Files
Abstract
A growing body of literature suggests a relationship between nutrition and brain health, particularly in old age. The overarching goal of the present research project was to extend this literature, focusing specifically on the micronutrient lutein (L) and its isomer zeaxanthin (Z). L and Z are xanthophylls within the carotenoid family that accumulate preferentially in the macular region of the eye and have long been shown to benefit visual functions. More recently, L and Z have demonstrated a positive relation to cognition in young and older adults. The current randomized controlled trial aimed to investigate underlying neural mechanisms using both task-based and resting state functional magnetic resonance imaging (fMRI). It was hypothesized that L and Z supplementation in old age would enhance neural efficiency and benefit overt cognitive performance on an fMRI-adapted verbal learning task relative to placebo. Supplementation was also expected to improve intra-network integrity of default mode network (DMN) and reduce inter-network connectivity between DMN and other resting state networks. Participants were drawn from a community-dwelling older adult sample (N = 75; mean age = 73 years) randomly assigned to receive a daily supplement containing L and Z (12 mg) or aphysiologically inert placebo for a period of one year. Results indicated that L and Z supplementation significantly influenced brain function relative to placebo, though not all effects were in the hypothesized direction. Task-based fMRI revealed increased blood-oxygen-level-dependent signal in left dorsolateral prefrontal cortex and anterior cingulate cortex during learning in the supplemented group (p < .05, family-wise-error corrected). L and Z supplementation also appeared to buffer decline in overt cognitive performance on the verbal learning task (Cohens d = .84) but the effect was not statistically significant (p > .05). Resting-state fMRI yielded significantly increased inter-network connectivity (Cohens d = .89) and no significant effect on intra-network connectivity. Taken together, these results suggest that L and Z may facilitate the aging brains capacity for neuroplastic compensation by increasing prefrontal activation during cognitive task performance and enhancing integration between functionally segregated neural networks while the brain is at rest.