Insulin resistance, a key component of type 2 diabetes, may contribute to language problems in women that can potentially signal early dementia, new research suggests.
The association was not seen in men, although the researchers could not determine exactly why that was so.
In the study, the Finnish researchers measured what is called low verbal fluency, which is the rate at which you produce words.
"Preclinical Alzheimer's disease typically starts with episodic memory decline. However, verbal fluency is a measure of executive function, and also deficits in executive function can be found early in the disease," said study author Dr. Laura Ekblad, a researcher at the University of Turku. Executive function includes higher-order processes such as working memory, planning and problem solving.
But Ekblad added that the findings aren't cause for immediate concern for women. She said that due to the design of the study, they could only show an association between insulin resistance and low verbal fluency. "We cannot show cause-and-effect," she explained.
"Not all individuals with insulin resistance will develop cognitive [thinking and memory] impairment or dementia later in life," she added.
Still, another expert noted that increasing evidence is linking insulin resistance and type 2 diabetes to memory troubles.
And the relationship between gender and Alzheimer's disease has been a very hot topic in research lately, said Keith Fargo, director of scientific programs and outreach at the Alzheimer's Association.
"The majority of people with Alzheimer's disease are women. Women are about twice as likely to get Alzheimer's disease. What we don't know for sure is why," Fargo said.
The current study, published August 12 in the journal Diabetologia, included almost 6,000 people in Finland. Their ages ranged from 30 to 97, with a mean age of 52.5 years. The researchers tested brain health using a variety of tests, including verbal fluency. To test verbal fluency, the study volunteers were asked to name as many animals as they could in 60 seconds.
The investigators also looked at whether or not people had insulin resistance, and if they had a gene that's linked to a higher risk of Alzheimer's disease called APOE-E4.
Insulin is a hormone that helps cells use sugar from foods as fuel. When someone develops insulin resistance, they still produce enough insulin, but it doesn't work as effectively.
The researchers found that women with higher levels of insulin resistance were more likely to score poorly on the verbal fluency test.
"Poorer scores could be noticeable in difficulties or slowness in trying to name several objects of the same kind," Ekblad explained. But, generally, the effect of poorer verbal fluency scores wouldn't be very noticeable unless they were quite low, she added.
Ekblad said while this study didn't delve specifically into how these changes might occur, the researchers suspect that changes in the blood vessels linked to insulin resistance, or a change in the number of lesions in the brain's white matter, might explain the association with poorer verbal fluency. And those factors are more common in women than in men, she explained.
Another surprising finding was that people who had higher levels of insulin resistance and the APOE-E4 gene did not score worse on verbal fluency. People who only had high insulin resistance had worse scores on verbal fluency, she said.
According to Fargo, "This study raises more questions than it answers, and we definitely don't have as many answers as we need. The only way to get those answers is through more research."
Dr. Mark Stecker, chairman of the department of neurosciences at Winthrop-University Hospital in Mineola, N.Y., agreed that more research is needed.
"It would be nice to have this information confirmed in multiple groups. Seeing what happens in other patients would be very helpful. Are these findings due to vascular problems? Other problems? It's hard to know from one study. We're early in the science," he said.
Ekblad said that women should be aware that lifestyle factors - such as diet and exercise - may have an effect on brain health, even in early adulthood.
And Fargo said that while the study can't provide specific advice to prevent thinking and memory problems, "it's been fairly well established that the better your overall health is, the better your cognition."