Older diabetics whose blood sugar drops to dangerously low levels have a higher risk of developing dementia, U.S. researchers said on Tuesday.
The study by researchers at Kaiser Permanente in Oakland, California, suggests that aggressive blood sugar control resulting in blood sugar so low it requires a trip to the hospital may increase dementia risks in older adults with type 2 diabetes.
"We know that having blood sugar that is too high is not good," Rachel Whitmer, a Kaiser research scientist whose study appears in the Journal of the American Medical Association, said in a telephone interview.
"You want to keep that blood sugar at a good level, but you don't want to go too low," she said.
Several studies have found that diabetics have a higher risk of developing Alzheimer's disease — the most common form of dementia — than do the general population. And others have shown that diabetics who take insulin and pills to help control their disease have a lower Alzheimer's risk.
"The very current issue here is balance of blood sugar control," Whitmer said.
She said a number of things such as a missed meal can cause severe low blood sugar in diabetics, but the chief cause is too much insulin, which can happen in people who take insulin injections or with oral diabetes drugs such as sulfonylureas or glimepiride that cause the body to make more insulin.
She and colleagues looked at more that two decades of data in more than 16,600 patients with type 2 diabetes.
The team checked to see if prior episodes of low blood sugar that were severe enough to require a trip to the hospital were associated with a higher risk of dementia.
They found that compared with people who had no severe bouts of low blood sugar, diabetics with single or multiple episodes had higher dementia risks, and risk levels rose depending on the number of severe hypoglycemic episodes.
"In older patients with a history of one episode, they had a 26 percent greater risk of dementia. Patients with two episodes had a 115 percent greater risk of dementia. And patients with three or more episodes had a 160 percent greater risk of dementia," Whitmer said.
She said the study offers more evidence that aggressive measures to control blood sugar can cause harm in elderly diabetics.
It follows three recent trials that found tight glycemic control could cause heart disease and death in some elderly diabetics.
She and colleagues plan to look at dementia risks for people in the study who took glitazones — a class of drugs that help diabetics use insulin better. Drugs in this class include GlaxoSmithKline's Avandia or rosiglitazone and Takeda Pharmaceutical's Actos or pioglitazone.
Alzheimer's is the most common form of dementia among older people, affecting 5.2 million people in the United States, according to the Alzheimer's Association. Some 23.6 million Americans have diabetes, according to the American Diabetes Association.