Foods from animal sources contain vitamin A. But many plant foods contain carotenoids, which your body turns into vitamin A. More than 500 carotenoids have been identified, with beta-carotene being the best known. You can overdose on vitamin A, but it's highly improbable that you'll ever suffer carotene poisoning.
Beta-Carotene
In the liver, beta-carotene turns into vitamin A, a light-yellow alcohol. Vitamin A is necessary for keeping the linings of the eyes, urinary and digestive tracts in good shape. Deficiencies result in poor night vision -- even blindness -- and a compromised immune system. But the body can change only a limited amount of beta-carotene into Vitamin A. After that level is reached, beta-carotene works as an anti-oxidant, fighting off free radicals and protecting cell membranes. Beta-carotene may significantly lower your risk of heart disease. But this seems to be true only when beta-carotene comes from food sources, rather than supplements.
Overdose
It is possible to overdose on vitamin A, but it’s very rare. The recommended daily allowance for women is 700 micrograms. For men, it’s 900 micrograms. Vitamins are also measured in international units. Nine hundred micrograms are about 3,000 international units. An adult who regularly takes 25,000 IU or more may develop symptoms of vitamin A poisoning. Children and infants could become sick from smaller doses or even from the amount of vitamin A found in some lotions. However, while vitamin A can make you sick, large amounts of beta-carotene won’t. The main symptom of excessive beta-carotene consumption is yellow/orange skin, as beta-carotene gives carrots and other orange vegetables their color. Your skin will go back to normal once you stop consuming so much beta-carotene.
Upper Limits
While overdosing on vitamin A is usually caused by supplements, it’s also possible to consume too much in food. This can damage your skin and lead to brittle bones. The upper limit for vitamin A is 10,000 IU per day, which is four times the recommended daily allowance for a woman and more than three times the allowance for a man. Pregnant women should be especially careful, as vitamin A overdose can cause birth defects.
Deficiency More Likely
Vitamin A deficiency is much more common than vitamin A or carotene poisoning. While not a problem in the United States, populations in some 75 countries around the world suffer from insufficient vitamin A. The World Health Organization reports that 350,000 children go blind every year because of lack of vitamin A. Of these children, 60 percent die within three months of losing their sight.
