beta-carotene

Vitamin A (another type - retinol) can also be had from meat, especially liver. A well nourished adult can get by without new sources of Vitamin A for about 2 years (because of liver stores). However, most of the world gets their Vitamin A as beta carotene from plant sources. Vitamin A deficiency can cause blindness or in less severe cases bad night vision. This is the "eat your carrots, they are good for your eyes" basis. In much of our world where meat and fruit or vegetables are not available, large populations just doesn't get enough Vitamin A. The resulting deficiency is responsible for "at least a million children who die every year because they are weakened by vitamin-A deficiency and an additional 350,000 who go blind."

Rice is a stable amoung many of the poor and malnourished people of the developing world (for those who have food at all). But rice alone didn't provide enough Vitamin A. Recently genetic engineering has created a "golden rice" by blending the gene's of common rice with DNA from bacteria and daffodils yielding a rice with built in beta carotene.

reference:  Friday, March 16, 2001 
Grains Of Hope 
BY J. MADELEINE NASH/ZURICH
www.time.com

The carotenoid plant pigment beta carotene is also a powerful antioxidant. There have been claims that taking beta carotene supplements can help prevent cancer and heart disease and boost a one's immune system.

The results of research investigating these claims have been mixed. However, two high-quality medical studies showed that male smokers who take beta carotene supplements (even small amounts in the range of 30 milligrams per day) had an increased risk of lung cancer.

Thus, most medical experts advise that people get their beta carotene from eating vegetables rather than from supplement pills.