Wednesday, June 28, 2006

What doesn't kill you...

Immersing yourself in a moderate amount of filth might be a way to self-innoculate:
Gritty rats and mice living in sewers and farms seem to have healthier immune systems than their squeaky clean cousins that frolic in cushy antiseptic labs, two studies indicate. The lesson for humans: Clean living may make us sick.

The studies give more weight to a 17-year-old theory that the sanitized Western world may be partly to blame for soaring rates of human allergy and asthma cases and some autoimmune diseases, such as Type I diabetes and rheumatoid arthritis. The theory, called the hygiene hypothesis, figures that people's immune systems aren't being challenged by disease and dirt early in life, so the body's natural defenses overreact to small irritants such as pollen.

The new studies, one of which was published Friday in the peer reviewed Scandinavian Journal of Immunology, found significant differences in the immune systems between euthanized wild and lab rodents.
This sounds plausible. It's basically the same concept we use for most shots--take small injections of the disease now so the body will build an immunity to more threatening levels in the future.

But I'm not yet convinced. I wonder about the relationship between these diseases and a population's median age. This study found the average age of incidence for rheumatoid arthritis to be 58 (and a decreasing trend in disease rate). The Western world is old and getting older. In addition to becoming top-heavy with entitlement obligations that will smother a shrinking youthful base, the West is collectively going to witness a steady increase in medical costs and a general decrease in the average health of its citizenry as it ages.

A bigger question mark exists in the actual subjects of the study:
Parker said his study has drawbacks because he can't be sure that the age of the wild and lab rodents are equivalent, although he estimates the ages based on weight. He also could not control what happened in the past to the wild rats to see if they had unusual diseases before being captured and killed.
The survival rate of lab rats compared to feral sewer rats strikes me as being of larger concern. If the average age of both cohorts was two, what proportion of lab rats make it to the age of two? What's the survival rate to the age of two for sewer rates? Lower than that of lab rats, presumably. What if in the wild, generally less healthy rats die off earlier, while in the lab all are preserved (outside of experimentation)? It seems to me that causation can only be, at best, speculated about. Immune strength might be coming from natural selection, not a Lamarckian enhancement of general immune system functionality.

A rough analogy: A la Battle Royale, 100 children are thrown into the tundra with the simultaneous release of rabid pit bulls in the area. Twenty children make it out alive, the rest are ripped to shreds. Those twenty are then put into an experiment testing athleticism along with twenty other randomly selected children from the area. Not surprisingly, the twenty children who managed to avoid rabid pit bulls in the tundra are in better shape than the twenty average kids.

This hardly suggests that being exposed to rabid pit bulls makes one more athletic. But over successive generations, if one line was constantly chased by pit bulls and another lived softly, the former would become more athletic. This might be a silly microcosm for the world today, where countries with higher mortality rates selecte for stronger immune systems among their populations. That takes us to the epigonic discussion of college kids after a night of Halo--are humans destroying themselves with medicine like an overgrown forest that's not allowed to burn from time to time?

To know for sure, Parker should separate lab rats into two cohorts at birth, with one being exposed to various diseases comparable to what would be experienced in the sewer, while the other is kept immaculate, and then at some point in the future compare the immune system functionality (and mortality rate) of the two groups.

++Addition++Parker already plans on doing just that:
Parker said he hopes to build a 50-foot artificial sewer for his next step, so that he could introduce the clean lab rats to an artificial dirty environment and see how and when the immunity was activated.
The data that this elicits will be more conclusive.


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