Prevalence of obesity in asthma and its relations with asthma severity and control

Prevalência de obesidade na asma e suas relações com gravidade e controle da asma

Abstracts

OBJECTIVE: To determine the prevalence of obesity in asthmatic patients attending at an outpatient clinic, and to investigate its relationships with asthma severity and level of asthma control. METHODS: In a cross-sectional study we recruited patients aged 11 years and older with confirmed asthma diagnosis from the outpatient asthma clinic of Hospital de Clínicas de Porto Alegre, Brazil. They underwent an evaluation by a general questionnaire, an asthma control questionnaire and by pulmonary function tests. Nutritional status was classified by body mass index (BMI). RESULTS: 272 patients were included in the study. Mean age was 51.1 ± 16.5 years and there were 206 (74.9%) female patients. Mean BMI was 27.5 ± 5.3 kg/m², and 96 (35.3%) patients were classified as normal weight, 97 (35.7%) as overweight and 79 (29%) as obesity. There was a significant higher proportion of female than male patients (34.3% vs. 13.2%, p = 0.002) in the obesity group. There were no significant differences with respect to asthma control (p = 0.741) and severity classification (p = 0.506). The FEV1% predicted was significantly higher in the obese than in the non-obese group (73.7% vs. 67.2%, p = 0.037). Logistic regression analysis identified sex (OR = 3.84, p = 0.002) as an independent factor associated with obesity. CONCLUSIONS: This study showed a high prevalence of obesity in asthmatic patients. Obese and non-obese subjects were similar in regard to asthma severity and level of asthma control. Female sex was associated with obesity in this asthma population.

Obesity; Lung function; Asthma control; Disease severity; Body mass index

OBJETIVO: Determinar a prevalência de obesidade em pacientes asmáticos atendidos no ambulatório clínico, e investigar sua relação com a gravidade e controle da asma. MÉTODOS: Estudo transversal, envolvendo pacientes, com idade igual ou superior a 11 anos e diagnóstico de asma confirmado, do ambulatório clínico do Hospital de Clínicas de Porto Alegre, Brasil. Os pacientes foram submetidos à avaliação através de um questionário geral, questionário de controle da asma e teste de função pulmonar. O estado nutricional foi classificado conforme o índice de massa corporal (IMC). RESULTADOS: Foram incluídos no estudo 272 pacientes, sendo 206 (74,9%) pacientes do sexo feminino. A média de idade foi 51.1 ± 16.5 anos. O IMC médio foi 27.5 ± 5.3 kg/m², sendo 96 (35.3%) pacientes classificados como eutróficos, 97 (35,7%) como sobrepeso e 79 (29%) como obesidade. Observou-se significativamente maior proporção de pacientes do sexo feminino no grupo de obesidade quando comparados aos pacientes do sexo masculino (34.3% vs. 13.2%, p = 0.002). Não houve diferença significativaemrelação ao controle da asma (p = 0.741) e classificação de gravidade (p = 0.506). O FEV1% predito foi significativamente maior nos pacientes obesos quando comparados aos não obesos (73.7% vs. 67.2%, p = 0.037). A análise de regressão logística identificou gênero como fator independente associado com a obesidade. (OR = 3.84, p = 0.002). CONCLUSÃO: O presente estudo observou alta prevalência de obesidade em pacientes asmáticos. Indivíduos obesos e não obesos tiveramsimilaridade para gravidade e controle da asma. O gênero feminino foi associado com obesidade nesta população asmática.

Obesidade; Função pulmonar; Grau de controle; Gravidade da doença; Índice de massa corporal

ORIGINAL ARTICLE

Prevalence of obesity in asthma and its relations with asthma severity and control^*

Gabriele Carra Forte^I; Denis Maltz Grutcki^I; Samuel Millán Menegotto^I; Rosemary Petrik Pereira^I; Paulo de Tarso Roth Dalcin^I,II,**

^IFaculdade de Medicina, Universidade Federal do Rio Grande do Sul, Porto Alegre, RS, Brazil

^IIService of Pneumology, Hospital das Clínicas de Porto Alegre, Porto Alegre, RS, Brazil

ABSTRACT

OBJECTIVE: To determine the prevalence of obesity in asthmatic patients attending at an outpatient clinic, and to investigate its relationships with asthma severity and level of asthma control.

METHODS: In a cross-sectional study we recruited patients aged 11 years and older with confirmed asthma diagnosis from the outpatient asthma clinic of Hospital de Clínicas de Porto Alegre, Brazil. They underwent an evaluation by a general questionnaire, an asthma control questionnaire and by pulmonary function tests. Nutritional status was classified by body mass index (BMI).

RESULTS: 272 patients were included in the study. Mean age was 51.1 ± 16.5 years and there were 206 (74.9%) female patients. Mean BMI was 27.5 ± 5.3 kg/m², and 96 (35.3%) patients were classified as normal weight, 97 (35.7%) as overweight and 79 (29%) as obesity. There was a significant higher proportion of female than male patients (34.3% vs. 13.2%, p = 0.002) in the obesity group. There were no significant differences with respect to asthma control (p = 0.741) and severity classification (p = 0.506). The FEV₁% predicted was significantly higher in the obese than in the non-obese group (73.7% vs. 67.2%, p = 0.037). Logistic regression analysis identified sex (OR = 3.84, p = 0.002) as an independent factor associated with obesity.

CONCLUSIONS: This study showed a high prevalence of obesity in asthmatic patients. Obese and non-obese subjects were similar in regard to asthma severity and level of asthma control. Female sex was associated with obesity in this asthma population.

Keywords: Obesity; Lung function; Asthma control; Disease severity; Body mass index

Introduction

The prevalence of asthma has been increasing in recent years throughout the world.¹ In Brazil, it is estimated that asthma affects more than 16 million people, approximately 10% of the population.^2,3 It is observed an alarming concomitant increase in obesity, which prevalence reaches epidemic proportions.⁴ Survey data (POF 2008/2009) showed that being overweight affects 50.1% of men and 48% of adult women, and of that group, 12.4% of men and 16.9% of women are obese.⁵ In Brazil, these two diseases have become a serious public health problem, thus increasing costs from the public and private sectors.⁴

An increasing body of literature suggests that there is an association between obesity and asthma.^6-9 Although the exact nature of this association remains unclear, many investigators have interpreted the data suggesting that obesity both increases the risk of incident asthma and alters prevalent asthma toward a more difficult-to-control phenotype.¹⁰

A variety of reported observations suggest that obesity might impact the lung in multiple ways.^11-15 Moreover, studies report that individuals with persistent asthma are significantly limited in the practice of physical activity, thus reducing energy expenditure, a fact that contributes to the growing increase in the prevalence of overweight and obesity.^14,16 Likewise, obesity seems to have negative impact on the level of asthma control.^17-19. Lessard et al. showed that obese individuals are more likely to have not controlled asthma when compared to non-obese.²⁰ A previous study, however, did not find a relationship between asthma severity and obesity.²¹

The objective of this study was to determine the prevalence of obesity in asthmatic patients attending at an outpatient clinic in a large tertiary care hospital in Southern Brazil, and to investigate its relationships with asthma severity and level of asthma control.

Methods

This is a secondary analysis of a larger study conducted to determine the factors associated with asthma control. It was a cross-sectional study with prospectively collected data. All patients who volunteered were sequentially included. The protocol was approved by the Ethics Committee of Hospital de Clínicas de Porto Alegre (HCPA) and all participants or their parents - in case of patients younger than 18 years - gave written informed consent.

The patients selected were referred from a public institution. All patients were recruited from the outpatient Asthma Clinic of HCPA, Porto Alegre, RS, Brazil. The study included patients above 11 years of age, with a physician's diagnosis of asthma. The diagnosis was confirmed following three criteria: symptoms of asthma, reversible airflow obstruction with improvement of 12% or more and 200 mL in forced expiratory volume in one second (FEV₁) after administration of a short-acting β₂-agonist, or bronchial hyperresponsiveness to a bronchoconstricting agent. Patients who refused to participate, as well as those who did not complete all the evaluations required by the study protocol and patients with chronic pulmonary diseases other than asthma such as emphysema, chronic bronchitis or bronchiectasis were excluded.

After a scheduled outpatient consultation with an asthma specialist, all subjects were interviewed by a researcher using a structured questionnaire that evaluated the influence of the following variables: age, gender, race, marital status, educational level, socioeconomic status, smoking status, comorbid conditions, asthma severity and asthma control. All subjects underwent a comprehensive clinical, nutritional and pulmonary function evaluation.

According to World Health Organization (WHO) criteria,²² nutritional status was classified by body mass index (BMI), which was calculated as weight in kilograms divided by the square of height in meters (kg/m² ). In accordance with the International Standard Definition,²² normal/underweight were defined as a BMI < 25 kg/m² , overweight was defined as a BMI of 25-29.99 kg/m² , and obesity was defined as BMI > 30 kg/m². Obesity was classified in three classes according to the BMI classification: class I (BMI > 30 and < 35 kg/m² ), class II (BMI > 35 and < 40 kg/m² ), and class III (BMI > 40 kg/m² ). Body weight was measured with subjects wearing light clothes and no shoes, and height was measured with an anthropometer attached to the scale.²

Pulmonary function was assessed with a computerized spirometer (Jaeger, v 4.31, Germany). Forced vital capacity (FVC), FEV₁ and FEV₁/FVC were measured three times, the best trial being reported. All parameters were reported as percent of the predicted for age, height, and gender.²³ PEF was measured using a portable Peak Flow Monitor (Vitalograph; Boehringer Ingelheim, Germany). Three successive expiratory maneuvers were performed, and the one with the highest value was recorded. The result was reported as percentage of the predicted for age, height and gender.²⁴

We used the 2002 GINA classification system to assess disease severity according to the daily medication regimen,²⁵ which divides patients into 4 severity categories (mild intermittent; mild, moderate, and severe persistent asthma) based on frequency of symptoms, spirometric data and intensity of drug therapy.

The classification of asthma control was based on the 2011 GINA guidelines ²⁶. Asthma was considered to be controlled if all the following features were present: daytime symptoms only twice a week or less and no asthma attack (requiring oral corticosteroids, hospitalizations or emergency visits) in the last 3 months, no limitation of activities, no nocturnal symptoms or awakenings, need for reliever/rescue treatment only twice a week or less, normal airflow (FEV₁ and peak expiratory flow rate - PEF - equal to or greater than 80% of predicted value). Asthma was considered to be partly controlled if one or two of the above features were absent. Asthma was considered to be uncontrolled if more than two features were absent or if asthma had caused hospital/emergency department admission in the previous 12 months.

Statistical analysis

All analyses were performed with the Statistical Package for the Social Sciences, version 19.0 for Windows (SPSS Inc., Chicago, IL, EUA). Statistical analyses included simple frequencies and descriptive statistics of the variable of interest. The results obtained are presented as cases (proportion), mean ± SD, or median (interquartile range).The Chi-square test and the Student's t test or the Mann-Whitney U test were, respectively, used for testing differences among categorical variables and among continuous variables. Nominal statistical significance was set atap< 0.05 for all the analyses.

Multivariate analyses were performed by using logistic regression techniques with enter method. The odds ratio (OR) from this analysis is the OR for obesity. Selected non collinear variableswithap< 0.10 were introduced in the binary logistic regression, controlled by gender and age.

Results

Three hundred thirty-four eligible subjects were examined in this study. Thirty patients refused to participate, 27 patients were excluded because they had another chronic pulmonary disease, and 5 patients were excluded because they failed to complete all the evaluations required by the study protocol. Thus, 272 patients were included in the study.

The general characteristics of the patients are presented in Table 1. There were 204 (75%) females. Mean age was 51.1 ± 16.5 years and median age at asthma diagnosis was 25 years (IR = 38.8 years). There were 229 (84.2%) white and 43 (15.8%) nonwhite patients. Mean BMI was 27.5 ± 5.3 kg/m² , and 96 (35.3%) patients were classified as having normal weight, 97 (35.7%) as being overweight, 56 (20.6%) as with obesity class I, 17 (6.3%) as with obesity class II and 6 (2.2%) as with obesity class III. There were 38 (13.9%) patients with mild intermittent or persistent asthma, 93 (34.2%) with moderate asthma and 141 (51.8%) with severe asthma. Asthma was controlled in 48 (17.6%) patients, partly controlled in 74 (27.2%) and uncontrolled in 150 (55.1%). The mean FVC was 83.8 ± 21.4% of the predicted, the mean FEV₁ was 69.1 ± 23.1% of the predicted, the mean FEV₁/FVC was 66.1 ± 12.5%, the mean FEV₁/FVC was 81.0 ± 14.1% of the predicted and the mean PEF was 64.1 ± 22.1% of the predicted.

The comparison of patient characteristics and their relationship to BMI group classification is showed in Table 2. There was a significant higher proportion of female than male patients (34.3% vs. 13.2%, p = 0.002) in the obesity group. There were no significant differences with respect to race (p = 0.711), age at diagnosis (p = 0.301), educational level (p = 0.491), income level (p = 0.344), smoking status (p = 0.783), asthma control (p = 0.741), GINA severity classification (p = 0.506), PEFR % predicted (p = 0.291) and FVC% predicted (p = 0.209). The FEV₁% predicted and the FEV₁/FVC% predicted were significantly lower in the non-obese group than in the obese group (67.2% vs. 73.7%, p = 0.037; and 79.5% vs. 84.9%, p = 0.011, respectively).

A logistic regression analysis (Table 3) identified sex (OR = 3.84, p = 0.002) as an independent factor associated with obesity.

Discussion

This cross-sectional study showed a high prevalence of obesity (29.1%) in patients who attended at an outpatient asthma clinic in a large, tertiary care, university-affiliated hospital in Southern Brazil. Obese and non-obese subjects were similar in regard to asthma severity and level of asthma control. However, FEV₁ was found to be higher in obese than in non-obese subjects. Female sex was an independent factor associated with obesity in this asthma population.

Similarly to the present study, Pelegrino et al.²¹ studied 200 patients (72.5% were women) and reported that 32% presented a BMI > 30 kg/m². Barros et al.²⁷ studied 508 patients (79.3% were women) with severe asthma in an asthma reference center. The mean BMI was 28.03 ± 5.88. The patients were classified as follows: 17.9% of patients in obesity class I, 10.3% in obesity class II and 3.7% in obesity class III.

In our sample, the prevalence of obesity was higher among the women. This is consistent with previous studies that found that the increased risk of asthma associated with obesity was only significant in women, but not in men.²⁸

Asthma is more common in women than in men, which is reflected in various frequency measures including prevalence,²⁹ incidence³⁰ and hospitalization.^31,32 In the present study, 75% of the patients were women. This finding is consistent with previous studies in our institution that reported a higher proportion of females than male patients with asthma (from 70.9 vs. 73.9%).^33-36 In the present study, asthma severity was assessed by the GINA classification system according to the daily medication regimen.²⁵ With this approach, effective therapy could control the disease, but would not interfere with the classification of disease severity. In contrast to our study, Fitzpatrick et al.³⁷ found that obesity was associated with more severe asthma and Ackerman et al.³⁸ showed a positive relationship between weight and asthma severity. However, our data demonstrates that the asthma severity of obese individuals did not differ from that of non-obese people. In agreement to our results, Pelegrino et al.²¹ found no correlation between asthma severity and obesity.

Asthma control, which is defined as the extent to which the various manifestations of asthma are reduced or removed by treatment, is increasingly receiving attention, both in clinical trials and clinical practice.³⁹ In the present study we used a composite measure of asthma control according to a scheme based on GINA guidelines.²⁵ Although this measure has not yet been validated, it simultaneously takes into account several markers of uncontrolled asthma. More recently, several studies have used this measure to evaluate asthma control.³⁹ In the present study, obesity was not related to asthma control. In contrast, previous cross-sectional studies found that obese adults were more likely to report poor asthma control.²⁷ Saint-Pierre et al., in a prospective study, evaluated that non-obese patients, compared to obese asthmatics, were more likely to have poorly controlled asthma.¹⁷ Also, Lavoie et al.,¹⁸ in a cross-sectional study, showed that obesity is associated with a decline in asthma control. In contrast, a questionnaire-based study of asthma control in primary care clinics demonstrated no significant association with obesity.⁴⁰

Obesity is associated with a reduction in residual volume, functional residual capacity and expiratory reserve volume that were reversed by weight loss with bariatric surgery. Obesity also causes a reduction of both FEV₁ and FVC with a preserved FEV₁/FVC ratio.²⁰ However, previous studies yielded contradictory data on whether obesity affects respiratory function in asthmatic subjects.^41,42 We found that subjects with asthma who were obese were more likely to have a higher FEV₁ than their counterparts of normal weight, despite similar levels of asthma severity and control. One possible explanation for this finding was the more difficult control of the disease in obese patients, despite better pulmonary function, assessed by spirometric tests, when compared to non-obese patients.

The present study has some potential limitations. It is a cross-sectional study, and therefore it is not possible to establish the temporal sequence between asthma and obesity. Our study population is made up of people with lower income and education. So, our patient sample is biased toward the socially disadvantaged. Also, the study population was selected from patients referred to a reference center and was probably biased toward the more severely diseased.

Conclusion

In conclusion, this study showed a high prevalence of obesity in patients who attended at an outpatient asthma clinic in Southern Brazil. Obese and non-obese subjects were similar in regard to asthma severity and level of asthma control. Female sex was associated with obesity in this asthma population.

As excess weight is highly prevalent in Brazil and increasing in many parts of the world, and because it is potentially preventable, clinical counseling about obesity should be part of asthma education programs aimed at helping those patients who are overweight to improve health status and outcomes.

Funding

This study was supported by Fundo de Pesquisa do Hospital de Clínicas de Porto Alegre (FIPE-HCPA) and Pró-Reitoria de Extensão da Universidade Federal do Rio Grande do Sul.

Conflicts of interest

The authors declare no conflicts of interest.

Received 2 May 2013

Accepted 30 June 2013

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*

Study conducted at Universidade Federal do Rio Grande do Sul, Porto Alegre, RS, Brazil.

Publication Dates

• Publication in this collection
  19 Dec 2013
• Date of issue
  Dec 2013

History

• Received
  02 May 2013
• Accepted
  30 June 2013