In cross-sectional studies, the risk factors for presence in:

  1. Airway narrowing are atopy, family history of asthma, gender (male), and parental smoking;

  2. Airway size are low birth weight, parental smoking, and diet (low magnesium or antioxidant intake);

  3. Airway hyperresponsiveness are atopy, family history of asthma, high allergen exposure, and diet (high sodium/magnesium or low omega-3 fatty acid intake).

In longitudinal studies, the risk factors for ongoing conditions from:

  1. Airway narrowing are atopy early in childhood, gender (female), parental smoking, symptoms that begin before age 5, persistent wheeze in childhood in the absence of respiratory infection, and reduced expiratory flow rate;

  2. Airway size are atopy, gender (female), and airway hyperresponsiveness;

  3. Airway hyperresponsiveness are atopy in early childhood, airway hyperresponsiveness in childhood, reduced expiratory flow rate, and gender (female).

Important future longitudinal studies will be those that divide the broad spectrum of asthma into phenotypic groups.


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