People with impaired glucose tolerance or diabetes mellitus may have a significantly higher risk of developing Alzheimer’s disease, vascular dementia, and all-cause dementia.
Diabetes mellitus and higher levels of two-hour postload plasma glucose were shown to play important roles in the development of all-cause dementia and its subtypes, according to a report in the September 20 Neurology.
“We investigated the association between glucose tolerance status defined by a 75-g oral glucose tolerance test and the development of dementia,” lead author Tomoyuki Ohara, MD, and colleagues from the Graduate School of Medical Sciences at Kyushu University in Fukuoka, Japan, wrote. “Our findings suggest that diabetes is a significant risk factor for all-cause dementia, Alzheimer’s disease, and probably vascular dementia.”
Impaired Glucose Tolerance Increased Dementia Risk
Dr. Ohara and the group of investigators performed a prospective cohort study of dementia in a Japanese community-dwelling population; all 1,017 members of their cohort were 60 or older and dementia free at enrollment and underwent oral glucose tolerance testing. Those who were determined to have impaired fasting glycemia (73), impaired glucose tolerance (235), or diabetes (150) had higher BMI, total cholesterol, and frequencies of hypertension.
During the 15-year follow-up, 232 subjects (153 women, 79 men) developed dementia, the researchers reported. “Compared with those with normal glucose tolerance, the age- and sex-adjusted incidence and hazard ratio of all-cause dementia were significantly higher in subjects with impaired glucose tolerance as well as those with diabetes.” This association remained significant after the investigators adjusted for other dementia risk factors, including hypertension, high BMI, history of stroke, and EKG abnormalities.
Participants with impaired glucose tolerance and diabetes were twice as likely to develop vascular dementia in the initial analysis, but the association did not remain significant after multivariate analysis. No significant associations were observed between glucose tolerance levels and the risk of other dementia.
Elevated Plasma Glucose Levels Raise Dementia Incidence
When the investigators compared participants’ plasma glucose levels with incidence of these dementia subtypes, they found similar associations. Although there was no change in the incidence and hazard ratios of all-cause dementia or any subtypes and fasting plasma glucose levels, participants with elevated two-hour plasma glucose levels were significantly more likely to develop all-cause dementia and its subtypes.
“We demonstrated that diabetes that was assessed 15 years earlier was a significant risk factor for the development of all-cause dementia, Alzheimer’s disease, and vascular dementia,” the researchers concluded. “Moreover, the risks of developing all-cause dementia and its subtypes progressively increased with elevating two-hour plasma glucose levels,” they stated, adding that this finding supports the view that postprandial glucose regulation is critical to prevent future dementia. They also noted that further investigations into the possible pathophysiologic mechanisms through which diabetes or elevated blood glucose levels might initiate dementia are necessary.
—Ariel Jones