 The neuroprotective effects of antioxidant nutrients e.g. vitamins E and B-vitamins e.g. folate have been at the forefront of cognitive aging and nutritional epidemiology research over the past two decades.2 Vitamin Ds role in preserving cognitive function with aging has recently gained attention in epidemiological investigations.3 Its public health significance lies in the fact that vitamin D deficiency 25-hydroxyvitamin D3 25OHD11 ngml 27.5 nmolL is a highly prevalent condition, particularly among the poor and among African-Americans.4, 5 Vitamin D is a steroid hormone with its primary function being to regulate body levels of calcium, phosphorus and bone mineralization. While sunlight exposure is its primary source through skin synthesis from 7-dehydrocholesterol, dietary and supplemental intakes of vitamin D play a key role in its overall status. 3 The active form of vitamin D3, namely 1,25-dihydroxy vitamin D3 influences many metabolic pathways through genomic and nongenomic actions which help maintain and stabilize intracellular signaling pathways involved in memory and cognitive function.. 3, 6, 7 The neuroprotective role of vitamin D may be mediated through vasculo-protection and preservation of neurons partly through the expression of neurotrophins and other neurotransmitters which help protect against cognitive dysfunction, through the suppression of inflammatory cytokines.3, 5, 8 Vitamin D can also down-regulate receptors in memory-relevant regions and enhance amyloid phagocytosis and clearance. 8 Serum 25OHD and dietary vitamin D were shown to influence cognitive outcomes in large epidemiological studies. 9-34 This study will examine associations between vitamin D status and intake with longitudinal change in various domains of cognition among a large sample of ethnically and socio-economically diverse US urban adults. It also explores those associations systematically across sexage groups and race. We hypothesize that both vitamin D status and intake are associated with slower decline in domain-specific cognitive performance over time, but perhaps differentially by agesex and race. 