Vitamin A

The active form of vitamin A is retinol, which we obtain from foods of animal origin, including liver, egg yolks, fortified dairy products (e.g., vitamin A and D milk), margarine, and fish oil. The DRI ranges between 700 retinol activity equivalents (RAE) for women and 900 RAE for men. One RAE equals

• 1 microgram of retinol,
• 12 micrograms of beta-carotene,
• 24 micrograms of alpha-carotene, or
• 24 micrograms of beta-cryptoxanthin.

Vitamin A has a well-established relationship with normal vision; helps keep bones, skin, and red blood cells healthy; and is also needed for the immune system to function normally. There is no evidence that taking extra vitamin A aids athletic performance. Since the vitamin has clearly toxic effects when taken in excess (the maximum upper limit that poses the risk of adverse effects is 3,000 RAE for women and men), athletes should be cautioned against taking supplemental doses. Toxicity of vitamin A manifests itself in several ways, including dry skin, headache, irritability, vomiting, bone pain, and vision problems. Excess vitamin A intake during pregnancy is associated with an increase in birth defects.

A precursor to vitamin A is beta-carotene. (A precursor is a substance that, under the proper conditions, is converted to the active form of the vitamin.) Therefore, consuming foods with beta-carotene is an indirect way of obtaining vitamin A. Beta-carotene is found in all red, orange, yellow, and dark green fruits and vegetables (carrots, sweet potatoes, spinach, apricots, cantaloupes, tomatoes, and so on). It is a powerful antioxidant, protecting cells from oxidative damage that could lead to cancer, and it can be converted to vitamin A as we need it. Unlike preformed vitamin A (retinol), beta-carotene does not exhibit the same clear toxic effects if excess doses are consumed. However, a consistently high intake of carrots, sweet potatoes, and other foods high in beta-carotene may cause a person to develop a yellowish skin tone as the beta-carotene accumulates in subcutaneous fat.

It is conceivable that beta-carotene may, as an antioxidant, prove to be effective in reducing postexercise muscle soreness and may aid in postexercise recovery. However, this is a theoretical connection only; no study makes a direct link between beta-carotene intake and reduced soreness and improved recovery. Nevertheless, given its relatively low toxicity potential and its potential benefits, the U.S. Olympic Committee has recognized beta-carotene's potential as an antioxidant.