Studies on Alzheimer Disease - Metformin Connection - A Brief Review

Metformin is the widely prescribed first line oral antidiabetic drug used in diabetes mellatus, type 2.
The global sales turnover of metformin runs into millions of dollars. The Increased risk of metformin
(Met) users for developing Alzheimer disease (AD) is reported first in a study conducted in 2011.
Since then, the subject has attracted the attention of the researchers as well as the pharmaceutical
industry, resulting in a number of studies, both clinical as well as experiments on animals. Confusing
results poured in, ranging from confirmation of the risk of AD to protection against developing AD,
making the scenario, all the more intriguing. Added to the confusion, is the diversity of various studies
as well as the parameters interpreting their results. Of the many clinical trials, some are retrospective
cohort studies (Tseng Chin-Hsiao [1]), case control studies (Imfeld P, et al. [2]) Randomised studies
(Hsu CC, et al. [3]), double blind, cross over pilot studies. (Aaron Koenig et al. [4]) and some
longitudinal studies (Ng TP, et al. [5]), besides studies doing meta analysis. Of these studies most of
the trials estimate the risk of development of dementia with metformin alone (Tseng Chin-Hsiao [1]) or
in comparison with other OHAs (Hsu et al. [3], Cheng et al. [6]). The other studies studied the effect of
metformin on the cognition (Moor EM, et al. [7]). These trials have different out come measures, (like
Hazard ratio, (HR) Odds (OR) ratio, relative risk (RR) etc.) which don’t mean one and the same. So
the multiplicity of the types of studies and different out- comes with different conclusions will be surely
baffling to an average reader who tries to take cognisance of the involved issues. The article attempts
to take stock of the overall developments in this regard. The author adopted a reader friendly
approach which is discussed in the article, at the outset. Finally, it is reiterated that future prospective
studies only can resolve the conflict of opinion on the nexus between metformin and Alzheimer’s
disease.