Researchers have discovered that those with a high blood sugar level, even if they do not have diabetes, may have an increased risk of developing dementia compared with those who have a normal blood sugar level.

The study, published in the New England Journal of Medicine, analyzed 2,067 participants without dementia aged 65 and over, from a study called Adult Changes in Thought (ACT).

In order to examine the relationship between glucose levels and the risk of dementia, researchers from the University of Washington involved in a Group Health study analyzed average measurements of glycated hemoglobin levels and glucose levels over a period of 6.8 years.

The team compiled specific data from the participants using a Cox regression model - a predictive model that uses time-dependent factors. These included:

Results of the study revealed that in the participants with diabetes, the risk of dementia was 40% higher for those with an average glucose level of 190 milligrams per deciliter (mg/dl), compared with participants who had an average glucose level of 160 mg/dl.

However, the results also showed that in the participants without diabetes, the risk of dementia was 18% higher for those with an average glucose level of 115 mg/dl versus those with an average of 100 mg/dl.

Dr. Paul Crane, an associate professor at the University of Washington School of Medicine, says:

"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.

There was no threshold value for lower glucose values where risk leveled off."

The researchers note the strength of this research lies in it being based on the ACT study, which is a long-term cohort study analyzing people throughout their lives.

Eric Larson, a senior investigator at Group Health Research Institute, adds:

"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 researchers say that including both glucose levels and glycated hemoglobin in the measurements was key. They add that blood sugar levels rise and fall throughout the the day, but glycated hemoglobin does not vary as much over short periods.

However, the researchers add that these results do not necessarily mean that people should eat foods with a lower "glycemic index," but exercise may help.

"Your body turns your food into glucose, so your blood sugar levels depend not only on what you eat but also on your individual metabolism: how your body handles your food," says Dr. Crane.

In conclusion, the researchers say that although the results show that higher glucose levels are linked to higher dementia risk, there is no data to suggest people who make changes to lower their glucose levels will reduce the risk of dementia.

Dr Crane adds:

"Those data would have to come from future studies with different study designs."