Older people with Type 2 diabetes whose blood sugar levels drop to dangerously low levels even once may be at a greater risk of developing dementia, a new study suggests.

In Wednesday's theme issue of JAMA — which was devoted to diabetes — researchers in the U.S. looked at whether bouts of hypoglycemia or low blood sugar level that required hospitalization or a trip to emergency were associated with an increased risk of dementia.

"It really adds to the evidence base out there that perhaps very low glycemic targets might not be the best way to go in elderly patients with Type 2," said the study's lead author, Rachel Whitmer of Kaiser Permanente Division of Research in Oakland, Calif.

The study included 1,465 people with Type 2 diabetes and an average age of 65 who had one or more serious episodes of hypoglycemia. The condition may cause dizziness, disorientation, fainting or seizures.

Between 1980 and 2002 and in the following four years, nearly 17 per cent of the study's participants with seriously low blood sugar were diagnosed with dementia compared with 10.3 per cent of those with no history of hypoglycemia.

The risk also increased as the number of severe hypoglycemic episodes went up: a 26 per cent greater risk of dementia for one episode, 115 per cent greater risk for two episodes and 160 per cent higher for three or more, the researchers found.

Hypoglycemia may affect the brains of older and younger people differently, the researchers said.

"However, a major concern with this study is establishing the direction of causality — mild or undetected cognitive impairment may predispose patients to hypoglycemia," Dr. David Nathan of the MGH Diabetes Center in Boston said in a journal commentary accompanying the study.

Hypoglycemia can result after missing a meal or when insulin levels are too high.

Insulin can rise after taking insulin injections or oral diabetes drugs such as sulfanylureas or glimepiride that cause the body to make more insulin.

The researchers said they would like to see if brain imaging tests show how severe episodes of hypoglycemia affect the brain.

Certain drugs known as glitazones (such as Avandia or rosiglitazone and Actos or pioglitazone) are meant to help people with diabetes to use insulin better. The researchers are also interested in testing whether the drugs make a difference for dementia risks.

Dementia is a collection of symptoms that significantly impair thinking, and normal activities and relationships.