Why do I need vitamin A?
You've probably heard that the vitamins in carrots can help you see in the dark. That old tale is actually true -- the beta carotene in carrots and many other vegetables is converted in the intestines to vitamin A (also known as retinol), and vitamin A is undoubtedly good for the eyes. But night vision is only the beginning; vitamin A is also vital for healthy skin, strong bones, and a well-prepared immune system. If you don't get enough A, your skin will dry out, you'll be more prone to infections, and, of course, you won't be able to see well in low light. Eating foods rich in beta carotene may also help protect you against heart disease and certain forms of cancer.
How much should I be getting?
The recommended daily allowance is 700 micrograms a day for women an 900 micrograms a day for men. Most Americans have no trouble reaching this goal; recent dietary surveys suggest that the average American gets 990 micrograms of vitamin A each day. There's no magic threshold of A to ward off heart disease and cancer, but eating five to nine servings of fruits and vegetables a day should leave your body well prepared to fend off all sorts of illnesses.
What are some sources of Vitamin A?
There are six milligrams of beta carotene in one large carrot -- enough to convert to 1,000 mcg of vitamin A. Likewise, you can expect a good dose of A from the orange, red, yellow, and dark green pigments found in other vegetables and fruits. Just one red bell pepper or half a cup of spinach will give you as much A as you need for the day. This is one reason why nutritionists recommend a colorful diet.
Liver is by far the richest source of straight-up vitamin A, no conversion required. Fish and egg yolks also have plenty, and milk is usually fortified with A. (It helps your bones soak up calcium.)
Should I take a supplement?
If you're like most people, you won't need a supplement to get enough A. In fact, the Institute of Medicine recommends against beta carotene or vitamin A supplements except in certain cases. Doctors sometimes recommend vitamin A supplements for young children, especially if they are malnourished or hospitalized with the measles.
Can I get too much vitamin A?
It's definitely possible to get too much. Consumers should read vitamin labels and not take a supplement that nears the upper safe limit (3,000 micrograms of vitamin A). An excess of vitamin A stored in the body can cause birth defects, liver damage, and central nervous system disorders, among other things. It's not possible to overdose on beta carotene or carotenoids in food, however. Your body won't turn these pigments into vitamin A unless there's a need.
Mayo Clinic. Vitamin A (retinol).
National Institutes of Health. Office of Dietary Supplements. Vitamin A and carotenoids.
Linus Pauling Institute at Oregon State University.