Australasian Science: Australia's authority on science since 1938

Sugar Shrinks the Brain

By Stephen Luntz

High blood sugar levels, even within what is considered the normal range, can contribute to dementia, a study published in Neurology suggests.

“Numerous studies have shown a link between Type 2 diabetes and brain shrinkage and dementia, but we haven’t known much about whether people without diabetes with blood sugar on the high end of normal experience these same effects,” says Dr Nicolas Cherbuin of the Australian National University’s Centre for Research on Ageing, Health and Wellbeing.

Cherbuin used MRI scans to measure the hippocampus in 249 people aged 60–64, and repeated the measurement 4 years later noting: “Hippocamporal atrophy is one of the early makers of future cognitive decline”. Fasting blood glucose levels were also measured.

“A normal blood glucose level is considered to be between 4.0 and 6.1 mmol/L,” says Cherbuin. “Those with higher blood sugar levels within the normal range were more likely to have a loss of brain volume in the areas of the hippocampus and the amygdala – areas that are involved in memory and cognitive skills – than those with lower blood sugar levels.”

Age, high blood pressure, smoking, obesity and alcohol use all contribute to brain shrinkage, but sugar levels in the top quartile of those in the normal range still accounted for 6–10% of shrinkage once these other factors were controlled for. The effect may seem small, but Cherbuin says it is robust, and extended over 20 years could mean the loss of 5% of important areas of the brain, even without other factors. “Since blood sugar levels are also known to contribute to cardiovascular disease and obesity, the total effect would be larger,” he adds.

Cherbuin stresses that blood sugar levels are a product of much more than sugar intake, with stress, lack of exercise and foods with high glycaemic index scores being important contributors.

“It’s not clear whether we need to redefine diabetes so that people in the upper level of the normal range are included, or if we need to think about managing blood sugar at any level,” Cherubin adds, noting that the increase in brain shrinkage had a roughly linear correlation with sugar levels throughout the normal range.