7. Gender differences
Several recent cross-sectional studies have documented
a significant association between BMI and asthma in women
but not in men. In contrast to the findings for adults, associations
between obesity and asthma are inconsistent for
children and adolescents. Some studies demonstrated that
BMI was positively associated with wheezing and bronchial hyper-responsiveness in girls but not in boys, whereas another
study found BMI to be associated with asthma in both
boys and girls. One plausible hypothesis is that female sex
hormones play an important role in the etiology of asthma
and that these hormones are influenced by obesity. Progesterone
upregulates beta-2 receptors. One hypothesis is that
obesity reduces progesterone levels, which reduces beta-2
adrenoreceptor function, which in turn reduces bronchial
smooth muscle relaxation. BMI may not be an equivalent
measure of fatness in men and women. The fact that men
tend to have more muscle mass and women more fat mass
may also contribute to the apparent gender-specific relation
between obesity and asthma