Vegetables are the major dietary source of beta carotene. Therefore, the people who eat the most vegetables are the ones who have the highest blood levels of beta carotene.
Vegetables contain many other phytochemicals that are known to prevent heart attacks and cancers.
So, eating vegetables, rather than just taking beta carotene, prevents heart attacks and cancers. There are at least two studies that show that large doses of beta carotene deplete the body of vitamin E which can increase your risk for cancer. These studies show that you should eat lots of fruits, vegetables, whole grains and beans. I'm Dr. Gabe Mirkin on Fitness. NEJM April 14, 1994.