NEW YORK (Reuters Health) - The anti-allergy effects of an agricultural upbringing persist well into old age, new research from Sweden shows.
Dr. Jonas Eriksson of the University of Gothenburg and colleagues found that people who spent the first five years of their lives on a farm were about 20 percent less likely to have itchy, runny eyes and noses due to allergies, from age 16 up through to age 75.
So-called allergic rhinitis has become increasingly common since the mid-20th century, Eriksson and his team note, although the reasons for the increase are unknown. A study they conducted found nearly 30 percent of adults in West Sweden had the condition. “The prevalence found in this study is high, but in some countries, e.g. Australia, even higher prevalence has been reported,” Eriksson told Reuters Health via e-mail.
A number of studies have found allergies are less common among children and adults raised on farms but it has not been known if this protection lasts into middle and old age.
To investigate, Eriksson and his colleagues surveyed 18,087 residents of West Sweden about their respiratory health and whether they lived on farms as children. They also looked at whether living in a more urban setting during adulthood affected allergic rhinitis risk.
Twenty percent of people who’d lived on a farm up to age 5 had allergic rhinitis, compared to 28 percent of people who hadn’t been raised on a farm. The effect was strongest among 16- to 30-year-olds (20 percent vs. 31 percent), and weakest among 61- to 75-year-olds (17 percent vs. 19 percent).
Eriksson and his team also found that people living in the most urban area — within the town of Gothenburg, with a population of 700,000 — had the highest risk of allergic rhinitis, at 28 percent; this risk steadily declined as urbanization decreased, with 23 percent of rural residents suffering from the condition.
While the protective effect of early farm life remained significant up until age 75, urbanization’s effects weren’t statistically significant, meaning they could have been due to chance, after age 35.
If farm life reduced a person’s risk of allergic rhinitis by 20 percent, this could make a significant difference in regions like Western Sweden where the condition is common; for example, the 30 percent risk for the general adult population would drop to 24 percent for people who started their lives on a farm.
Only farms with livestock confer this protection, Eriksson noted. How contact with farm animals might cut allergy risk isn’t clear, he added, although drinking unpasteurized milk and exposure to certain types of bacteria are two mechanisms that have been proposed.
How urban living might up allergy risk isn’t clear either, the researcher said. “Higher levels of diesel exhaust particles in the urban environment could be one factor,” he wrote.
“Hypothetically, there could also be a higher disease awareness in urban than in rural areas, which could explain some of the difference.”
Allergy, online May 17, 2010.