Several compounds make up vitamin A, a fat-soluble vitamin naturally found in milk, liver and whole eggs in the form of retinol. Vitamin A in the form of provitamin A carotenoids occurs naturally in brightly colored fruits and vegetables such as carrots, spinach and sweet potatoes. Like other fat-soluble vitamins, your liver can store excess amounts of vitamin A in the liver and tissues until needed.
Storage
Your liver can store up to a two-year supply of vitamin A if you take in more than you need on a daily basis, according to registered dietitian Joanne Larson, M.S on her site, Ask the Dietitian. If your liver stores become saturated, the vitamin starts to accumulate under your skin, where it's most noticeable in the hands and soles of the feet.
Lab Values
Your serum levels of vitamin A can indicate whether you have adequate liver stores of the vitamin. Normal levels fall between 0.30 and 1.2 mg/L. A serum level above 0.30 mg/L indicates adequate liver stores, according to ARUP Laboratories, while levels below 0.10 mg/L indicate a vitamin A deficiency. Have blood drawn after fasting for 12 hours and abstaining from alcohol for 24 hours before the test for accurate results.
Daily Requirements
You need 3,000 International Units or 900 micrograms of Retinol Activity Equivalents -- one measurement of how much vitamin A food has -- of vitamin A if you're a male over age 14. Women over age 14 need 2,310 IU or 700 mcg RAE. The tolerable upper limit over age 14 is 10,000 IU, or 3,000 mcg, for both men and women. An intake of 34,000 IU per day can turn your skin yellow, a sign that your liver has become saturated with vitamin A, according to Larson.
Toxicity
Vitamin A toxicity occurs when your body contains more vitamin A in the form of retinol than retinol binding protein, to which it normally binds for storage in the liver. Once the liver becomes saturated, your skin and whites of the eyes may turn yellow. If this happens, you're taking in too much vitamin A and should reduce your intake. High levels of vitamin A in the body can lead to liver damage, osteoporosis and central nervous system disorders, as well as causing birth defects.
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