It’s one of the most widely used prescription drugs in the world, hailed for its ability to lower blood glucose levels, impressive safety profile, and low cost. Metformin — the first-line oral drug for Type 2 diabetes — has been prescribed in Europe since the 1950s and the United States since 1995, and achieved much of its formidable reputation through the UK Prospective Diabetes Study (UKPDS), published in 1998.
But a new study may have slightly dimmed — possibly just for a moment — metformin’s bright halo. The study — not yet published, but presented last week at the 13th International Conference on Alzheimer’s and Parkinson’s Diseases in Vienna — looked at about 9,300 people with Type 2 diabetes in Taiwan for up to 12 years. As noted in a Medscape article on the study, during the follow-up period, the risk of participants who took metformin developing Alzheimer’s or Parkinson’s was more than twice as high as it was for those who didn’t take the drug. This was true even after adjusting for certain characteristics — like age and diabetes severity — that might affect whether someone was taking metformin in the first place.
The risk of developing Parkinson’s disease, in particular, was 2.27 times as high in participants who took metformin as in those who didn’t. The risk of dementia from all causes was 1.66 times as high, and the risk of Alzheimer’s in particular was 2.13 times as high. Overall, taking a higher dose of metformin and taking it for a longer duration were both associated with a higher risk of developing one of the measured conditions. For example, taking metformin for less than 180 days was associated with a 1.77-times-as-high risk of Parkinson’s, while taking the drug for 400 days or longer was associated with a 4.49-times-as-high risk of Parkinson’s. Similarly, taking metformin for less than 180 days was associated with a 1.02-times-as-high risk of developing dementia — barely any different than not taking the drug — while taking the drug for 400 days or longer was associated with 2.84-times-as-high risk of dementia.
Of course, it’s possible that the outcomes found in the study aren’t directly related to metformin, but rather to some unknown third factor that links taking metformin to developing Parkinson’s or Alzheimer’s. It’s also possible that even if metformin does somewhat increase the risk for these conditions, it’s not the only diabetes drug or treatment that does this. For this reason, the researchers stated their intention to look at the effects of other treatments — like insulin and sulfonylureas — in future studies.
It’s worth noting that some doctors and other medical experts, when presented with the study’s findings, didn’t believe that they were valid due to the lack of similar findings in previous large-scale studies of people with diabetes. In any case, one relatively small study of this nature should be considered an outlier unless it’s confirmed by other, preferably larger studies.
What’s your reaction to this study — are you alarmed that taking metformin might raise the risk of developing Alzheimer’s or Parkinson’s? Even if this risk were to be confirmed by other studies, would you be comfortable taking metformin if its health benefits in other areas (like cardiovascular health) outweighed its risks, in terms of overall longevity? Do you think it would be reasonable to reconsider taking a drug if you’re personally more afraid of one risk that it raises — like Alzheimer’s — than another even greater risk that it lowers, like heart disease? Leave a comment below!