Cognitive Impairment and Glycemic Status among U.S. Adults

Several studies have shown that cognitive impairment is a complication of diabetes, however, this association has not been assessed in an older, nationally representative U.S. sample. This study determined the association between diabetes and cognitive function overall and by participant characteristics among adults age ≥60 years in the 2011-2014 National Health and Nutrition Examination Surveys (N=1,552). Participants had diabetes if they reported a physician diagnosis of diabetes, had an A1c ≥6.5%, or fasting plasma glucose ≥126 mg/dL. Cognitive function was assessed by three tests: Consortium to Establish a Registry for Alzheimer’s Disease Word Learning subtest (CERAD W-L), which measures the ability to learn new verbal information; the Animal Fluency test, which measures executive function; and the Digit Symbol Substitution Test (DSST), which measures working memory. The standardized effect size (Cohen’s d; value ≥0.2-<0.5=small, ≥0.5-<0.8=moderate, ≥0.8=large) for each cognitive test was determined for those with diabetes vs. those without diabetes. Overall, adults with diabetes performed consistently lower on the cognitive assessments compared to those without diabetes. The overall effect size was moderate for the CERAD W-L and DSST assessments (Cohen’s d range -0.44 to -0.51), and was small for the Animal Fluency score (Cohen’s d = -0.33) for those with diabetes vs. those without. For the CERAD W-L, the effect size was greatest (≥ -0.50) for youngest ages (60-69 years), non-Hispanic Asians, never smokers, those with normal weight, and no hypertension, compared to counterparts. For the DSST assessment, the effect size was greatest (≥ -0.50) for those age 60-69 years, Mexican Americans, females, former or never smokers, those who did not consume alcohol, those who exercised, those with hyperlipidemia, and those without hypertension.

In conclusion, diabetes was associated with a lower ability to learn new verbal information and poorer working memory but had less of an effect on executive function.