Aerobic fitness and cognitive function in midlife: an association mediated by plasma insulin

Abstract

Insulin resistance in midlife increases the risk of dementia in late-life. In contrast, habitual aerobic exercise is an established strategy to ameliorate insulin resistance which may translate into better cognitive outcome. To determine the role of plasma insulin in mediating the relation between cardiorespiratory fitness and cognitive function, fifty-eight adults completed assessments of plasma insulin levels, maximal oxygen consumption (VO2max), and neuropsychological test performance. Endurance-trained subjects demonstrated better cognitive outcome (total composite z-score: 0.21 ± 0.08 versus -0.26 ± 0.10, P = 0.001) and lower concentrations of plasma insulin (12.6 ± 0.6 versus 21.3 ± 1.5 ulU/mL, P < 0.001) than sedentary subjects. Greater VO2max was significantly associated with higher memory performance (β = 0.37, P = 0.01) and lower plasma insulin levels (β = -0.68, P < 0.001). The significant association between VO2max and memory performance was abolished when the indirect effect of plasma insulin was statistically removed (β = 0.24, P = 0.19). Fitness-related cognitive enhancement may be mediated, at least in part, by plasma insulin levels.

Figure

A model illustrating that plasma insulin mediates the relation between maximal oxygen consumption and memory performance. Greater maximal oxygen consumption was associated with better memory performance (path c) and lower plasma insulin level (path a). Lower plasma insulin level was related to better memory performance (path b). Finally, the significant association between maximal oxygen consumption and memory performance was abolished after controlling for plasma insulin level (path c’). Covariates entered: path a=age and sex, paths b & c=age, sex, and education, and path c’=age, sex, education, and plasma insulin.