Oranges are at their freshest beginning in the late fall, and orange juice is many people's go-to when they feel a cold coming on, for good reason. One-hundred percent orange juice contains vitamin C, a nutrient that strengthens our immune systems by protecting cells and promoting the production and function of immune cells. One eight-ounce glass of OJ provides more than 100 percent of your recommended daily value of vitamin C, and there are also many carotenoids found in pure orange juice — including beta carotene, alpha carotene, and beta cryptoxanthin — which can help form vitamin A in the body, an important nutrient for immune function.