Carotenoids are phytonutrients (nutrients from plants). The most familiar carotenoids known are Beta-Carotene, Alpha-Carotene, Beta-Cryptoxanthin, Zeaxanthin, Lutein, and Lycopene.
Carotenoid knowledge is still in its infancy, current research appears to show Carotenoid benefits derive from their anti-oxidant properties.
It appears Carotenoids are beneficial for eye health (protection from macular degeneration and cataracts) and cardiovascular health.
It is important to point out that the beneficial effects seem to be synergistically involved with other nutrients (Vitamin E, Vitamin C), so Carotenoids should be consumed in their whole food form and not in concentrated supplements.