Obesity, waist size and prevalence of current asthma in the California Teachers Study cohort

Background: Obesity is a risk factor for asthma, particularly in women, but few cohort studies have evaluated abdominal obesity which reflects metabolic differences in visceral fat known to influence systemic inflammation. A study was undertaken to examine the relationship between the prevalence of asthma and measures of abdominal obesity and adult weight gain in addition to body mass index (BMI) in a large cohort of female teachers. Methods: Prevalence odds ratios (ORs) for current asthma were calculated using multivariable linear modelling, adjusting for age, smoking and race/ethnicity. Results: Of the 88 304 women in the analyses, 13% (n = 11 500) were obese (BMI >= 30 kg/m(2)) at baseline; 1334 were extremely obese (BMI >= 40 kg/m(2)). Compared with those of normal weight, the adjusted OR for adult-onset asthma increased from 1.40 (95% confidence interval (CI) 1.31 to 1.49) for overweight women to 3.30 (95% CI 2.85 to 3.82) for extremely obese women. Large waist circumference (>88 cm) was associated with increased asthma prevalence, even among women with a normal BMI (OR 1.37, 95% CI 1.18 to 1.59). Among obese women the OR for asthma was greater in those who were also abdominally obese than in women whose waist was <= 88 cm (2.36 vs 1.57). Obese and overweight women were at greater risk of severe asthma episodes, measured by urgent medical visits and hospital admissions. Conclusions: This study confirms the association between excess weight and asthma severity and prevalence, and showed that a large waist was associated with increased asthma prevalence even among women considered to have normal body weight.