Diabetes shrinks elderly brain

An Australian research team led by Associate Professor Katherine Samaras (Garvan Institute of Medical Research) found that the aging brain is vulnerable to worsening blood sugar levels even before type 2 diabetes is diagnosable.

While some brain volume loss is a normal part of aging, the researchers found that elderly people with blood sugar levels in flux, as well as type 2 diabetes, lost almost two and a half times more brain volume than their peers over two years. The reduction in size of the frontal lobe -- associated with higher mental functions like decision-making, emotional control, and long term memory -- has a significant impact on cognitive function and quality of life.

Diabetes is a very common disorder caused by high levels of sugar in the bloodstream. It affects 6.4% (285 million) of the worldwide population and is associated with an increased risk of heart attacks, stroke and damage to the eyes, feet and kidneys. In type 2 diabetes, which accounts for 90% of all cases, insulin -- a hormone that allows cells to take sugar from the bloodstream and store it as energy -- does not work properly. 344 million people also have pre-diabetes, a condition with mildly elevated blood sugar levels that gives them a 50% risk of developing the disease over ten years.

This research -- a follow-up of 312 participants from the Sydney Memory and Ageing Study -- compared MRI scans taken from the beginning and end of a two-year period. The participants were elderly community-dwelling Australians aged between 70 and 90 years old (average age 78, 54% male) and free from dementia. At the start of the study 41% had pre-diabetes and 13% had type 2 diabetes.

At the end of the study the participants were divided into four groups: (1) those with normal, stable glucose levels (102 people); (2) those with stable pre-diabetes (120 people); (3) those whose glucose levels had worsened (57 people); and finally, (4) those with type 2 diabetes from the start (33 people).

The MRI scans showed that the normal group lost an average of 18.4 cm3 total brain volume over two years. In comparison, the stable pre-diabetic group lost 1.4 times more brain volume (26.6 cm3). Both the third group (worsening glucose levels) and fourth group (type 2 diabetes) lost 2.3 times the stable group's brain volume loss (41.7 cm3 and 42.3 cm3, respectively).

The researchers -- using statistical models that accounted for other variables -- concluded that a person's blood sugar status after two years can significantly predict their decline in brain volume.

Associate Professor Katherine Samaras, from the Garvan Institute of Medical Research, said:

"These findings highlight the importance of prevention of diabetes. They also emphasise that, in the elderly, clinicians and allied health professionals need to understand that the complexity of diabetes care needs to accommodate expected declines in cognitive function.

"We need to understand why these changes in cognition and brain size occur. Is it due merely to higher blood sugars? Is the brain subject to the toxic effects of glucose, just as peripheral nerves are? To what extent do other factors associated with diabetes also contribute to the decline in brain size and function, for example inflammation or blood fat levels?

"We also need to learn how we can prevent or deter the negative effects of diabetes on the brain."