Peanut allergies vex researchers Reactions rare in Asia, climbing in West
By CAROLYN ABRAHAM MEDICAL REPORTER Wednesday, March 12, 2003 - Page A7
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The Chinese cook them with chilies in kung pao chicken, and Thais shower them over the tamarind noodles of pad thai. But peanuts rarely provoke allergic reactions in Asian countries, though those are among the world's top producers and consumers of the increasingly troubling legume.
While research efforts to battle peanut allergies intensify, scientists are still stumped to explain why the numbers seem to be ballooning in Western countries while holding low and steady in the East.
Hugh Sampson, a leading pediatric allergist at Mount Sinai School of Medicine in New York, noted this week that "China has virtually no peanut allergy cases."
The numbers are similarly skimpy in countries like Thailand and Singapore, where peanuts are also pillars of the local diet.
Researchers suspect that the disparity may in part reflect the fact that Eastern cuisine uses boiled or fried peanuts, while peanuts in the U.S. are typically roasted, said Dr. Sampson, whose Mount Sinai colleagues recently investigated the issue.
They concluded that roasting uses a higher temperature that seems to increase the allergenic properties of a peanut, allowing its protein to bind more easily to the IgE antibody that triggers the intolerant reaction.
More than 150,000 Canadians are estimated to suffer from peanut allergies, as are 1.5 million Americans, numbers that seem to have soared in the past two decades.
No Canadian studies have documented the incident rate over time, but it's likely to be similar to data collected elsewhere, said Karen Binkley, an allergist and clinical immunologist at St. Michael's Hospital in Toronto. A British study published last November, for example, found peanut allergies have tripled since 1989, to 3.3 per cent of children.
The report, echoing a Canadian finding in 2001, also suggested that eating peanut products while pregnant or breastfeeding contributes to the increase.
But this week, a study by Gideon Lack of Imperial College in London, England, found no such link. His report, published in the New England Journal of Medicine, concludes that use of topical lotions or ointments that contain peanut oils, either by nursing mothers or on infants with broken skin from diaper rashes or eczema, is a significant contributor to peanut allergies.
Jane Salter, president of Anaphylaxis Canada, an education and support group for people with severe allergies, said that with so many possible explanations and no definite answers, "I wonder if we are chasing after cures instead of chasing the root causes."
Dr. Salter, whose daughter has a peanut allergy, said she would like to see further investigation of Dr. Lack's finding that an infant's exposure to soy products in the first six months of life may also increase the risk of peanut allergies.
Although an allergy to peanuts does not imply an allergy to soy, the two legumes do share a similar chemical structure. Theoretically, soy may trigger an immune-system response that contributes to a peanut allergy.
And soy, Dr. Salter noted, has been part of the Asian diet for thousands of years, yet prevalent in Western food only in recent decades. She noted that soy is found in both cattle and chicken feed, and in an array of different food sources.
Four-year-old Dana McNeil, who has a severe peanut allergy, was six months old when her mother switched her to a soy milk formula after finding that cow's milk upset her stomach. "She was on soya for a few months," said Karen McNeil, of Pickering, Ont. "Now this really makes me think and wonder if this had anything to do with triggering the allergy."
Dr. Binkley said the increase in peanut allergy rates despite the relative immunity of Asian countries is not likely to be explained by a single factor.