Body Mass Index and the Risk of Adult-Onset Asthma: A Prospective Observational Study among 59,668 Middle-Aged Men and Women in Finland

Introduction: Obesity, in addition to many other negative health consequences, affects pulmonary function and is a potential risk factor for asthma. Methods: We analyzed the association of body mass index (BMI) with incident asthma among 60,639 Finnish men and women aged 25 to 74 years who participated in a population-based chronic disease risk factor survey in 1972, 1977, 1982, 1987, 1992, 1997, 2002, 2007, or 2012. Data on lifestyle factors such as smoking and physical activity, as well as medical history, were obtained, and various physical measurements, including height and weight, were taken at baseline. Incident asthma events were ascertained from the National Social Insurance Institution's register data. The study cohorts were followed-up until the end of 2017 through registers. Results: During the follow-up, 4612 (14%) women and 2578 (9.3%) men developed asthma. The risk of asthma was analyzed in the following three BMI categories: <24.9 (reference category), 25-29.9 (overweight) and >= 30 kg/m(2) (obesity). Hazard ratios (95% CI) were 1.34 (1.24-1.43) and 1.57 (1.44-1.71) in women and 1.25 (1.14-1.37) and 1.63 (1.44-1.83) in men. The observed association was independent of smoking, height and leisure-time physical activity. In women, 30.8% (19.2% in men) of the total asthma incidence was attributed to overweight and obesity. Conclusions: Overweight and obesity are important risk factors for asthma.