Researchers in Australia have explored possible reasons why people with diabetes are at a higher risk of developing Alzheimer’s disease.
Their findings suggest that diabetes could be contributing to brain cell loss by driving a build-up of the hallmark Alzheimer’s protein tau, even in people not affected by Alzheimer’s. The study is published on September 2 in the online version of the journal Neurology.
Damage to the brain in Alzheimer’s disease is thought to be driven by a build-up of the proteins amyloid and tau, which interfere with the way nerve cells work and communicate and result in symptoms like memory loss and confusion. While scientists have known for some time that people with type 2 diabetes are more likely to develop Alzheimer’s, they don’t yet fully understand the mechanisms leading to this increased risk.
This study, led by a team at the University of Melbourne, examined data collected from 816 older people who had taken part in a large US brain imaging study called the Alzheimer’s Disease Neuroimaging Initiative. The participants included 191 people with Alzheimer’s disease, 397 with early memory problems called mild cognitive impairment, and 228 people who had no memory and thinking problems. A total of 124 people had type 2 diabetes.
The researchers analysed samples of participants’ cerebrospinal fluid (CSF) – a clear substance which surrounds the brain and carries away waste material – for indications of a build-up of amyloid and tau in the brain. In order to study any differences in the structure of participants’ brains, the researchers also examined brain scans.
While the study found no relationship between diabetes and levels of the amyloid protein, the results showed that people with diabetes had greater levels of the tau protein in the CSF, indicating more tau clumping together as tangles in the brain. The researchers found this relationship in those people who didn’t have a diagnosis of Alzheimer’s, as well as those with memory and thinking problems. Brain scans revealed that people with diabetes also tended to have a thinner cortex – the outermost layer of the brain which is responsible for language, problem solving, storing memories and many other aspects of thinking. The link between diabetes and the thickness of the cortex was found to exist regardless of whether the participants had memory and thinking problems or not.
The study authors concluded that brain cell loss from diabetes could be separate from the usual course of Alzheimer’s disease. They suggest that diabetes could be adding to damage caused by Alzheimer’s by leading to more tau tangles but not a build-up of the amyloid protein.
Dr Simon Ridley of Alzheimer’s Research UK said:
“We have known for some time that there is a strong link between Alzheimer’s and diabetes, and clinical trials are currently underway to determine whether medications for diabetes could benefit people with Alzheimer’s. While these trials are promising, we still do not fully understand the molecular mechanisms linking the two conditions.
“The research suggests diabetes could damage the brain through a protein called tau, rather than through damage to blood vessels, but as the study was just one snapshot in time, it’s hard to determine cause and effect. Previous research has indicated an association between diabetes and the Alzheimer’s protein, amyloid, so more research will be necessary to build a clearer picture in this complex area. It’s interesting to see that the brain changes associated with diabetes seemed to be independent of dementia but it would be important to see if people with those changes were more likely to go on to develop the condition in future.
“Diabetes is one risk factor for Alzheimer’s but the disease is caused by a complex mix of age, genetics and lifestyle factors. Current evidence suggests that not smoking, keeping blood pressure and cholesterol in check, eating a balanced diet, drinking in moderation and staying mentally and physically active call all help to maintain brain health as we age.”