A 24-year long asthma study is answering doctors' questions about asthma and its causes.
Doctors have concluded that children do not usually outgrow asthma after puberty as was previously assumed. There are also other factors that contribute to the onset of asthma in test subjects, including infection and obesity.
The Tucson Children's Respiratory Study started with a group of 1200 children born between 1980 and 1984 and studied the patterns of asthma in them.
The subjects began the study at birth and every two years after that the parents of the children completed questionnaires on their children's health. The children began filling them out at age 16. Approximately every five years, the subjects would go into the office for lung function tests, skin allergy tests, and give blood samples for studies related to allergy and respiratory diseases.
Over the years, the study has lost participants but about 70 percent of the original group are still being studied.
"People get fed up with questionnaires, tests, taking blood," said Fernando Martinez, principal investigator of the study.
A major branch of the study has shown that children with a small difference in their lungs caused by something before or just after birth makes them more susceptible to asthma.
Dr. Martinez has found that children that develop respiratory infections such as bronchialitis and pneumonia at a very young age or before birth started life with lungs that were different, and they are predisposed to develop asthma.
He said that if mothers smoke or the child is born prematurely, they are at a greater risk of developing these infections. Preventing these infections early in life is easier than trying to erase the asthma.
Another branch of the study has shown that after puberty the subjects continue to have asthma or wheezing, which contradicts earlier studies.
"It is believed that many children can outgrow asthma," said Stefano Guerra, an assistant professor of public health and researcher for the study.
The doctors researched the presence of wheezing after puberty as compared with before puberty and more than half of the subjects had persistent asthma or wheezing after puberty, Guerra said.
Only 40 percent of subjects had an absence of wheezing four years after they went through puberty.
The purpose of the study is to get a certain fraction of the population to see how asthma is developed and either grown out of or continued through life. Other studies across the University of Arizona and the world have shown similar results to that of Tucson's studies. With the random sampling of so many subjects, the doctors are able to say that the results of this study can be true for the rest of the population.
A child that was obese at a young age is far more likely to develop asthma in later life.