Their claim to fame: There appears to be a link between carotenoids (including beta-carotene, lutein, zeaxanthin, and lycopene) and a decreased risk of age-related macular degeneration, cataracts, and some cancers. However, no clinical trial has shown that carotenoids -- compounds found in red and yellow plants -- are responsible for lowering risk.
"There is encouraging research with certain carotenoids in the prevention of some diseases, but not enough to say what the requirement should be," says Susan Taylor Mayne, Ph.D., associate professor of epidemiology and public health at Yale University School of Medicine. There are some promising associations, such as with lutein and macular degeneration, but they are preliminary, she says.
So all the articles written about lycopene's effect on prostate cancer don't mean much? "It's all interesting data, but at this point, it is far from proven," Mayne says. "And most of the studies have been done on food, not pills." Mayne recommends getting your carotenoids by eating a variety of foods.
Old RDA: None. There never was one.
New RDA: None, although the NIH report recommends eating 5 fruits and vegetables a day to take in 3 to 6 mg.
Recommended upper limit: Beta-carotene supplements are not advised other than as a source of vitamin A. Beta-carotene and lycopene in excess of 30 mg per day -- whether from foods or in supplemental form -- can cause a harmless yellowing of the skin. (This goes away when the intake is reduced.) The NIH review of the research suggests that excessive intake from food sources is otherwise not harmful, though high doses of supplements may pose some risk.
Best food sources: Sweet potatoes, carrots, tomatoes, peppers, spinach, kale, collard greens, squash, apricots, mangoes, cantaloupe, and papayas.