Researchers studied 50 overweight and 50 normal weight people in the early stages of Type 2 diabetes. All had been given a diagnosis within the previous five years. They compared both groups with 50 healthy control subjects.

The scientists performed M.R.I. examinations of their brains and psychological tests of memory, reaction time and planning. Those with diabetes scored worse than the healthy controls on tests of memory and reaction times.

M.R.I. scans revealed significant differences in brain areas related to memory, planning and the visual processing of information. Compared with the controls, those with Type 2 diabetes had more severe thinning of the cortex and more white matter abnormalities. Overweight people with diabetes had more brain deterioration than people with diabetes having normal weight.

Are these changes reversible? Probably not, according to a co-author, Dr. Donald C. Simonson of Brigham and Women’s Hospital in Boston. “When structural changes are seen on an M.R.I. scan, the processes leading up to them have probably been going on for years,” he said. “On the positive side, patients who maintain good control of their diabetes do seem to have a slower rate of deterioration.”

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