Although diabetes is a risk factor for cognitive decline and dementia in the U.S., scientists have been unsure if such memory deficits occur in other cultures.

In a new study, scientists from Mayo Clinic and Huashan Hospital in Shanghai explored the association between diabetes and cognitive impairment to find out if the relationship varies in different populations. They found that American and Chinese adults with Type II diabetes are at similar risk for memory impairment.

Study participants had not been diagnosed with memory-related diseases, such as vascular dementia or Alzheimer's dementia.

For the study, the researchers evaluated data from two large, ongoing, population-based studies: the Shanghai Aging Study (SAS) and the Mayo Clinic Study of Aging (MCSA). Both use similar designs and methodologies.

For example, both studies recruit participants from a defined population, include an on-site, in-person evaluation, use similar or comparable tests of cognition, and include participants over age 50.

The SAS uses neuropsychological tests adapted from Western tests to harmonize with Chinese culture.

The scientists analyzed medical data from 3,348 Chinese adults and 3,734 American adults, all of whom had undergone cognitive testing and were dementia-free. Participants' medical records were used to determine whether they had Type II diabetes.

The researchers found that all of the participants who had Type II diabetes, regardless of their population study, performed significantly worse on cognitive tests, compared to participants who did not have diabetes.

These findings suggest that diabetes is linked to cognitive impairment in both Eastern and Western cultures.

"We wanted to study diabetes and cognitive impairment in these two completely different ethnic groups to see whether there are any differences. We found that in both cohorts, having a history of diabetes was associated with greater impairment in cognitive function," said study co-author Rosebud Roberts, M.B., Ch.B., an epidemiologist at Mayo Clinic.

Researchers found similar results, even after adjusting for age, gender, and education, as well as vascular problems.

More specifically, the American and Chinese study participants with diabetes performed considerably worse on executive function tests, compared to people in both study populations who did not have diabetes.

Executive function is the ability to make decisions, plan and problem-solve, and is associated with the frontal lobe of the brain.

In the Shanghai population, a diabetes diagnosis also was associated with poorer performance on tests of memory, visual-spatial skills and language. One possible reason for this difference is that the population studied in China developed diabetes at an earlier age, compared to the population studied by the Mayo researchers.

Roberts said the research shows that impairment in executive function may be an early effect of diabetes, and earlier age at diabetes diagnosis results in greater cognitive deficits.

However, she said, the overall effects of diabetes on cognition are similar in Western and Eastern populations.