"Prediabetes" – where blood sugar levels are high but not yet tipped over into full-blown diabetes – might pose a threat to brain health, new British research suggests.
"As an observational study, it cannot prove higher blood sugar levels cause worsening brain health; however, we believe there is a potential connection that needs to be investigated further," said study lead author Victoria Garfield. She is at the Institute of Cardiovascular Science and MRC Unit for Lifelong Health and Aging, at University College London.
In their research, Garfield's team analyzed U.K. Biobank data on a half-million people, average age 58. Compared to those with normal blood sugar ("glucose") levels, people with prediabetes had a 42% higher risk of mental decline over an average of four years, and were 54% more likely to develop vascular dementia – a common type of dementia caused by reduced blood flow to the brain – over an average of eight years.
The associations between prediabetes and mental ("cognitive") decline/vascular dementia remained even after the researchers accounted for other potential risk factors, including age, smoking, weight, level of heart disease, and poverty.
Prediabetes was not associated with an increased risk of Alzheimer's disease, Garfield's team noted.
One U.S. diabetes expert said the findings are not surprising, given the fact doctors have long known that full-blown diabetes raises dementia risks.
"The takeaway is that cognitive risk related to elevated glucose levels occurs across a spectrum," said Dr. Minisha Sood, an endocrinologist at Lenox Hill Hospital in New York City.
So even in the prediabetic stage, "where the body overproduces insulin in order to maintain normal blood sugar levels," damage to the brain might be underway, she said.
Sood believes people who are in a prediabetic state should be warned by their physicians of the dangers.
The British team also looked at people with full-blown type 2 diabetes, and found they were three times more likely to develop vascular dementia, and also more likely to develop Alzheimer's disease, than those with normal blood sugar levels.
The study was published online recently in the journal Diabetes, Obesity and Metabolism.
"Previous research has found a link between poorer cognitive outcomes and diabetes, but our study is the first to investigate how having blood sugar levels that are relatively high – but do not yet constitute diabetes – may affect our brain health," Garfield noted in a university news release. Dr. Barbara Keber is chair of family medicine at Glen Cove Hospital in Glen Cove, N.Y.
Reading over the new findings, she said it "makes sense" prediabetes might harm blood flow in the brain, since it has the same effect elsewhere in the body.
But Keber also noted too-tight blood sugar control has been linked to hypoglycemia (dangerous dips in blood sugar levels) in patients, which has also been linked to "increased risks for development of cognitive decline and dementia."
So, "the take-home here is that we need to prevent prediabetes and diabetes as well as control the glucose levels for those who have been diagnosed without causing hypoglycemia, to prevent the development of cognitive decline and vascular dementia," Keber said.
In the meantime, there is also a lot the average person with prediabetes can do to rid themselves of this threat to their health.
"For the lay population, they need to follow a diet which reduces the risks of developing diabetes, exercise regularly – both isometric (strength training) and aerobic (cardiac training) – to reduce weight gain and prevent the development of both prediabetes and diabetes," Keber said.