|
This item originally appeared in the March 2009 issue of Lifescape magazine EpidemicThe developed world is in the middle of an epidemic of allergies. The rate in the UK has been rising for at least 50 years, and rising steeply for the last 20. A large study in 2007 found an increase of 27 per cent over just four years; in 2005 one person in nine in the UK had a recorded diagnosis of “any allergic disease” (who knows how many haven’t bothered to get diagnosed). Hospital admissions, not the most reliable indicator, but most liable to underestimate, for food allergy rose, in the period 1990-1 to 2003-4, 5-fold in adults and 6.5-fold in children (Chart 1). The same pattern prevails for asthma, hay fever and every form of allergy. Anaphylaxis admission rates have risen even faster — 7-fold over the same period. Why?Each succeeding generation or birth cohort has more allergies than the previous, and each cohort has more allergies as they get older. While we know that allergies in general do have genetic components, our genes cannot change perceptibly over 50 years, so that can’t explain it. Why then such an increase? One explanation that has become popular is the “Hygiene hypothesis”; this suggests that exposure to lots of infections in childhood is healthy for the immune system, and that we have all cleaned up our homes too much, and we should let our kids eat a bit of dirt now and then. |
Nobody has really tested this theory, and there is one big problem with it; dirt just isn’t what it used to be. When I was a medical student, long ago, we were taught that indoor dirt was made up in large part of human skin debris, plus stray food, bits of soft furnishings etc. That’s no longer true; we think of dirt as dusty dry stuff, but the dirt inside our homes has a large enough oil component that it forms an oily film on any surface, made up of oils from us, from cooking, from exhaust pollution and so on and on. And because most of the environmental pollutants around us are fat-soluble (that’s why the first step in the body’s detoxing and excretion process is to make them water-soluble), they will absorb into that film. Every time someone touches the surface they pick up a bit of both the oil and the pollutants. Some recent studies looked at this and in particular at the levels of PBDEs (polybrominated diphenyl ether flame retardants). You can find a good summary of all this at Rachel’s Democracy and Health News, http://www.precaution.org/ — an excellent subscribable newsletter. Flame retardants must be put in soft furnishings by law, and some of the boards in your computer may be as much as 40% flame retardant. No surprise then that the US researchers found levels of PBDEs were 20 times higher inside the houses than outside. |