Interactive effects of diabetes and impaired kidney function on cognitive performance in old age: a population-based study

BACKGROUND: The interactive effect between diabetes and impaired kidney function on cognitive impairment in older adults has not yet been reported. The aim of this study was to investigate the association of diabetes and impaired kidney function with cognitive impairment among Chinese older people living in a rural area. METHODS: This cross-sectional study included 1,358 participants (age ≥60 years; 60.5 % women) in the population-based Confucius Hometown Aging Project in Shandong, China. Data on demographics, lifestyle factors, health history, use of medications, global cognitive function, and kidney function were collected through structured interviews, clinical examinations, and blood tests. We defined diabetes as a fasting plasma glucose level ≥7.0 mmol/l or use of hypoglycemic agents, impaired kidney function as glomerular filtration rate estimated from cystatin C (eGFR(cys)) <60 ml/min/1.73 m(2). Cognitive impairment was defined using the education-based cut-off scores of Mini-Mental State Examination (MMSE). Data were analyzed using multiple general linear and logistic regression models. RESULTS: Cognitive impairment was defined in 197 (14.5 %) persons. The multi-adjusted β coefficient of MMSE score associated with diabetes was −0.06 (95 % confidence interval [CI], −0.16, 0.03); the corresponding figures associated with eGFR(cys) <60, 60–89.9, and ≥90 ml/min/1.73 m(2) were −0.15 (−0.28, −0.02), −0.01 (−0.10, 0.08), and 0 (reference) (P(trend) = 0.046), respectively. Diabetes and impaired kidney function showed an interactive effect on cognitive impairment (P(interaction) = 0.02). Compared with individuals having neither diabetes nor impaired kidney function, those with both conditions had a multi-adjusted odds ratio of 4.23 (95 % CI, 2.10–8.49) for cognitive impairment. The relative excess risk due to interaction was 2.74. CONCLUSIONS: This study suggests that concurrent presence of diabetes and impaired kidney function is associated with a substantial likelihood for cognitive impairment in older adults.