WASHINGTON - High-dose folic acid pills — providing as much of the nutrient as 2.5 pounds of strawberries — might help slow the cognitive decline of aging. So says a Dutch study that’s the first to show a vitamin could really improve memory. The research, unveiled Monday at a meeting of Alzheimer’s researchers, adds to mounting evidence that a diet higher in folate is important for a variety of health effects. It’s already proven to reduce birth defects, and research suggests it helps ward off heart disease and strokes, too.