| Both low sodium values and poor glycemic control have been suggested to have a deleterious effect on cognitive function in diabetes mellitus. This study hypothesized that serum sodium moderates the relationship between glycemic control and cognitive function and that this relationship may be best described as quadratic in fashion. Participants (55--76 years) were 149 outpatients (72 females and 77 males) diagnosed with non-insulin-dependent diabetes mellitus. In a longitudinal study, glycemic control measures were recorded and cognitive measures were collected 18 months later. The cognitive measures included the Vocabulary subtest of the WAIS, a verbal fluency task, and a reaction time task. Results showed that in regards to vocabulary and verbal fluency performance, the relationship between glycemic control and cognitive function was best characterized as a quadratic relationship in which serum sodium served as a moderator. That is, optimal vocabulary and verbal fluency performance was associated with relatively moderate glycemic control (HbA1c around 10--12%) among participants with lower serum sodium levels (Na+ < 139 mmol/L). In addition, there was a main effect of serum sodium levels and HbA1c levels on the transit time component of the reaction time task. As serum sodium levels increased, transit time decreased. Transit time performance also improved as HbA1c levels increased. In conclusion, moderate glycemic control may be more beneficial than tight control in regards to cognitive performance. In addition, the results indicated that electrolyte disturbances, specifically low serum sodium levels, may contribute to cognitive impairment in Type 2 diabetes. |
