(This article was originally published at Statistical Modeling, Causal Inference, and Social Science, and syndicated at StatsBlogs.)
Mark Tuttle points to a post, “Common anticholinergic drugs like Benadryl linked to increased dementia risk” by Beverly Merz, Executive Editor, Harvard Women’s Health Watch. Merz writes:
In a report published in JAMA Internal Medicine, researchers offers compelling evidence of a link between long-term use of anticholinergic medications like Benadryl and dementia. . . .
A team led by Shelley Gray, a pharmacist at the University of Washington’s School of Pharmacy, tracked nearly 3,500 men and women ages 65 and older who took part in Adult Changes in Thought (ACT), a long-term study conducted by the University of Washington and Group Health, a Seattle healthcare system. They used Group Health’s pharmacy records to determine all the drugs, both prescription and over-the-counter, that each participant took the 10 years before starting the study. Participants’ health was tracked for an average of seven years. During that time, 800 of the volunteers developed dementia. When the researchers examined the use of anticholinergic drugs, they found that people who used these drugs were more likely to have developed dementia as those who didn’t use them. Moreover, dementia risk increased along with the cumulative dose. Taking an anticholinergic for the equivalent of three years or more was associated with a 54% higher dementia risk than taking the same dose for three months or less. . . .
Scary. But then I scroll down, and here’s the very first comment, from Joe (no last name):
Took a look at the study
The diffence between the people that were in the non users and heavy users is massively different. 3x higher on EVERY risk factor stroke, obese, etc.. Odd this would get so much traction with the press.. Borderline irresponsible of Harvard to publish this on their blog. Nothing here even hints at causality
So whassup? I can click too . . . so let’s see what the study says.
They used Cox proportional hazard regression, adjusting for a bunch of background variables:
They excluded people where any of these covariates were missing.
And here are their results:
Seems pretty clear. Although I guess they’re relying pretty heavily on their regression model. Maybe it would make sense to clean the data first by doing some matching so that you have treatment and control groups that are more similar, before running the regression.
Anyway, this all indicates some of the challenges of statistical communication.
For more, see this article by Natalie Smith with the provocative title, “Clinical Misinformation: The Case of Benadryl Causing Dementia,” and this article by Cynthia Fox with the opposite spin: “Strong Link Found Between Dementia, Common Anticholinergic Drugs.”
Tuttle writes:
For all the reasons this article speculates on this could be true – these medications cause dementia.
But, as you know only too well there are so many confounding variables here – the simple one is that currently unknown precursors of dementia cause people to take these drugs.
I don’t really know what to say here. On one hand, yes, lots of potential confounders, also the usual issues of statistical uncertainties, garden of forking paths, etc. On the other hand, it does seem valuable for researchers to find out what is currently happening. The whole thing is a challenge, especially given people’s inclination to base their views on N=1 anecdotal evidence.
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