Controlling blood sugar levels improved the ability to clearly think, learn and remember among people with type 2 diabetes who were overweight, say researchers.

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"It's important to properly control your blood sugar to avoid the bad brain effects of your diabetes," said study author Owen Carmichael from the Pennington Biomedical Research Centre in the US. "The study, published in the Journal of Clinical Endocrinology and Metabolis, examined close to 1,100 participants in the Look AHEAD (Action for Health In Diabetes) study. One group of participants was invited to three sessions each year that focused on diet, physical activity, and social support. The other group changed their diet and physical activity through a program designed to help them lose more than seven percent of their body weight in a year and maintain that weight loss.

Cognitive tests - tests of thinking, learning, and remembering - were given to participants between 8 to 13 years after they started the study. The research team theorised that people with greater improvements in blood sugar levels, physical activity and weight loss would have better cognitive test scores. This hypothesis proved partially true. Reducing your blood sugar levels did improve test scores. But losing more weight and exercising more did not always raise cognitive test scores. "Every little improvement in blood sugar control was associated with a little better cognition," Carmichael said. "Lowering your blood sugar from the diabetes range to prediabetes helped as much as dropping from prediabetes levels to the healthy range," Carmichael.

The study also revealed that more weight loss was either better or worse depending on the mental skill involved. People who lost more weight improved their executive function skills: short-term memory, planning, impulse control, attention, and the ability to switch between tasks. But their verbal learning and overall memory declined, the study said. "People with diabetes who let their obesity go too far, for too long may be past the point of no return, cognition-wise," the authors noted.