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 > or = 30 kg/m(2)) at baseline; 1334 were extremely obese (BMI > or = 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 < or = 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.