Glycated hemoglobin levels and intellectual activity in an aged population

OBJECTIVES: To examine the association between glycated hemoglobin (GHb) and aspects of daily activities in an elderly population. DESIGN: Cross-sectional population-based survey. SETTING: Nangai village, an agricultural community with a population of about 5,000 located in Akita prefecture in the north of Japan. PARTICIPANTS: Nine hundred thirty-five people aged 65 and older. MEASUREMENTS: GHb percentages, self-reported measures of activities of daily living (ADLs) and instrumental activities of daily living (IADLs), intellectual activity (IA), and social role (SR). RESULTS: An exploratory analysis indicated that nondiabetic subjects in the lowest tertile of GHb tend to have lower IA than those in the middle tertile, if they were aged 70 and older. No consistent association appeared between GHb and ADLs, IADLs, or SR. Linear and logistic regression analyses, controlling for other risk factors, indicated significantly lower IA scores in the low and high GHb tertiles (P < .001 and P = .04, respectively) than in the middle in nondiabetic subjects aged 70 and older and without stroke history or IADL impairments. The value of GHb related to the maximal IA score was 5.0% to 5.2% as the middle tertile; or 5.2%, assuming a logistic regression model including a squared term with GHb as a continuous variable. A similar relationship was observed in the whole nondiabetic sample aged 70 and older but not in the younger counterpart. CONCLUSION: There is an inverted U-shaped relationship between GHb and intellectual activity in older people without diabetes mellitus. One possible interpretation is that suboptimal blood glucose could contribute to intellectual inactivity in older people.