Is the increase in allergic respiratory disease caused by a cohort effect?

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Abstract
Background Changes in lifestyle or environmental factors are responsible for the increasing prevalence of allergic respiratory disease. Establishing the time at which the increase began may provide a clue as to what factors possibly could have contributed to the increase. Many cross‐sectional studies have shown that the prevalence of allergic sensitization decreases with increasing age. This could reflect the natural course of allergic sensitization. Alternatively, this could reflect that the increase in sensitization is caused by a cohort effect, i.e. an increase among subjects born during recent decades. Objective The aim was to investigate age‐specific changes in the prevalence of allergic sensitization in a cohort of adults. Methods A total of 599 subjects aged 15 to 69 years participated in a cross‐sectional general population study in 1990. In 1998 they were invited to a follow‐up, and 64.4% (386/599) were re‐examined. Serum samples obtained from the participants in 1990 and 1998 were analysed for specific IgE to six common inhalant allergens with the same assay. Results The prevalence of allergic sensitization (specific IgE to at least one allergen) increased among subjects who were less than c. 30 years at baseline (1990), i.e. subjects born during the 1960s or later, while the prevalence was unchanged among subjects who were more than c. 30 years at baseline. Conclusions The results support the notion that the increasing prevalence of allergic respiratory disease is caused by a cohort effect. Thus, changes in lifestyle or environmental factors that occurred around or after 1960 may have contributed to this increase.