"Vitamin A is best known for promoting healthy vision, but it's also important for bone growth, cell production, reproduction and regulating the immune system. It may also make white blood cells more effective infection fighters. Infection increases the levels of free radicals in your body, so as an immune system-booster, vitamin A further helps reduce free radicals (1)."
"The juice of one large lemon contains about 3 international units, or IU, of vitamin A, which helps you a little bit in meeting the recommended dietary allowance of 3000 IU, if you're male, or 2,310 IU, if you're female (1)."
Read more: (1) http://www.livestrong.com/article/523617-does-lemon-water-contain-antioxidants/#ixzz29OhL1zla