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Re: Therapeutic implications of sex differences in asthma and atopy.

Dear Editor

With great interest I read the review by M Osman [1] on the sex- related differences of prevalence and severity of asthma and atopy before and after puberty.

Dr Osman postulates that testosterone and female sex steroids directly affect the immunological respons to e.g. allergens. If these hormones do play a role at physiological levels in vivo there is, indeed, most certainly a reason to consider what the therapeutical implications are. However, there is at least one other good physiological explanation for the changes in the reported prevalence and severity of asthma during childhood and adolescence. There is convincing evidence that airway patency in neonates and infants is reduced in males compared to females, and that this lasts till puberty. Because of the small size of the bronchial tree, infants are especially vulnarable to any increase in airways resistance. As symptoms may be considered the top of the iceberg, the higher reported morbidity of respiratory disease in male infants may simply mean that they develop symptoms earlier in the disease process than females do. During puberty, airway growth and function in males exhibits a growth spurt that surpasses that of females, and men have larger airways than females in early adulthood.[2-6] These biological phenomena help to explain not only why male infants and children demonstrate more morbidity from bronchiolitis, Cystic Fibrosis, asthma and infectious disease in general, but also why this reverses after puberty.[7,8] In addition, factors such as gender-related differences in exposure to outdoor and indoor allergens and air pollution may play an additional role. I think these aspects should have been addressed in this review article as well.

References

(1) Osman, M. Therapeutic implications of sex differences in asthma and atopy. Arch Dis Child 2003;88:587-90.

(2) Merkus, PJ, GJ Borsboom, W Van Pelt, PC Schrader, HC Van Houwelingen, KF Kerrebijn, PH Quanjer. Growth of airways and air spaces in teenagers is related to sex but not to symptoms. J Appl Physiol 1993;75:2045-53.

(3) Martin, TR, RG Castile, JJ Fredberg, ME Wohl, and J Mead. Airway size is related to sex but not lung size in normal adults. J Appl Physiol 1987;63:2042-7.

(4) Gibellino F, DP Osmanliev, A Watson, NB Pride. Increase in tracheal size with age. Implications for maximal expiratory flow. Am Rev Respir Dis 1985;132:784-7.

(5) Merkus, PJ, AA ten Have-Opbroek, PH Quanjer. Human lung growth: a review. Pediatr Pulmonol 1996;21:383-97.

(6) Becklake, M. Gender differences in airway behaviour (physiology) over the human lifespan. Eur Respir Mon 2003;25:8-25.

(7) Postma, D. Gender differences in the natural history of pulmonary disease. Eur Respir Mon 2003;25:74-81.

(8) Hibbert M, Lannigan A, Raven J, Landau L, Phelan P. Gender differences in lung growth. Pediatr Pulmonol 1995 ;19:129-34.