Cause or Effect?

There was a fascinating article in the New Scientist this week discussing a new hypothesis about the cause of Alzheimers, called "We may finally know what causes Alzheimer’s – and how to stop it,” by Debora MacKenzie. Wouldn’t it be amazing if they have finally figured out how to treat this terrible disease?

To summarize this article, there is suggestive evidence that the bacteria, Porphyromonas gingivalis, that causes chronic gum disease may also cause Alzheimer's either by directly attacking brain tissue or indirectly through producing toxic enzymes called gingipains that slice up tau proteins in ways that causes damage to neurons.

This supersedes a previous theory that amyloid plaques invade the brain to cause alzheimers. The recent study suggests that amyloid plaques are in fact produced in the fight against the bacteria, so are a side effect rather than a cause. (This earlier history is nicely summarized here - this article also covers some of the prion theories.)

It’s fascinating how complicated these studies are, and how difficult it is to isolate correlation, cause, and effect. One minute something is thought to be the cause; the next, it’s dumped into the effect category.

This reminded me of another article I remember from several years ago about the Nun Study which looked at other major factors that seem related to the development of Alzheimers. One of the studies suggested that people who are less mentally and physically active outside their jobs when young have an increased risk of Alzheimer’s in later life than their more active counterparts. Use it or lose it? The same study also found that positive outlook early in life was also linked to longer and healthier life.

Now you’ll have to excuse me. I’m going to go brush my teeth and read a funny book.

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