Vitamin A is an antioxidant that maintains the immune system; protects eyesight; keeps skin and tissues of the digestive tract and respiratory system healthy; and supports bone growth.

How Much: Recommended dietary allowance (RDA) = 3,000 international units (IU) for men and women. 

Too Much: Tolerable upper limit (UL)  = 10,000 IU from retinol. Vitamin A is obtained in two ways: as vitamin A from animal sources such as fish oil, egg yolks and dairy products; and as pro-vitamin A carotenoids (including beta carotene) from fruits and vegetables, which your body then converts into vitamin A. 

Three or more times the recommended amount of vitamin A from animal sources or supplements may increase hip fracture risk. Beta- carotene supplements have been linked to an increased risk of lung cancer in smokers. 

Too Little: Rare; night blindness and weakened immune system.

Foods: Liver, eggs, fortified milk; richly colored fruits and vegetables, such as carrots, cantaloupes, sweet potatoes and spinach.

Interactions: Orlistat (Alli, Xenical); mineral oil; oral contraceptives; isotretinoin (Accutane); acitretin (Soriatane); and bexarotene (Targretin).

Research Note: Studies suggest a form of vitamin A called all-trans-retinoic acid – used to treat acne and some types of cancer – may be helpful in controlling rheumatoid arthritis (RA) by suppressing inflammatory cytokines.