People with diabetes are at significantly higher risk of developing all types of dementia, including Alzheimer's disease, finds a new study that bolsters previous research connecting the two illnesses.
The study of more than 1,000 people in Japan found that 27% of those with diabetes developed dementia, compared to 20% of people with normal blood sugar levels.
"We have clearly demonstrated that diabetes is a significant risk factor for the development of dementia, especially of Alzheimer's disease, in (the) general public," said Dr Yutaka Kiyohara, a professor in the graduate school of medical science at Kyushu University in Fukuoka.
The study, conducted from 1988 to 2003, is published in Neurology. Noting the global increase in type 2 diabetes, Kiyohara said controlling the illness is more important than ever.
Diabetes and dementia linked
The study followed 1,017 men and women, age 60 and older, who took a glucose test to find out if they were diabetic or pre-diabetic. They were then tracked over an average of 11 years each. In all, 232 developed dementia, either Alzheimer's, vascular dementia, all-cause dementia or another form.
Of the 150 who had diabetes, 41 developed dementia, compared to 115 of the 559 people without diabetes. Among the 308 people with pre-diabetes, 76, or 25 %, developed dementia.
Even having high levels of sugar two hours after taking glucose was linked to dementia, the researchers said, noting the importance of consistent blood sugar control.
Diabetes affects close to 26 million children and adults in the United States, with 7 million of them undiagnosed, according to the American Diabetes Association. Another 79 million have pre-diabetes. Obesity increases the risk of diabetes, and as Americans become heavier, more are developing diabetes.
In type 2 diabetics, the more common form of the disorder, people don't have enough of the hormone insulin to convert glucose in food into energy, or they don't process insulin properly.
Diabetes control demands a careful diet, exercise and, in some cases, insulin or other medications. If not properly managed, the illness can cause blindness, kidney and heart disease, and even death.
Treating dementia with insulin
While prior research has shown a link between diabetes and dementia, the Japanese study is important because of its size and duration, said another expert.
"This is a large study over a long period of time showing a possible connection between diabetes and dementia," said Heather Snyder, senior associate director of medical scientific relations at the Alzheimer's Association in Chicago. "We do know that diabetes increases the risk of dementia, but we don't really know why."
Snyder said the Alzheimer's Association is funding the next step in recently reported research that showed success treating early dementia with insulin.
"The last two years have been a very exciting time in research about Alzheimer's," she said. Alzheimer's, an age-related brain disorder, gradually interferes with thinking and functioning.
Another expert noted that diabetes could be connected to dementia because it contributes to vascular disease, disrupting the flow of oxygen to the brain and other organs.
"Diabetes is a major risk factor for vascular disease," said Dr Spyros Mezitis, a clinical endocrinologist at Lenox Hill Hospital in New York City. "If the blood vessels are not allowing enough oxygen to get to the brain, you can get dementia."
The study will "change the way we practise medicine" and could lead to quicker referral of diabetics to neurologists when they show signs of memory loss or other cognitive problems, he said.
The goal for patients is to avoid the progression of vascular disease and to maintain proper blood sugar levels, he noted.
More research on the scale of the Framingham heart study is needed, said Snyder, referring to a multi-generational study begun in 1948 in Framingham, Mass., that has contributed enormous amounts of data about cardiovascular disease.
To learn more about Alzheimer's disease, visit the U.S. National Institute on Aging.
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