Wednesday, December 9, 2009

More germs = less disease?

So says an article in today's Science Daily, which reports on a recent study at Northwestern of children from the Philippines. The study finds that children from the Philippines have much lower levels of C-reactive protein (CRP), which indicates better resistance to disease. Exposure to germs was much higher for the children in the Philippines.

So what's wrong with this study? It's a very tenuous association, and from what I can gather in the articles, no attempt was made to ensure the children in the U.S. that were compared to the children in the Philippines were similar in other ways. They might be different in CRP due to other environmental or hereditary factors. Perhaps it's the weather? The diet? One of any number of things could account for the difference.

In addition, the study appears to ignore the much higher infant mortality rate and much lower life expectancy in the Philippines (you can try for life expectancy and other information by country). In other words, even if higher germ exposure does mean lower CRP, does it actually mean less disease and longer life? The broad indication is that it does not.

In order for the study to be valid, it needs to adjust for whatever inherent differences (in addition to germ exposure) exist between Phillipino and US children, and then see if CRP levels are still different. An even better way to do such a study would be to study children living in similar environments (same place, socio-economic situation, etc.) and determine if the ones exposed to more germs had lower levels of CRP when they reached adult-hood.

I've seen articles (see this for example, but I can't find a more definitive one at this time) that indicate that children with early exposure to farm animals have fewer allergies, but nothing showing exposure to more serious germs is good. And some of the germs that we are exposed to are more than just common germs--they are deadly. It might be that those who are exposed to these deadly germs early, and live, are much better off later in life, but that is no reason to expose them to those germs unnecessarily. Of course, you wouldnt give your child a deadly disease so that, if they survived, they'd be resistant to it later in life.

We live in a society that is sometimes alarmist concerning germs, and I have written about this. Yet this doesn't mean that, on the whole, a clean environment does not promote good health, and the article cited above seems to only have the most tenous of indications that it may not.


Jonathan Scott said...

Combining this study and the following article, maybe letting kids use germ infested cell phones is actually good for them:

Sounds like survivor bias. Like when people will say, "We didn't use car seats when I was a kid, and we grew up fine!". Well, those of you that survived grew up fine.

冰冰有理 said...
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Alan Salzberg said...

Not sure what the chinese one says...anyone care to translate?

Alan Salzberg said...

Found out the chinese one is an ad--having nothing to do with probability!

CrisisMaven said...

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Tom Rees said...

If you read the paper (, you can see that they base their conclusions upon the statistical association between infections and CRP levels within the Phillipines cohort:

...higher levels of microbial exposure in infancy were associated with lower CRP. These associations were independent of socioeconomic status, measures of current body fat and other health behaviours.

The comparison with the US is just the University's press officer attempting to make the story newsworthy.