Participation in School Sports Clubs and Related Effects on Cardiovascular Risk Factors in Young Males

Transcription

1 227 Original Article Participation in School Sports Clubs and Related Effects on Cardiovascular Risk Factors in Young Males Hiroshi KAWABE, Kazuko MURATA *, Hirotaka SHIBATA, Hiroshi HIROSE, Minako TSUJIOKA, Ikuo SAITO, and Takao SARUTA The effects of belonging to sports clubs on male high school students was evaluated. The relationships between the type and extent of school-based exercise were examined in conjunction with percent body fat, blood pressure (BP), and other key metabolic parameters. A total of 264 male Japanese high school students (age range: years old) were studied. Percent body fat was measured and blood was collected in the fasting state during a routine health check. Subjects were divided into two groups. The exercise (E) group (n=150) included students who had belonged to a sports club during the past 2 years. The non-exercise (NE) group (n=114) included students who did not belong to a sports club during the past 2 years. The body mass index was significantly greater in group E (21.7±2.3 (SD) kg/m2) than in group NE ( kg/m2, p < 0.01). However, the percent body fat in group E (13.6±3.4%) was significantly lower than that in group NE (14.9±3.8%, p<0.01). The diastolic BP and heart rate in group E (64±7 mmhg, 70± 11/min) were significantly lower in group E than in group NE (66±8 mmhg, p< 0.05; 76± 14/min, p < 0.01). The serum triglyceride level was significantly lower, and the HDL cholesterol level was higher in group E than in group NE. The homeostasis model assessment (HOMA) index, used as an index of insulin resistance, was similar in the two groups. However, the level of the HOMA index was significantly lower among the 62 subjects in group E who preferred highly dynamic exercise (1.50±0.46) than it was among those in group NE (1.66 ± 0.49, p < 0.05). Results indicate that belonging to sports clubs influences the BP and lipid profiles of adolescent males, as well as their percent body fat. In view of the reduction of cardiovascular risk factors, it is recommended that even young males practice regular exercise, especially aerobic exercise. (Hypertens Res 2000; 23: ) Key Words: exercise, body fat, blood pressure, lipid, insulin resistance Introduction The value of lifestyle modifications for the prevention of, or as the initial therapy for, hypertension is widely recognized (1, 2). As most previous studies have focused on adults, the importance of lifestyle modifications in younger subjects remains to be analyzed. An increase in body mass is a recognized determinant of an increase in blood pressure (BP) levels in childhood and adolescence (3). Recently, we reported sexual differences in the relationship between body weight and BP in young Japanese students; a significant positive relationship was seen in males but not in females (4). These results have indicated that lifestyle modifications, including a diet to control weight, should be started as early as possible, especially in male adolescents. However, a strict diet is impractical during childhood and adolescence. The present study therefore evaluated daily physical activity, which tends to be reduced in industrialized societies (5). To investigate the usefulness of regular exercise during adolescence, we evaluated differences in BP From the Health Center, Keio University, Tokyo, Japan, and * Department of Internal Medicine, School of Medicine, Keio University, Tokyo, Japan. Address for Reprints: Hiroshi Kawabe, M.D., Health Center, Keio University, 35 Shinanomachi, Shinjuku-ku, Tokyo , Japan. Received November 17,1999; Accepted in revised form December 27, 1999.

2 228 Hypertens Res Vol. 23, No. 3 (2000) Table 1. Classification of Sports Evaluated and cardiovascular risk factors, including obesity, between male adolescents who belonged to sports clubs and male subjects of the same age group who did not belong to sports clubs. Subjects Subjects and Methods This study included 331 male high school students (17-18 years old) who came for an annual medical check-up. This high school was a private male institution and was located in Saitama prefecture, in the suburbs of Tokyo. Each subject was administered a questionnaire concerning his physical activity during the last 2 years. Key questions were: 1) Have you belonged to a sports club during the past 2 years? 2) If yes, what is the name of the sports club? 3) When did you join the present club? 4) How many days do you practice each week? 5) How long do you exercise each day? The 17 sports clubs included in this study are listed in Table 1. For students who did not belong to a sports club, we asked these additional questions; 1) Do you take part in any sports? 2) If yes, how many days per week do you exercise and how long is one practice session? Based on the questionnaire results, the subjects were divided into an exercise (E) group (n = 150), which included students who belonged to a sports club during the past 2 years, and a non-exercise (NE) group (n =114), which included students who did not belong to a sports club and who did not exercise regularly during the past 2 years. We eliminated from the study 24 students who did not belong to a sports club but who performed regular exercise. We also excluded 43 students who exercised less than 3 days per week and/or those who exercised for a very short time (less than 2 h per session). Types of sport were classified into 9 subgroups based on peak dynamic and static components during competition, as reported XXVIth Bethesda Conference (Table 1) (6). Informed consent was obtained from each subject prior to the study, and the protocol for the study was approved by the review committee of the Health Center at Keio University. Methods Each subject's BP and percent body fat were measured in addition to height and body weight at an annual health check-up. Trained nurses who were not aware of the results of the questionnaires used an automatic device (BP- 103Nii, Nihon Colin, Komaki, Japan) to perform two consecutive BP measurements. Each subject was placed in a sitting position after resting for at least 3 min and BP values were averaged. The percent body fat was measured twice by a trained nurse using a fitness analyser (BFT-3000, Kett Science Laboratories, Tokyo, Japan) and the results were averaged (7, 8). Near infrared interactance spectra were measured on the anterior midline of the biceps halfway between the antecubital fossa and the acromion. Height and body weight were measured using an automatic device for determining height and body weight (PHS-S, Yagami, Japan). After the subject removed shoes and clothing, standing height was measured to the nearest centimeter and body weight was determined to the nearest 100 g. After subjects had fasted 10 to 12 h overnight, we collected blood in order to determine serum levels of total cholesterol (TC), HDL cholesterol (HDLC), triglycerides (TG), uric acid, insulin, and plasma glucose. Serum levels of TC, TG, and uric acid were measured with an autoanalyzer. Serum insulin was measured by RIA, and plasma glucose was measured by the glucose-oxidase method. Insulin resistance was evaluated using a homeostasis model assessment, the HOMA index [fasting plasma glucose (mg/dl) X fasting serum insulin (pu/ml)/405], according to

3 Kawabe et al: Exercise and Cardiovascular Risk Factors 229 Table 2, Differences between the Exercise and the Non-Exercise Groups the method of Matthews et al. (9). The first voided morning urine was collected for the measurement of sodium (Na), potassium (K), creatinine (Cr), and albumin concentrations. The urinary albumin concentration was determined by a turbidimetric immunoassay. Results were expressed as the value divided by grams of Cr. Statistical Analysis Values are expressed as mean ± SD. All statistical analyses were performed using StatView for Macintosh (version 4.5, Abacus Concepts Inc., Berkeley, California). Significant differences between the two groups were assessed using either the two-tailed unpaired Student's t-test or the Mann-Whitney U test, as appropriate, and the chisquare test. Analysis of variance and Fisher's Protected Least Significant Difference were used to evaluate differences among the three groups. A level of p < 0.05 was considered to be statistically significant. Results The clinical characteristics of the two groups appear in Table 2. Height, body weight, and BMI were greater in group E than in group NE. The percentage of body fat was significantly lower in group E than in the NE group. Although systolic BP in group E tended to be lower than that of the NE group, the difference was not statistically significant. Diastolic BP and heart rate in group E were significantly lower than those in the NE group. Upon admission to high school (age, years old), there was no difference between the E and NE groups as regards systolic BP (123 ± 12 mmhg vs. 123 ± 12 mmhg), diastolic BP (67 ± 7 mmhg vs. 67 ± 7 mmhg), or heart rate (79 ± 14/min vs. 79 ± 14/min), respectively. Although the serum levels of TC were identical, the serum TG level was significantly lower in group E. The HDLC level was higher in group E than in group NE. Serum levels of uric acid were similar in both groups, as were the levels of fasting plasma glucose, serum insulin, and the HOMA index. Urinary excretion of Na was significantly greater in group E than in group NE. Albumin excretion in group E tended to be lower than in group NE, but not to a significant extent (p = 0.061). Table 3 shows differences in percent body fat, BP, lipid data, and HOMA index among the three subgroups,

4 230 Hypertens Res Vol. 23, No. 3 (2000) Table 3. Comparison of Three Exercise Subgroups which are classified according to the type and intensity of exercise. The distribution of three static levels (Table 1) among the three subgroups was similar. The percent body fat was significantly lower in the highly dynamic exercise group than that in the less dynamic exercise group. Systolic and diastolic BP tended to be lower in the highly dynamic exercise group than in the other two groups. However, systolic BP was significantly different between the highly and moderately dynamic exercise groups. The heart rate of the less dynamic exercise group was significantly higher than that of the other two groups. Serum levels of TG and the fasting insulin level were also significantly higher in the less dynamic exercise group than in the other two groups. The highly dynamic exercise group had a significantly lower HOMA index than the less dynamic exercise group. There was no difference in the BMI of the highly dynamic exercise group and group NE. However, BP (p < 0.05) and heart rate (p < 0.01) were significantly lower in the highly dynamic exercise group than in group NE (Table 2, 3). The highly dynamic exercise group showed a significantly higher value of HDLC (p < 0.05) and a lower TG level (p < 0.01) and H.OMA index (p < 0.05), as compared with the NE group (Table 2, 3). Discussion We found that males of high school age who belonged to sports clubs had a lower percentage of body fat, a lower diastolic BP value and a lower heart rate, as well as a higher concentration of HDLG, and a lower concentration of TG than did the age- and sex-matched subjects who did not belong to sports clubs. Although belonging to sports clubs showed little effect on BP and cardiovascular risk factors, we nevertheless conclude that it is important for boys to begin exercising regularly starting at this age. The reduction of physical activity in adults in industrialized countries is becoming a serious problem with respect to lifestyle-related diseases such as hypertension (5), diabetes mellitus, and hyperlipidemia. Although the reduction of exercise seems to be less detrimental to high school students than to adults, these problem can affect even the younger generations (10). Circa 40% of our subjects who were aged years did not belong to sports clubs. It has been reported that childhood BP and lipid profiles were related to findings in adults (11, 12). If the reduction of exercise in high school students negatively influences BP and serum lipid levels, steps must be taken to correct the lifestyle of such students. Many reports have demonstrated the usefulness of regular exercise on preventing hypertension, or as initial therapy for hypertension. The fifth (1) and sixth (2) reports of the Joint National Committee have also recommended regular exercise. The present study therefore pursued an analysis of the relationships between belonging to sports clubs and BP, lipid profile, and insulin resistance. These variables were examined in a cross-sectional study of males of high school age. We found that subjects who belonged to sports clubs exhibited lower BP, higher

5 Kawabe et al: Exercise and Cardiovascular Risk Factors 231 HDLC concentrations, and lower TG concentrations than subjects who did not belong to sports clubs. No differences in insulin resistance were found between group E and group NE; however, a significant difference was found between students who preferred dynamic exercise and students in the NE group. In general, there are two types of cardiovascular risk factors, namely, one that can be reversed by behavioral changes and one that cannot be autonomously reversed. Age, gender, and a family history of cardiovascular disease are irreversible factors. Reversible factors other than regular exercise could also explain the differences in BP and serum lipid levels observed between the two groups included in the present study. Diet might be among several reversible factors. In our previous study (13), however, we found that group E (n =143) had a significantly greater total calory intake [2874 ± 533 kcal (group E) vs ± 492 kcal (group NE)], protein intake (109 ± 25 g vs. 99 ± 20 g), fat intake (105 ± 27 g vs. 94 ± 24 g), carbohydrate intake (355 ± 68 g vs. 326 ± 68 g), and Na intake (6,080 ± 1,810 mg vs. 5,520 ± 1,350 mg) than group NE (n =103). We therefore consider the influence of diet on the intergroup differences in percent body fat, BP, and serum lipids to be small, since group E showed lower percent body fat, BP, and TG and yet had a significantly greater total calory intake of fats, carbohydrate, and Na. One explanation for the difference in BP between the two groups is differences in family history of hypertension; it is considered an irreversible risk factor. Although we did not examine family history in detail, the number of students with a positive family history for hypertension, as described in their health-check cards, did not differ between the two groups (Table 2). Since the parents of our subjects were still young, it might have been difficult to identify the hypertensives among them. Even if there were a marked difference between the two groups as regards the family predisposition to hypertension, only the subjects with environmental factors such as high salt intake or obesity would have suffered from hypertension. In this respect, the early promotion of exercise in subjects with a predisposition to hypertension is important. In a meta-analysis of 29 studies, Halbert et al. (14) examined the effectiveness of exercise training in lowering BP. However, there was no discussion of the relationship between exercise and BP in young people in the Halbert et al. study. In contrast, other reports have explicitly supported the present results. One study considered 88 African American girls (age: 15 years old) with high-end BP (above the 67th percentile of those of similar age); that study showed a greater decrease in systolic BP in those subjects who performed aerobic exercise than in the control group (15). Another study of 18 healthy boys aged 10 to 14 years showed that two months of aerobic exercise, measured by a bicycle ergometer, increased the level of HDLC and 6-keto-PGF1a (16). In the present study, the students who preferred dynamic exercise exhibited lower BP, TG, and a lower HOMA index than both students who did not belong to sports clubs and those who preferred less dynamic exercise. Furthermore, a higher HOMA index was observed in students who preferred less dynamic exercise than in the students who did not belong to a sports club. It should be noted that the terms "dynamic" and "static" exercise characterize activity based on mechanical action, and thus these terms differ from "aerobic" and "anaerobic" exercise. Nevertheless, highintensity dynamic exercise that lasts for more than several minutes is considered to be performed primarily aerobically. Clearly, the advantage of aerobic exercise should be encouraged. In addition, it should be also be noted that less aerobic exercise encourages insulin resistance. The present study showed that belonging to sports clubs exerts a limited effect on BP and on cardiovascular risk factors in teen-aged boys. Aerobic exercise should be recommended, even in teenagers, to help reduce the risk factors for cardiovascular disease References Joint National Committee on Detection, Evaluation, and Treatment of High Blood Pressure: The fifth report of the Joint National Committee on Detection, Evaluation, and Treatment of High Blood Pressure (JNC V). Arch Intern Med 1993; 153: Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure: The sixth report of the Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure. Arch Intern Med 1997;157: Lieberman E: Hypertension in childhood and adolescence, in Kaplan NM (ed): Clinical Hypertension, Baltimore, Williams & Wilkins,1998, pp Kawabe H, Shibata H, Hirose H, Tsujioka M, Saito I, Saruta T: Sexual differences in relationships between birth weight or current body weight and blood pressure or cholesterol in young Japanese students. Hypertens Res 1999; 22: Anderssen N, Jacobs DR, Sidney S, et al: Change and secular trends in physical activity patterns in young adults: a seven-year longitudinal follow-up in the coronary artery risk development in young adults study (CARDIA). Am J Epidemiol 1996; 143: Mitchell JH, Haskell WL, Raven PB: Classification of sports. Med Sci Sports Exerc 1994; 26 (Suppl): Conway JM, Norris KH, Bodwell CE: A new approach for the estimation of body composition: infrared interactance. Am J Clin Nutr 1984; 40: Himeno E, Nishino K, Okazaki T, Nanri H, Ikeda M: A weight reduction and weight maintenance program with long-lasting improvement in left ventricular mass and blood pressure. Am J Hypertens 1999;12: Matthews DR, Hosker JP, Rudenski AS, Naylor BA,

6 232 Hypertens Res Vol. 23, No. 3 (2000) Treacher DF, Turner RC: Homeostasis model assessment: insulin resistance and /3-cell function from fasting plasma glucose and insulin concentrations in man. Diabetologia 1985; 28: Shea S, Basch CE, Gutin B: The rate of increase in blood pressure in children 5 years of age is related to changes in aerobic fitness and body mass index. Pediatrics 1994; 94: Kotchen JM, McKean HE, Kotchen TA: Blood pressure trends with aging. Hypertension 1982; 4 (Suppl III): III- 128-III Webber LS, Srinivasan SR, Wattigney WA, Berenson GS: Tracking of serum lipids and lipoproteins from childhood to adulthood. The Bogalusa Heart Study. Am J Epidemiol 1991;133: Tanaka M, Tsuji S, Hoshiyama K, Kawabe H, Saito I: Influence of regular exercise on calory intake, serum lipid levels, and body composition in male high school students (in Japanese). The Bulletin of Keio University Health Center 1997; 15: Halbert JA, Silagy CA, Finucane P, Withers RT, Hamdorf PA, Andrews GR: The effectiveness of exercise training in lowering blood pressure: a meta-analysis of randomised controlled trials of 4 weeks or longer. J Hum Hypertens 1997; 11: Ewart CK, Young DR, Hagberg JM: Effects of schoolbased aerobic exercise on blood pressure in adolescent girls at risk for hypertension. Am J Public Health 1998; 88: Stergioulas A, Tripolitsioti A, Messinis D, Bouloukos A, Nounopoulos Ch: The effects of endurance training on selected coronary risk factors in children. Acta Paediatr 1998; 87: