Diabetes may be a risk factor for dementia

By Sally Robertson
21 September 2011
Neurology 2011; 77: 1126–1134

MedWire News: Diabetes is a potential risk factor for all-cause dementia, Alzheimer's disease (AD), and vascular dementia (VaD), research shows.

The study, published in the journal Neurology, revealed that elevated 2-hour postload glucose (PG) levels are closely associated with increased risk for developing dementia and its subtypes.

“We have clearly demonstrated that diabetes is a significant risk factor for the development of dementia, especially of AD, in the general public,” lead investigator Yutaka Kiyohara (Kyushu University, Fukuoka, Japan) told MedWire News.

“Our findings show that the risk for developing dementia significantly increased with rising blood sugar levels at 2 hours after ingestion of 75 g glucose, which corresponds to blood sugar levels in a post-meal state.”

“This suggests that high blood sugar levels after meal increase the risk of dementia,” he added.

Kiyohara and team performed an oral glucose tolerance test (OGTT) in 1017 dementia-free individuals aged 60 years or over. They then followed them up for an average of 10.9 years, during which 232 individuals developed dementia.

The team found that the age- and gender-adjusted incidence of all-cause dementia, AD, and VaD were significantly higher in participants with diabetes than in those with normal glucose tolerance, as judged by World Health Organization criteria.

After further adjustment for confounding factors, the associations remained significant for all-cause dementia (hazard ratio =1.74) and for AD (HR=2.05), but not for VaD.

Moreover, the team found that the risk for developing dementia and its subtypes rose with elevating 2-hour PG levels, whereas no such associations were observed for fasting plasma glucose (FPG) levels.

Compared with those who had 2-hour PG levels of less than 6.7 mmol/L, the adjusted risks for all-cause dementia and AD significantly increased in individuals with 2-hour PG levels of 7.8 mmol/L or more, and the risk for VaD was significantly increased in those with levels of 11.1 mmol/L or higher.

The authors say the findings support previous research showing that higher levels of 2-hour PG, but not FPG, are associated with increased risk for formation of neuritic plaques.

“It is reported that 2-hour PG values can be a good marker of oxidative stress levels arising from hyperglycemia and correlate with insulin resistance,” they write.

Kiyohara explained that higher oxidative stress and insulin resistance are believed to precede the accumulation of amyloid-β peptide and neurofibrillary tangles in the brain, resulting in increased risk of AD.

“Elevated oxidative stress and insulin resistance are also considered to accelerate arteriosclerosis and therefore the risk of vascular dementia,” he said.

The authors say their findings support the view that postprandial glucose regulation is critical to prevent future dementia.

“Further investigations are required to clarify the associations between 2-hour PG levels by the OGTT, and subtypes of dementia in other ethnic populations,” the team concludes.

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