PerspectivesAre you interested in submitting a Perspective Article? Be sure to read The Science Advisory Board's Editorial Guides for Perspective Articles. Click here. The Dirt on Dirt by Heather Kiefer, Ph.D. It has been estimated by the Environmental Protection Agency that children in the U.S. eat 200 to 800 mg of dirt per day. That is roughly 73 to 292 grams of dirt per year. To me, that doesn’t seem like very much. I realize that this is only an average, but I have to wonder if my particular toddler isn’t getting more than her fair share. An example of this would be on our trip to the beach last summer where she wanted to actually taste the various consistencies of sand rather than play with it. Much to my chagrin and against my best efforts to the contrary, at the end of the day it seemed like she may have ingested her annual allotment in one go. At home, things are slightly better, although we do loosely adhere to the “three second rule” as most parents of small children find themselves following by default. Of course we have the standard rules of not eating food off the floor when we are outside, or in public places, but I’m sure my children disregard this rule when we aren’t looking, or when we are just far enough away that we can’t prevent them from doing it anyway. I am sure some of you are horrified by this. And you may also cluck your tongues disapprovingly when you hear that my kids do not get baths every single night as so many children in the U.S. do (unless they are especially grimy or so sticky that they pick up dog fur around the house like mobile little lint brushes). We take the “spot clean” approach, their hands being the most frequent targets, after using the restrooms, before and after dinner, and after coating them with markers, or paint or chocolate etc. But I’m comforted by the fact that all this dirt may actually be helping to prevent my children from developing allergies, asthma and other diseases that have been increasing in prevalence in developed nations at an astounding rate. The hygiene hypothesis, first introduced by D.P. Strachen in the late 1980s, suggests that with the rise in cleanliness and reduction of early childhood illnesses, that childrens’ immune systems do not develop properly. This has been postulated to lead to an increased risk of autoimmune and allergic disease. Epidemiological correlations support this hypothesis, with the incidence of disorders such as asthma doubling over the last two decades. When an immune system has not been built correctly, it is thought that harmless agents like pollen may come to be treated as if they were dangerous invaders. Exposure to the immunomodulatory products of the right kinds of bacteria and viruses at an early age, may activate innate immune responses, induce regulatory responses, and prevent an imbalance in T lymphocytes from occurring. While this hypothesis remains up for debate (other factors may also play a role such as lack of exercise, obesity, and environmental pollutants), there are an increasing number of studies that lend it support. The more siblings a child has, the less likely he/she is to develop allergies. Children from small families who go to day care before the age of one have fewer allergies than children who do not. Growing up on a farm or having pets from birth also appear to be protective. Of course, no one is suggesting that we should purposefully expose our children to potentially dangerous infections. Certain respiratory viral infections may actually increase the risk of asthma attacks. And dust mites and cockroach allergens, components that are frequently associated with dirt, are also believed to contribute to the risk of having asthma-related illnesses. But is it possible that we are hurting ourselves with our paranoia about any type of germ? There are seemingly thousands of antibacterial products out there, from soaps, lotions and cleaning products, to toys and mattresses. If you listen to the advertisers, we should live in a completely sanitized world. However, using antibacterial products that contain ingredients such as triclosan, may actually encourage the spread of antibiotic-resistant strains of dangerous bacterial pathogens, potentially creating drug-resistant “super-bugs”, while ridding us of the nonpathogenic common bacteria that may promote healthier immune systems. The trick is to find the balance of keeping our kids clean and healthy, while still exposing them to the beneficial side of dirt. Other than sending them outside with a bucket and spade, express instructions on making mud pies and hoping for the best, there may be another way in the future. There are scientists who are trying to determine which components of dirt provide the best protection without actually causing infectious disease. Once these components are identified, it may be possible to dose ourselves with nonpathogenic bacteria or parasites without risk of actual infection. Some scientists have proposed creating a “dirt vaccine” for children who grow up in overly clean environments. Studies using nonpathogenic mycobacteria (a species found in large numbers in dirt that is related to the bacterium that causes tuberculosis) to vaccinate children showed a much lower rate of allergies and asthma in these kids compared to unvaccinated children. There appear to be less lactobacilli in the guts of children who have allergies, and lactobacilli probiotics may inhibit development of atopic eczema. Allergic disorders have been reported to be less common in people with parasitic helminth infections. Until fairly recent history, most kids in the U.S. had intestinal worms. In many underdeveloped countries, they still do. In one study, volunteers who suffer from Crohn’s disease (a chronic inflammation of the intestines) were asked to drink the eggs of a pathogen-free species of parasitic worm. The patients went into remission. While this may give many of us the heebie-jeebies, it does suggest that there may be something to the hygiene hypothesis worth paying more attention to. In any case, as I frantically attempt to reach my toddler before she actually pops the ladybug she was moments ago studying with such ferocious intensity into her mouth, I think to myself that my kids at least, will probably not be needing the “dirt vaccine”. ### << Previous Next >> [ View All Perspectives ] |
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