Development of allergic and respiratory symptoms in adolescence and early adulthood : Risk factors and gender differences

Abstract: Background: Asthma and allergic diseases have increased in prevalence for several decades and affect a substantial number of individuals in everyday life, as well as their families and public healthcare resources. Subjects with asthma report impaired self-rated health. Fractional exhaled nitric oxide (FeNO) is a marker of type 2 inflammation in the airways and higher levels may precede the development of allergic and respiratory disease.Aims: To investigate the development of allergic and respiratory symptoms in adolescence and early adulthood, and related baseline risk factors. Further, to study self-rated health in young adults with reported asthma.Methods: A total of 959 schoolchildren completed a standardized respiratory questionnaire and underwent lung function and FeNO measurements at baseline (12–15 years; early adolescence). Four (late adolescence) and sixteen (early adulthood) years later, 921 (96%) and 502 (52%) of these individuals completed a similar questionnaire. A total of 491 subjects participated in all three examinations. Nineteen clinically assessed non-asthmatic subjects with elevated FeNO and 28 control subjects with low FeNO and without symptoms of asthma or allergy in early adolescence were identified. Their FeNO, IgE sensitization, airway responsiveness, and inflammatory markers in blood and sputum were measured.Results: The main finding was that higher FeNO in early adolescence was associated with an increased risk of developing allergic symptoms to cat and dog, but not pollen allergens, during adolescence. Gender-stratified data showed that obesity at baseline in girls and an atopic constitution in boys were associated with increased risk of developing wheeze during adolescence. The prevalence of asthma and wheeze had increased in early adulthood, but the increase was significant only in females. Reduced lung function at baseline in females and higher FeNO in males were associated with an increased risk of incident asthma sixteen years later. The increase in allergic symptoms during this period was significant but without sex differences. Asthmatic females rated their health worse than non-asthmatic females, a difference not observed in males. Non-asthmatic adolescents with higher FeNO at baseline were to a higher extent sensitized, had more reactive airways, higher blood eosinophil counts, and lower systemic activation of neutrophils, compared with controls.Conclusions: It is important to detect risk factors for the development of allergic and respiratory diseases at an early stage to optimize health and wellbeing. Gender differences in respiratory development, associated risk factors, and treatment of respiratory symptoms must be taken into account.