A google search of the Dope* didn’t come up with anything on this topic, so I thought I would toss it out there. I read an article on the Guardian site which lead to a cover story from two weeks ago in New Scientist.
The thrust of both articles is that
According to both, the evidence is starting to pile up for this theory. Which is pretty interesting and all, but what I’d like to know, particularly as a type II diabetic, is why haven’t I heard about this before? Apparently, the idea has been floating around for at least seven years, but I had to find it out reading British sites? In any case, I would be interested in everyone’s thoughts on the subject.
I’ve never used Google to search a specific site so I read through the posting on the subject, but I’ve no idea if it worked properly.
This seems like nothing but sloppy terminology, where “diabetes” is equated with “metabolic/diet related disorder”. Which is crap. Diabetes is a very specific set of symptoms (high blood sugar) and it’s caused by misregulation of insulin signalling (in type 2, your body becomes insensitive to insulin, and in type 1 your pancreas doesn’t produce insulin). If it turns out that Alzheimers is caused by high blood sugar or improper insulin signalling, I’d be ok with a “type 3 diabetes” label.
So apparently there’s evidence that poor diet contributes to Alzheimers. OK, what’s the mechanism? Poor diet causes all sorts of problems – and only one specific disease is called “diabetes”. We don’t label diet-related cardiovascular problems as “type 4 heart diabetes”.
And there are forms of Alzheimers that have absolutely nothing to do with diet or metabolism – early onset genetic forms are very well understood, and are clearly caused by mutations that make amyloid plaques form in the brain. The more common late-onset form is much less well understood, and I’d bet that there are several underlying causes. For some people, it may very well turn out that their Alzheimers is caused by dietary factors (along with a mix of other things). Once we can categorize Alzheimers by different cause, we should just name them “Alzheimers type 1”. Call it “type 3 diabetes” if and only if high blood sugar and insulin regulation cause the Alzheimers.
ETA: I dug into the links a little bit, and some researchers are hypothesizing that alzheimers is caused by insulin resistance in the brain. Which is reasonable, but renaming the disease is not a job for early-stage basic research. Even if it’s a really catchy way to start you talks…
Hmm. My previous post was mostly in response to the New Scientist piece, which was a fluffy piece of crap that didn’t even mention insulin or blood sugar. The Guardian piece, in contrast, is actually a nice bit of science reporting. “We cannot yet state unequivocally that poor diet is a leading cause of Alzheimer’s disease, though we can say that the evidence is strong and growing.” I can’t argue with that. But I don’t think we yet know anywhere near enough to rename or reclassify Alzheimer’s disease.
This started out as more of a General Question, although I see a bit of potential controversy. I am still leaning toward moving it to General Questions, but I will hold off to see whether a real debate breaks out.
For those interested in such things, here is one of the key papers (JCI April 2012) describing the notion of a ‘insulin resistant brain state’ in Alzheimer’s. The authors do, in fact, employ the term “type 3 diabetes” (found by doing a Ctrl-F in the article looking for “type 3”).
As an aside, some of you may question the very idea that the brain can exhibit insulin resistance if for no other reason than traditional teaching is that glucose metabolism in the brain is a non-insulin-dependent process. However, as demonstrated in this work (among others), “there is a significant element of brain glucose uptake that is insulin sensitive”.
Intriguing. I’ll quote from that JCI 2012 paper, though:
And that study doesn’t really say whether insulin resistance causes alzheimers or vice versa. In fact, they mention that there’s a plausible mechanism for the reverse being true: Aβ oligomers inhibit the insulin receptor. Causality is particularly tricky in Alzheimers disease; we still don’t really know whether amyloid plaques are a cause or effect of the disease.