Effect of renal impairment on cognitive function during a 3‐year follow up in elderly patients with type 2 diabetes: Association with microinflammation

AIMS/INTRODUCTION: We investigated the effect of renal impairment on cognitive function during a 3‐year follow up in elderly type 2 diabetic patients, and an association with microinflammation. MATERIALS AND METHODS: Four cognitive function tests – Mini‐Mental State Examination (MMSE), word recall, Digit Symbol Substitution (DSS) and Stroop Color Word – were carried out in 67 patients. Renal impairment was defined as the presence of albuminuria and a decline in estimated glomerular filtration (eGFR) <60 mL/min/1.73 m(2). Inflammatory markers, such as highly sensitive C‐reactive protein (hs‐CRP), tumor necrotizing factor‐α (TNF‐α), interleukin (IL)‐1β and IL‐6, were measured at baseline. RESULTS: At baseline, cognitive decline was found in patients with renal impairment. The DSS test was independently associated with eGFR decline, whereas MMSE tended to be associated with albuminuria after adjusting for confounding factors. Regarding changes in cognitive function and renal impairment, changes in urinary albumin to creatinine ratios were strongly and independently associated with changes in word recall scores. In patients with persistent eGFR decline, there was a tendency toward a greater decrease in MMSE and DSS scores, whereas in those with newly detected albuminuria, there was a tendency toward a greater decrease in word recall scores. Increased baseline levels of hs‐CRP, TNF‐α and IL‐6 were associated with renal impairment and cognitive function, especially DSS tests, respectively. However, the increased levels were not independent predictors for cognitive decline. CONCLUSIONS: The present study showed a reciprocal relationship between cognitive decline and renal impairment, especially progression of albuminuria. Thus, monitoring treatment using renal biomarkers will be important for preserving both renal and cognitive function.