A common type 2 diabetes drug called metformin may have an unexpected, but positive, side effect: New research suggests that people taking the drug appear to have significantly slower declines in thinking and memory as they age.
"Our six-year study of older Australians with type 2 diabetes has uncovered a link between metformin use and slower cognitive [mental] decline and lower dementia rates," said study author Dr. Katherine Samaras. She's the leader of the healthy aging research theme at the Garvan Institute of Medical Research in New South Wales, Australia.
"The findings provide new hope for a means of reducing the risk of dementia in individuals with type 2 diabetes, and potentially those without diabetes," Samaras said.
Metformin helps the body use the hormone insulin more effectively. It's known as an insulin sensitizer. Insulin helps usher sugar into the body's cells to be used as fuel. People with type 2 diabetes don't use insulin effectively. This is called insulin resistance.
"Metformin is an insulin-sensitizing medication. However, it has a number of other effects in cells which allow them to remain metabolically healthy," Samaras explained.
Samaras noted that experts think that type 2 diabetes or insulin resistance may play a role in the degeneration of brain and nerve tissues, as well as lead to harmful changes in blood vessels. By boosting how well insulin works in the body, metformin may help hold off some of this damage.
The study followed more than 1,000 people, aged 70 to 90, for six years. At the start of the study, all of the volunteers were living at home and had no signs of dementia. They underwent a series of neuropsychological tests every two years.
Among the participants, 123 had diabetes and 67 were taking metformin.
People with diabetes who didn't take metformin had a five times higher risk of developing dementia during the study, the investigators found.
The researchers noted that this isn't the first study to show that metformin might be linked to lower dementia risk. Other studies have found a similar association. The authors aimed to see if the drug made a difference in declines in memory and thinking in an older group of people.
Samaras and her colleagues are now planning a three-year, randomized controlled clinical trial of metformin in people who don't have diabetes but who do have a high risk of developing dementia.
"Our study has provided promising initial evidence that metformin may protect against cognitive decline. [The new] trial will reveal whether metformin can assist in preventing against cognitive decline in older people more broadly," she said.
Metformin is an inexpensive drug and has few side effects, Samaras noted. Side effects, such as digestive problems, typically occur during the first few weeks of taking the drug and then subside.
The findings were published online Sept. 23 in Diabetes Care.
Heather Snyder, vice president of medical and scientific relations at the Alzheimer's Association, said while this isn't the first study to show metformin's possible brain benefits, this is "a big population and a different population followed over a period of years, specifically for this question. It's always encouraging to see similar results in different populations."
Snyder said it's hard to know exactly how metformin is helping to slow memory and thinking problems. But there are a number of trials looking to see whether or not metformin might be an effective treatment for slowing the onset of dementia. There's a large nationwide study in the United States, and British researchers will be looking at how metformin combined with healthy lifestyle changes might impact the risk of dementia.
In the meantime, if you'd like to take steps to potentially lower your risk of dementia, Snyder recommended talking with your doctor about what you can do, such as exercise regularly, eat a healthy diet and be socially engaged (as much as is safely possible during the coronavirus pandemic).
Learn more about possible ways to prevent dementia from the Alzheimer's Association.