People with diabetes who have low-blood-sugar episodes serious enough to land them in the hospital have a higher risk of being diagnosed with dementia later in life, new research suggests.

Kaiser Permanente researchers evaluated the health records of more than 16,000 people with type 2 diabetes, tracking episodes of severe hypoglycemia — low blood sugar — over a 22-year period. They then followed patients for four more years to track diagnoses of dementia.

Compared with patients with no hypoglycemia, patients with one severe hypoglycemic episode had a 26 percent increased risk of dementia; those with two episodes had an 80 percent increased risk; and people who had had three or more episodes had nearly double the risk, the authors report.

A large body of research suggests diabetics are more at risk for dementia, but the reason is unclear. Diabetes drugs that induce hypoglycemia may cause brain-cell death in older people, the authors suggest.

The study, published in today's edition of the Journal of the American Medical Association, underscores the juggling act that diabetics and their doctors face in regulating blood sugar.

Last year, researchers stopped a major federal study in midstream when it turned out intensive efforts to lower blood sugar to near normal levels led to more deaths among diabetics than controlling it a little less rigorously.

Blood sugar that rises too high can damage the kidneys, eyes, blood vessels and heart.

But blood sugar that sinks very low is also risky, because it can cause fainting, seizures or coma.

The Kaiser study suggests that severe bouts of hypoglycemia might also subtly damage the brain in the long run, providing yet another reason to err on the side of slightly higher blood sugar for some diabetics.

"You have to exert some caution," said Dr. Joe Selby, a co-author of the study and head of the Kaiser Permanente research division in Northern California.

"The older you get, the more severe and prolonged your diabetes has been, the greater the chances you might experience hypoglycemia if you push" to rigorously limit blood sugar, Selby said.

People with diabetes do benefit if their hemoglobin A1c, a protein used to track blood sugar, can be lowered from 10 percent to 8 percent, but the benefits of trying to get it down to 7 percent are much less clear-cut for older patients, Selby said.

The research is one of a collection of studies and commentaries in the journal, which this week focuses entirely on diabetes.

In another study in the medical journal, Yale University medical school researchers examined whether early screening for cardiovascular disease in adults with type 2 diabetes would affect their cardiovascular health long-term.

The study included 1,123 participants with type 2 diabetes. About half were randomly assigned to be screened for heart disease, and the rest were not screened. The average follow-up was nearly five years.

The study found that cardiac-event rates were low, and that screening did not lead to a significant reduction in heart attack rates or cardiac deaths compared with patients who were not screened.