Diabetics with high blood sugar levels score worse on tests of brain power later in life than those whose levels are under control, according to a new U.S. study.
The findings suggest that people who control their blood sugar or glucose levels early in life may also protect their brain's health, but the topic needs further study, the researchers write in the Annals of Internal Medicine.
"It gives you an enormous window of opportunity for prevention," said coauthor Dr. A. Richey Sharrett. "After all, I think people dread dementia more than they dread anything in old age."
It's well known that type 2 diabetes, in which the body can't control the amount of sugar in the blood, is linked to an increased risk of dementia. Less in known about the condition's relationship to cognitive decline, which precedes dementia and includes noticeable forgetfulness, absentmindedness and impulsiveness.
Sharrett, of the Johns Hopkins Bloomberg School of Public Health in Baltimore, told Reuters Health by phone that the new study may provide the best data yet that diabetics can avoid more dramatic cognitive decline with better control of their condition.
His team studied data on 13,351 adults from four U.S. communities, whose brain health was evaluated at three visits between 1990 and 2013. On average, participants were about 57 years old when they entered the study. About a quarter were black, and about 13 percent had diabetes.
Read: Diabetes and the brain
The results of the study
People with diabetes had a greater cognitive decline during the study, compared to people without diabetes. Also, people with so-called pre-diabetes had a steeper decline than people without pre-diabetes.
People with uncontrolled diabetes at the first visit had an even steeper decline over the 20 years than those who had their condition under control, they found.
Also, cognitive decline was steeper among people who were living with diabetes longer, compared to those who were more recently diagnosed.
"The earlier the prevention starts, the greater the benefit may be," Sharrett said.
Those without diabetes but with high blood sugar at that first visit also experienced greater cognitive decline during the study period, compared to those with better blood sugar control.
The suggestion that better blood sugar control can slow cognitive decline is in contrast to previous studies that found better blood sugar control among elderly participants doesn't affect brain power.
"This one says you got a 20-year lead time," Sharrett said. "You can do something about it now, when you're in your 50s - not later."
Lawrence Reagan, who was not involved with the new research but studies the effects of obesity and diabetes on the brain, said by phone that a number of factors linked to diabetes may lead to cognitive decline and dementia.
"I think that their data are very compelling," said Reagan of the University of South Carolina School of Medicine in Columbia. "It provides further support for a concept that should be pretty easy for people to understand."
For example, poor control over blood sugar can create an environment that decreases neuroplasticity, which ultimately makes the brain function as if it were older.
"We're getting more and more evidence that if your blood glucose levels are higher - even if you don't have diabetes - your cognition could be worse," said Gail Musen, who was also not involved with the new study.
The new study also strengthens the calls for people to take better care of themselves during the middle of their lives, said Musen of the Joslin Diabetes Centre in Boston.
"Take care of yourself in midlife, because even small differences in glucose levels, which can be modified by diet, exercise and lifestyle, will affect your brain and cognition when you're older," she said.
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