Those most at risk are people who have cancer, tuberculosis, pneumonia, chronic nephritis, urinary tract infections or prostate disease, all of which may increase the body's demands for vitamin A . Vitamin A is a fat-soluble substance, which means that you should eat a food that contains a small amount of fat when you take it. You can get vitamin A directly from a supplement. Or you can get it indirectly by eating fruits and vegetables that are loaded with beta-carotene . Your body will turn beta-carotene into the vitamin A it needs.
Many doctors prefer the second route.
Using Vitamin A Safely F or centuries, Arctic adventurers, Eskimos and even sled dogs have known that eating polar bear liver can make them sick. It's loaded with enough vitamin A to poison a full-grown adult. A single meal consisting of a half-pound to one pound of polar bear liver contains a whopping 3 million to 13 million international units of vitamin A , which is 6 to 26 times the amount needed to cause acute vitamin A poisoning. Only 500,000 international units of vitamin A , taken over a short period of time, can cause irritability, headaches, vomiting, bone pain, weakness and blurred vision. Regular use of even 50,000 international units a day can cause hair loss, weakness, headaches, enlarged liver and spleen, anemia, stiffness and joint pain.