Study Shows Lower Asthma Rates Among Farm Children

Children who live or have lived on farms have lower rates of wheezing or asthma than girls and boys who lived in non-farm rural areas, according to a study recently completed by Medical College of Wisconsin researchers at Children's Hospital of Wisconsin.

The data from the study, one of the largest of its kind ever undertaken, is in keeping with that from similar studies elsewhere in the US and other countries. A primary reason for the reduced incidence of asthma among children on farms, cited in much of the research, may very well be related to regular exposure to cattle.

"Rural asthma is a pretty hot topic; asthma in general is a hot topic," said Alan J. Adler, MD, Medical College Assistant Professor of Pediatrics, a pediatric pulmonologist at Children's Hospital and Principal Investigator for the Wisconsin study. "I've looked at it a little differently. There's always been an emphasis on urban, inner city asthma, and the asthma epidemic seems to be among inner city kids.

"I asked questions looking at the rural populations, because that is not a negligible number of children in this country. Just in Wisconsin there are probably about 800,000 rural children. These kids may have been somewhat neglected, not necessarily in the health care they receive but just in terms of being looked at as a population."

To reach that population for the study, Dr. Adler said, questionnaires were sent out to 37,500 families in school districts that were defined as rural by US Census data. Responses were received providing data for almost 5,000 children living in 70 out of the 114 rural school districts in the state.

Earlier Farm Life Increased Effect
Generally, the study found, the effect that living on a farm had on asthma or wheezing rates was most significant among very young children but was evident among older boys as well.

"What I've found very clearly is that your chances of ever having wheezing or asthma are significantly less if you have lived on a farm than if you live in a rural community but not on a farm," said Dr. Adler. "If you had time on the farm early in life, that effect is true and you tend to have less asthma. But if you go to the farm later in life, after the age of five or six years old, that effect does not appear to work. So whatever effect it is that being on the farm has against asthma, that effect seems to be somewhat time sensitive and time dependent."

"People have hypothesized that this effect is caused by exposures particular to the farm environment, especially to the cattle. The cattle in the field, cattle manure, the cattle dust - the hypothesis is that if you get early exposure to those types of things it primes your immune system in a direction away from allergy."

The difference in asthma and wheezing rates between children who had lived on farms and non-farm rural children was pronounced, Dr. Adler said. "It was statistically significant. I divided the population between children younger than ten years old and children older than ten, between boys and girls, and also between farm rural children and non-farm rural children.

"The only group that this did not hold true for were farm girls older than 10. I'm hypothesizing that it doesn't affect the girls so much because girls tend not to work out on the farm so much as they get older, and girls smoke more."

50% Reduction in Younger Children
With asthma, the lungs become inflamed and constrict, limiting airflow and making breathing difficult. Asthma incidence has increased in the US in recent years, and according to the US Food and Drug Administration the disease now affects about 15 million Americans, including almost five million children. Because of the way asthma manifests itself, and the timing of accurate diagnosis, the data comparing children younger than five to the rest of the study group was of particular interest to Dr. Adler.

"Children who wheeze when they're little kids aren't necessarily asthmatic," said Dr. Adler. "A lot of kids will wheeze for other reasons and they grow out of it. When we look at the children older than five we find the true asthmatics, because by the time you're five you're diagnosed."

"We found that if you lived on a farm only when you were more than five years old, the rate of wheezing was 35.9% (of the total population in the study). But if you lived on a farm both before and after you were five years old, the rate is 23.7%. That translates to a 50% reduction in asthma among children who lived on farms both before and after the age of five."

"This data is very much like data from other studies," said Dr. Adler. "There's a very large study called the ISAAC (International Study of Asthma and Allergies in Children). It's a study of asthma in 127 countries using the exact methods that I used in Wisconsin, and when you look at my data compared to the ISAAC data we're very similar. We're right on the money compared to data from anyone else who has used similar questions and methods."

Impact on Treatment
Dr. Adler said that the Wisconsin study and other research efforts will have an impact on assessing the standard of care for rural children as well as on long-term preventive treatment possibilities for all children at risk for asthma regardless of where they live.

"It's important in several ways," said Dr. Adler. "In and of itself, it will tell us how much asthma there is in rural areas, which no one has really known. In that sense it can measure how much asthma there is. And that can be a stepping off point. We can ask the questions: Are they treated the same as city kids with asthma? Are they all getting the same resources? Is their standard of care the same? It's important in really asking that kind of epidemiological question."

"From a research standpoint, if this is actually the case (that farm exposure plays a role in reducing asthma rates), and I've just talked to people from Minnesota who have similar data, then way down the road we might be able to say that if you're at high risk of asthma, we might be able to provide a very simple treatment when you're a little kid."

"That doesn't mean we'll put you in a barn, but maybe that we'll challenge you with some of those elements that have been found to be preventative on farms. So translationally it could be very important. It might be something very easy to give to high-risk kids, with very little risk because it's not actually a medication but something that occurs naturally. So it's important in two ways, both for the healthcare of the kids in the region as well as for what it might prevent."

Dan Ullrich
HealthLink Contributing Writer

MCW Health News presents up-to-date information on patient care and medical research by the physicians of the Medical College of Wisconsin.