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.
"Obesity is a stronger factor of incidence especially now with (asthma's) persistence," Guerra said.
In studies, doctors have determined that a girl who is overweight or obese between 6 and 11 years of age is likely to develop symptoms of asthma by the age of 13.
Doctors recommend that parents watch their children's eating habits at a young age so they do not develop obesity in their adulthood. Obesity not only affects respiratory symptoms, but could increase susceptibility to chronic respiratory diseases as adults, Guerra said.
The research is supported by a grant from the National Heart, Lung and Blood Institute, a division of the National Institute of Health. The grant is up for renewal every five years. The study continuing is based on the renewal of the grant. This term's funding was in the amount of $840,995.
Dr. Guerra said she hopes to continue the study through the subjects' adulthood. They will be studied into their thirties or later to understand the risk factor of the disease in children and on through late life.
"For example, we are very interested in determining whether the persistence of asthma in childhood through adolescence is associated with long-term consequences on lung function and lung health in adulthood and with an increased susceptibility to develop chronic obstructive pulmonary disease," Guerra said.