A joint study between Group Health and University of Washington, and published in the New England Journal of Medicine, has discovered higher blood sugar levels are associated with a higher risk of dementia, even among people who do not have diabetes.

By collecting data from them Adult Changes in Thought (ACT) study, blood sugar levels of more than 2000 Group Health patients  ages 65 and older were averaged over a 5-year period where higher blood sugar levels were found to be associated with a greater risk of developing dementia.

In patients without diabetes, the risk of dementia was about 18 percent higher for those that had an average glucose level of 115  milligrams per deciliter compared to those with an average glucose level of 100  milligrams per deciliter. In patients with diabetes, the risk of dementia was 40 percent higher for those who had an average glucose level of 190  milligrams per deciliter, compared to patients that had an average glucose level of 160 milligrams per deciliter.

“The most interesting finding was that every incrementally higher glucose level was associated with a higher risk of dementia in people who did not have diabetes,” said first author Paul K. Crane, MD, MPH, an Associate Professor of Medicine at the UW School of Medicine, Adjunct Associate Professor of Health Services at the UW School of Public Health, and Affiliate Investigator at Group Health Research Institute. “There was no threshold value for lower glucose values where risk leveled off.”

“One major strength of this research is that it is based on the ACT study, a longitudinal cohort study, where we follow people for many years as they lead their lives,” said senior author Eric B. Larson, MD, MPH, a senior investigator at Group Health Research Institute who also has appointments at the UW Schools of Medicine and Public Health. “We combine information from people’s research visits every other year with data from their visits to Group Health providers whenever they receive care. And this gave us an average of 17 blood sugar measurements per person: very rich data.”

The data used included various measurements such as blood glucose, some fasting and some not, and glycated hemoglobin, or HbA1c. Blood sugar levels rise and fall in peaks and valleys through the day, but glycated hemoglobin doesn’t vary as much over short intervals. Combining glucose and glycated hemoglobin measures into a composite measure required special statistical techniques, which co-authors Rod Walker, MS, a biostatistician, and Rebecca Hubbard, PhD, an associate investigator, both from Group Health Research Institute, had developed.

More research is planned to look into various possible mechanisms for the relationship between blood sugar and dementia. “This work is increasingly relevant,” Dr. Crane said, “because of the worldwide epidemics of dementia, obesity, and diabetes.”