Surprising everyday non-prevention

The NZ$ Herald (from the Telegraph) has a headline Five surprising everyday medications that can help prevent dementia. This is surprising, because the general consensus is that we don’t really have any medications to prevent dementia.

The first example is the shingles vaccine. Here there’s actually some evidence — a ‘natural experiment‘ in Wales, where the roll-out of the vaccine meant people born just before and just after a particular date had different eligibility.  This isn’t quite a randomised trial, since there are other things that vary by birth date, but it’s better than the usual correlations. In particular, it’s better because the claimed effect is pretty small: a 20% reduction in risk, which is much too small to see reliably in the usual correlational studies.  This one is also good because any dementia prevention is a pure bonus; you should already want to get the shingles vaccine to prevent shingles.

Next in the story are statins, the widely-used cholesterol-lowering drugs.  Here the headline evidence is correlation, saying a reduction of 13% in dementia risk was seen in statin users in a Korean study. People have been suggesting statins as dementia prevention for at least twenty-five years and the main change is that the estimates of benefit have gotten a lot smaller.  Again, it may not matter a lot whether this is true — if you’d benefit from statins for dementia prevention you’d probably benefit from them for heart attack prevention.

Viagra is always popular in settings like this — it’s already a repurposed drug, and it’s relatively safe — but for Viagra we don’t even have correlations, just the claim that it opens up smaller blood vessels and that maybe nitric oxide (which Viagra increases) is related to memory in some way we haven’t discovered.

The trendy new drug semaglutide is on the list, again for correlations.  It could be that they really prevent dementia (and if so, we will find out from clinical trials now underway) but it’s also quite feasible that it’s just correlation.  The basis of the claim is that people who got a new expensive injected treatment in short supply for diabetes had fewer new cases of dementia in the short term than people who got a standard drug treatment. This could easily be reversing cause and effect — people with mild pre-dementia symptoms could easily be less likely to get the fancy new drugs.  In New Zealand, it doesn’t really matter if Ozempic prevents dementia, since you can’t actually get it.

And finally, the old TB vaccination that we don’t use any more is on the list. That’s actually somewhat supported by randomised trials, but the trials are in bladder cancer patients who get the BCG bacteria injected into the bladder rather than being trials of ordinary vaccination.  More research is needed before this one could really be described as “can help prevent dementia”. It’s also worth noting that we stopped routine BCG vaccination for a reason: being vaccinated means you can’t straightforwardly be tested for TB exposure.

Overall, this is another example of the “aliens” problem with dementia research.  There aren’t any breakthroughs and there are very few promising treatments. It’s a very hard problem, like detecting alien life, so the news we get is either  genuine early research — “planet hundreds of light years away is the right temperature for liquid water” — or it’s crop circles and flying saucers.