Monday, August 16, 2010

Peanut allergies in a nutshell

This summer I met a family from Australia who’d mentioned their daughter was highly allergic to peanuts. Wondering if all the concern about peanut allergies was yet another case of Americans overreacting to anything health-related I asked if they’d ever heard of schools in Australia banning peanuts.

“Our daughter’s school has been peanut-free for years,” they replied, as if it were an odd question. They added, “Lots of schools are.”

Like many people, I’ve also wondered if the seeming rise in prevalence of peanut allergies was real. After all, how many times have I heard someone say, “Well, we all grew up with peanut butter, and I didn’t know anyone who was allergic. What’s all the fuss about now?”

Turns out -- according to several studies published in medical and allergy journals over the past decade -- that peanut and tree nut related allergies, or hypersensitivity of the immune system to specific proteins in these nut families, truly is on the rise in Australia, the US and other Westernized countries. It is now estimated that over 1% of the US population has peanut or tree nut allergies, and one study reported a doubling of peanut allergies in children over a five year period.

So what’s going on? Has something changed in the way we are exposed to peanuts, tree nuts and other increasingly allergenic foods (sesame, and soy for example)? Or is it simply that our immune systems are going haywire?

The immune response is complex. While we’re all familiar with the role of antibodies, which confer immunity to anything from the common cold to polio, they are only one of five different types of immune proteins, or immunoglobulins. Other immune proteins protect vulnerable regions of the digestive and respiratory tract from pathogens, elicit our bodies to produce antimicrobials, and help us get a “jump” on our response once pathogens have breached other protections and entered our bloodstream.

Then there is immunoglobulin E (IgE). Although recent studies suggest that IgE may protect against certain parasitic worms (less of a problem these days in western countries compared with other regions of the globe), IgEs are most notorious for their role in causing allergic reactions, or an inappropriate immune response to a relatively harmless substance. Basically, once a body is sensitized by a potential allergen, a bit of basement mold perhaps, or a whiff of pollen from the old oak tree, IgEs are then distributed thoughout the body in association with immune cells like mast cells and basophils, which lay in wait for the next exposure.

When subsequent exposure occurs, these sensitized immune cells release a slew of potent chemicals including histamine, cytokines, and prostaglandins. These are all useful chemicals when released at the appropriate time and place, as during a normal immune response when the body is combating a pathogen or healing a wound (and even then they may cause some damage to healthy cells and tissues.) But as far as anyone knows, there is no appropriate time or place for an allergic response. Yet no matter the reason, when these chemicals are released the body responds.

The allergic responses many of us experience are caused by the increases in vascular permeability, constriction of smooth muscles (including those around the smallest passages of our lungs), and increased mucus production caused by histamine and other chemicals. The impacts on a body can range from mild to severe.

So, while I might suffer through a month or two of asthma, sneezing and itchy eyes (along with the more than 20% of the U.S. population affected by allergies), thankfully my IgEs seem to respond relatively mildly. But for some, an IgE response can cause anaphylaxis, a far more severe and systemic condition which may include vomiting, constricted breathing, and plunging blood pressure. The onset of these life-threatening responses can lead to anaphylactic shock and can occur within minutes of exposure.

A 2008 study published in the journal Current Opinion in Allergy and Clinical Immunology estimated that allergic anaphylaxis may occur in up to 2% of the U.S. population at some point in their life, with varying degrees of severity. And the risk of occurrence, particularly in children, is on the rise.

Which brings us to some of the top triggers for anaphylaxis - a list that includes many common substances like latex, insect venom (e.g. bee stings), medications (e.g. penicillin) and certain foods including shellfish, milk, tree nuts, and peanuts. Of these, food allergies are among the most common triggers of anaphylaxis requiring emergency room treatment. By some estimates, in the US food allergies account for roughly 30,000 visits to the emergency room and at least 100 fatalities a year, and several reviews of the medical literature including a 2009 review published in Clinical Pediatrics conclude that peanuts and tree nuts cause the majority of reported allergy-induced fatalities.

When a food is allergenic, the allergic reaction is usually caused by a specific type of protein contained in the food. In peanuts, eight different allergens have been identified. What differentiates allergenic proteins from other food proteins is that they resist acid, heat, and enzymatic breakdown in the gut. So they tend to be identified by the body’s immune system as an intruder rather than a nutrient, with potentially devastating consequences.

Efforts to understand why the US and other Westernized populations has a higher prevalence of peanut allergies than, say, China, where peanut consumption is also high, have identified the U.S. food industry’s practice of dry roasting peanuts rather than boiling or frying peanuts as one potentially relevant factor. The higher temperatures reached by the dry roasting process increases the allergenicity of peanut proteins. Other factors contributing to higher prevalence likely include differences in diet, routes (oral or dermal) and timing of nut exposures. Additionally, scientists have hypothesized that improved hygiene and reduced disease incidence in young children may also contribute to increased prevalence of allergies in general. Scientists and allergists have also speculated that increased use of peanuts in common consumer products, from soaps to shampoos and skin creams, may contribute to creating a more sensitized population.

Whatever the underlying cause, some people, once they are sensitized, need only ingest a very small amount (50 millgrams, approximately 100th of a teaspoon, down to as low as 2 mg) of peanut product to cause what could become a life-threatening reaction.

It is a mind-boggling response. Consider the tiniest oral exposure setting off a systemic response within minutes. How does this happen?

“What you think of as low dose might contain plenty of stable antigen [or allergenic protein],” explains Southeastern Louisiana University Immunologist Dr. Penny Shockett. “Also,” Shockett added, “once the system is sensitized it doesn't necessarily take a high dose for tripping the mast cell response. If you are highly sensitized (i.e. allergic) you have more sensitized mast cells in tissues (or basophils in the blood) sitting and waiting for the allergen, which can potentially detect it quickly and strongly.”

Studies indicate that not only has the prevalence of peanut allergies risen over the past few decades, but also the risk of anaphylaxis in general, at least in the United States and other Western countries. As we alter our diets based on the ever-changing suggestions of health and nutrition experts, cultures adopt one another’s diets, and diseases are reduced through changes in hygiene and vaccines, scientists are in a quandary as to the causes of increased peanut and tree-nut sensitivity. Hopefully both the underlying causes and solutions for those who are allergic will be identified sooner than later.

For those currently affected by severe allergies, the focus is on management. In addition to education of individuals with allergies, particularly children, this means a range of options for schools. First and foremost involves appropriate medical and treatment plans in schools, followed by education of the school community, and strategies to avoid exposures for allergic individuals. In the case of peanut allergies avoidance in schools ranges from peanut free buildings to peanut free classrooms or separate lunch tables. As to the most effective management practice, the jury is still out.

Emily Monosson, Ph.D. writes and blogs as the Neighborhood Toxicologist, is a member of the GMRSD school committee, and is a member of the district’s Wellness Committee. The information presented here is the product of her own research into the issue and does not represent the opinion or work of the GMRSD school district, or the Wellness Committee.

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