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
Allergies in Pregnancy
Questions first arise during pregnancy, when a mother-to-be in a family with allergies starts to think about the food she eats and the effect on her fetus. She is likely to wonder: will succumbing to late-night cravings for peanut butter cups mean my child will be burdened with anaphylaxis to that legume? It’s still common for general practitioners to counsel pregnant patients to avoid highly allergenic foods in the last trimester. But there is a gulf between that advice and what scientists in the know believe is necessary.
For instance, Cyr says, “There’s little evidence that avoiding nuts or allergenic foods in pregnancy is helpful. A lot of people still say it. We don’t have evidence that says it’s harmful.”
So little has been proven definitively that perhaps even the precautions an expecting mother takes to minimize the risk of allergy – such as avoiding peanuts – might in fact make the fetus more susceptible. “It is possible that avoiding peanuts is harmful,” says Cyr, an investigator working with AllerGen, the federally funded allergy research network. Peanut exposure might actually mitigate against allergy. The fact is, scientists do not yet know.
So what’s a parent to do? “Just do what you know is good for your baby,” advises Dr. Michael Kramer, Scientific Director of the Institute of Human Development, Child and Youth Health (one of the government of Canada’s CIHR research institutes, as well as a professor at McGill University in the departments of pediatrics and epidemiology, biostatstics and occupational health.
And that, he says, is exclusive breastfeeding for six months and then for as long as the mother and child are comfortable after that. “That’s one thing we know she (the mother) can do for her child’s health.” Kramer is the principal investigator of a long-term study out of Belarus that is tracking the offspring of several thousand women for what the research team hopes will be several decades. Breastfeeding and asthma and allergy the risk of atopic dermatitis (eczema) or at least afford some protection from it in the first year, says Kramer.
But a mother’s milk does not guarantee an allergy-free future. In 2002, Sears (now head of the CHILD project) and some colleagues released results from a long-running birth cohort study in Dunedin, New Zealand. From the time they were age 9 until they were 26, every two to five years the participants in that group were tested for allergies and their lung function was a d. In the 2002 report, Sears and his team used data from this study to analyze the relationship between breastfeeding and allergies. To the surprise of many in the medical community, the group who had been breastfed proved more likely to have asthma from age 9 onward than those who had been breastfed for four weeks or less. From the age of 13, the breastfed group also showed more allergy and asthma to cats and to dust mites.
California scientists also suggest in a 2006 review of studies that whether breastfeeding has a protective or sensitizing effect may depend on the mother’s own genetics. Meantime, a British scientific review noted that, “the jury is still out as to whether breastfeeding protects or not against the development of allergic disease.” None of this, however, makes breastfeeding any less than a good thing. Both Kramer and Dr. Mark Greenwald, chair of the medical and scientific committee of the Asthma Society of Canada, stress the dozens of health advantages to feeding a baby mother’s milk. These range from assisting cognitive development to reducing the risk of numerous chronic diseases. Greenwald says that all health issues considered, the benefits of breastfeeding far outweigh any risk of developing allergies. “With breastfeeding, I will not tell them to do anything in terms of restricting their diet,” says allergist Dr. Zave Chad.
The proteins in the foods a mother eats have been shown to make it into her breast milk. So the new mother might worry about whether those tree nuts or peanuts she ate a few hours before her baby’s feed might sensitize her child. “You can demonstrate peanut allergen in breast milk,” says Cyr. “But again, whether that increases the risk (of allergy) is debatable.”
Allergists across North America have been taking note of study findings that have sparked the debate. Dr. Zave Chad, president of the allergy section of the Canadian Paediatric Society and an Ottawa allergist, says that faced with pregnant patients with allergies in the family: “I don’t change their diets at all. With breastfeeding, I will not tell them to do anything in terms of restricting their diet.” He’ll make one exception with breastfeeding: “If a woman has another child with peanut allergy and she’s really worried about it, I might say to exclude peanuts. Even then, I will tell her that it’s not based on any evidence.”
Another contentious subject is the topic of “when” to introduce certain solid foods to a baby at risk of food allergy Many pediatricians and family doctors have been telling parents to follow the guidelines set out by the American Academy of Pediatrics. These recommend that the at-risk child not be fed dairy products until after the age of 1, eggs until after the age of 2 and that parents avoid giving the child tree nuts, peanuts or fish until the age of 3.
But allergy specialists, who also work with new mothers, point out that these guidelines come with no guarantees. They say the theories behind these recommendations are not rooted in science. “It’s more than mumbo-jumbo, it’s a mess,” says Dr. Milton Gold, a staff member in the Division of Immunology and Allergy at the Hospital for Sick Children and author of The Complete Kids Allergy and Asthma Guide. The logic behind withholding peanuts from at-risk children until they are 3 years old is based on the fact that many infants will outgrow allergies to milk and eggs by the age of 3. “Because of that, people felt that age 3 was probably OK for peanuts,” says Gold. “That’s all it is.”
From the lab, Cyr agrees that “the evidence underlying these guidelines isn’t great.” He cites studies that have resulted in conflicting conclusions. “My recommendation is that you should breastfeed. After that, I don’t have strong feelings about when you can introduce peanut and egg, just because of the controversy in the (medical) literature.”
Adding to the confusion, in July 2006, the American College of Allergy, Asthma and Immunology issued a consensus statement suggesting that it was “prudent” to prolong the delay of potentially allergenic solids in young children at risk of allergies – and then it offered a list of ages or introducing eggs, peanuts and seafood that mirrors the AAP guidelines. The statement prompted the food allergy experts from the Mount Sinai School of Medicine and the Duke University Medical Center to write a letter protesting that the recommendations were too definitive and “not a logical conclusion of the material presented.” The letter noted that some studies suggested extended avoidance of certain solid foods might even increase the risk of atopic ‘It’s more than mumbo- jumbo, it’s a mess,” Dr. Milton Gold says of the age guidelines on introducing solid foods. disease. “Everyone wants to say: ‘Do this to make it better,” says Dr. Scott Sicherer, an allergist and associate professor at Mount Sinai. “But what if you don’t know that doing this is going to make it better?” Given the lack of clarity, in Canada, Chad and his colleagues at the pediatric and allergy societies are developing a position paper on infants and allergies. Chad says it is not likely to uphold the precise ages for introducing potentially allergenic solids. In the United States, the AAP guidelines are also being reviewed.
Thankfully, there is at least consensus on one aspect of giving food to children at risk of allergy The experts agree that, after four to six months of exclusive breastfeeding, solid foods may be introduced. Doctors want to avoid solids before the digestive system has had some time to mature.
Regardless of whether food allergies run in the family, parents are advised to start some foods before others. In North America, rice cereal is a child’s first taste of food other than milk, followed by grains like barley and oats and then green vegetables and yellow vegetables such as carrots, sweet potatoes and squash. Pediatricians also recommend feeding all babies only one new food at a time over a period of every few days – to make sure a child isn’t showing signs of an allergic reaction to the new food.
Next: Testing and Precautions
Testing and Precautions
When it comes to introducing the foods that most often trigger allergic reactions – cow’s milk, eggs, peanuts and tree nuts, Gold is not in favor of simply restricting your young child’s diet. Instead, if one of the parents or a sibling has an allergy, he recommends that the child be evaluated by a pediatric allergist.
Gold’s advice is that the allergist’s assessment take place about the time a child will be staying regularly in an environment over which the parent has limited control- such as daycare or preschool. There are techniques and tests to determine, even in infancy, whether a child has specific allergies.
While researchers and specialists such as Gold may doubt the benefits of AAP guidelines, even Subbarao, a colleague at Sick Kids, follows some of them. Subbarao is pregnant and atopic and, in the absence of finite answers, she’s taking some of the precautions – just in case they can minimize the risk to her baby. She plans to breastfeed and follow the guidelines on introducing solid foods. “Other than that, I’m not going to try to get rid of every dust mite in the house.”
While the precise causes of allergy and asthma in young children are unresolved, Cyr is definitive about one thing: it is not mom’s fault. “I see others blame themselves and there is no basis.” If an individual “has the right genetic setup to develop peanut allergy, you are probably going to develop it in the long run. At best, you can hope to postpone the disease. Based on current findings, there’s little evidence you can prevent it.” Kramer says the unprecedented growth in allergies remains a mystery. While theories such as the hygiene hypothesis link the rise to immune systems lacking exposure to germs and parasites, newer research is also finding flaws in that argument. On peanut allergies, for instance, he says: “We still don’t have a clue why they are becoming more common and severe.”
Perhaps one day, research such as Kramer’s Belarus study and the CHILD study will provide missing answers on allergies and asthma and early life. In the meantime, expecting mothers should relax, eat nutritiously throughout the pregnancy, and speak to their allergists about wl1at’s best for the child, given the allergic history. Remember that, as Cyr says: “lt’s not something you ate; it’s not something you did. It may be your genetics, but those you cannot control.”
The New Mother’s Questions:
Q: If my baby has eczema, does this mean she will develop asthma or a food allergy?
A: Eczema, or atopic dermatitis, is an indication of the tendency to develop allergy (known as atopy). While the itchy rash doesn’t guarantee that your child will develop food allergies or asthma, this condition indicates there is a much higher chance of either.
Q: If there are only environmental allergies in our family, is my baby at risk of developing food allergies?
A: Yes. Allergic disease is hereditary and can manifest itself in one (or all) of: hay fever, eczema, asthma and food allergies.
Q: Can I use my EpiPen if I have an allergic reaction while pregnant?
A: Yes. One obstetrician put it bluntly: “It’s better for the baby if you’re not dead.” Dr. Michael Cyr reminds that, “in a life-threatening reaction, use it right away.”
Q: If my child develops a wheeze, does this mean he’ll develop asthma?
A: Dr. Padmaja Subbarao says 50 per cent of children have episodes of wheezing by the age of 6. However, more than half outgrow wheezing as preschoolers, and only 10 to 15 per cent will show signs of the persistent allergic wheezing that is asthma. “Most children wheeze because of viruses,” she says. “This causes inflammation of the airways. It’s like narrowing a straw when you blow through it: it will make noise.” However, if a child has persistent wheezing, she advises making an appointment for asthma testing.
Q: If I quit smoking during pregnancy, can I reduce my baby’s risk of asthma?
A: If a woman quits smoking early in the pregnancy, there is a huge benefit to the child’s lungs. If a mother smokes while pregnant, the risk of a baby developing breathing and wheezing difficulties, regardless of whether the mother is asthmatic, increases dramatically. Babies born to smokers have smaller airways.
Q: Will one peanut exposure before the age of 3 trigger a food allergy in my child?
A: “The evidence that delaying the introduction of more allergic foods like eggs and nuts and fish is not very strong,” says Dr. Michael Kramer. He points out, though, that studies show the early introduction of cow’s milk may contribute to an allergy to cow’s milk. Rather than worry bout specific foods, he says, parents should keep a healthy household. “one thing you can do for your kid if you are an allergic parent is to make sure they’re physically active, that they don’t eat (fatty) food, and don’t spend a lot of time in front of ht TV and computer screen.”
Q: Should we allergy-proof our new baby’s room?
A: Ottawa allergist Dr. Zave Chad does see benefits in trying to cut down the at-risk infant’s exposure to dust mites. If you’re renovating to ready baby’s room, he recommends that you avoid carpet and “not buy a million stuffed animals.”
Q: Can probiotics (such as those in yogurt) help to prevent asthma and allergies?
A: The hygiene hypothesis theorizes that modern society has left the immune systems of the allergic person with nothing better to do than to fight proteins such as those in peanuts or pollens. Extrapolating on this, some experts wondered if exposing the body to good microbes, through probiotics, would lower allergy rates. According to Dr. Mark Greenwald: “We know that, in certain conditions, probiotics are used to restore a microbiotic balance (such as after a course of antibiotics to treat strep throat). In asthma he says, “this has in no way been proven” to work. But the debate remains open, and Kramer isn’t ready to dismiss probiotics just yet. He says more studies need to be conducted. – Staff
With staff files from the CSACI conference in Montreal. Article reviewer: Dr. Adelle Atkinson, staff immunologist, Division of Immunology and Allergy at the Hospital for Sick Children and Assistant Professor of Pediatrics at the University of Toronto.
First published in Allergic Living magazine.
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