose was significantly higher among males (94.9 mg·dL−1, SD = 12.8) versus females (89.3 mg·dL−1, SD = 8.7); systolic and diastolic blood pressure were both significantly higher among males as compared to females and the use of hypertensive medication was significantly higher (P < 0.05) among males (12%) versus females (3%). These differences in baseline measures between men and women remained significant after 5 years of follow-up (data not shown). The differences between males and females at baseline and after 5 years remained significant with minimal changes in the beta coefficient for sex when age was included in the model.

Body weight and BMI significantly increased in males (2.5 ± 0.2 kg; P < 0.001) (0.8 ± 0.1 kg·m−2; P < 0.001) and females (2.5 ± 0.8 kg; P < 0.01) (1.0 ± 0.3 kg·m−2; P < 0.001) across the 5-year period (Table 2). LDL cholesterol levels significantly increased among males (4.9 ± 1.2 mg·dL−1; P < 0.001) and females (7.8 ± 3.1 mg·dL−1; P < 0.05), while diastolic blood pressure decreased in males (−2.4 ± 0.4 mm Hg; P < 0.001) and in females (−2.7 ± 0.9 mm Hg; P < 0.01). Blood glucose significantly increased in males (2.6 ± 0.6 mg·dL−1; P < 0.001) with a nonsignificant change among females (−1.1 ± 1.0 mg·dL−1).

TABLE 2
TABLE 2:
5-year Changes in Measures of Cardiovascular Health Within Male and Female Firefighters

The prevalence of obesity significantly increased (P < 0.001) from 29% to 38% among males over the 5-year period and there was a nonsignificant change from 10% to 15% in female firefighters (Table 3). The prevalence of hypercholesterolemia increased significantly (P < 0.01) from 32% to 39% and primary hypercholesterolemia increased significantly (P < 0.01) from 10% to 15% among males over the 5-year period, while there were nonsignificant changes in the prevalence among females. The prevalence of low-HDL cholesterol was not significantly different across the 5-year time period in males or females; however, the prevalence at follow-up was 27% and 25% among males and females, respectively. The percentages of males with blood glucose levels above 125 mg·dL−1 significantly increased (P < 0.01) over the 5-year period from 2% to 4% and a nonsignificant change was shown among females (0% vs 2%). Among males, the percentages with stage 1 or 2 hypertension significantly decreased (P < 0.01) over time from 58% to 46% among males with a nonsignificant change of 42% to 29% among females. The percentage of males using hypertensive medications increased significantly (P < 0.001) from 12% to 18% over the 5-year period.

TABLE 3
TABLE 3:
Percentages of Male and Female Firefighters With CVD Risk Factors over a 5-year Period

DISCUSSION

This study investigated changes in cardiovascular health measures over a 5-year period within male and female career firefighters. Similar to previous studies, the findings from this study showed high prevalence of several CVD risk factors among firefighters. The results also extend previous work by reporting that many of the cardiovascular health measures worsened over the 5-year period despite increased awareness of the need to address CVD risk factors in the fire service.4,5,13,14 Female firefighters had more favorable cardiovascular health measures at the initial measurement. The percentage of male firefighters classified as having above normal cholesterol and high blood glucose increased over the 5-year period. Mean absolute blood pressure values for both male and female firefighters decreased over time; however, 46% of males and 29% of females had blood pressure measurements within the range of stage1 or 2 hypertension after 5 years. The results from this study support the growing body of knowledge that suggests that firefighters, both males and females, have a high prevalence of CVD risk factors. In addition, new findings were reported on the increasing prevalence of CVD risk factors among firefighters over a 5-year period while working in the fire service.

Female firefighters had more favorable measurements of cardiovascular health as compared to their male counterparts at baseline and after 5-years of follow-up, and these differences remained significant after controlling for age. These findings with respect to metabolic risk factors are consistent with the results of a cohort of male and female firefighters in Colorado7 and within the range of previous estimates of the prevalence of obesity among career female firefighters (range of 11% to 17%),7–9 and male firefighters (range of 23% to 52%).7,8,10,21,22 The prevalence of obesity among male and female firefighters in this cohort were lower than the national estimates of 36% and 37% among 30- to 40-year-old men and women in 2009/2010.23 While the definition of high cholesterol varies across studies, the percentage of male firefighters with total cholesterol levels above 200 mg·dL−1 in this study was lower than a previous cohort which reported a prevalence of 69%.11 Previous studies have shown that total cholesterol levels above 200 mg·dL−1 were associated in unadjusted models with a 2.4-fold and 4.4-fold increase in the risk of coronary heart disease related retirement and on-duty death in the fire service, respectively.24,25 Storer et al5 reported a prevalence of hyperlipidemia in firefighters of 34% using cut-offs of ≥130 mg·dL−1 for LDL cholesterol or <40 mg·dL−1 for HDL cholesterol. Previous estimates of low-HDL cholesterol reported by Li et al7 were 31% and 23% among male and female firefighters, respectively,7 and these results are similar to the findings reported in the current study. The prevalence of combined stage 1 and stage 2 hypertension (systolic blood pressure ≥130 mm Hg or diastolic blood pressure ≥80 mm Hg) among males in the current study was 58% as compared to previous estimates of stage 1 hypertension under the new guidelines19 of 58% among career firefighters26 and 74% among both volunteer and career firefighters.27 The high prevalence of hypertension across studies suggests additional prevention efforts are needed given that hypertension is predictive of on-duty deaths in firefighters.25

Both male and female firefighters gained 2.5 kg over the 5-year period. This increase of ∼0.5 kg/yr on average is similar to increases in body weight that have been reported in the general population (0.3 to 0.8 kg/yr)28–30 and in a cohort of male firefighters from 1996 to 2001 (0.5 kg/yr).10 Although both body weight and BMI increased, changes in other measures of cardiovascular health were mixed. Among male firefighters, total cholesterol, LDL cholesterol, and blood glucose increased, whereas diastolic blood pressure decreased. Among females, LDL cholesterol increased, whereas systolic and diastolic blood pressure decreased. Previous cohorts with male firefighters have shown stable blood pressure and decreases in total cholesterol from 224 to 214 mg·dL−1 over a 4-year period.11,12 Future research is needed to examine if the changes reported in the current study reflect changes at the national level in both male and female firefighters. To the author's knowledge, this study is the first to report changes in measures of cardiovascular health with female firefighters and presents a more holistic view of recent changes over time in multiple measures of cardiovascular health within male firefighters.

In addition to reporting the mean changes in measures of cardiovascular health, this study also examined the change in prevalence of CVD risk factors over the 5-year period. Baseline percentages of males and females with obesity, low-HDL cholesterol and high blood pressure were similar to a previous study from a cohort of firefighters in Colorado,7 which indicates that the high prevalence of CVD risk factors among male and female firefighters is not a regional issue. With respect to changes over time, the prevalence of obesity significantly increased from 29% to 38% in males with a nonsignificant change of 10% to 15% in females. The change in obesity rates among males was larger than previously reported (35% to 40%),10 but could be explained by the mean BMI of 28.4 kg·m–2 at baseline in the current cohort which indicates a large percentage of firefighters would have been just below 30 kg·m–2 at baseline. The prevalence of elevated cholesterol, high blood glucose, and use of antihypertensive medication were shown to increase over the 5-year period in male firefighters. A previous prospective cohort with firefighters showed a decrease in total cholesterol,11 relatively stable prevalence of elevated blood pressure,12 and an increase in use of hypertensive medications from 6% to 10%.12 The change in rates of antihypertensive medication usage in the current study suggest that the decrease in males with hypertension was likely due to a combination of lifestyle and medication changes, whereas the low medication rates among females would suggest that the lowering of blood pressure was primarily the result of lifestyle modifications. Previous estimates have shown that only 26% of hypertensive firefighters demonstrate adequate control of their blood pressure.12 In both males and females, the prevalence of elevated blood pressure compared to the relatively low rates of antihypertensive medications usage suggest that further efforts (lifestyle and medication) are needed among all firefighters.

Examining the medical records from a fixed cohort of firefighters provides researchers with a better understanding of how cardiovascular health changed over time while working in the fire service. A limitation of a fixed cohort approach is that the results do not represent the entire fire service as recent recruits or firefighters who retired/left during the 5-year period were not included. An additional strength of this study was the inclusion of female firefighters in the cohort, although the relatively small sample size could have limited the ability to detect significant changes over time in the percentages of female firefighters with elevated measures of CVD risk. Lastly, the medical exams were obtained from career firefighters in a large, but regional cohort which limits the ability to generalize the findings to all firefighters, both career and volunteer, in the United States.

CONCLUSIONS

The findings from this study contribute to the growing body of evidence that consistently shows a concerning prevalence of obesity and other CVD risk factors among firefighters. Our findings also support previous studies with female firefighters that suggest that female firefighters have more favorable measures of cardiovascular health compared to their male counterparts. However, both male and female firefighters gained weight, and both had a deteriorating blood glucose and/or lipid profile over the 5-year period. The lowering of blood pressure values in both males and females over the 5-year period provides evidence that some positive changes were made, although the prevalence of high blood pressure at follow-up remains a serious concern. Given the large percentages of firefighters, particularly males, who had CVD risk factors that increased over the 5-year period, continual efforts are needed to identify effective strategies to help firefighters manage and maintain their cardiovascular health throughout their careers.

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Keywords:

cardiovascular health; female firefighters; firefighters; obesity; risk factors; weight gain

Copyright © 2020 The Author(s). Published by Wolters Kluwer Health, Inc. on behalf of the American College of Occupational and Environmental Medicine.