What is known about Vitamin A at this time is that there are animal sources (retinol) and vegetable sources (carotenes) in foods. Animal sources are about six times more potent than vegetable sources and can be toxic if taken in excess. Because of this, Vitamin A supplements are restricted to carotenes and under limited to under 25,000 IU per pill. One ounce of polar bear liver contains enough Vitamin A (retinol) to kill a person!
Your body uses Vitamin A for growth, healthy skin and cells (epithelial) that line any opening to the body (nose, throat, lungs, mouth, stomach, intestines, vagina and urinary tract) and good night vision. Absorption of vitamin A is dependent on fat from food sources and bile (cholesterol substance produced by your liver and stored by your gallbladder and used to break down fats, seeds, and skins). Your body can store two year’s worth of Vitamin A in your liver. If you don’t eat enough Vitamin A, it can cause blindness or in milder cases, your ability to see or drive at night.
Good food sources are fish oil, liver (pork, lamb, chicken, turkey or beef), eggs, butter, and orange or yellow vegetables or fruits. Broccoli is a good source of Vitamin A, but the chlorophyll (green) camouflages the yellow carotene color. If it weren’t for chlorophyll, broccoli would be yellow or orange.
Some researchers have found that large amounts of Vitamin A can prevent the development of cancer in epithelial cells and yet other researchers have found the opposite is true. But, if you take large quantities of Vitamin A, your skin and even the whites of your eyes can turn yellow when your body stores for Vitamin A become saturated. If this happens, discontinue the vitamin A supplements and the yellow coloring in the whites of your eyes, palms of your hands and soles of your feet will go away in a few months. If the whites of a person’s eyes are yellow and not caused by Vitamin A supplements, they could have a liver disease like cirrhosis and should see their doctor immediately.
Hope this info helps your understanding of Vitamin A.