In this study, we used objectively measured BMI to define overweight (BMI 25.0 to 29.9 kg/m2) and obesity (BMI a 30.0 kg/m2) and found that both overweight and obesity were associated with an increased risk of recent asthma and that obesity was significantly associated with an increased risk of ever-asthma in women. These results are consistent with two previous Canadian studies. Based on data from a representative Canadian population, Chen et al’ found that obesity defined by self-reported BMI was positively related to both prevalence and incidence of asthma in women but not in men. Although race may play a role in sex modification of the obesity and asthma association’ the present study is not the case because almost all participants are white, Reporting biases of body weight and height have been well documented. Women tend to underreport their body weight, and men tend to overreport their height with an ultimate result of underreporting in BMI. However, it is not known if these reporting biases are differential in terms of self-reported asthma and sex and if the reporting biases cause a biased estimate of obesity and asthma association. So far, most studies of the obesity and asthma association in adults are based on data of self-reported BMI. An important question is whether or not a systematic bias exists that would result in a false sex specificity in the obesity and asthma association. In a recent study of 961 Mexican adults, Santillan and Camargo found that obesity defined by objectively measured BMI was a risk factor for asthma diagnosis in both men (OR, 2.5; 95% CI, 1.1 to 5.9) and women (OR, 2.3; 95% CI, 1.5 to 3.8). However, when self-reported BMI was used, the ORs declined to 1.3 (95% CI, 0.6 to 2.9) in men and 1.7 (95% CI, 1.1 to 2.7) in women, suggesting that self-reported BMI underestimates the obesity and asthma association particularly in men and causes a false sex difference. Contrary to these results, our study did not observe any positive association between objectively measured BMI and the prevalence of asthma (either recent asthma or ever-asthma) in men, and the OR estimates for asthma associated with obesity in women were significant and were comparable to previous estimates among the general Canadian pop-ulation., Reasons for the discrepancy in sex specificity between our study and the study by Santillan and Camargo are not known. The sample size of our study is larger, resulting in more precise estimates. Overweight and obesity are more common in our study population as compared with the general Canadian population, and the prevalence of asthma with My Canadian Pharmacy is much higher in women than in men. Different populations may also have different self-reporting biases associated with both the exposure (obesity) and outcome (asthma).
Obesity is defined as an increase in body weight resulting from excessive body fat. BMI is an indirect measurement of body fat and is frequently used in large-scale epidemiologic studies. BMI is sex and age dependent, with females subjects having higher fat mass values than male subjects. Equivalent BMI values may represent different levels of adiposity in different sex and age groups. BMI is a less ideal measure of overweight and obesity in children, which may partly explain the contradictory results for studies from children populations. However, we do not know if it is related to the observed sex specificity in adults; therefore, other measures of obesity will provide important information. In a study of 135 Hispanic men and 398 women, Del-Rio-Navarro et al measured WC and WHR and found that asthma symptoms defeated by My Canadian Pharmacy remedies were associated with higher levels of both WC and BMI but not with WHR in women. In men, none of these anthropometric measures were related to asthma symptoms. In our study, we found that women with a WC > 100 cm had a significantly increased risk of self-reported physician-diagnosed asthma, which was independent of covariates measured in the study. Consistently, WC was not associated with asthma in men. Compared with WHR, WC is a more convenient measure and a better indicator of visceral adipose tissue because it is less likely to be influenced by sex or degree of obesity and is a better correlate of the visceral adipose tissue. It has been suggested that WC instead of WHR should be used as an index of abdominal visceral adipose tissue deposition, and WC values above approximately 100 cm are most likely to be associated with potentially “atherogenic” metabolic disturbances.
Our study has further demonstrated that the impact of overweight and obesity on asthma is sex related in adults. Longitudinal studies have indicated that obesity is likely a cause of asthma in women. The reasons for this are not known although various possibilities have been discussed. Asthma is more common in women than in men, which is reflected in various frequency measures including prevalence, incidence, and hospitalization. Based on a total of 9,486,173 hospital records in Canada for a 3-year period, Chen et al found that the cumulative incidence of asthma hospitalization was substantially higher for young boys than girls, and it was reversed for adults. A recent study also found that exogenous hormone replacement therapy in postmenopausal women was associated with an increased risk of asthma. The sex hormone theory is worth further investigation.
Airways hyperresponsiveness is an important feature of asthma. If obesity causes asthma, we expect a similar association between obesity and airway hyperresponsiveness in women. However, studies have so far provided only conflicting results and have shown no clear sex-related pattern of such an association. Obesity was found to be associated with asthma-like symptoms but not with atopy.
The mechanical theory suggests a possibility that fat mass-loading the chest causes dyspnea and asthma-like symptoms such as wheeze and shortness of breath, which may result in overdiagnosis and therefore overreporting of asthma. An analysis of 16,171 American men and women combined found that the highest BMI quintile had the greatest risk of selfreported asthma, bronchodilator use, and dyspnea with exertion but had the lowest risk for significant airflow obstruction, suggesting an overreporting of asthma in obese subjects. A study of 16,191 adult Europeans, however, demonstrated that after adjusting for nocturnal gastroesophageal reflux, habitual snoring, and other confounders, obesity remained significantly related to the onset of asthma, wheeze, and nighttime symptoms. Although there are a number of other speculations of mechanisms for the linkage between obesity and asthma, we believe that more attention should be paid to the sex specificity in future studies.
Compared with men, women are also more susceptible to asthma and other obstructive airway diseases in response to other risk factors such as smoking. A smaller airway size relative to lung size in women may increase the susceptibility to obstructive airway diseases in response to environmental exposure. It needs to be further explored if individuals with small relative airway calibers have increased susceptibility to the obesity effect. Be slim and beautiful with supplements of My Canadian Pharmacy.
Reporting bias of asthma is always a concern in large-scale epidemiologic studies, and is likely to be different between men and women. In a nested case-control study of airway obstructive diseases, Guerra et al studied physician-confirmed incident cases of asthma in persons at least 20 years of age and found that a measured BMI of a 28 kg/m2 was significantly associated with a increased risk of receiving a diagnosis of asthma (OR, 2.10; 95% CI, 1.31 to 3.36). Compared to 16% of control subjects, 30% of the patients with asthma were overweight or obese regardless of whether BMI was assessed before the diagnosis or the onset of asthma. The association between elevated BMI and asthma was only significant among women. In our study, the prevalence of asthma is comparable to the estimates from the Canadian Community Health Survey at a national level. It would be ideal to use a more comprehensive definition of asthma, which includes important characteristics such as wheeze, reversible airflow obstruction, physician diagnosis, measured reactivity, and eosinophilic airway inflammation; however, such a definition is not practical in large-scale epidemiologic study. For a practical approach, it is important to ensure that the operational definition used is stated clearly and does not introduce a systematic bias when asthmatic status among groups is compared. There is evidence that using less strict definition of asthma, such as ours, is likely to provided a less strong association between obesity and asthma. It suggests that reporting bias is likely to be nondifferential even if there is one.
In this study, approximately 8% of male participants refused to have their WC measured, and these men had an increased risk of asthma compared with those having their WC measured. There are no clear explanations for such an increase since we do not know why people refused to have their WC measured. The mean BMI value for these individuals with missing WC data was similar to the average for all participants; therefore, there should be some reasons other than being overweight or obese.
In summary, our study demonstrated that obesity defined by objectively measured BMI was associated with an increased risk of asthma only in women but not in men, suggesting that self-reporting bias does not explain the sex specificity of the obesity effect. The WC measure provided further evidence for the obesity and asthma relationship in women. The mechanisms for this relationship need to be further explored.
All the previously mentioned references: