Risk of cardiovascular disease and death in retired professional American football players may be higher than that in the general population. Previously published data have demonstrated that American football players have less glucose intolerance, less smoking, similar lipid profiles, and higher blood pressure despite a much larger body compared to the general population, although the presence of subclinical atherosclerosis in these subjects has not been evaluated. This study compared the prevalence of subclinical atherosclerosis in active professional American football players to that in age-, gender-, and race-matched controls derived from the Bogalusa Heart Study. Carotid intimal–medial thickness (CIMT) was used as an indicator of subclinical atherosclerosis in 75 active American football players (23 to 35 years old, 31 white, 44 African-American) as measured by B-mode ultrasonography at Mayo Clinic, Scottsdale, Arizona, on September 13 and 14, 2009. CIMT measurements of 75 athletes were compared to those of 518 matched controls who had CIMT determinations in 1995 and 1996. Two-group t tests determined population similarities between groups. In a generalized linear model, players (overall and by race) had lower CIMT values than controls after age and race adjustment (p <0.001 for all comparisons). Nonlinemen and linemen had lower CIMT values than controls (p <0.001 and p = 0.004, respectively). In conclusion, active professional American football players, regardless of position, had mean CIMT values similar to or lower than those in a matched general population cohort, suggesting that if the prevalence of subclinical atherosclerosis is increased in retired professional American football players, this occurs after retirement.
As a measurement of subclinical atherosclerosis, carotid intimal–medial thickness (CIMT) is independently associated with adverse cardiovascular events. Subclinical atherosclerosis as measured by CIMT may represent the cumulative effect of cardiovascular risk factors rather than just an estimate of the probability of disease and may allow for more accurate identification of risk than traditional risk factors. To quantify subclinical atherosclerosis in active professional American football players, we evaluated CIMT, demographic, and laboratory data in 2 professional American football teams.
Methods
The study was approved by the Mayo Clinic Institutional Review Board. All study subjects agreed to participate in this study and provided informed consent. The study was performed on September 13 and 14, 2009 at Mayo Clinic, Scottsdale, Arizona. Exclusion criteria for our analysis were refusal to consent to carotid ultrasonography and race other than white or African-American.
The comparison cohort was obtained from the Bogalusa Heart Study database. The Bogalusa Heart Study population was derived from the community of Bogalusa, Louisiana in 1995 and 1996 (n = 1,420, 20 to 38 years old, 71% white, 39% men). An age-, race-, and gender-matched cohort of subjects who underwent B-mode ultrasonography of the carotid artery was selected as the control group. All men in the Bogalusa Heart Study who had CIMT values were included in our study.
Demographic and laboratory data methods and definitions are described in our previous study of retired professional American football players. All studies were performed at Mayo Clinic by sonographers experienced in the acquisition of CIMT images. Age, race, position played, and histories of diabetes, hypertension, smoking, and vascular disease were noted. Height (meters) and weight (kilograms) were recorded. Blood pressure and pulse were recorded 3 times and averaged. Fasting lipid profile and glucose determination were performed by the Mayo Medical Laboratories.
Demographic and laboratory data from the Bogalusa cohort were obtained from the published study. Personal communications with the Bogalusa Heart Study authors (P. Das Mahapatra, written communication, March 2011) were used when needed data were not reported.
CIMTs of the 2 carotid arteries were determined using the protocol recommended by the American Society of Echocardiography Carotid Intima–Media Thickness Task Force with imaging on a Siemens Sequoia system with an 8-MHz frequency linear array transducer (Acuson Sequoia, Mountain View, California). A thorough plaque screening was performed. Studies were recorded in Digital Imaging and Communications for Medicine format for analysis. Measurements were performed by a single reader (C.B.K.) who was blinded to all demographic criteria. A second reader independently made 108 blinded measurements.
In the Bogalusa cohort B-mode ultrasound was used to determine the maximum CIMTs for the right and left far wall of the common carotid artery, carotid bulb, and internal carotid artery.
Mean ± SD for continuous variables and frequency (percentage) for categorical variables were used to characterize the Bogalusa group and our cohort. Two-sample t tests were used to compare clinical measurements for white versus African-American athletes and nonlinemen versus linemen in our cohort. Paired t tests were used to compare left and right CIMT differences for linemen and nonlinemen. Mean ± SD of maximal CIMT and mean ± SD of blood pressure, lipid levels, body mass index, and cholesterol measurements of white and African-American subjects from the Bogalusa data were compared to our population. Two-sample t tests were performed to derive p values using the group mean ± SD and number of available observations between the Bogalusa group and our group when age or race was the same. A generalized linear model was used to compare CIMT between groups with age as an adjusting factor. Any p value <0.05 was considered statistically significant. The interclass correlation coefficient and its 95% confidence interval were used to assess absolute agreement of CIMT measurements made by 2 observers performing the same measurements on the athletes. The Cohen kappa coefficient criteria on agreement were used for the interclass correlation coefficient and an interclass correlation coefficient ≥0.75 indicated excellent consistency. All statistical analyses were performed using SAS 9.2 (SAS Institute, Cary, North Carolina).
Results
All 109 members of 2 United Football League teams were invited to participate in this study. Eighty-three subjects consented and all 83 men had interpretable carotid examinations. Subjects were excluded from the final analysis if they were of mixed white and African-American descent, Hispanic, or Polynesian because there were no controls for these racial/ethnic designations. Demographic, laboratory, and anthropometric data were analyzed in the study cohort of 75 athletes.
The participants’ average age was 27 ± 3 years; 44 (59%) identified themselves as African-American and 33 (44%) were linemen ( Table 1 ). Demographic features and risk factor profiles of the players are also presented in Table 1 .
| Variable | Overall | White Players | African-American Players | p Value ⁎ |
|---|---|---|---|---|
| (n = 75) | (n = 31) | (n = 44) | ||
| Age (years) | 27 ± 3 | 27 ± 3 | 27 ± 3 | 0.98 |
| Maximal right common carotid artery (mm) | 0.70 ± 0.12 | 0.68 ± 0.11 | 0.72 ± 0.12 | 0.16 |
| Maximal left common carotid artery (mm) | 0.71 ± 0.11 | 0.67 ± 0.10 | 0.73 ± 0.11 | 0.02 |
| Maximal carotid intimal–medial thickness | 0.70 ± 0.10 | 0.67 ± 0.09 | 0.73 ± 0.10 | 0.03 |
| Height (m) | 1.88 ± 0.07 | 1.91 ± 0.07 | 1.86 ± 0.07 | 0.004 |
| Weight (kg) | 112 ± 22 | 117 ± 19 | 110 ± 23 | 0.21 |
| Body mass index (kg/m 2 ) | 32 ± 5 | 42 ± 4 | 31 ± 5 | 0.79 |
| Heart rate (beats/min) | 62 ± 9 | 62 ± 10 | 62 ± 9 | 0.95 |
| Systolic blood pressure (mm Hg) | 123 ± 13 | 124 ± 16 | 122 ± 11 | 0.60 |
| Diastolic blood pressure (mm Hg) | 75 ± 10 | 74 ± 10 | 76 ± 9 | 0.37 |
| Total cholesterol (mg/dl) | 189 ± 46 | 186 ± 46 | 192 ± 47 | 0.67 |
| Triglycerides (mg/dl) | 138 ± 112 | 181 ± 134 | 105 ± 78 | 0.01 |
| High-density lipoprotein cholesterol (mg/dl) | 53 ± 15 | 46 ± 15 | 59 ± 12 | 0.001 |
| Low-density lipoprotein cholesterol (mg/dl) | 110 ± 41 | 108 ± 36 | 112 ± 45 | 0.71 |
| Linemen | 33 (44%) | 19 (61%) | 14 (32%) | 0.01 |
The Bogalusa database included the CIMTs of 518 African-American and white men obtained in 1995 and 1996. The group’s mean age was 36 years and the group total cholesterol and triglyceride levels were statistically similar to those of the athlete participants ( Table 2 ), but systolic and diastolic blood pressure, body mass index, low-density lipoprotein cholesterol, high-density lipoprotein cholesterol, and age were significantly different between groups. Comparative measurements for African-American and white players and controls are listed in Table 2 .
| Variable | White Players (n = 31) | White Controls (n = 381) | p Value ⁎ | African-American Players | African-American Controls | p Value ⁎ |
|---|---|---|---|---|---|---|
| (n = 44) | (n = 137) | |||||
| Age (years) | 27 ± 3 | 36 ± 4 | <0.001 | 27 ± 3 | 36 ± 4 | <0.001 |
| Systolic blood pressure (mm Hg) | 124 ± 16 | 118 ± 11 | 0.005 | 122 ± 11 | 128 ± 16 | 0.02 |
| Diastolic blood pressure (mm Hg) | 74 ± 10 | 80 ± 8 | <0.001 | 76 ± 9 | 86 ± 12 | <0.001 |
| Total cholesterol (mg/dl) | 186 ± 46 | 194 ± 40 | 0.29 | 192 ± 47 | 192 ± 46 | >0.99 |
| Triglycerides (mg/dl) | 181 ± 134 | 165 ± 127 | 0.50 | 105 ± 78 | 128 ± 106 | 0.19 |
| High-density lipoprotein cholesterol (mg/dl) | 46 ± 15 | 41 ± 11 | 0.02 | 59 ± 12 | 49 ± 15 | <0.001 |
| Low-density lipoprotein cholesterol (mg/dl) | 108 ± 36 | 129 ± 34 | 0.001 | 112 ± 45 | 90 ± 45 | 0.005 |
| Body mass index (kg/m 2 ) | 32 ± 4 | 29 ± 5 | 0.001 | 31 ± 5 | 29 ± 7 | <0.001 |
Table 3 presents comparisons between linemen and nonlinemen. Linemen were larger than nonlinemen and had higher systolic blood pressure, higher triglyceride levels, and lower high-density lipoprotein cholesterol levels.
| Variable | Nonlinemen | Linemen | p Value ⁎ |
|---|---|---|---|
| (n = 42) | (n = 33) | ||
| Age (years) | 27 ± 3 | 27 ± 2 | 0.79 |
| Maximal right common carotid artery (mm) | 0.69 ± 0.12 | 0.71 ± 0.12 | 0.40 |
| Maximal left common carotid artery (mm) | 0.70 ± 0.10 | 0.71 ± 0.13 | 0.73 |
| Maximal carotid intimal-medial thickness (mm) | 0.70 ± 0.09 | 0.71 ± 0.11 | 0.57 |
| Height (m) | 1.84 ± 0.05 | 1.94 ± 0.05 | <0.001 |
| Weight (kg) | 98 ± 11 | 132 ± 17 | <0.001 |
| Body mass index (kg/m 2 ) | 29 ± 3 | 35 ± 5 | <0.001 |
| Heart rate (beats/min) | 59 ± 8 | 67 ± 8 | <0.001 |
| Systolic blood pressure (mm Hg) | 118 ± 9 | 130 ± 14 | <0.001 |
| Diastolic blood pressure (mm Hg) | 74 ± 9 | 77 ± 10 | 0.25 |
| Total cholesterol (mg/dl) | 183 ± 39 | 197 ± 54 | 0.26 |
| Triglycerides (mg/dl) | 86 ± 44 | 205 ± 136 | <0.001 |
| High-density lipoprotein cholesterol (mg/dl) | 59 ± 13 | 47 ± 15 | 0.003 |
| Low-density lipoprotein cholesterol (mg/dl) | 107 ± 38 | 114 ± 46 | 0.56 |
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