Fewer Canadian children are being diagnosed with asthma, likely because of reduced exposure to cigarette smoke, Statistics Canada says in a new study.
Rates of the chronic inflammatory disease fell to their lowest level in more than a decade among children aged two to seven.
"A wide range of environmental factors, including reduced exposure to cigarette smoke, may have contributed to these trends," the study says.
Statscan found that 9.8 per cent of kids aged two to seven were diagnosed with asthma in 2008-09, down from 13.2 per cent in 2000-01.
The drop is likely because fewer Canadian children live in homes where adults smoke, the study says.
Six per cent of youngsters aged 11 and under were regularly exposed to tobacco smoke at home in 2008, down substantially from 24 per cent in 2000. Overall, 13 per cent of people aged 15 and older smoked daily in 2008, down from 19 per cent in 2000.
So few parents now smoke that there were no statistically significant differences in asthma rates between kids in smoking and non-smoking households between 2006-07 and 2008-09.
"This suggests that … adult smoking rates have become low enough that parental smoking has ceased to be [a]major cause of asthma in young children," the paper says.
The link between reduced smoking and lower asthma rates is not unique to Canada. After Scotland banned smoking in public places, severe episodes of asthma dropped among preschool and school-aged children.
Researchers in western countries have generally found that asthma rates among children increased steadily for several decades before levelling off or even declining.
Statscan said the lower disease rates could also be because of changes in the population structure, changes in diagnostic practices, decreases in the prevalence of respiratory allergies, improvements in air quality and changes in hygiene practices.
Statistics Canada also found that ear infections declined significantly among two- and three-year-olds. In addition, upper respiratory infections dropped or remained constant in most regions among youngsters of the same age.
Like asthma, ear infections are linked to exposure to cigarette smoke.
The national statistics agency found that asthma prevalence declined in the Atlantic provinces, Quebec and Ontario, but remained relatively stable in the West.
The survey also found that the percentage of children who had had an asthma attack in the past 12 months fell to 36 per cent in 2008-09 from 53 per cent in 1994-95.
The study is based on data from the National Longitudinal Survey of Children and Youth, a long-term study that collects information from thousands of families. The survey has been conducted every two years since 1994-95.