Writing in the New England Journal of Medicine, researchers from the USA reveal that people who high blood sugar levels over a long period of time may be at a higher risk of developing dementia.
Led by Professor Paul Crane from the University of Washington, USA, the research team averaged yearly blood sugar levels of more than 2,000 people for five years before tracking their later incidence of dementia.
"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," explained Crane."There was no threshold value for lower glucose values where risk levelled off."
Indeed, the team revealed that risk for dementia was 18% higher for people with an average glucose level of 115 milligrams per decilitre (mg/dl) compared to those with an average glucose level of 100 mg/dl.
"What we found was that people with higher levels of glucose had a higher risk of dementia, on average, than did people with lower levels of glucose," said Crane, emphasising that his teams results come from an observational study.
"While that is interesting and important, we have no data to suggest that people who make changes to lower their glucose improve their dementia risk," he added. "Those data would have to come from future studies with different study designs."
It has been widely suggested that type 2 diabetics are at a higher risk of developing dementia, however until now it has remained unknown whether high blood sugar levels - that are implicated in diabetes but are also common issues in non-diabetics - were implicated in the risk of dementia.
The team analysed data from 2067 participants of the Adult Changes in Thought (ACT) study, all of whom had at least one follow-up visit and had at least five measurements of glucose or glycated hemoglobin over the course of 2 or more years before study entry.
Blood sugar levels were averaged over a five-year period were and then analysed for and links to the risk of dementia.
In addition to finding up to an 18% increased risk of dementia in non-diabetic participants the research team revealed that in people with diabetes, whose blood sugar levels are generally higher, dementia risk was 40% higher for people with an average glucose level of 190 mg/dl compared to those with an average glucose level of 160 mg/dl.
"We found that higher glucose levels were associated with an increased risk of dementia in populations without and with diabetes," said Crane and his colleagues. "The findings were consistent across a variety of sensitivity analyses."
"These data suggest that higher levels of glucose may have deleterious effects on the aging brain," they commented.
"Our findings underscore the potential consequences of temporal trends in obesity and diabetes and suggest the need for interventions that reduce glucose levels."
However, Crane added that people should not necessarily try to eat less sugar — or foods with a lower glycemic index: "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," he said.
Crane commented that more research is planned to explore the various possible mechanisms for the relationship between blood sugar and dementia.
"This work is increasingly relevant," he said, "because of the worldwide epidemics of dementia, obesity, and diabetes."
Source: New England Journal of Medicine
Published online ahead of print, doi: 10.1056/NEJMoa1215740
"Glucose Levels and Risk of Dementia"
Authors: Paul K. Crane, Rod Walker, Rebecca A. Hubbard, et al