It is vital for patients to keep their blood sugar levels under control
Failure to control type 2 diabetes may have a long-term impact on the brain, research has suggested.
Severe hypoglycaemic episodes - hypos - occur when blood sugar levels drop dangerously low.
A University of Edinburgh team found they may lead to poorer memory and diminished brain power.
The study, based on 1,066 people with type 2 diabetes aged between 60 and 75, was presented at a conference of the charity Diabetes UK.
Hypoglycaemia is caused by a lack of sugar (glucose) reaching the brain, which uses it as fuel
Symptoms can include sweating, fatigue, hunger, feeling dizzy, feeling weak, a higher heart rate than usual and blurred vision
More severe episodes can led to temporary loss of consciousness, convulsions and coma
The volunteers completed seven tests assessing mental abilities such as memory, logic and concentration.
The 113 people who had previously experienced severe hypos scored lower than the rest of the group.
They performed poorly in tests of their general mental ability, and vocabulary.
There are at least 670,000 people in England aged between 60 and 75 years old who have Type 2 diabetes and around a third of them could be at risk of a hypo.
Lead researcher Dr Jackie Price said: "Either hypos lead to cognitive decline, or cognitive decline makes it more difficult for people to manage their diabetes, which in turn causes more hypos.
"A third explanation could be that a third unidentified factor is causing both the hypos and the cognitive decline.
"We are carrying out more research to establish which explanation is the most likely."
Dr Iain Frame, director of research at Diabetes UK, said: "This study reinforces previous evidence which suggests that poorly controlled diabetes affects the functioning of the brain.
"We already know that type 2 diabetes increases the risk of developing Alzheimer's disease, which is a type of dementia, and this research adds another piece to a very complex jigsaw puzzle.
"However, more research is needed before we can come to any firm conclusions."
There are 2.5 million people diagnosed with diabetes in the UK and up to 500,000 who have type 2 diabetes but do not know it.
It is predicted that by 2025 there will be up to four million people with diabetes in the UK.