Health behaviors, including increasing intake of fish and several other components of the Mediterranean dietary pattern, have been postulated as potentially promising strategies for slowing age-related cognitive decline. One of the pathways through which diet has been hypothesized to slow cognitive decline is by contributing to improved vascular control, though research demonstrating this link is limited. Using a prospective cohort of community-dwelling adults at least 55 years who completed a cognitive screening test at two or more waves of the China Health and Nutrition Survey in 1997, 2000 or 2004, we aimed to determine the relation between diet (particularly fish consumption and dietary patterns), vascular conditions such as blood pressure (BP) and the rate of cognitive decline. In aim 1, we evaluated if consumption of fish predicted slower decline in cognitive function. We found that consuming at least one serving per week of fish was associated with slower decline of cognitive function for individuals 65+. Aim 2 evaluated how changes in cognitive scores were associated with an adapted Mediterranean diet (aMeDi) score and two dietary pattern scores derived from principal factor analysis. Our results have shown that greater consumption of an aMeDi, and a factor analysis derived dietary pattern rich in wheat, fish, fruits, and nuts, which we labeled a wheat-based diverse diet, were both associated with slower decline of cognitive function for adults 65+. In Aim 3, we calculated the long-term mean BP, visit-to-visit variability in BP represented by the standard deviation and coefficient of variation across visits. Higher visit-to-visit variability in BP independent of mean BP predicted a faster decline of cognitive function. We did not observe a relation between aMeDi and visit-to-visit variability in BP. In conclusion, our findings suggest a potential role of fish intake, and higher adherence to either a Mediterranean diet or a wheat-based diverse diet, to reduce the rate of cognitive decline in later life. Our study also suggests a possibility that controlling long-term blood pressure instability could be a strategy in preserving cognitive function among older adults, although lifestyle factors that may help to meet this objective are yet to be identified.