Vitamin D is a fat-soluble vitamin that occurs naturally in a limited number of foods, so fortified foods including milk, margarines and breakfast cereals and dietary supplements are the major source for most Americans.

CNN: How much vitamin D should someone over 55 take?

Beta carotene is a type of carotenoid, a plant pigment that is a provitamin for vitamin A. During its digestion and metabolism, a percentage is converted to vitamin A, a fat-soluble vitamin that is important for vision, growth and development, and healthy immune and reproductive function.

CNN: Should I take beta carotene as a supplement?