From the Allergic Living archives. First published in the magazine in 2007.
The answer to why a baby becomes an allergic child is the modern version of the Poincaré conjecture – a puzzle for which we have yet to find the solution. In this age of unparalleled understanding of the human body, scientists still don’t know why it is one child develops an allergic reaction to, say, peanuts while another child can eat them by the handful.
At a time when allergy and asthma have risen at rates never seen before in human history, such questions have become pressing. Between 1997 and 2002, according to a study by allergy researchers at the Mount Sinai School of Medicine in New York, the prevalence of food allergy alone doubled in North America; about 6 per cent of young children today have food allergies. After a surge that started in the 1980s, asthma rates have leveled off, but at least 12 per cent of children on this continent have been diagnosed with the disease.
In pursuit of elusive answers, scientists have turned to the beginning of life. The time in the womb, and the first days, months and years of a human being’s existence, they believe, are critical to the understanding of allergic disease. “Your immune system goes to school in the first couple of years. We know that’s a very unique time when we think we can influence allergies,” says Dr. Michael Cyr, an allergist and clinical immunologist at McMaster University in Hamilton, Ontario.
Scientists hypothesize that it’s something the baby with an allergic tendency is coming in contact with in the early days – or possibly not coming in contact with – that is causing the allergies. If they could discover what these factors are, then perhaps the incidence of allergy could be significantly curtailed.
While so much about allergy is a mystery, one thing is certain: genes play an important role. According to the World Health Organization, if both of a baby’s parents have allergies, that infant has a risk four times greater of getting asthma and allergies than the baby born to parents who don’t have allergic disease. If only one parent has allergies, then the child is twice as likely to develop allergies.
As well, a 2000 study of peanut allergy, done by researchers at Mount Sinai’s Jaffe Food Allergy Institute, found that a sibling of a peanut allergic person is 10 times as likely to develop a peanut allergy as the general population.
There is much interest in “atopy,” the inherited predisposition to allergy. But scientists now know that the development of allergy is not only about genes. “Family history plays a big role, but it is not definitive,” says Dr. Padmaja Subbarao, a pediatric respirologist at the Hospital for Sick Children in Toronto and an assistant professor at the University of Toronto. “That cuts both ways for the predisposed and the genetically free. Just because you don’t have risk factors, doesn’t mean your child won’t have asthma.”
In researching allergy, scientists have a wide range of factors to consider: from maternal diet during breastfeeding through the age at which a child first eats solid food; exposure to air pollution – outside and indoors; even ethnicity, birth order and delivery by Caesarean section.
A major Canadian study has applied for funding to begin assessing the different variables. The study, called the Canadian Healthy Infant Longitudinal Development Study (or CHILD cohort study for short), will recruit several thousand pregnant women in Canada. CHILD is led by Dr. Malcolm Sears, the research director of the Firestone Institute for Respiratory Health and a professor of medicine at McMaster, and involves a cross-country team of experts from about 20 medical and academic disciplines. CHILD’s researchers will examine environmental and genetic factors in allergy and asthma: everything from the levels of dust in the pregnant women’s homes to lifestyle factors such as stress and their family’s medical history. The researchers plan to follow the babies through childhood and, if the funding is available, into adolescence.
But even if CHILD does start to find clues, it will be a few years before it can show results. Its findings then need to be compared to other large cohort studies to draw definitive conclusions. That leaves expectant parents today wondering what they can do to help prevent their newborns from going on to develop allergies and asthma.
Next: Allergies in Pregnancy