One in three people can expect to be diagnosed with asthma in their lifetimes, Ontario research suggests.

Asthma is more likely to develop in childhood, but can also occur in adults, with a 33 per cent risk over a lifetime, Ontario research suggests.Asthma is more likely to develop in childhood, but can also occur in adults, with a 33 per cent risk over a lifetime, Ontario research suggests. (Canadian Press)

Researchers followed the medical histories of more than nine million Ontarians for 16 years, between April 1991 and March 2007. A study of the data found the lifetime risk of developing asthma was 33.9 per cent.

"Asthma is a disease that affects a huge number of people, either because they suffer from it personally or because they have a child, another relative, or a friend who does," the study's co-author, Dr. Andrea Gershon said.

Researchers at the Institute for Clinical Evaluative Sciences, the Hospital for Sick Children and Sunnybrook Heath Sciences Centre collaborated on the study, full details of which are published in the Feb. 15, 2010, issue of American Journal of Respiratory and Critical Care Medicine.

Although patients of all ages were included, the data suggested the risk of developing asthma was highest in children.

But even a person who had not been diagnosed with asthma by age 10 still had a 20 per cent risk of being diagnosed with asthma during the rest of his or her lifetime. Likewise, a person who had not been diagnosed by age 30 still had a 13 per cent risk of being diagnosed, the study found.

At more than 33 per cent, the lifetime risk of being diagnosed with asthma was comparable to that of being diagnosed with diabetes or any type of cancer, the study's authors said. But while other chronic diseases tend to develop in older people, the effects of asthma could be greater, because asthma is more likely to develop in the young and last a lifetime, the authors suggested.

Other factors besides age

There were factors besides youth that increased the likelihood of an asthma diagnosis. Women, people of lower socioeconomic status, and people living in rural areas had a higher risk of being diagnosed with asthma than men, people of higher socioeconomic status, and people living in urban areas.

"A lot of work still needs to be done to look at the actual causes or the etymology of asthma so we could actually prevent asthma from developing," said Dr. Teresa To, the principal investigator of the study.

The data was drawn solely from Ontario medical records, but the one in three chance can be applied to the rest of Canada, To said.