Diabetes and dementia, connection found

By Dr. Ananya Mandal, MDSep 20 2011

A new study revealed that people with diabetes may be at an increased risk of developing dementia. Scientists have suspected the link between the two diseases for several years, but several experts say this latest study highlights how treating preventable diseases like diabetes and obesity may be useful in preventing the onset of dementia.

“Our findings emphasize the need to consider diabetes as a potential risk factor for dementia,” said study author Dr. Yutaka Kiyohara, of Kyushu University in Fukuoka, Japan. “Diabetes is a common disorder, and the number of people with it has been growing in recent years all over the world. Controlling diabetes is now more important than ever.”

Kiyohara’s team began studying residents of the town of Hisayama, Japan, in 1961, monitoring the numbers of people who got cardiovascular diseases. In 1985, they began measuring the numbers of people who developed dementia. The researchers followed more than 1,000 people for an average of 11 years.

Results showed that 27 percent of the people with diabetes developed dementia, compared with 21 percent of people without diabetes. The study was published in the latest issue of the journal, Neurology. Researchers found that people with diabetes were twice as likely as the other study participants to develop Alzheimer's disease within 15 years. They were also 1.75 times more likely to develop dementia of any kind.

Dr. Richard Caselli, a neurologist at the Mayo Clinic, said the connection isn't particularly new, but its implications for the importance of treating diabetes are. “Nobody doubts that diabetes is associated with a higher incidence of dementia,” Caselli said. “But this is one more reason for people to be aware of the potential ravages of diabetes and to treat it aggressively and adequately and try to prevent consequences.”

According to the American Diabetes Association (ADA), 25.8 million adults and children have diabetes in the United States, creating $174 billion in health care costs. And 79 million more Americans are prediabetic. Add those numbers to the $183 billion it costs to care for the 5.4 million Americans who have Alzheimer's disease. “Given how common diabetes is, we would expect that the economic implications would be tremendous, if it was linked to dementia,” said Dr. Zoe Arvanitakis, a neurologist at Rush Alzheimer's Disease Center in Chicago.

“There is some evidence that the brain is very sensitive to fuels like sugar and hormones like insulin,” said Dr. Joel Zonszein, a professor of clinical medicine at the Albert Einstein College of Medicine. “How exactly it happens is really speculation, we really don't know.”

Diabetes could contribute to dementia in several ways, which researchers are still sorting out. Insulin resistance, which causes high blood sugar and in some cases leads to type 2 diabetes, may interfere with the body's ability to break down a protein (amyloid) that forms brain plaques that have been linked to Alzheimer's. High blood sugar (glucose) also produces certain oxygen-containing molecules that can damage cells, in a process known as oxidative stress.

“Having high glucose is a stressor to the nervous system and to the blood vessels,” says David Geldmacher, M.D., a professor of neurology at the University of Alabama at Birmingham. “The emerging information on Alzheimer's disease and glucose shows us that we do need to remain vigilant on blood sugar levels as we get older.” Another recent study showed that an insulin-based nasal spray was effective against the symptoms of Alzheimer's disease.

However, Dr. Michael Perskin, chief of geriatrics at New York University's Tisch Hospital, said preventing more cases of diabetes doesn't necessarily mean that the numbers of people with dementia will dwindle. “If people aren't dying of strokes and heart attacks, they're living longer and are more likely to get dementia,” Perskin said. “If you do a good job of treating cardiovascular symptoms, of course you're going to see more dementia.”

The next step say researchers will be to understand whether controlling blood sugar and reducing risk factors for type 2 diabetes also reduces dementia risk.