Diabetes mellitus is associated with decline in cognitive ability in old people, says a new study. Poor glucose control, according to the authors, is associated with poor performance in cognitive tests.

More than 3,000 people participated in the study. All the participants completed cognitive tests at the beginning of the study and at regular intervals during the next 10 years.

At the start of the study some 700 people had diabetes mellitus. Another 100 odd people developed diabetes mellitus over the next 10 years.

Researchers found that people with diabetes mellitus obtained poorer scores in the cognitive tests than people who did not have the disease. They also found that people who developed diabetes mellitus over the years showed a decrease in the test scores compared to people who never had the disease.

"Among well-functioning older adults, DM and poor glucose control among those with DM are associated with worse cognitive function and greater decline. This suggests that severity of DM may contribute to accelerated cognitive aging," researchers wrote.

"This study supports the hypothesis that older adults with DM have reduced cognitive function and that poor glycemic control may contribute to this association. Future studies should determine if early diagnosis and treatment of DM lessen the risk of developing cognitive impairment and if maintaining optimal glucose control helps mitigate the effect of DM on cognition," the authors conclude.

Other studies said that diabetes is associated with lower levels of cognitive function in older women; also that the cognitive decline associated with diabetes type-2 may result in dementia.

An estimated 27 percent or 10 million people in the U.S. over the age 65 have diabetes mellitus.

The study is published in the journal Archives of Neurology.