Association of body mass index with the development of methacholine airway hyperresponsiveness in men: the Normative Aging Study

Obesity and asthma

Over the last two decades, the convergence of secular trends indicating increases in the prevalence of obesity and asthma has led to a hypothesis that these two disorders might be related. Although the mechanisms underlying a putative relationship between obesity and asthma have not been fully described, a relatively mature body of literature suggests that obesity increases the risk of incident asthma. This article addresses studies that could be interpreted as supporting the hypothesis that obesity leads to asthma. We evaluate animal studies that provide biological underpinnings to an association between the two disorders and clinical and epidemiologic studies that suggest that the relationship between these two disorders is clinically important.

Risk factors related to fixed airway obstruction in patients with asthma after antiasthma treatment

BACKGROUND

There are many unanswered questions about the role of airway remodeling in asthma.

OBJECTIVE

To evaluate the physiologic factors related to airway remodeling after antiasthma drug treatment for 1 year.

METHODS

We gave 582 patients with asthma long-term control medication for 1 year according to the severity of their asthma. Airway remodeling was defined using forced expiratory volume in 1 second/forced vital capacity and a predicted forced expiratory volume in 1 second of less than 75% after antiasthma treatment.

RESULTS

Of the 582 patients, 49 (8.4%) had airway remodeling. Severe asthma resulted in more airway remodeling than mild-to-moderate asthma. Asthmatic patients with airway remodeling were significantly older and had a longer duration of asthma. Asthmatic patients with airway remodeling had more emphysema on high-resolution computed tomography, a higher rate of near-fatal asthma attacks, a lower percentage of sputum eosinophils, a lower atopy frequency, a greater response to short-acting bronchodilators, and a lower body mass index (BMI) than those without airway remodeling. Age, asthma duration, and BMI were important discriminators of airway remodeling.

CONCLUSION

Nonatopy, asthma duration, emphysema on high-resolution computed tomography, sputum eosinophils, age, and BMI before antiasthma treatment are important factors related to airway remodeling in patients with asthma.

Paternal asthma, mold exposure, and increased airway responsiveness among children with asthma in Costa Rica

BACKGROUND

Little is known about the determinants of airway hyperresponsiveness (AHR) among children with asthma in Hispanic America.

METHODS

We examined the relations among selected familial and environmental factors, markers of allergy, spirometric measures of lung function, and AHR in a cross-sectional study of 403 Costa Rican children with asthma between the ages of 6 and 14 years. Study participants completed a protocol that included questionnaires, spirometry, measurements of serum total and allergen-specific IgE, peripheral blood eosinophil count, and body mass index, and the assessment of airway responsiveness to methacholine (ie, a methacholine challenge test [MCT]). AHR to MCT was defined as the provocative dose of methacholine causing a 20% fall in FEV(1). Linear regression was used for the univariate and multivariate analyses.

RESULTS

Of the 403 asthmatic children who underwent an MCT, 350 (86.8%) had AHR to methacholine. In a multivariate analysis, paternal asthma (p = 0.004), parental report of mold/mildew in the child's home (p = 0.04), FEV(1)/FVC ratio (p < 0.0001), and a positive IgE response to Der p 1 (p = 0.008) were significantly associated with AHR among Costa Rican children with asthma.

CONCLUSION

Our results suggest that paternal asthma and environmental exposure to mold/mildew are strong determinants of AHR in Costa Rican children with asthma. FEV(1)/FVC ratio may be a useful measure of AHR (a marker of asthma severity) among Costa Ricans and other Hispanic Americans for whom reference values for FEV(1) are not currently available.

Effect of obesity on breathlessness and airway responsiveness to methacholine in non-asthmatic subjects

BACKGROUND

Obesity is associated with increased prevalence and incidence of asthma, but the mechanism is unknown. Obesity reduces lung volumes, which can increase airway responsiveness, and increases resistive and elastic work of breathing, which can increase dyspnea.

OBJECTIVE

To determine if the intensity of dyspnea due to airway narrowing or if airway responsiveness is increased in obese, non-asthmatic subjects.

SUBJECTS

Twenty-three obese (BMI (body mass index) > or =30 kg m(-2)) and 26 non-obese (BMI <30 kg m(-2)) non-asthmatic subjects, aged between 18 and 70 years.

METHODS

High-dose methacholine challenge was used to determine the sensitivity and the maximal response to methacholine. Respiratory system resistance (Rrs) and reactance were measured, using the forced oscillation technique, as indicators of resistive and elastic loads during challenge. Perception of dyspnea was measured by the Borg score during challenge. Static lung volumes were measured by body plethysmography.

RESULTS

Static lung volumes were reduced in the obese subjects. There were no significant differences in the sensitivity or maximal response to methacholine between obese and non-obese subjects. The magnitude of change in Rrs was similar in both groups, but obese subjects had more negative reactance after challenge (P=0.002) indicating a greater elastic load. The intensity of dyspnea was greater in obese subjects (P=0.03).

CONCLUSIONS

Obesity reduces lung volumes, but does not alter the sensitivity or maximal response to methacholine. However, obese subjects have enhanced perception of dyspnea, associated with greater apparent stiffness of the respiratory system, and may therefore be at greater risk of symptoms.

[Relationship between obesity and asthma]

The prevalences of both obesity and asthma have clearly increased in recent decades, giving rise to speculation that they may be related. Studies have found that obesity precedes and predicts the onset of asthma (time effect), that increased obesity leads to more severe asthma (dose-response effect), that weight reduction (by diet or gastric bypass) improves asthmatic symptoms, and that obesity co-occurs with intermediate asthma phenotypes (obese young girls undergoing early menarche). In the light of that evidence, we can finally suggest a causal relationship between obesity and asthma. Various biological mechanisms (immunologic and inflammatory, hormonal, genetic, nutritional, mechanical, and others related to physical activity) have been put forth to explain the relationship. However, this relation is complex, involving not only the interaction of genetic and environmental factors in triggering both diseases but also the likely participation of several mechanisms at once.

Effect of obesity on airway inflammation: a cross-sectional analysis of body mass index and sputum cell counts

BACKGROUND

Several observational studies have demonstrated an association between obesity and asthma. Studies evaluating exhaled nitric oxide levels and obesity have revealed that a higher body mass index (BMI) is associated with elevated exhaled nitric oxide levels. Airway inflammation using sputum cell counts has not been assessed in obese patients with airway diseases.

OBJECTIVE

The primary aim of this study was to determine whether obesity (based on BMI) is associated with eosinophilic or neutrophilic bronchitis.

METHODS

The results from a database of induced sputum cell counts were compared with BMI and analysed using correlation statistics, regression and parametric and non-parametric analysis.

RESULTS

Seven-hundred and twenty-seven adult participants with an equal number of sputum samples were included in the analysis. BMI varied from 14.5 to 55 kg/m(2). Sputum total cell count (mean+/-SD: 12.9 x 10(6) cell/g+/-21.5), eosinophil percent (median; min to max: 0.3%; 0-89.0), and neutrophil percent (mean+/-SD: 63.5+/-26.6%) were within normal limits. Participants with asthma had a higher percentage of sputum eosinophils than those without asthma (P=0.01). However, there was no difference in the total or differential cell counts among the obese and non-obese participants, when the data were analysed according to BMI category, gender, dose of inhaled corticosteroid, and presence or absence of asthma.

CONCLUSION

In this large sample of adult asthmatic and non-asthmatic participants, there was no association between BMI and airway inflammation measured by sputum cell counts. Other mechanisms to explain the relationship between obesity and asthma will need to be explored if this association is to be better understood.

Determinants of forced expiratory volume in 1 second (FEV1), forced vital capacity (FVC), and FEV1/FVC in chronic spinal cord injury

OBJECTIVE

To assess factors that influence pulmonary function, because respiratory system dysfunction is common in chronic spinal cord injury (SCI).

DESIGN

Cross-sectional cohort study.

SETTING

Veterans Affairs Boston SCI service and the community.

PARTICIPANTS

Between 1994 and 2003, 339 white men with chronic SCI completed a respiratory questionnaire and underwent spirometry.

INTERVENTIONS

Not applicable.

MAIN OUTCOME MEASURES

Forced expiratory volume in 1 second (FEV(1)), forced vital capacity (FVC), and FEV(1)/FVC.

RESULTS

Adjusting for SCI level and completeness, FEV(1) (-21.0 mL/y; 95% confidence interval [CI], -26.3 to -15.7 mL/y) and FVC (-17.2 mL/y; 95% CI, -23.7 to -10.8 mL/y) declined with age. Lifetime cigarette use was also associated with a decrease in FEV(1) (-3.8 mL/pack-year; 95% CI, -6.5 to -1.1 mL/pack-year), and persistent wheeze and elevated body mass index were associated with a lower FEV(1)/FVC. A greater maximal inspiratory pressure (MIP) was associated with a greater FEV(1) and FVC. FEV(1) significantly decreased with injury duration (-6.1 mL/y; 95% CI, -11.7 to -0.6 mL/y), with the greatest decrement in the most neurologically impaired. The most neurologically impaired also had a greater FEV(1)/FVC, and their FEV(1) and FVC were less affected by age and smoking.

CONCLUSIONS

Smoking, persistent wheeze, obesity, and MIP, in addition to SCI level and completeness, were significant determinants of pulmonary function. In SCI, FEV(1), FVC, and FEV(1)/FVC may be less sensitive to factors associated with change in airway size and not reliably detect the severity of airflow obstruction.

Effect of obesity on clinical presentation and response to treatment in asthma

Obesity is a risk factor for being diagnosed with asthma, but there is conflicting evidence on whether obesity is a risk factor for lung function abnormalities characteristic of asthma. We studied a cohort of 488 subjects, 47% of whom were obese. Obese and non-obese subjects with asthma had similar airflow limitation and bronchodilator responsiveness, but obese participants had increased sleep disturbance and gastroesophageal reflux disease, higher cytokine levels, and a trend towards increased exacerbations when treated with theophylline. Obese and non-obese asthmatics have similar lung function abnormalities, but comorbidities and altered responses to medications may significantly affect asthma control in obese people.

Longitudinal changes in food patterns predict changes in weight and body mass index and the effects are greatest in obese women

The prevalence of obesity is increasing in most parts of the world. The objective of this study was to examine whether changes in food patterns were associated with changes in BMI among women over 9 y. Data were from 33,840 women participating in the Swedish Mammography Cohort in 1987 and 1997. Diet was assessed with a FFQ at both time points and 4 food patterns were derived using confirmatory factor analysis (Healthy, Western/Swedish, Alcohol, and Sweets). Our exposure variables were defined as change in factor score for each food pattern from 1987 to 1997. Our outcome variable was defined as change in BMI during the same period, and we also examined change in weight. Normal weight and overweight women had positive changes in weight and BMI during follow-up, whereas obese women had negative changes in BMI and weight; we observed a significant interaction between change in food patterns and baseline BMI. Obese subjects who increased their factor score for the Healthy pattern had larger decreases in BMI (beta = -0.18 kg/m(2) for a 1 unit increase in SD score, CI: -0.26 to -0.10; P < 0.0001), whereas normal weight and overweight women who increased their Healthy pattern score had smaller increases in BMI (-0.05 kg/m(2) and -0.11 kg/m(2), respectively; P < 0.05 for both). Obese women who increased their Healthy pattern score >3 SD had almost a 4 kg decrease in weight and a 1 unit decrease in BMI at follow-up. In conclusion, changes in eating patterns were significantly related to changes in BMI over 9 y and the effect was modified by baseline BMI. Pattern analysis is helpful in generating hypotheses regarding the role of diet in obesity, and additional research is needed to understand which elements of our patterns are protective or risk factors for weight gain.

Boys with high body masses have an increased risk of developing asthma: findings from the National Longitudinal Survey of Youth (NLSY)

OBJECTIVE

To determine the relation between body mass index and the development of asthma in children.

DESIGN

Prospective study of 4393 asthma-free children followed for up to 14 years.

SETTING

Children of participants in the National Longitudinal Survey of Youth.

METHODS

Analysis was limited to children who were followed from birth and were asthma-free during the first 24 months of life. The outcome was the development of asthma during follow-up (incident asthma). Body mass index (BMI) was our main predictor of interest. Survival analyses, using time to development of asthma as the main endpoint, were stratified by sex and controlled for race/ethnicity, poverty status, and prenatal maternal smoking.

RESULTS

Asthma developed in 218 (5.0 %) children during the follow-up period. The relation between BMI and incident asthma varied by sex. A BMI > or =85th percentile at age 2-3 years was a risk factor for subsequent asthma development in boys (hazard ratio (HR) 1.6 95% confidence interval (CI) 1.1, 2.4) but not girls (HR 0.8, 95% CI 0.5, 1.4). Similarly, boys with BMIs always > or =85th percentile were at increased risk for subsequent asthma development (HR 2.4, 95% CI 1.4, 4.4) but not girls (HR 1.5, 95% CI 0.7, 2.9).

CONCLUSION

Boys with high body masses may be at an increased risk for developing asthma.

Inflammatory markers and particulate air pollution: characterizing the pathway to disease

BACKGROUND

Increased concentrations of particles in air have been related to changes in inflammatory markers that in turn are hypothesized in mediating the particle effects on cardiovascular disease. The present work examined this association in an elderly cohort in the Greater Boston area and addresses the relative role of particles from different sources.

METHODS

The study included 710 subjects, active members of the VA Normative Aging Study cohort with measurements of blood markers. Concentrations of particle number (PN), black carbon (BC), fine particulate matter (PM(2.5)), and sulphates were measured at a central site near the examination site.

RESULTS

Positive associations were found between traffic-related particles (PN and BC) and inflammatory markers, but only suggestive associations were found with exposures to PM(2.5) and sulphates. The particle effect on the inflammatory markers was greater among subjects older than 78 years and among obese. A suggestion for a greater effect of particles on inflammatory markers among GSTM1-null subjects and non-users of statin drugs was also seen.

CONCLUSIONS

The findings of the study support the hypothesis that particles can induce cardiovascular disease through inflammatory pathways, suggestive of a greater toxicity of traffic-related particles.

Airway hyperresponsiveness and body mass index: the Child Health and Environment Cohort Study in Hesse, Germany

Increased body mass index has been linked to wheezing, a diagnosis of asthma, and morbidity. We investigated the association between body mass index (BMI), breastfeeding, and airway hyperresponsiveness (AHR) in 536 German schoolchildren. We analyzed consecutive surveys in 1994-1995 and 1997, conducted as part of the Child Health and Environment Cohort Study in Hesse, Germany. The questionnaire included questions adapted from the German version of the International Study of Asthma and Allergy in Childhood (ISAAC). A bronchial challenge test using 4.5% hypertonic saline was conducted during the 1997 survey. AHR was defined as a fall in forced expiratory volume in 1 sec (FEV(1)) of > or = 15%. Of 536 children who participated in the 1997 survey (median age, 10.3 years), 82 (15%) tested positive for AHR. In a multivariate analysis, there was no association between AHR determined at age 10 years and the highest quintile of BMI compared to the lowest quintile at age 4 years (odds ratio (OR), 1.4; 95% confidence interval (CI), 0.5-3.6), 7-8 years (OR, 0.6; 95% CI, 0.1-2.5), or 10 years (OR, 1.1; 95% CI, 0.2-4.3). Breastfeeding for 12 weeks or longer protected against AHR (OR, 0.4; 95% CI, 0.2-0.9). However, when children in the highest quintile of BMI at age 4 years had been breastfed for 8 weeks or less, the prevalence of AHR at age 10 years was significantly increased (27.7%, P = 0.01). In conclusion, our results demonstrate a protective effect of breastfeeding against AHR, and reinforce the need to encourage breastfeeding. Although there was no association between BMI and AHR, our finding of an interactive effect of high BMI and short breastfeeding on AHR suggests a complex etiological pathway that needs to be further explored.

Obesity and asthma

Asthma and obesity are prevalent disorders, each with a significant public health impact, and a large and growing body of literature suggests an association between the two. The systemic inflammatory milieu in obesity leads to metabolic and cardiovascular complications, but whether this environment alters asthma risk or phenotype is not yet known. Animal experiments have evaluated the effects of leptin and obesity on airway inflammation in response to both allergic and nonallergic exposures and suggest that airway inflammatory response is enhanced by both endogenous and exogenous leptin. Cross-sectional and prospective cohort studies of humans have shown a modest overall increase in asthma incidence and prevalence in the obese, although body mass index does not appear be a significant modifier of asthma severity. Studying the obesity-asthma relationship in large cohorts, in which self-reports are frequently used to ascertain the diagnosis of asthma, has been complicated by alterations in pulmonary physiology caused by obesity, which may lead to dyspnea or other respiratory symptoms but do not fulfill accepted physiologic criteria for asthma. Recent investigations toward elucidating a shared genetic basis for these two disorders have identified polymorphisms in specific regions of chromosomes 5q, 6p, 11q13, and 12q, each of which contains one or more genes encoding receptors relevant to asthma, inflammation, and metabolic disorders, including the beta(2)-adrenergic receptor gene ADRB2 and the glucocorticoid receptor gene NR3C1. Further research is warranted to synthesize these disparate observations into a cohesive understanding of the relationship between obesity and asthma.

Association between leptin and asthma in adults

BACKGROUND

Leptin, a pro-inflammatory cytokine produced by adipose tissue, has previously been shown to be associated with asthma in children. We hypothesised that high serum leptin concentrations would also be associated with asthma in adults.

METHODS

The Third National Health and Nutrition Examination Survey is a cross sectional study that included fasting serum leptin concentrations and self-report of doctor diagnosed asthma. Data were analysed using multivariable logistic regression analysis.

RESULTS

Of 5876 participants, those with current asthma had a higher mean unadjusted leptin concentration than those who had never had asthma (geometric mean (SE) 9.2 (0.6) microg/l v 7.6 (0.2) microg/l; p = 0.02). After adjustment for triceps skinfold thickness and other covariates, the association between leptin and asthma appeared stronger in women than in men, and in premenopausal women than in postmenopausal women. Body mass index (BMI) was also associated with current asthma in women, but this association was not significantly affected by adjustment for leptin concentrations.

CONCLUSIONS

The results of this large population based study support the hypothesis that leptin is associated with asthma in women. In addition, while BMI also is related to asthma in women, this study does not support the suggestion that leptin contributes significantly to this association.

Body mass index and physical activity in relation to asthma and atopic diseases in young adults

BACKGROUND

Obesity has been shown to increase the risk of asthma and wheezing. Conditioning exercise might decrease the asthma risk, and that could partly explain the association. The relation between obesity and allergic diseases is quite conflicting.

METHODS

The association between body mass index (BMI) and physician-diagnosed asthma, allergic rhinitis or conjunctivitis, atopic dermatitis, and self-reported wheezing was investigated in a questionnaire study among 10,667 Finnish first-year university students aged 18-25 years. Logistic regression was used to evaluate possible confounding by parental education, passive smoking at age 0-2, childhood residential environment, current and past smoking and leisure time physical activity index.

RESULTS

In men, there was a greater risk of asthma, but not wheezing with increasing BMI. Compared to those with BMI below 20, OR for male asthma was 1.98 (95% CI 1.11-3.52) in BMI category 20.0-22.4, 1.90 (95% CI 1.05-3.41) in BMI 22.5-24.9, and 3.5 (95% CI 1.63-7.64) in BMI > or = 27.5. Among women, the risks of asthma and wheezing were about two-fold among the overweight-obese subjects. Moderate leisure time physical activity was associated with lower risk of asthma in men (OR 0.62, 95% CI 0.62 (0.42-0.92), but not among women. The risk of allergic rhinoconjunctivitis and atopic dermatitis increased quite linearly with BMI among women but not men.

CONCLUSIONS

Low leisure time physical activity seems not to explain the greater risk of asthma among obese men and women. The quite linear association between BMI and both allergic rhinoconjunctivitis and wheezing among women suggests the independent effect of body fat on atopic diseases.

Applying epidemiologic concepts of primary, secondary, and tertiary prevention to the elimination of racial disparities in asthma

Despite medical and scientific advances, racial and ethnic disparities persist in US asthma morbidity and mortality rates. Progress in the elimination of these disparities will involve disentangling the contribution of social constructs, such as race, socioeconomic status, and culture, from that of the physical environment and genetic susceptibility. One approach to reducing asthma disparities is through the traditional disease prevention stages of intervention. As such, primary prevention targets reductions in asthma incidence; secondary prevention is the mitigation of established disease and involves disease detection, management, and control; and tertiary prevention is the reduction of complications caused by severe disease. Once causative factors at each level of disease prevention are understood, this knowledge can be translated into clinical practice and public health policy.

Body mass index, asthma and allergic rhinoconjunctivitis in Swedish conscripts-a national cohort study over three decades

Obesity and overweight have been associated with an increased risk of asthma in children as well as adults. The association between atopy and body mass index (BMI) is less clear. It has also been suggested that the link between a high BMI and asthma could be a recent phenomenon. The objective of this study was to assess whether the association with BMI differed between allergic rhinoconjunctivitis and asthma and if these associations have changed over time. The Swedish Military Service Conscription Register was linked to the Register of the Total Population and the Population and Housing Censuses. Asthma (with and without allergic rhinoconjunctivitis) and allergic rhinoconjunctivitis at conscription were analysed in relation to BMI for 1,247,038 male conscripts in successive cohorts born between 1952 and 1977. Obesity was associated with asthma without allergic rhinoconjunctivitis, adjusted OR 1.53 (95% CI 1.43-1.63), and with asthma with allergic rhinoconjunctivitis, adjusted OR 1.34 (95% CI 1.20-1.50), but not with allergic rhinoconjunctivitis, OR 1.00 (95% CI 0.97-1.03) after multivariate analyses with adjustments for confounders. The odds ratios were similar in three successive cohorts (conscripts born in 1952-1961, 1962-1971 and 1972-1977). Underweight was associated with a slightly increased risk for all three conditions. The increased risk of asthma in young Swedish men with obesity has remained unchanged over a period of three decades.

Increased pulmonary responses to acute ozone exposure in obese db/db mice

Epidemiological studies indicate the incidence of asthma is increased in obese and overweight humans. Responses to ozone (O(3)), an asthma trigger, are increased in obese (ob/ob) mice lacking the satiety hormone leptin. The long form of leptin receptor (Ob-R(b)) is required for satiety; mice lacking this receptor (db/db mice) are also substantially obese. Here, wild-type (WT) and db/db mice were exposed to air or O(3) (2 ppm) for 3 h. Airway responsiveness, measured by the forced oscillation technique, was greater in db/db than WT mice after air exposure. O(3)-induced increases in pulmonary resistance and airway responsiveness were also greater in db/db mice. BALF eotaxin, IL-6, KC, and MIP-2 increased 4 h after O(3) exposure and subsided by 24 h, whereas protein and neutrophils continued to increase through 24 h. For each outcome, the effect of O(3) was significantly greater in db/db than WT mice. Previously published results obtained in ob/ob mice were similar except for O(3)-induced neutrophils and MIP-2, which were not different from WT mice. O(3) also induced pulmonary IL-1beta and TNF-alpha mRNA expression in db/db but not ob/ob mice. Leptin was increased in serum of db/db mice, and pulmonary mRNA expression of short form of leptin receptor (Ob-R(a)) was similar in db/db and WT mice. These data confirm obese mice have innate airway hyperresponsiveness and increased pulmonary responses to O(3). Differences between ob/ob mice, which lack leptin, and db/db mice, which lack Ob-R(b) but not Ob-R(a), suggest leptin, acting through Ob-R(a), can modify some pulmonary responses to O(3).

Genetic pleiotropy between asthma and obesity in a community-based sample of twins

BACKGROUND

Asthma and obesity are common conditions that are strongly associated. This association might be due to shared genetic or environmental causes.

OBJECTIVE

We sought to determine whether a shared genetic cause is responsible for the association between asthma and obesity and to estimate the magnitude of shared genetic cause.

METHODS

The analyses were performed with 1001 monozygotic and 383 dizygotic same-sex twin pairs within the University of Washington Twin Registry. The presence of asthma was determined by self-report of a physician diagnosis of asthma, and body mass index (BMI) was calculated by using self-reported height and weight. Obesity was defined as a BMI of 30 or greater. The association between asthma and BMI was assessed by means of mixed-effects ordinal regression. Twin correlations examined the association of asthma and obesity. Univariate and bivariate structural equation models estimated the components of variance attributable to genetic and environmental effects.

RESULTS

A strong association between asthma and BMI was identified in the sample population (P < .001). Substantial heritability was detected for asthma (53%) and obesity (77%), which is indicative of additive genetic influences on each disorder. The best-fitting model of shared components of variance indicated that 8% of the genetic component of obesity is shared with asthma.

CONCLUSION

The covariation between obesity and asthma is predominantly caused by shared genetic risk factors for both conditions.

Sex specificity of asthma associated with objectively measured body mass index and waist circumference: the Humboldt study

STUDY OBJECTIVE

To investigate the possibility of sex specificity for the association of obesity and asthma using objective measures of body mass index (BMI) and waist circumference (WC).

DESIGN

Cross-sectional study of adults (n = 2,057) living in Humboldt, SK, Canada in 2003.

SETTING

A rural community.

MEASUREMENTS

Ever-asthma was defined as lifetime physician-diagnosed asthma, and recent asthma was defined as asthma diagnosed by a physician during the past 12 months. BMI and WC were objectively measured.

RESULTS

Among the participants, 5.6% of men and 10.0% of women reported having ever-asthma, and 2.7% and 6.0% had recent asthma, respectively. Higher levels of both BMI and WC were significantly associated with asthma in women but not in men. The adjusted odds ratios for women with a BMI of at least 30.0 kg/m2 relative to women with a BMI of < 25.0 kg/m2 were 2.06 (95% confidence interval [CI], 1.42 to 4.05) for ever-asthma and 3.47 (95% CI, 1.64 to 7.32) for recent asthma.

CONCLUSIONS

Our study demonstrated that the increased risk of asthma associated with obesity was only significant in women but not in men even when BMI was objectively measured, and this association was robust to the anthropometric measures.

Obesity and asthma

Obesity is an important public health problem. An increasing body of data supports the hypothesis that obesity is a risk factor for asthma. These data include numerous large cross-sectional and prospective studies performed in adults, adolescents, and children throughout the world. With few exceptions, these studies indicate an increased relative risk of asthma in the obese and overweight and demonstrate that obesity antedates asthma. Obesity appears to be a particularly important issue for severe asthma. Studies showing improvements in asthma in subjects who lose weight, as well as studies showing that obese mice have innate airway hyperresponsiveness (AHR) as well as increased responses to certain asthma triggers also suggest a causal relationship between obesity and asthma. The mechanistic basis for this relationship has not been established. It may be that obesity and asthma share some common etiology, such as a common genetic predisposition, common effects of in utero conditions, or that obesity and asthma are both the result of some other predisposing factor such as physical activity or diet. However, there are also plausible biological mechanisms whereby obesity could be expected to either cause or worsen asthma. These include co-morbidities such as gastroesophageal reflux, complications from sleep-disordered breathing (SDB), breathing at low lung volume, chronic systemic inflammation, and endocrine factors, including adipokines and reproductive hormones. Understanding the mechanistic basis for the relationship between obesity and asthma may lead to new therapeutic strategies for treatment of this susceptible population.

Asthma in Hispanics

Hispanic individuals trace their ancestry to countries that were previously under Spanish rule, including Mexico, large parts of Central and South America, and some Caribbean islands. Most--but not all--Hispanics have variable proportions of European, Amerindian, and African ancestry. Hispanics are diverse with regard to many factors, including racial ancestry, country of origin, area of residence, socioeconomic status, education, and access to health care. Recent findings suggest that there is marked variation in the prevalence, morbidity, and mortality of asthma in Hispanics in the United States and in Hispanic America. The reasons for differences in asthma and asthma morbidity among and within Hispanic subgroups are poorly understood but are likely due to the interaction between yet-unidentified genetic variants and other factors, including environmental tobacco smoke exposure, obesity, allergen exposure, and availability of health care. Barriers to optimal management of asthma in Hispanics in the United States and in Hispanic America include inadequate access to health care, suboptimal use of antiinflammatory medications, and lack of reference values for spirometric measures of lung function in many subgroups (e.g., Puerto Ricans). Future studies of asthma in Hispanics should include large samples of subgroups that are well characterized with regard to self-reported ethnicity, country of origin, place of birth, area of residence, and indicators of socioeconomic status. Because Hispanics are disproportionately represented among the poor in the United States, implementation of adequate access to health care and social reforms (e.g., improving housing conditions) would likely have a major impact on reducing asthma morbidity in this population.

Obesity and asthma, what are the links?

PURPOSE OF REVIEW

Obesity is a major cause of morbidity accounting for approximately 300 000 deaths each year and about 7% of the health care budget with an economic impact greater than US dollar 100 billion annually in the United States. Obesity and its sequelae such as cardiovascular disease, diabetes, arthritis or cancer have been on the rise over the last decades. The parallel time trend with an increasing prevalence of asthma has induced a lively debate about a potential link between both conditions.

RECENT FINDINGS

A number of prospective studies have shown that weight gain can antedate the development of asthma. Effect modification by sex may occur as some studies have shown effects of body mass index on asthma only among females. However, sex differences are not consistent. Several hypotheses have been proposed to explain the epidemiological associations including alterations in airway mechanics and immune responses, hormonal influences and genetic factors.

SUMMARY

There is evidence that obesity and overweight are associated with the development of asthma. Yet, the mechanisms underlying this relation are unclear. Weight reduction among asthmatic patients can result in improvements of lung function demonstrating the potential clinical impact of the findings.

The asthma epidemic and our artificial habitats

Background

The recent increase in childhood asthma has been a puzzling one. Recent views focus on the role of infection in the education of the immune system of young children. However, this so called hygiene hypothesis fails to answer some important questions about the current trends in asthma or to account for environmental influences that bear little relation to infection.

Discussion

The multi-factorial nature of asthma, reflecting the different ways we tend to interact with our environment, mandates that we look at the asthma epidemic from a broader perspective. Seemingly modern affluent lifestyles are placing us increasingly in static, artificial, microenvironments very different from the conditions prevailed for most part of our evolution and shaped our organisms. Changes that occurred during the second half of the 20th century in industrialized nations with the spread of central heating/conditioning, building insulation, hygiene, TV/PC/games, manufactured food, indoor entertainment, cars, medical care, and sedentary lifestyles all seem to be depriving our children from the essential inputs needed to develop normal airway function (resistance). Asthma according to this view is a manifestation of our respiratory maladaptation to modern lifestyles, or in other words to our increasingly artificial habitats. The basis of the artificial habitat notion may lie in reduced exposure of innate immunity to a variety of environmental stimuli, infectious and non-infectious, leading to reduced formulation of regulatory cells/cytokines as well as inscribed regulatory pathways. This could contribute to a faulty checking mechanism of non-functional Th2 (and likely Th1) responses, resulting in asthma and other immuno-dysregulation disorders.

Summary

In this piece I discuss the artificial habitat concept, its correspondence with epidemiological data of asthma and allergy, and provide possible immunological underpinning for it from an evolutionary perspective of health and disease.

Prevalence and incidence of asthma related to waist circumference and BMI in a Swedish community sample

Both asthma and obesity have become more common in affluent societies during the recent decades and several studies have shown a correlation between the presence of asthma and obesity. In order to further study this association we have investigated a population from a community in southern Sweden, where almost all inhabitants had their body indices measured as part of a study on diabetes at a primary care centre. An asthma unit working with a structured care programme for asthma was available. This organisation enabled us to study whether body mass index and waist circumference was associated with having or developing asthma. There was a significant association between both overweight, increased waist circumference and asthma, P < 0.01. The risk for developing asthma was associated with increased body weight and abdominal circumference, P < 0.05. The increase in asthma morbidity in the overweight subjects was found almost exclusively in the non-atopic asthma patients. This study confirms earlier findings of an increased prevalence of asthma in obese and overweight patients. Increased obesity and especially abdominal obesity is thus a risk factor for asthma, which probably contributes to the high prevalence of asthma in affluent societies.

Asthma severity is associated with body mass index and early menarche in women

Asthma severity in relation to body mass index (BMI) has rarely been studied. The relation between BMI and asthma severity was studied by sex in 366 adults with asthma from the Epidemiological Study on the Genetics and Environment of Asthma, a case-control and family study on asthma. Factors related to asthma severity and BMI such as smoking, FEV(1), bronchial hyperresponsiveness, and dyspnea were taken into account. The influence of early menarche was studied to assess the potential role of hormonal factors. Clinical asthma severity in the last 12 months was assessed by a score (0-7) based on the frequency of asthma attacks, persisting symptoms between attacks, and hospitalization. Asthma severity, which was unrelated to sex, increased with BMI in women (p = 0.0001) but not in men (p = 0.3). In women, the association remained after adjustment for age, FEV(1), smoking habits, and BMI-adjusted dyspnea and taking into account familial dependence (p = 0.0001). The association between BMI and severity was stronger in women with early menarche than in women without early menarche (p interaction = 0.02). Findings support the hypothesis of hormonal factors involved in the severity of asthma.

Effect of obesity on asthma among adult Indian women

OBJECTIVE

Both obesity and asthma are on the rise worldwide. This study examined the association between obesity and asthma prevalence in adult women in India.

METHODS

The analysis used information on 82 464 nonpregnant, ever-married women aged 15-49 y, included in India's 1998-99 National Family Health Survey. The effects of measured Body Mass Index (BMI) on reported asthma were estimated using logistic regression, after adjusting for tobacco smoking (active and passive), cooking smoke, age, education, work status, media habits, food habits, house type, separate kitchen, indoor crowding, religion, caste/tribe, household living standard, urban/rural residence, and geographic region.

RESULTS

Obese women (BMI>/=30.0 kg/m(2)) were about twice as likely as those with a normal BMI (18.5-25.0 kg/m(2)) to report suffering from asthma (OR=1.92; 95% CI: 1.40-2.65). The association between obesity and asthma remained strong and statistically significant even when the effects of other selected risk factors and potential confounders were controlled (OR=1.85; 95% CI: 1.30-2.63). Overweight women (25.0</=BMI<30.0 kg/m(2)) also reported significantly higher adjusted asthma prevalence than those with a normal BMI (OR=1.32; 95% CI: 1.07-1.63). Results hold in separate analysis for younger (15-29 y) and older (30-49 y) women.

CONCLUSION

The study finds a strong positive association between obesity and asthma among adult Indian women. To validate this relationship and to establish causality, prospective epidemiological studies, with better measures of overweight conditions and clinical measures of asthma, are needed in developing-country settings.

Beta 2-adrenergic receptor polymorphisms and haplotypes are associated with airways hyperresponsiveness among nonsmoking men

STUDY OBJECTIVE

To investigate the relationship of common single nucleotide polymorphisms (SNPs) of the beta(2)-adrenergic receptor (AR) gene at codons 16 and 27, and the intermediate phenotype of airways hyperresponsiveness.

DESIGN

A case-control study in 543 white men (152 case patients and 391 control subjects), who were nested in an ongoing longitudinal cohort.

SETTING

Subjects were selected from the Normative Aging Study, an ongoing longitudinal cohort of healthy aging.

PARTICIPANTS

Case patients were defined as those having a positive response to methacholine challenge testing. Control subjects were selected among those who did not have a diagnosis of asthma and who had no response to methacholine.

RESULTS

There was a trend for an association of the Arg16 SNP genotype with airways hyperresponsiveness (odds ratio, 1.25; 95% confidence interval, 0.96 to 1.64 [in an additive model]). In stratified analyses, the effect of the Arg16 variant was seen mainly among nonsmokers. Smokers had increased risks for airway hyperresponsiveness regardless of genotype at either SNP. Using a program to estimate haplotype frequencies, three common haplotypes were identified. Adjusting for age, baseline FEV(1), serum IgE level, and smoking status, the Gly16/Gln27 haplotype was negatively associated with airways hyperresponsiveness in the full complement of case patients and control subjects (score statistic, - 2.43; p = 0.02). The effect of the beta(2)-AR haplotypes was much stronger among lifelong nonsmokers, among whom the Gly16/Gln27 haplotype remained negatively associated with airways hyperresponsiveness (score statistic, - 3.114; p = 0.002), whereas the Arg16/Gln27 haplotype was positively associated with airways hyperresponsiveness (score statistic, 3.142; p = 0.002). No effects were seen among ever-smokers.

CONCLUSIONS

In this cohort of middle-aged to older white men, beta(2)-AR polymorphisms were associated with airways hyperresponsiveness, particularly among lifelong nonsmokers. Our results illustrate an instance in which greater power is obtained by performing haplotype analyses as opposed to single SNP analysis.

Body mass index and the risk of asthma in adults

Asthma and obesity are both chronic conditions and their prevalences have risen in affluent societies. A positive association between asthma and being overweight or obese has been reported in children and women, but associations in men are less clearly described. The objective of this study was to explore the association between body mass index (BMI) and asthma in men and women of diverse ethnic and socioeconomic background living in New York State, USA. In this study, we analyzed cross-sectional data on 5524 subjects aged 18 years and older who were interviewed by telephone in the 1996 and 1997 New York State Behavioral Risk Factor Surveillance System. Asthma (doctor-diagnosed), and weight and height were self-reported. BMI (kg/m2) was used as a measure of adiposity. Weighted logistic regression analysis, with stratification by gender and age, was used to examine the relationship between asthma prevalence and BMI, adjusting for race/ethnicity, education, health insurance, time since last physical examination, physical activity and smoking status. The results showed that the prevalence of asthma was 4.6% (CI: 3.6-5.5%) among men and 8.1% (CI: 7.1-9.1%) among women. In women, the prevalence of asthma was significantly increased in those with a BMI 25 kg/m2 or higher (BMI 25-27.5: OR = 1.76, 95% CI: 1.06-2.94; BMI 27.5-29.9: OR = 2.45, 95% CI: 1.41-4.25; BMI > or = 30: OR = 2.67, 95% CI: 1.66-4.29) when compared to the reference category (BMI: 22-24.9 kg/m2). In men, the prevalence of asthma was increased in the lowest weight category, BMI < 22 kg/m2 (OR = 3.05, 95% CI: 1.37-6.78) and in the highest category, BMI > or = 30 kg/m2 (OR = 2.92, 95% CI: 1.39-6.14). This U-shaped association persisted when restricting the analysis to men who had never smoked and was more pronounced for those between 18 and 49 years of age. In conclusion, this cross-sectional study showed that men and women differ significantly in the association between BMI and asthma prevalence only with respect to the lowest weight category. While women had a monotonic association, men showed a U-shaped relationship, indicating that both extremes of weight are associated with a higher prevalence of asthma.

Sex-race differences in the relationship between obesity and asthma: the behavioral risk factor surveillance system, 2000

PURPOSE

Although prospective data are limited, recent cross-sectional studies support obesity as a cause of asthma. They also suggest that the association is present only among women. Our analysis examines possible sex-race differences in the relationship between obesity and asthma.

METHODS

We examined data from the 2000 Behavioral Risk Factor Surveillance System. To minimize diagnostic bias, the sample was limited to adults aged 18 to 34 years. All cases had doctor-diagnosis of asthma and ongoing symptoms. Multiple logistic regression was used to examine risk factors for current asthma vs. never having asthma.

RESULTS

Obesity and asthma were more strongly related among women than men (test for interaction, p<0.01). Across increasing categories of body mass index (BMI), we observed a dose-response relationship among women (odds ratios: 0.9, 1.0 [reference], 1.0, 1.3, 1.5, 1.8, and 3.2) but only a non-significant increased risk in severely obese men (odd ratio: 2.0). In subgroup analyses, however, the obesity-asthma association was present in four of six sex-race/ethnicity subgroups, including black and Hispanic men.

CONCLUSIONS

Although the obesity-asthma association is stronger among women than men, our analysis demonstrates a strong positive association among men from minority groups. These race-specific results may help explain some of the "inconsistencies" in prior studies.

Exploring neighborhood-level variation in asthma and other respiratory diseases: the contribution of neighborhood social context

OBJECTIVE

We explore differences in the prevalence of asthma and other respiratory diseases at the neighborhood level. In addition to traditional metrics of neighborhood structure (e.g., concentrated disadvantage, residential stability), we incorporate residents' evaluations of neighborhood context. We examine the extent to which indicators such as disorder (observable signs of physical and social decay) and collective efficacy (trust and shared expectations for beneficial community action) account for differences in the prevalence of asthma and other respiratory diseases.

METHODS

We examine 338 Chicago neighborhoods, combining 3 data sources from the 1990s: 1) the Metropolitan Chicago Information Center Metro Survey; 2) the Decennial Census; and 3) the Project on Human Development in Chicago Neighborhoods Community Survey. We use a multilevel statistical approach to disentangle neighborhood- from individual-level effects.

MEASUREMENTS

A survey-based response to whether a physician has diagnosed asthma, bronchitis, emphysema, or other breathing problems.

RESULTS

Findings indicate that individual- and neighborhood-level factors are associated with asthma/breathing problems. At the individual level, female gender, smoking, and a weight problem are positively associated with asthma/breathing problems, while Latino ethnicity is protective. At the neighborhood level, collective efficacy is protective against asthma/breathing problems. Residential stability is positively associated only when levels of collective efficacy are controlled.

CONCLUSIONS

Neighborhood context, particularly collective efficacy, may be an underlying factor that reduces vulnerability to asthma and other respiratory diseases. Collective efficacy may enhance the ability to garner health-relevant resources, eliminate environmental hazards that trigger asthma, and promote communication among residents which, in turn, enables dissemination of information relevant to respiratory ailments.

Responses to ozone are increased in obese mice

Epidemiological data indicate an increased incidence of asthma in overweight adults and children. Ozone (O3) is a common trigger for asthma. Accordingly, the purpose of this study was to compare O3-induced airway hyperresponsiveness and airway inflammation in lean, wild-type (C57BL/6J) mice and mice that are obese as a consequence of a genetic defect in the gene encoding the satiety hormone leptin (ob/ob mice). The ob/ob mice eat excessively and weighed more than twice as much as age- and gender-matched wild-type mice. Airway responsiveness to intravenous methacholine was measured by forced oscillation. In air-exposed controls, baseline pulmonary resistance was greater, and the dose of methacholine required to double pulmonary resistance was lower in ob/ob than wild-type mice. Exposure to O3 (2 parts/million for 3 h) caused AHR and airway inflammation in both groups of mice, but responses to O3 were enhanced in ob/ob compared with wild-type mice. Administration of exogenous leptin did not reverse the enhanced inflammatory response observed in ob/ob mice, but augmented airway inflammation in wild-type mice. The inhaled dose of O3 per gram of lung tissue was greater in ob/ob than wild-type mice. Our results indicate that O3-induced airway responses are enhanced in ob/ob mice and suggest that inhaled O3 dose may be one factor contributing to this difference, but other aspects of the obese phenotype may also contribute. Our results also indicate that the hormone leptin, which is increased in the obese, has the capacity to increase airway inflammation.

Dietary patterns and changes in body mass index and waist circumference in adults

BACKGROUND

Obesity has increased > 20% in the past decade in the United States, and more than one-half of US adults are overweight or obese.

OBJECTIVE

Our objective was to further elucidate the nutritional etiology of changes in body mass index (BMI; in kg/m(2)) and waist circumference by dietary intake pattern. We hypothesized that a healthy dietary pattern would lead to smaller changes in BMI and waist circumference than would other dietary patterns.

DESIGN

Subjects were 459 healthy men and women participating in the ongoing Baltimore Longitudinal Study of Aging. Diet was assessed with the use of 7-d dietary records, from which 41 food groups were created and entered into a cluster analysis.

RESULTS

Five dietary patterns were derived (healthy, white bread, alcohol, sweets, and meat and potatoes). The mean annual change in BMI was 0.30 +/- 0.06 for subjects in the meat-and-potatoes cluster and 0.05 +/- 0.06 for those in the healthy cluster (P < 0.01). The mean annual change in waist circumference was more than 3 times as great for subjects in the white-bread cluster (1.32 +/- 0.29 cm) as for those in the healthy cluster (0.43 +/- 0.27 cm) (P < 0.05).

CONCLUSIONS

Consuming a diet high in fruit, vegetables, reduced-fat dairy, and whole grains and low in red and processed meat, fast food, and soda was associated with smaller gains in BMI and waist circumference. Because foods are not consumed in isolation, dietary pattern research based on natural eating behavior may be useful in understanding dietary causes of obesity and in helping individuals trying to control their weight.

Extending the understanding of leukotrienes in asthma

PURPOSE OF REVIEW

Leukotriene modifiers have recognized utility in the management of asthma. The aim of this review is to put into context recent research findings that extend our understanding of cysteinyl leukotriene synthesis and actions in the pathogenesis of asthma and allergic disease.

RECENT FINDINGS

Previous literature has shown that T helper type 2 cytokines thought to favor asthma and allergic diseases upregulate leukotriene synthesis. Recent findings show that interleukins-4 and -13 also upregulate cysteinyl leukotriene 1 receptor expression. Conversely, the regulation of cytokine expression by leukotrienes has also been explored: cysteinyl leukotrienes upregulate type 2 cytokine expression and decrease type 1 cytokine expression, favoring an allergic phenotype. Genetic determinants of the expression of leukotriene-forming enzymes include polymorphisms of the 5-lipoxygenase and LTC(4) synthase promoters. Novel actions of leukotrienes continue to be recognized, and a role for leukotrienes in the development of airway remodeling accompanying chronic asthma is discussed. Mounting evidence implicates leukotrienes in the pathogenesis of asthma following viral infections. Finally, advances in the measurement of leukotrienes are reviewed.

SUMMARY

Leukotrienes and their receptors play an important role in the pathogenesis of asthma. Advances in our understanding of the synthesis and actions of these lipid mediators provide the scientific rationale for appropriate utilization of leukotriene modifiers and for envisioning novel leukotriene-based therapeutic approaches in the clinical management of asthma.