Different associations of premorbid intelligence vs. current cognition with BMI, insulin and diabetes in the homebound elderly

Premorbid intelligence does not decline through life even at the early stages of Alzheimer's disease (AD). However, other cognitive measures such as Mini Mental State Examination (MMSE) decline with aging and severely with dementia. In this study, we examine the associations of premorbid intelligence vs. current cognition with body mass index (BMI), insulin and diabetes in elderly adults. Using a cross-sectional, population-based study, we assessed BMI, plasma insulin and the evidence of diabetes in homebound elders. The North American Adult Reading Test (NAART) and MMSE were conducted. Associations were assessed by T-test, linear correlation and multivariate regression analysis. Subjects were divided into four subgroups: 1) BMI <25; 2) 25 < BMI <30; 3) 30 < BMI <35 and 4) BMI >35. Lower verbal IQ, assessed by NAART, was associated with higher BMI (β=-0.28; P<0.01), elevated insulin (β= -0.02, P=0.02), and diabetes (β=- 3.18, P<0.01). Multivariate regression analyses showed that all three clinical conditions - obesity, hyperinsulinaemia and diabetes - were associated with lower premorbid intelligence assessed by verbal IQ, but only diabetes was associated with current cognitive impairment assessed by MMSE. These relationships persisted after adjustment for education. Premorbid intelligence is associated with diabetes precursors - obesity and high insulin - and diabetes itself, but cognitive impairment is related to diabetes only. Understanding the mechanisms that link verbal IQ to diabetes precursors might suggest targeted interventions for the prevention of diabetes and cognitive decline caused by diabetes.