relationship between asthma, overweight, and ...

Journal of Community Health, Vol. 31, No. 6, December 2006 ( 2006) DOI: 10.1007/s10900-006-9026-4

RELATIONSHIP BETWEEN ASTHMA, OVERWEIGHT, AND PHYSICAL ACTIVITY AMONG U.S. HIGH SCHOOL STUDENTS Sherry Everett Jones, PhD, MPH, JD; Sarah L. Merkle, MPH; Janet E. Fulton, PhD; Lani S. Wheeler, MD; David M. Mannino, MD

ABSTRACT: Asthma is a leading chronic illness among children and adolescents in the United States. This study examined the relationship between asthma and both overweight and physical activity levels. Results are based on data from the Centers for Disease Control and Prevention’s 2003 national Youth Risk Behavior Survey, a cross-sectional survey of health risk behaviors among a representative sample of high school students in the United States. The overall survey response rate was 67% and the results are based on weighted data. SUDAAN was used for all data analysis (prevalence estimates and logistic regression) because it accounts for the complex sampling design of the survey. Significantly more students with current asthma than without were overweight (odds ratio [OR] = 1.4; 95% confidence interval [CI] = 1.1, 1.6) and described themselves as overweight (OR = 1.2; 95% CI = 1.0, 1.4). Significantly more students with current asthma than without used a computer for non-schoolwork 3 or more hours/day (OR = 1.3; 95% CI = 1.1, 1.5). No significant differences were found for participation in sufficient vigorous or moderate physical activity or strengthening exercises among students with and without current asthma. Unlike some other risk factors for developing or exacerbating asthma, overweight and physical activity are generally modifiable. School and community policies and programs can play an important role in asthma management, including promoting the maintenance of an appropriate weight and encouraging continued physical activity. KEY WORDS: asthma; physical activity; overweight; youth; adolescent.

The findings and conclusions in this report are those of the authors and do not necessarily represent the views of Centers for Disease Control and Prevention. Requests for reprints should be addressed to Sherry Everett Jones, PhD, MPH, JD, Centers for Disease Control and Prevention, 4770 Buford Hwy, NE, MS K33, Atlanta, GA 30341, USA; e-mail: [email protected].

469 0094-5145/06/1200-0469 2006 Springer Science+Business Media, Inc.

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INTRODUCTION It is important for adolescents to be physically active, yet some youths with asthma may restrict their physical activity, concerned that participation will provoke an asthma episode or attack.1 Up to 90% of people with asthma experience exercise-induced asthma.2 Particularly vigorous physical activity causes asthma symptoms for most young people with asthma that is not well managed.3 Current treatments can successfully control asthma and allow youths to engage in physical activity with little or no restriction,3 and evidence suggests physical activity may reduce asthma symptoms through better lung functioning.4–7 Universal agreement in the literature does not exist,8–11 but growing evidence suggests obesity may exacerbate existing asthma and increase the risk of developing asthma.8,11–16 Promoting both physical activity and healthy weight maintenance may be important aspects in asthma management and primary prevention. In this study, we examined the relationship between self-reported asthma (current asthma and recent asthma episode or attack) and both overweight and levels of physical activity. This is the first study to examine these relationships on such a wide variety of measures and among a nationally representative sample of high school students.

METHODS The national Youth Risk Behavior Survey (YRBS), developed by the Centers for Disease Control and Prevention (CDC), monitors six categories of priority health-risk behaviors—unintentional injury and violence; tobacco use; alcohol and other drug use; sexual behaviors that contribute to unintended pregnancy and sexually transmitted diseases, including human immunodeficiency virus (HIV) infection; unhealthy dietary behaviors; and physical inactivity—and addresses issues of overweight and asthma.17 The national YRBS sampling strategies and the psychometric properties of the questionnaire have been described in detail elsewhere.17–19 Briefly, in 2003, the YRBS was administered to a nationally representative sample of private and public school students in grades 9–12 using a three-stage cluster sample design. Participation in the survey was anonymous and voluntary and local parental permission procedures were used. Students recorded their responses directly on a self-administered computer-scannable questionnaire with 97 items.

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A weighting factor was applied to each student record to adjust for nonresponse and for varying probabilities of selection, including those resulting from oversampling of black and Hispanic students. The school response rate was 81%, the student response rate was 83%, and the overall response rate was 67%. CDC’s Institutional Review Board granted clearance for the national YRBS. The questionnaire included two questions about asthma: Question 1, answered by 13,553 students, asked ‘‘Has a doctor or nurse ever told you that you have asthma?’’ (response options were ‘‘yes,’’ ‘‘no,’’ and ‘‘not sure’’). Question 2, answered by 13,232 students, asked ‘‘During the past 12 months, have you had an episode of asthma or an asthma attack?’’ (response options were ‘‘I do not have asthma’’; ‘‘no, I have asthma, but I have not had an episode of asthma or an asthma attack during the past 12 months’’; ‘‘yes, I have had an episode of asthma or an asthma attack during the past 12 months’’; and ‘‘not sure’’). Each student was expected to respond to both questions, and 13,222 did so. ‘‘Lifetime asthma’’ was defined as ever having been told by a doctor or nurse that the student had asthma. ‘‘Current asthma’’ was defined as having lifetime asthma and, during the 12 months preceding the survey, reporting either having asthma but no episode or attack or having an asthma episode or attack. ‘‘Asthma episode or attack’’ was calculated among students with current asthma and was defined as having had an asthma episode or attack during the 12 months preceding the survey. To determine the percentage of students who were overweight, selfreported height and weight data were applied to reference data from the National Health and Nutrition Examination Survey.20 ‘‘Overweight’’ was defined as a body mass index ‡ 95th percentile by age and sex. Students also reported their perception of their weight status; whether they had participated in sufficient vigorous physical activity (exercised or participated in physical activities that made them sweat and breathe hard for ‡ 20 minutes on ‡ 3 of the 7 days preceding the survey), sufficient moderate physical activity (physical activities that did not make them sweat and breathe hard for ‡ 30 minutes on ‡ 5 of the 7 days preceding the survey), or strengthening exercises (e.g., push-ups, sit-ups, or weightlifting on ‡ 3 of the 7 days preceding the survey to strengthen or tone their muscles); sports team participation (run by their school or community groups during the 12 months preceding the survey); and both television watching and non-schoolwork computer use (3 or more hours per day on an average school day). The prevalence of overweight and levels of physical activity among high school students in the United States based on YRBS data have been reported elsewhere.17

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SUDAAN,21 which accounts for the complex sampling design of the survey, was used to generate all point estimates and 95% confidence intervals (CI). A previous analysis examined sex, race/ethnicity, and grade differences in self-reported asthma22 and found subgroup differences in lifetime asthma, current asthma, and asthma episode or attack prevalence among students with current asthma. Thus, logistic regression models controlled for sex, race/ethnicity, and grade in analyses used to identify statistically significant differences (p £ 0.05) in overweight status and physical activity levels among students with current asthma and among those with current asthma, those who had an asthma episode or attack. Eighty-five percent of students who reported lifetime asthma also reported current asthma. Of the remaining students with lifetime asthma, 9% reported they did not have asthma and 6% reported they were not sure whether they had an asthma episode or attack during the 12 months preceding the survey (in the analysis, both groups were deemed not to have current asthma). Because of the high correlation between lifetime and current asthma, this paper reports only on current asthma and asthma episode or attack among students with asthma and their associations with physical activity levels and overweight.

RESULTS Approximately one in six high school students (16.1% [95% CI = ± 1.2]) reported having current asthma, and among students with current asthma, 37.9% (95% CI = ± 2.5) reported having an asthma episode or attack during the 12 months preceding the survey. Significantly more students with current asthma than without were overweight (odds ratio [OR] = 1.4; 95% CI = 1.1, 1.6) and described themselves as overweight (OR = 1.2; 95% CI = 1.0, 1.4) (Table 1). Significantly more students with current asthma than without used a computer for non-schoolwork three or more hours/day (OR = 1.3; 95% CI = 1.1, 1.5) (Table 2). No significant differences were found in participation in sufficient vigorous or moderate physical activity or for participation in strengthening exercises among students with and without current asthma (Table 3). None of the behaviors studied in this analysis varied by students with current asthma who had and had not had an asthma episode or attack during the 12 months preceding the survey. Because some literature suggests sex differences in the association between obesity and asthma,10,12–15 females and males were compared separately (controlling for grade and race/ethnicity). Significantly more


TABLE 1 Asthma Status and Overweight and Perceived Overweight Overweighta

Described Themselves as Overweight

% (95% CIb)

OR (95% CI)c

% (95% CI)

OR (95% CI)

Current asthmad Yes 14.8 ( ± 2.5) No 11.6 ( ± 1.2)

1.4 (1.1, 1.6)* 1.0

34.0 ( ± 4.1) 29.8 ( ± 1.3)

1.2 (1.0, 1.4)* 1.0

36.3 ( ± 5.6) 32.6 ( ± 5.2)

1.0 (0.7, 1.5) 1.0

Asthma episode or attacke Yes 12.3 ( ± 3.5) 0.8 (0.5, 1.2) No 16.3 ( ± 3.1) 1.0 a

Students who were ‡ 95th percentile for body mass index, by age and sex, based on reference data. b Confidence interval. c Univariate logistic regression models, controlling for sex, race/ethnicity, and grade. d Was ever told by a doctor or nurse that the student had asthma and, during the 12 months preceding the survey, the student either had asthma but no episode of asthma or asthma attack or had an episode of asthma or asthma attack (n = 1,943). e Among the 16.1% of students with current asthma, had an episode of asthma or asthma attack during the 12 months preceding the survey (n = 710). *p £ 0.05.

females with current asthma than those without were overweight (10.6% [95% CI = ± 2.8] versus 7.7% [95% CI = ± 1.4]; OR = 1.5 [95% CI = 1.1, 2.0]) and described themselves as overweight (41.8% [95% CI = ± 6.0] versus 35.5% [95% CI = ± 2.4]; OR = 1.3 [95% CI = 1.03, 1.6]). Significantly more males with current asthma than those without were overweight (19.2% [95% CI = ± 3.0] versus 15.3% [95% CI = ± 1.5]; OR = 1.3 [95% CI = 1.1, 1.6]) and used a computer for non-schoolwork 3 or more hours/ day (32.6% [95% CI = ± 5.8] versus 26.6% [95% CI = ± 2.9]; OR = 1.3 [95% CI = 1.0, 1.8]).

DISCUSSION Consistent with other studies,8,11–16 an examination of YRBS data found that, compared with high school students without current asthma, students with current asthma were significantly more likely to be overweight and to describe themselves as overweight. Other studies have suggested that the relationship between obesity and asthma is stronger in females than in males.10,12–15 In this study, we found that for both males and females,

1.0 (0.8, 1.3) 1.0

Asthma episode or attackf Yes 58.1 ( ± 5.1) No 59.2 ( ± 4.2) 41.6 ( ± 5.0) 40.4 ( ± 4.1)

1.1 (0.9, 1.4) 1.0

1.0 (0.9, 1.2) 1.0

25.6 ( ± 3.9) 25.4 ( ± 4.5)

25.5 ( ± 3.4) 21.5 ( ± 2.6)

% (95% CI)

1.1 (0.8, 1.5) 1.0

1.3 (1.1, 1.5)* 1.0

OR (95% CI)

Used Computer for Non-schoolwork 3 or More Hours/dayb

b

Run by their school or a community group during the 12 months preceding the survey. On an average school day. c Confidence interval. d Univariate logistic regression models, controlling for sex, race/ethnicity, and grade. e Was ever told by a doctor or nurse that the student had asthma and, during the 12 months preceding the survey, the student either had asthma but no episode of asthma or asthma attack or had an episode of asthma or asthma attack (n = 1,943). f Among the 16.1% of students with current asthma, had an episode of asthma or asthma attack during the 12 months preceding the survey (n = 710). *p £ 0.05.

a

1.1 (1.0, 1.2) 1.0

Current asthmae Yes 58.8 ( ± 3.1) No 56.7 ( ± 2.2) 40.8 ( ± 3.7) 39.9 ( ± 3.1)

% (95% CI)

OR (95% CI)d

% (95% CIc) OR (95% CI)

Watched 3 or More Hours/Day of TV b

Played on 1 or More Sports Teamsa

Asthma Status and Played on a Sports Team, Watched 3 or More Hours/Day of Television, and Used a Computer for Non-Schoolwork for 3 or More Hours/Day

TABLE 2

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1.1 (1.0, 1.3) 1.0

1.2 (0.9, 1.6) 1.0

Current asthmaf Yes 65.4 ( ± 4.1) No 63.2 ( ± 2.0)

Asthma episode or attackg Yes 67.1 ( ± 4.3) No 64.3 ( ± 5.8) 1.1 (0.8, 1.4) 1.0

1.1 (0.9, 1.3) 1.0

56.2 ( ± 6.0) 55.6 ( ± 6.9)

55.8 ( ± 5.3) 52.7 ( ± 2.6)

% (95% CI)

1.0 (0.8, 1.4) 1.0

1.2 (1.0, 1.5) 1.0

OR (95% CI)

Did Strengthening Exercisesc

a Exercised or participated in physical activities that made students sweat and breathe hard for ‡ 20 minutes on ‡ 3 of the 7 days preceding the survey (e.g., basketball, soccer, running, swimming laps, fast bicycling, fast dancing, or similar aerobic activities). b Physical activities that did not make students sweat and breathe hard for ‡ 30 minutes on ‡ 5 of the 7 days preceding the survey (e.g., fast walking, slow bicycling, skating, pushing a lawn mower, or mopping floors). c For example, push-ups, sit-ups, or weightlifting on ‡ 3 of the 7 days preceding the survey to strengthen or tone their muscles. d Confidence interval. e Univariate logistic regression models, controlling for sex, race/ethnicity, and grade. f Was ever told by a doctor or nurse that the student had asthma and, during the 12 months preceding the survey, the student either had asthma but no episode of asthma or asthma attack or had an episode of asthma or asthma attack (n = 1,943). g Among the 16.1% of students with current asthma, had an episode of asthma or asthma attack during the 12 months preceding the survey (n = 710).

25.3 ( ± 3.6) 24.8 ( ± 3.6)

25.0 ( ± 2.7) 24.1 ( ± 1.3)

% (95% CI)

OR (95% CI)e

% (95% CId) OR (95% CI)

Participated in Sufficient Moderate Physical Activityb

Participated in Sufficient Vigorous Physical Activitya

Asthma Status and Participation in Sufficient Vigorous Physical Activity, Moderate Physical Activity, and Strengthening Exercises

TABLE 3


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significantly more students with than without current asthma were overweight. Some authors have suggested biologically plausible mechanisms to explain the relationship between obesity and asthma.8 The relationship between obesity, the presence of respiratory symptoms, and the development of asthma is complex. Some evidence suggests there is a direct link, perhaps related to inflammatory or immune processes, but there are also data suggesting an indirect link mediated by sleep-disordered breathing, gastric reflux, and other conditions associated with obesity.8 In this study, students with asthma were as likely as students without asthma to report playing on one or more sports teams, engaging in strengthening exercises, and participating in sufficient vigorous and moderate physical activity. The literature describing physical activity and fitness levels among children with asthma provides inconsistent results. In a review of studies examining aerobic and anaerobic fitness among children and adolescents with asthma, Welsh and colleagues identified seven studies in which no differences existed between youths with and without asthma and seven studies in which fitness levels among youths with asthma were lower than among youths without asthma.7 Welsh and colleagues also reviewed studies comparing physical activity levels among children and adolescents and concluded that activity levels among students with and without asthma were comparable.7 Some studies suggest child and parental beliefs, more so than asthma status or severity, may determine physical activity and aerobic fitness among students with asthma.1,23 To encourage schools to help students with asthma participate in physical activity, the National Asthma Education and Prevention Program in partnership with other national organizations developed a guidance document called ‘‘Breathing Difficulties Related to Physical Activity for Students with Asthma: Exercise-Induced Asthma’’.24 Working with health care providers and families, schools can identify students with asthma and ensure that their prescribed medications are available during periods of physical activity; encourage students to prepare for physical activity such as using their prescribed pre-exercise treatment and using a warm-up period before vigorous physical activity; and modify their physical activity when symptoms are present or when environmental conditions are of concern (e.g., ozone alerts, high pollen counts).24 When asthma is appropriately managed, not only is it safe for students with asthma to participate in physical activity, it is strongly recommended.6,24 In a review of the effects of physical conditioning on children and adolescents with asthma, many studies reported improved aerobic


fitness after training.6 In the same review, some studies found a reduced severity in exercise-induced asthma, although most found no change in the occurrence or degree of exercise-induced asthma6 suggesting no increased risk of asthma attacks or episodes because of increased physical activity. Being physically active and maintaining a healthy body weight may actually reduce asthma symptoms and help control the disease.6,8,24 The findings in this report are subject to at least three limitations. First, these data apply only to adolescents who attend high school. Nationwide, among persons aged 16–17 years, approximately 5% are not enrolled in a high school program and have not completed high school 25. Second, the data in this report are based on self-report and the extent of underreporting or overreporting of height, weight, and physical activity levels cannot be determined. Asthma status was not confirmed by medical records and asthma episode or attack was not defined. Third, the data in this report are from a cross-sectional survey and thus only associations and not causes and effects can be determined. In conclusion, unlike some other risk factors for developing or exacerbating asthma, overweight and physical activity levels have the advantage of being modifiable. Physically active youth are more likely to have stronger bones, be of normal weight, and, if hypertensive, show reductions in blood pressure.26 Health care providers are a trusted source of medical information and can educate youths with asthma and their families about the benefits of achieving and maintaining an appropriate weight and getting sufficient physical activity. Likewise, school and community policies and programs can play an important role in asthma management, including promoting the maintenance of an appropriate weight and continued physical activity. Although this analysis did not show an association between asthma and physical activity, current efforts for all youths to obtain recommended amounts of physical activity26,27 should be encouraged. REFERENCES 1. Pianosi PT, Davis HS. Determinants of physical fitness in children with asthma. Pediatrics 2004; 113:e225–e229. 2. Wilber RL. Incidence of asthma and exercise-induced asthma. In KW Rundell, RL Wilber and RF Lemanske (Eds.). Exercise-Induced Asthma: Pathophysiology and Treatment. Champaign, IL: Human Kinetics, 2002, pp 39–68. 3. National Heart, Lung, and Blood Institute. Asthma and Physical Activity in the School: Making a Difference. Washington, DC: National Institutes of Health National Heart, Lung, and Blood Institute, 1995, NIH Publication No. 95–3651. 4. Fitch KD, Blitvich JD, Morton AR. The effect of running training on exercise-induced asthma. Ann Allergy 1986; 57:90–94.

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5. Matsumoto I, Araki H, Tsuda K, et al. Effects of swimming training on aerobic capacity and exercise induced bronchoconstriction in children with bronchial asthma. Thorax 1999; 54:196– 201. 6. Welsh L, Roberts RGD, Kemp JG. Fitness and physical activity in children with asthma. Sports Med 2004; 34:861–870. 7. Welsh L, Kemp JG, Roberts RGD. Effects of physical conditioning on children and adolescents with asthma. Sports Med 2005; 35:127–141. 8. Tantisira KG, Weiss ST. Complex interactions in complex traits: obesity and asthma. Thorax 2001; 56:ii64–ii73. 9. Wilson MM, Irwin RS. The association of asthma and obesity: is it real or a matter of definition, Presbyterian minister’s salaries, and earlobe creases? Arch Intern Med 1999; 159:2513–2514. 10. Bibi H, Shoseyov D, Feigenbaum D, et al. The relationship between asthma and obesity in children: is it real or a case of over diagnosis? J Asthma 2004; 41:403–410. 11. Weiss ST, Shore S. Obesity and asthma: directions for research. Am J Respir Crit Care Med 2004; 169:963–968. 12. Hancox RJ, Milne BJ, Poulton R, et al. Sex differences in the relation between body mass index and asthma and atopy in a birth cohort. Am J Respir Crit Care Med 2005; 171:440–445. 13. Beckett WS, Jacobs DR Jr, Yu X, Iribarren C, Williams OD. Asthma is associated with weight gain in females but not males, independent of physical activity. Am J Respir Crit Care Med 2001; 164:2045– 2050. 14. Castro-Rodrı´guez JA, Holberg CJ, Morgan WJ, Wright AL, Martinez FD. Increased incidence of asthmalike symptoms in girls who become overweight or obese during the school years. Am J Respir Crit Care Med 2001; 163:1344–1349. 15. Gold DR, Damokosh AI, Dockery DW, Berkey CS. Body-mass index as a predictor of incident asthma in a prospective cohort of children. Pediatr Pulmonol 2003; 36:514–521. 16. Sulit LG, Storfer-Isser A, Rosen CL, Kirchner L, Redline S. Associations of obesity, sleep-disordered breathing, and wheezing in children. Am J Respir Crit Care Med 2005; 171:659–664. 17. Grunbaum JA, Kann L, Kinchen S et al. (2004) Youth Risk Behavior Surveillance—United States, 2003. In Surveillance Summaries, May 21, 2004. MMWR 53(No. SS-2): 1–96. 18. Brener ND, Kann L, McManus T, et al. Reliability of the 1999 Youth Risk Behavior Survey questionnaire. J Adolesc Health 2002; 31:336–342. 19. Brener ND, Kann L, Kinchen SA, et al. (2004) Methodology of the Youth Risk Behavior Surveillance System. In: Recommendations and Reports, September 24, 2004. MMWR 53(No. RR-12): 1–13. 20. Kuczmarski RJ, Ogden CL, Grummer-Strawn LM, et al. (2000) CDC Growth cCharts: United States. Washington, DC: US Department of Health and Human Services, Centers for Disease Control and Prevention, National Center for Health Statistics. Advance data from vital and health statistics; December 4, (revised). Publication No. 314. 21. Research Triangle Institute. SUDAAN: software for the statistical analysis of correlated data, release 8.0 [software and documentation]. Research Triangle Park, NC: Research Triangle Institute, 2001. 22. Merkle S, Everett Jones S, Wheeler L, Mannino DM. Self-reported asthma prevalence among high school students in the United States—2003. MMWR 2005; 54:765–767. 23. Lang DM, Butz AM, Duggan AK, Serwint JR. Physical activity in urban school-aged children with asthma. Pediatrics 2004; 113:e341–e346. 24. National Asthma Education and Prevention Program. Breathing difficulties related to physical activity for students with asthma: exercise induced asthma. Ways to Help Students with Asthma Participate in Physical Activity. Bethesda, MD: National Institutes of Health, National Heart, Lung, and Blood Institute, March 2005, Available at: http://www.nhlbi.nih.gov/health/prof/lung/ asthma/exer_induced.htm. Accessed July 21, 2005. 25. Kaufman P, Alt MN, Chapman CD (2004) Dropout Rates in the United States: 2001. Washington, DC: US Department of Education, National Center for Education Statistics, NCES 2005-046. 26. Strong WB, Malina RM, Blimkie CJ, et al. Evidence based physical activity for school-age youth. J Pediatr 2005; 146:732–737. 27. US Department of Health and Human Services, US Department of Agriculture. Dietary Guidelines for Americans 2005. Washington, DC: US Department of Health and Human Services, 2005, HHS Publication No. HHS-ODPHP-2005-01-DGA-A. Available at: http://www.healthierus.gov/dietaryguidelines. Accessed September 15, 2005.