Purple sweet potatoes are an excellent source of vitamin A. A medium potato serving yields 1,643 retinol activity equivalents -- retinol being a form of vitamin A used in measuring vitamin amounts. The daily recommendation for vitamin A is 600 to 900 micrograms of retinol activity equivalents. The brightly hued tuber also contributes 812 milligrams of potassium toward your 4,700-milligram-per-day adequate intake and 58 milligrams of calcium toward the 1,000-milligram-per-day recommendation