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 Based on more than 2,400 adults in the Netherlands, researchers
found that people who lived within 327 meters (1,073 feet) of a
farm, but were not farmers themselves, were about 21 percent less
likely to experience a range of allergies compared to those living
500 m (1,640 ft) away or more.
The results were similar when researchers looked specifically at
proximity to cattle or pig farms, though not for poultry farms. The
apparent protection was also seen among people without allergy
symptoms, but whose blood test showed a tendency to have an immune
reaction associated with common allergies, food allergies, asthma
and eczema.
"For 20 years, a large number of studies have shown that allergies
are less prevalent in farmers and farmers' children," said senior
study author Lidwien Smit of Utrecht University.
"Farming is actually one of the few environmental exposures
consistently linked to respiratory allergies," she told Reuters
Health by email. "It's important because the number of people
affected by respiratory allergies has sharply increased over the
last few decades."
From the study participants' blood samples, the research team
measured allergy antibodies to house dust mites, grass, cats and
dogs. They used geographic and weather data to determine the
distance of each person's home from neighboring farms, the number
and types of animals on those farms, and to estimate fine dust
emissions from each farm.
About 30 percent of participants had allergies, mostly to grass and
house dust mites, and about a third had lived on a farm during
childhood. The research team also analyzed the number of years the
participants lived in their current house.
"You could argue that selective migration might play a role, that
is, less healthy people move away to more urbanized areas," Smit
said. "However, we didn't find this, which strengthens the idea that
environmental exposures are responsible for the protective effect."
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The apparent protection tied to living close to a farm was strongest
for those who lived near pig or cattle farms, as well as those who
grew up on a farm, the study team reports in Occupational and
Environmental Medicine.
The study doesn't prove whether or how exposure to farms might
reduce allergic sensitivity. Smit said the researchers are
continuing to explore whether the rich diversity of microbes carried
on wind-borne dust from farms might play a role in modulating the
immune responses of non-farming neighbors.
"Most allergy studies focus on finding new ways to treat symptoms,"
said Grethe Elholm of Aarhus University in Denmark, who wasn't
involved in the study.
"It is also important to keep drawing attention to some of the
apparent negative effects of Westernized lifestyle with its current
fixation on cleanliness," Elholm said in an email. "Farms may be
considered dirty and smelly, but they might actually be doing our
immune system a favor."
In the United States, researchers are also focused on the house dust
mite, which is the most common allergen worldwide, and how dust,
pets and allergens in the home build immunity early in life.
"If you're growing up in an environment devoid of all exposures to
animals and allergens, your risk of developing allergic disease
tends to be higher," said Dr. Alexander Adami of the University of
Connecticut School of Medicine in Farmington, who wasn't involved in
the study.
"That doesn't necessarily mean you have to live near a farm or go
visit one," Adami said in a telephone interview. "Go play outside,
get a pet or expose yourself to new environments."
SOURCE: https://bit.ly/2K9faym Occupational and Environmental
Medicine, online April 30, 2018.
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