Childhood Onset Adult Asthma: A Comparison of Asthma Development with Exposure to High and Reduced Levels of Air Pollution

Abstract

In the 1960s when air pollution levels were high in Kanagawa prefecture as same as in other Japanese metropolises, the prevalence of asthma increased distinctly. Air pollution has been reduced rapidly from the 1970s, but asthma morbidity has not decreased and therefore air pollution has not been considered as an essential factor in asthma development. However, air pollution may be considered as a risk factor for infantile asthma. To clarify the influence of air pollution on infantile asthma development, we compared the background of adult asthmatics who were born in 1960s and in 1970s. We studied 10,823 adult asthma patients who underwent examination at Sagamihara hospital from 1972 to 1995. We investigated the ratio of young onset (equal to or less than 19 years old, 3264 cases) asthma in adult asthma year by year. In order to ascertain the influence of air pollution on airway hypersensitivity, we compared the asthmatics born in 1960s (born in 1963–1970) when air pollution was severe with those born in 1970s (born in 1971–1978) when air pollution levels were reduced. Childhood onset (less than 15 years old) asthma held a constant ratio in adult asthma from 1972 to 1980. However, infancy onset (0–4 years old) asthma increased in 1980, peaked in 1988, and then decreased. From a viewpoint of the birth year, young onset asthma has increased since 1945. In particular, the ratio of infancy onset (0–4) asthma had become distinctly higher than the other onset groups since 1960, peaking in 1970 and then decreasing. The fluctuation of infancy onset asthma coincided with the indices of air pollution in Japan. Lung function tests in the three groups (group I ; born in 1955–62, group II ; born in 1963–70, group III ; born in 1971–78) did not have a difference among each other. However, we were able to find a difference in threshold of non-specific airway hypersensitivity. The airway hypersensitivity of the infancy onset asthmatics born in 1960s was much more enhanced than that of the asthmatics born in 1970s. The dramatic increase of infancy onset asthmatic born after 1960 coincided with the increases in levels of air pollution. The infancy onset adult asthmatics born in 1960s were more hypersensitive to nonspecific bronchial stimuli than those born in 1970s. This strongly suggested that the air pollution of 1960s might have accelerated the development of infancy onset asthma and aggravated non-specific bronchial hyperreactivity.