NEW YORK (Reuters Health) - Diabetes may hasten progression to dementia in older people with mild thinking impairment, new research shows.

So-called mild cognitive impairment, or MCI, increases a person's risk of developing Alzheimer's disease and other types of dementia. But aside from a person's severity of mental impairment, there is currently no way to predict which people with MCI will go on to develop full-blown dementia.

Diabetes has been tied to mental decline and dementia in aging, but it is not currently known whether people with MCI who have diabetes are at greater risk of future dementia.

To investigate, Dr. Latha Velayudhan of the Institute of Psychiatry in London and her colleagues followed 103 men and women with MCI over age 65 for four years, during which time 19 developed dementia. Most of these individuals had "probable or possible" Alzheimer's.

The 16 individuals in the study with diabetes were nearly three times as likely to develop dementia as the study participants without diabetes, the researchers report in the British Journal of Psychiatry.

While the study is small, Velayudhan and her colleagues note, it is fairly representative of the population at large because participants were recruited from primary care centers, not specialized memory clinics.

There are several ways that diabetes could speed mental decline, the researchers say, for example through its effects on insulin, which plays a key role in how the brain uses glucose for fuel.

"Whatever the mechanism, with an expected increase in the prevalence of diabetes in people of all ages including older adults, the risk of developing dementia may increase," Velayudhan and her colleagues say.

"Identification of those at particular risk of progression might help to target early treatment -- both pharmacological and social," they conclude.

SOURCE: The British Journal of Psychiatry, January 2010.