Prevalence of Cardiovascular Disease Risk Factors Among National Football League Players FREE

Concern exists about the cardiovascular health implications of large size among professional football players and those players who aspire to professional status. An estimated 4.3 million youth ages 6 to 17 years participated in football in 2000 in the United States, including tackle, touch, and flag football.¹ A 2005-2006 high school participation survey estimated that 1.1 million students participated in US football in that year,² and participation levels continue to increase.³ Approximately 14% of male students in grades 9 through 12 in the United States participate in football.¹

Studies have suggested that fitness may provide protection against the health risks of obesity,⁴ although other studies have found that physical activity is beneficial but does not eliminate these risks.⁵ This issue is of interest in large, active athletes. A significant increase in body mass index (BMI, calculated as weight in kilograms divided by height in meters squared) for offensive and defensive linemen has been noted during the past 30 years,⁶ and BMI fitting the category of class II obesity was reported in more than a quarter of National Football League (NFL) players in 2003.⁷ In the late 1970s and early 1980s, the rules of football were changed to allow offensive linemen more use of their hands with both pass and run blocking. Although quickness and agility were important for offensive line play in the past, large size has become increasingly important to linemen during the past 2 decades.

In a study of 1 NFL team,⁸ linemen had the highest total cholesterol, low-density lipoprotein cholesterol (LDL-C), and triglyceride levels, and the lowest high-density lipoprotein cholesterol (HDL-C) levels of all position groups. In 1994, the Centers for Disease Control and Prevention reported that retired NFL players experienced an overall 46% lower mortality rate compared with the general population, but retired offensive and defensive linemen had a 52% greater risk of dying from heart disease.⁹ Greater player size and sporadic deaths of active and young retired professional football players have raised questions about an associated increase in cardiovascular disease (CVD) risk.¹⁰

Previous studies of NFL players have been limited to single teams or smaller groups that may not be representative of active players overall.^6- 8 Furthermore, earlier studies have generally used BMI as a measure of body size. Reliance on BMI alone as a size indicator for CVD risk may not be appropriate in NFL players because BMI does not take into account lean muscle mass.¹¹ There is a need for further investigation of active NFL players using appropriate measures of size and cardiovascular health to assess the prevalence of CVD risk factors, with implications for the larger number of amateur athletes who aspire to the professional ranks.¹² Our goal was to compare the prevalence of CVD risk factors in NFL players with men of the same age in the general US population. The second goal was to assess the association of risk factors in the NFL with player size and race.

This cross-sectional study included active, veteran football players in the NFL. A convenience sample of 12 of the 32 NFL teams was selected based on team access to a body composition device. These teams used an air displacement body composition device, whereas other teams used various other methods, such as skinfold or body impedance measurements. Recruitment of teams using the same device ensured consistent measurement of body composition across the study group. Institutional review board approval was obtained, and the NFL Subcommittee on Cardiovascular Health, composed of NFL-associated and independent medical personnel, oversaw the study.

Veteran players on the 12 teams were approached to participate in the study (n = 604). Veteran players included all players on an active roster at the team mini-camp between April and July 2007. Not included in this definition were rookies and rookie free agents drafted or signed in spring and summer 2007. The investigators (A.M.T., R.A.V., A.E.L., L.W.C., R.A.H., and A.P.Y.) provided a study overview to groups of players at the team facilities, and players interested in participating completed informed consent documents according to a protocol approved by the institutional review board of MedStar Research Institute, Washington, DC.

In a pilot study of 4 teams, hypertension was found in 10 of 72 players (13.9%). Based on this finding and 9.6% prevalence of hypertension among males 24 to 35 years old from the National Health and Nutrition Examination Survey 2003-2004 data, we determined that 408 participants were needed to obtain 80% power to observe a 4% prevalence difference between the groups, with α=.05. Assuming a participation rate of 75%, we solicited 600 players from 12 teams.

Two investigators (A.M.T. and A.E.L.) compiled and distributed a manual of operations to all participating teams before physical examinations were conducted, and at least 1 investigator was present to provide training and observe data collection.

Data collected during team mini-camps between April and July 2007 included health histories; height; weight; neck, waist, and hip circumferences; body composition; fasting glucose; total cholesterol, LDL-C, HDL-C, and triglycerides; blood pressure; pulse; and electrocardiograms. Each team was assigned to receive either home sleep testing, echocardiography, or carotid intima-medial thickness testing. Because of logistic and financial constraints, 6 teams were selected to undergo sleep testing using a portable monitor, 3 teams received echocardiograms, and 3 teams underwent carotid intima-medial thickness testing. Demographic data for nonparticipants were obtained from each team's Web site at the time of the team's mini-camp. Data obtained from carotid ultrasound and sleep monitoring will be reported elsewhere.

Data from the 2007 physical examination were recorded from medical records by team physicians, athletic trainers, or both and added to the study database in deidentified, password-protected format. Player weight and body fat percentage were recorded by team strength coaches during body composition testing (BOD POD, Life Measurement Inc, Concord, California) within 1 month of the annual physical examination. This device has been validated for measurement of body composition.¹³ Height was self-reported from player questionnaires.

Blood pressure, electrocardiogram, blood analyses, echocardiogram, and carotid intima-medial thickness measurements were obtained at the mandatory annual physical examination. Early morning was the most common time allotted for these measurements, and no practices, individual or group workouts, or strength or aerobic conditioning were scheduled on that day.

A single blood pressure measurement was obtained by automated cuff (Welch Allyn Spot Vital Signs BP monitor, Welch Allyn Inc, Skaneateles Falls, New York). The study protocol required all 12 teams to use the same blood pressure measurement device. A Gulick measuring tape was used to measure the mid-bicep circumference of each player, and the data collection form specified the cuff size to use according to the biceps measurement. The blood pressure cuff was wrapped snugly around the bare arm, and blood pressure data were collected with the player seated with feet flat on the floor. Players were asked to sit quietly for 5 minutes before the measurement. The majority of blood pressure measurements were obtained under the prespecified conditions.

Neck, waist, and hip circumference were recorded with Gulick tape measures using standard techniques.¹⁴ Neck circumference was measured midway between the midcervical spine and the midanterior neck. In participants with a pronounced laryngeal prominence (Adam's apple), the measurement was made just inferior to the prominence. Waist circumference was determined at the end of a normal expiration in a horizontal plane at the smallest horizontal circumference midway between the player's tenth rib and the superior edge of the iliac crest. Hip circumference was measured around the participant's hips in a horizontal plane at the maximum extension of the buttocks. All circumferences were measured with the player standing upright with the tape measure in contact with, but not compressing, the player's skin.

Blood samples for fasting glucose, total cholesterol, LDL-C, and HDL-C, and triglyceride measurements were collected at the time of the routine annual physical examination and were shipped on dry ice to Penn Medical Laboratory of MedStar Research Institute for analysis.

We compared our data with that obtained from an age- and race-equivalent population sample from the Coronary Artery Risk Development in Young Adults (CARDIA) study, a population-based observational study of 5115 participants aged 18 to 30 years recruited in 1985-1986.^15- 16 The CARDIA data used for comparisons with the NFL players were restricted to the age range that included 97% of the NFL participants, from the examination conducted during year 5 in 1990, resulting in our including CARDIA participants aged 23 to 35 years. For glucose comparisons, the CARDIA year 7 data were used because glycemia data were not available in year 5. Our survey instrument was adapted from the CARDIA protocol and collected data on demographics, personal and family medical history, dietary habits, alcohol intake, cigarette smoking, use of medications and nutritional supplements, and sleep habits. The use of consistent survey instruments allowed comparison of CVD risk factors from the active player population with men of the same age group from the general population.

Data on race were collected because of known differences among racial groups in CVD risk factors, especially prevalence of hypertension.¹⁶ The participants were asked to categorize their race on a self-administered questionnaire, which included a write-in option.

Standard 12-lead electrocardiograms at 25 mm/s speed and amplification of 0.1 mV/mm were obtained during the mini-camps and interpreted by 1 investigator (R.A.V.). Three measurements of left ventricular hypertrophy were obtained (maximum precordial R or S wave, S wave in lead V₁ + maximum R wave in lead V₅ or V₆ [Sokolow], and R wave in lead AV_L). The criteria for left ventricular hypertrophy by these 3 measurements were at least 3.0 mV, at least 3.5 mV, and at least 1.1 mV, respectively. Echocardiograms were obtained from players on 3 teams during the mini-camp by certified sonographers employed by a sports-oriented medical imaging company (Ultrasound Services Inc, Newtown, Pennsylvania). Studies were recorded digitally and analyzed by 2 investigators (R.A.V. and D.C.A.). Borderline and definite left ventricular hypertrophy was considered to be present when the interventricular septal or posterior left ventricular wall thickness in diastole was 1.3 to 1.4 cm and at least 1.5 cm, respectively.¹⁷

Descriptive statistics (mean [95% confidence interval {CI}] or number [percentage]) were calculated to evaluate anthropometric and cardiovascular characteristics, as well as prevalence of CVD risk factors, in participating NFL players and the CARDIA participants. Players were categorized for data analysis based on position as a general indicator of size, using groupings employed in previous studies of NFL players.⁶ Comparisons were made within the NFL group by player position and between the NFL and CARDIA samples. Demographic, position, and NFL tenure data were calculated for participating and nonparticipating players to determine whether the participants were representative of the active players.

The CVD risk factors were defined by hypertension (systolic blood pressure of at least 140 mm Hg, diastolic blood pressure of at least 90 mm Hg, or current use of antihypertensive medication); prehypertension (systolic blood pressure of at least 120 mm Hg and less than 140 mm Hg or diastolic blood pressure of at least 80 mm Hg and less than 90 mm Hg); dyslipidemia (total cholesterol of at least 240 mg/dL, LDL-C of at least 160 mg/dL, HDL-C of less than 40 mg/dL, or triglycerides of at least 150 mg/dL); impaired fasting glucose of 100 to 125 mg/dL; and glucose intolerance of at least 126 mg/dL. To convert total cholesterol, LDL-C, and HDL-C to millimoles per liter, multiply by 0.0259; triglycerides to millimoles per liter, multiply by 0.0113; and glucose to millimoles per liter, multiply by 0.0555.

Linear regression models were used to estimate systolic blood pressures, lipids, and fasting glucose levels in the study and reference populations with covariate adjustment for age, race, BMI, and race × population interaction. All analyses were performed by a biostatistician (R.E.D.) using R: A Language and Environment for Statistical Computing version 2.7.1 (R Foundation for Statistical Computing, Vienna, Austria). The level of significance was set at α = .05; with P ≤ .05 considered statistically significant.

A total of 504 veteran players were recruited from 604 players available at the 12 sites. The 504 participating players represent approximately 26% of the total nonrookie players in the league at that time, based on an estimated 1920 nonrookie players, or approximately 60 on each of 32 NFL teams. Completeness of data collection for the core data elements varied from 99% (survey: 500 of 504) to 86% (blood tests: 432 of 504). Participating NFL players were similar to nonparticipants in age, years in league, racial distribution, and player position (Table 1). The nonparticipant group represents the veteran players on NFL rosters at the time of the study on all clubs with archived rosters (18 of the 20 nonparticipant clubs; 18 teams × approximately 60 veteran players per club). The higher weight and BMI in the study group (Table 1) reflect the efforts of team medical staff and the investigators to encourage the largest players to participate, which resulted in an oversampling of linemen compared with smaller players. The NFL population estimates were obtained as weighted averages of per-player position estimates, using weights inversely proportional to the sampling rates by position.

The NFL players were taller and heavier than the CARDIA group (Table 2). Despite their larger size, the NFL group had lower mean fasting glucose (P < .001) compared with the CARDIA group, and there were no significant differences in total cholesterol, LDL-C, HDL-C or triglycerides between the groups. Systolic and diastolic blood pressure were higher in the NFL player group overall (P < .001) compared with the CARDIA group. Furthermore, systolic blood pressure in each player position group was significantly higher than that in the CARDIA group (P < .001). NFL players were not different in total cholesterol or LDL-C based on position, but mean values for all other characteristics varied significantly across positions (Table 3).

Electrocardiograms were obtained in 461 of the 504 players (91.5%). Left ventricular hypertrophy by the maximum precordial R or S wave, S wave in lead V₁ + maximum R wave in lead V₅ or V₆, and R wave in lead AV_L (RAV_L) criteria was present in 28, 76, and 2 players, respectively. Among these measurements, only RAV_L was significantly associated with systolic blood pressure in a simple linear regression analysis. Specifically, a 1-unit increment in RAV_L was associated with a 1.03-mm Hg greater systolic blood pressure. Borderline and definite left ventricular hypertrophy by echocardiography was present in 16 (15%) and 4 (4%) of 106 players, respectively, but wall thickness was not significantly associated with systolic or diastolic blood pressure in a simple linear regression analysis.

The NFL players had a significantly lower prevalence of impaired fasting glucose and smoking compared with the CARDIA group (Table 4). The NFL group did not differ from the CARDIA group in the prevalence of high total cholesterol, high LDL-C, or low HDL-C. The NFL players had significantly higher prevalence of hypertension and prehypertension compared with the CARDIA group. There was no significant difference in hypertension (P = .21) or prehypertension (P = .98) based on position, although there tended to be higher rates among those players with higher BMI (Table 5). Furthermore, prevalence of above-normal blood pressure (hypertension or prehypertension) was not different between white (146 of 179 [82%]; 95% CI, 75%-87%) and black (205 of 273 [75%]; 95% CI, 70%-80%) players (P = .13). Of the 504 NFL players, 7 were taking antihypertensive medication currently or in the past month, 3 of whom were identified as having hypertension only by their medication use. In the NFL group, 100 of 504 (20%; 95% CI, 17%-24%) reported use of nonsteroidal anti-inflammatory drugs in the past month.

A multivariable analysis, adjusting for age, race, and BMI with a race-population interaction term, showed significant effects of population group and BMI on the level of mean systolic blood pressure, lipids, triglycerides, and fasting glucose. Race was significantly related to systolic blood pressure in the CARDIA group, but not in the NFL group. Comparing men of the same age and BMI, mean systolic blood pressure among white NFL players was 13 mm Hg higher than among white CARDIA participants and 10 mm Hg higher among black NFL players than among black CARDIA participants, reflecting the 3-mm Hg difference between white and black systolic blood pressures in the CARDIA group. Comparing men of the same race and age, mean systolic blood pressure was 0.58 mm Hg higher per BMI unit in the combined population.

Results of multivariable linear regression models of CVD risk factors for the NFL and CARDIA groups, each model adjusted for age, BMI, race, and population with a race × population interaction term, are shown in Table 6. Body mass index was positively associated with total cholesterol, LDL-C, triglycerides, and fasting glucose and with decreased HDL-C in both the NFL and the CARDIA samples. As with blood pressure, population effects were observed for these CVD risk factors. In addition, black race was associated with higher HDL-C and lower triglyceride levels.

Our study found that the NFL population, characterized by large size and intense physical activity, had a CVD risk profile that was similar to the general population. In the combined population, size measured by BMI was associated with increased levels of CVD risk factors.

Smoking prevalence was lower in the NFL group than in the general population group. Despite a mean weight of approximately 30 kg greater than the general population group, the NFL group had significantly lower mean fasting glucose than the CARDIA participants. There were no differences in prevalence of abnormal total cholesterol, LDL-C, or HDL-C between the groups. As previously reported by Lee et al,⁴ high physical activity in the player group appears to have substantially mitigated the effect of large size.

The combined prevalence of hypertension and prehypertension was high in all player groups, ranging from 96 of 105 (91%) in the largest players to 15 of 19 (78%) in the smallest players compared with 581 of 1957 (30%) in the CARDIA general population group. The prevalence of hypertension and prehypertension did not differ significantly according to position. No difference in prevalence of hypertension was found between players based on race, consistent with a study on elite US college football players assessed at the 2000 to 2005 National Invitational Scouting Combine (NFL Combine),¹⁷ which found elevated blood pressure in both black and white players. In that study,¹⁷ mean (SD) systolic blood pressure for white (n = 598) and black (n = 1321) players was 130.5 (15.2) mm Hg and 130.0 (14.1) mm Hg, respectively.

The largest factor responsible for hypertension appeared to be player status as opposed to size. However, multivariable analysis showed that size was a secondary factor for elevated blood pressure and also for lipids and fasting glucose. This unexpected prevalence of prehypertension and hypertension has led to plans for an NFL-wide survey and in-depth investigation of the mechanisms of these findings. Proposed areas for investigation include strength and resistance training,^18- 20 long-term use of nonsteroidal anti-inflammatory drugs,²¹ salt intake,^22- 24 and sleep-disordered breathing.^25- 27

There are several potential limitations in our study. Only 1 automated blood pressure measurement was obtained in the NFL participants. However, all measurement sessions were monitored by an investigator and we used an automated cuff for blood pressure measurement, which has been shown to reduce “white coat” hypertension or high initial blood pressure readings.²⁸ Furthermore, the mean difference between the first blood pressure and the average of the other 2 measurements in our reference population was 0.5 mm Hg, which was not considered clinically important. Players may have underreported their use of antihypertensive medication in self-administered questionnaires. However, more accurate reporting of antihypertensive medication use would increase the already high prevalence of hypertension found in the NFL group. Seasonal influences on blood pressure have been reported, with lower blood pressure occurring in the summer and higher in the winter.^29- 30 Our measurements were obtained in the spring, and the season for the CARDIA measurement was unspecified.

The National Health and Nutrition Examination Survey 2000 data included more current CVD risk factor data for young men, but the racial distribution differed from the NFL group. For this racially different but more current and age-comparable population, mean systolic blood pressure was 119 mm Hg. This finding was slightly higher than in the CARDIA group, but is still considerably lower than the findings in the NFL group.

Race and height were self-reported. Smoking was self-reported and was not validated in the NFL group, but was also self-reported in the CARDIA group in the years used for the comparison.

We grouped players by position, which is not an absolute representation of body habitus. For example, among defensive linemen, nose tackles and defensive tackles often have a BMI similar to offensive linemen, whereas defensive ends tend to have lower BMI. However, grouping based on position has been established in the literature⁶ and generally categorizes the size of players. The NFL group had an overrepresentation of larger players compared with the nonparticipating players, probably as a result of efforts to encourage participation by players in typically heavier positions. An adjustment for this oversampling by position did not result in a change in estimated mean systolic blood pressure.

Although all NFL players are highly physically active, an assessment of fitness by maximal oxygen consumption was beyond the scope of this study. Our echocardiographic findings are inconclusive and should be interpreted with caution because criteria for left ventricular hypertrophy are commonly observed in large athletes.¹⁷

In conclusion, compared with a sample of healthy young-adult men, taller and heavier active NFL players had a lower prevalence of impaired fasting glucose and similar prevalence of dyslipidemia. Of concern was the higher prevalence of prehypertension and hypertension among NFL players. Investigation into the causes and long-term trends in hypertension in the NFL is currently under way.