The answer is simple: it’s not. Orange juice is simply healthier and has many nutrients, in addition to being a rich source of vitamin C itself. Therefore, there is a greater benefit to having a whole food (fruit in this case) than a vitamin in a pill form.
A recent study published in the U.S. Journal of the National Cancer Institute (March 2006) showed that the risk of pancreatic cancer among people who consumed foods high in folic acid was significantly lower than in those who consumed foods low in folic acid. Similar reduced risk was not observed for people who took folic acid as a supplement. These findings suggest that it might be more beneficial to eat whole foods with vitamins in them than to consume vitamins as supplements.
So, stick to whole foods for essential nutrients such as vitamins and minerals; vitamin pills are not a substitute for healthy, balanced, wholesome food. And remember, it’s your life, your future, YOUR HEALTH FIRST.