Vitamin A

What is it?

The term vitamin A is used to describe all substances that result in vitamin A activity in biologic systems. This includes retinol, retinoic acid, and retinyl esters (such as the retinyl-palmitate, found in vitamin capsules.)

What does it do?

A form of vitamin A called retinal forms some of the light-sensitive pigment in the retina of the eye. It helps certain tissues develop normally both in the embryo and in adults. (Too much, in fact, causes developmental abnormalities, too.) While important to the function of most tissues in the body, vitamin A is especially important for the skin, reproduction and the immune system. It retards the formation of certain cancers. (See the Lancet January 7, 1995 for an overview.)

Which form of vitamin A is best?

It is best to eat a diet that provides all the vitamin A activity you need. Your daily requirement of vitamin A can be obtained from the carotene in a serving of sweet potato, carrot, spinach, pumpkin,collard greens, broccoli, watermelon, cantaloupe,apricots, nectarine, and many other foods. Vitamin A is present in liver and other animal foods.Vitamin A is stored in the body for a long time, so you could eat a big piece of liver once a week and you'd have all the vitamin A you needed.(Assuming you like liver. I'll take the pumpkin pie.)

Some vegetables are yellow and orange because they contain carotene. In the body, carotene is transformed into vitamin A as needed. To provide extra vitamin A activity, a doctor may prescribe either vitamin A or beta-carotene. Vitamin A is much less expensive but there is the risk of overdose. One cannot overdose on beta-carotene but it is more difficult to absorb and it's about five times as costly. Beta-carotene can interfere with the absorption of other carotenoids resulting in harm.  Also, your body may not make enough vitamin A from beta-carotene to correct every vitamin A-responsive condition.

Why take vitamin A?

Vitamin A helps maintain a healthful skin, bones,teeth and gums. It is required for good night vision.

Self care with vitamin A

Because vitamin A can be toxic in excessive amounts, I don't recommend vitamin A use without the advice of someone familiar with your health situation. To inspire you to eat a diet rich in vegetables with vitamin A in it, let me tell you that intake of vitamin A has been shown to be protective against cancer of the mouth, cervix and breast.  Communities in which vitamin A supplements are given to all the children have a significant reduction in mortality among those children. Studies show that people with an acute infection have an increased need for vitamin A.

Prevention with Vitamin A

A study in Belgium found that people with higher levels of vitamin A in the blood recovered more quickly and completely from stroke ( Lancet1992;339:1562). The British Medical Journalreported that elderly people with higher levels of vitamin A had an enhanced immune response.Adequate intake of vitamin A can help prevent cancer of the cervix (Nutrition and Cancer1984;6:49), cancer of the head and neck (Eur Arch Otolaryngol 1990; 247:368), cancer of the prostate(Cancer Research 1990; 50:2311), high blood pressure (Science 1984 224;1392), upper respiratory infection in children (Aust Paediatr J1986;22:95), and age-related macular degeneration(American Journal of Epidemiology 1988;128:700).

Medical use of vitamin A

Vitamin A should not be used to treat medical conditions without the advice of your physician.   However, you should know that vitamin A has an antiviral effect and can strengthen the immune system.  Retin-A, an effective acne remedy, provides provides vitamin A activity in a synthetic molecule.  Impaired night vision is often due to vitamin A deficiency. 

Vitamin A deficiency

People who do not eat the proper kind of food can suffer vitamin A deficiency. We must be able to absorb fat in order to absorb vitamin A (and beta carotene),else we can be vitamin A deficient even while taking the best vitamin A supplement. Also people who are deficient in vitamin E or zinc or who have liver disease can fail to absorb vitamin A.

Vitamin A can be toxic in large doses

Adults can develop symptoms from doses in excess of 50,000 I.U. per day for a period of several years.An 18 year study of 72,000 post-menopausal women revealed more fractures in those women who had diets highest in vitamin A (including supplements). See our July 2002 newsletter for more details. Smaller doses might be harmful in people with liver disease or malnutrition. Signs of toxicity include dry, cracked skin, brittle nails, loss of hair, headache, muscle ache, irritability, fatigue and nausea. These signs disappear when the vitamin is discontinued.

Children are more susceptible to vitamin A toxicity as they are smaller in size and might accidentally take vitamin A supplements meant for adults. Vitamin A (as any supplement) must be kept out of the reach of children.

Optimal dose of vitamin A

As noted above, just one serving a day of carotene-rich vegetables and fruits will provide you with the recommended daily allowance.  In a group of people studied at the University of Alabama, those who consumed about 6,600 IU of vitamin A a day from food and supplements appeared to live the longest. However, women who consume more than 5000 units a day seem to increase their risk of hip fracture, at least on the average. Our newsletter points out that there maybe some trade-offs between longevity and bone strength.

Adults can reasonably and safely take an extra 100,000 units a day for a week to help end a cold or upper respiratory tract infection. If vitamin A doesn't appear to help your problem, you may not be absorbing it. Take pancreatic enzymes with each dose to enhance absorption.

The current recommended maximum intake for pregnant women and women who might become pregnant is 10,000 units of vitamin A per day. Higher doses may increase the risk of birth defects.

Vitamin A is toxic in excessive amounts. If you are pregnant, do not take it without your doctor's advice!