Association between insulin resistance and cognition in patients with depressive disorders: exploratory analyses into age-specific effects.

The current preliminary cross sectional study sought to examine the effects of insulin resistance (IR) and body mass index (BMI) on cognitive performance in adult patients with a history depression, currently not in an acute Major Depressive Episode (MDD). As an exploratory post hoc investigation, special consideration was given to adults <45 years and ≥45 years old. Subjects included men and women ages 19-71 (N = 39) with a history of a non-psychotic, non-melancholic MDD. All subjects underwent an insulin suppression test to determine Steady-State Plasma Glucose (SSPG), a battery of neuropsychological tests, and measurement of BMI. Multiple linear regressions were conducted to determine whether there were differential effects of direct (SSPG) and indirect (BMI) measures on cognition in the whole sample and within dichotomized age groups (<45 and ≥45 years). Preliminary results showed that in the sample as a whole, SSPG was not associated with worse performance on any cognitive variables, while higher BMI was associated with worse dominant hand fine motor skills. Within age groups, differential effects on cognition were found in relation to SSPG and BMI. Higher SSPG was associated with worse cognitive flexibility in the group <45 years, whereas higher BMI was associated with worse estimate of global intelligence in the group ≥45 years. The potential negative impact of IR in younger adults with depression raises concerns regarding the long-term impact on cognition and risk for Alzheimer's disease in undiagnosed younger adults with IR and depression. These negative consequences may not be seen with indirect measures of IR in younger adult populations. Overweight and obesity in older adults with a history of depression appear to have further negative impacts on cognition similar to deficits seen in patients with diabetes. CLINICALTRIALSGOV IDENTIFIER: Clinical Trial NCT01106313.