A study published in the New England Journal of Medicine found the risk of developing the neurological disease rose in step with rising levels of blood glucose.
Elderly people without diabetes but with a blood sugar level of 6.4mmol/L were 18% more likely to develop dementia within five years than those with blood sugar levels of 5.5mmol/L.
Lead author Dr Paul Crane of the University of Washington in Seattle said: ‘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. There was no threshold value for lower glucose values where risk levelled off.’
Study authors said high levels of glucose in the blood may lead to microvascular damage in the brain.
The researchers analysed 35,264 measurements of blood glucose levels and 10,208 readings of glycated haemoglobin from 2,067 participants without dementia aged around 76 years old.
Among those with diabetes, a blood glucose level of 10.5mmol/L led to a 40% increased risk of dementia compared with those at 8.9mmol/L.
N Engl J Med 2013;369:540-8