Over a five-year study period, patients taking metformin had a 20 percent reduced risk of developing dementia compared to those taking sulfonylureas.
Study author Dr. Rachel Whitmer, an epidemiologist in the division of research at Kaiser Permanente in Oakland, CA, said, "Metformin could have a possible neuroprotective effect in the brain." She emphasized, however, that, "This was an observational, retrospective, population-based study. We found an association, but didn’t prove cause and effect."
People with type 2 diabetes have double the risk of developing dementia compared to someone without diabetes, according to background information in the study. To see if any therapies might offer some protection against dementia, Whitmer and her colleagues reviewed data on nearly 15,000 people with type 2 diabetes who were just starting single-drug therapy for their disease.
All of those included in the study were aged 55 or older, and all had been diagnosed with type 2 diabetes. Whitmer said none of them were newly diagnosed; some had even been diagnosed with type 2 diabetes as long as 10 years earlier. But none had been taking medications for their disease when the study began.
"They initiated one of four single-agent therapies: metformin, sulfonylureas, thiazolidinediones (TZDs) or insulin," Whitmer said.
During the study, nearly 10 percent of the patients were diagnosed with dementia. (The study did not differentiate between Alzheimer’s disease and other forms of dementia.)
Compared to people taking sulfonylureas, those on metformin had a 20 percent decreased risk of developing dementia, according to the study. There was no difference in dementia risk for those on TZDs or insulin compared to those on sulfonylureas.
The researchers controlled the data for a number of factors, including age, duration of diabetes, blood sugar control, race and education, Whitmer said.
So what is it about metformin that might help protect the brain? Whitmer said one theory stemming from animal research is that metformin may play a role in the development of new brain cells. It has also been linked to reduced inflammation, she added.
Whitmer hopes to do more research to determine whether the long-term use of metformin would have an even greater effect, whether larger doses make a difference, and whether there would be a difference in risk reduction based on the type of dementia.
For now, she said, it’s important to remember this: "The brain isn’t isolated. When you think about your brain health you should be thinking about whole body health, and think about it over your life course. Dementia shows up late in life, but those changes start a decade or more before they show up. What’s good for the health of the heart is also what’s good for the brain."
Presented at the Alzheimer’s Association International Conference in Boston, July 2013