Because vitamin C is water-soluble, it washes out of your body when you urinate. Therefore, it is important to get several doses of vitamin C a day. To get enough vitamin C, I recommend taking at least two, usually three, doses of vitamin C daily. I do this by combining food and supplements. In the morning, I take a multivitamin containing 500 milligrams (mg) of vitamin C, have an orange or grapefruit at lunch, and take a multivitamin containing 500 mg of vitamin C with dinner (that multivitamin also has 200 international unit (IU) of vitamin E for breakfast and dinner), just to make sure I'm getting enough. I also get vitamin C from other things I eat, just in smaller amounts, such as tomatoes and salads. Vitamin C also tends to leech out of packaged or cut vegetables. In addition, cooking reduces vitamin C levels even more. That's another reason to eat plenty of fresh fruits and vegetables every day. Also, eat some fruit or take some of your vitamin C one to two hours before any vigorous exercise. Vigorous physical activity causes oxidant buildup, and vitamin C's antioxidant power may be one of the ways that vitamin C works to keep you younger.