(Reuters Health) - Exposure to farms seems to reduce the risk of allergy sensitivity, even among adults, and living close to a livestock farm in particular might curb common allergies, a Dutch study suggests.
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.”
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: bit.ly/2K9faym Occupational and Environmental Medicine, online April 30, 2018.
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