It's common knowledge that winter citrus fruits including oranges, tangerines and grapefruits are high in vitamin C. When cold season hits, the first sign of the sniffles prompts many to dose up on OJ. Citrus' cold-fighting abilities are well-documented, and it's nature's miracle that these fruits reach their peak during the virus-prone winter months. But the cold-fighting power of citrus is but one of its myriad health virtues.