The healthful qualities of tomatoes were not established until the mid-twentieth century. Tomatoes have considerable vitamin C and some vitamin A. Tomatoes rank thirteenth among other commonly consumed fruits and vegetables as a source of vitamin C and sixteenth as a source of vitamin A. Overall, tomatoes rank sixteenth nutritionally behind other vegetables. Despite this comparatively low ranking, tomatoes contribute more vitamin A and C and other nutrients to the American diet than do other fruits and vegetables because so many more tomatoes are consumed. In addition, medical researchers believe that tomatoes may be an anticancer weapon. Tomatoes contain lycopene, the plant pigment that makes fruits red. Research has demonstrated that people with more lycopene in their blood have lower rates of certain forms of cancer.