lundi 6 mai 2013

Being Born in the U.S. Puts Kids at Higher Risk of Allergies

(...) What does birthplace have to do with how the immune-system functions? The most likely explanation could involve the “hygiene hypothesis,” which suggests that improved sanitation methods and efforts to keep germs at bay may deprive young, still-developing immune systems from being trained to recognize and react appropriately to the right types of irritants. “The hygiene hypothesis suggests that early-life exposures to infection or an unclean environment may protect against allergies. Children born and raised outside the U.S. likely have more and/or different infectious exposures than those born in the U.S.,” says study author Dr. Jonathan Silverberg of St. Luke’s–Roosevelt Hospital Center in New York City. “That American cities are ‘too clean’ may be overstated. However, previous studies suggest that rolling in the dirt from time to time may be a good thing for kids.”
Parental behaviors and cultural practices may also play a role. “Parents born and raised outside the United States may, for example, follow a healthier diet or have foods with a different antigenic profile than typically encountered in the Western diet,” the authors write. “Some cultures more commonly use spices, such as curcumin, and green tea that have antiallergy and inflammatory properties.”
Such factors could explain why having foreign-born parents seemed to lower risk of allergic disease in their children even further; the finding held even after the researchers accounted for differences in race, ethnicity, socioeconomic status, and whether or not the child lived in a metropolitan area.
In terms of what features of the American lifestyle or culture could be contributing to an increased risk of these diseases, previous studies from the same team of scientists suggested that factors such as climate, obesity, the Western diet and various types of infections could play a role. The current study wasn’t designed to identify which specific environmental factors might be the most influential, but Silverberg says, “one of our goals is to determine which factor [or factors] have the greatest impact on allergic disease, and to help develop public-health interventions to decrease rates of allergic disease in the U.S.” — because those influences would likely be far easier to change than where you’re born. 

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