WEDNESDAY, Feb. 23 (HealthDay News) -- In a European study that
echoes the findings of other scientists, researchers have found
that children who grow up on farms are less likely to develop
The risk of asthma was reduced by as much as 51 percent for
children living on farms, and researchers suspect that it's the
diversity of exposure to different microbes that may offer
protection against the airway disease.
"The risk of asthma decreased with an increase in the diversity of microbial exposure," said study author Dr. Markus Ege, a researcher at Munich University Children's Hospital in Germany.
"Within the microbial spectrum under investigation, several germs with a potential for asthma prevention were identified," he added.
Results of the study are published in the Feb. 24 issue of the
New England Journal of Medicine.
Asthma is a chronic lung disease that causes inflammation of the
airways. This inflammation narrows the airways, making it difficult
to breathe. Symptoms include wheezing, coughing, chest pain and
tightness, and shortness of breath, according to the National
Heart, Lung, and Blood Institute (NHLBI).
The exact cause of asthma remains unknown. People with a family
history of the disease are more likely to develop asthma,
suggesting a possible genetic component to the disease. But
environmental exposures, such as encountering certain viruses, are
also associated with the development of the condition, according to
Numerous studies have also found that exposure to a variety of
microbes in the environment, such as bacteria or fungi, appear to
provide protection against asthma, perhaps by helping the body
create a tolerance for allergens.
And, other research has found that children living on farms --
especially those exposed to cows, pigs and hay -- seem to be less
likely to have asthma and allergies.
Exactly how exposure to a variety of microbes might protect
against asthma is still unclear, researchers noted.
"How these microorganisms reduce the asthma risk remains largely unknown," said Ege. "A combination of environmental microorganisms might stimulate the innate immune system and counterbalance an asthma-prone immune status. Alternatively, the diversity of microbial exposure might prevent specific [disease-causing] microorganisms with an asthma-inducing potential."
The current study assessed the incidence of asthma in children
living on farms compared to children without farm exposure in two
different groups of youngsters. The researchers also tested dust
samples from the children's bedrooms and mattresses to get an idea
of what type of microbes the children were regularly exposed
The first group of children included 6,843 rural and suburban
elementary school children from southern Germany. This study,
dubbed PARSIFAL, also included dust samples from 489 children's
mattresses. The second study, called GABRIELA, included 9,668
elementary school kids from rural areas of Austria, South Germany
and Switzerland. Dust samples were collected from 444 children's
bedrooms in this study.
House dust from farm homes had a greater variety of bacteria and
fungi, a finding that was statistically related to a lower rate of
In both study populations, youngsters who lived on farms had
lower rates of asthma and allergies, according to the study. In the
PARSIFAL group, the risk of asthma was reduced by 51 percent in
children living on farms. In GABRIELA, the reduction was 24
percent, according to Ege.
The researchers also found that diversity of microbial exposure
lowered the odds of asthma by 38 percent in the PARSIFAL population
and by 14 percent in GABRIELA, according to the study.
"Not all microbes are detrimental; some are beneficial for asthma and allergies," explained Ege. But, he cautioned that this doesn't mean that dirt or microbes in general should be considered healthy, or that parents should try to deliberately expose their children to microbes.
"There are enormous numbers of different microorganisms which affect human health by various measures and in opposite directions. There are still dangerous infections, which should be prevented by vaccination or treated with antibiotics," Ege stressed.
One expert who wrote an accompanying editorial in the same
journal noted that it was "of critical importance" to figure out
how microbe exposure affects the biology of the lungs and immune
"This study shows that kids who grow up on farms are less likely to develop asthma, but I don't think there's anything that can be applied to treatment right now," said Dr. James Gern, a professor of pediatrics and medicine at the University of Wisconsin School of Medicine and Public Health in Madison.
"As we learn more about what these protective exposures are," he said, "it's possible we could come up with ways to prevent asthma in the future."
Read more about the causes of asthma from the
National Heart, Lung, and Blood Institute.