Vitamin A and Beta Carotene

Scientific/medical name(s):

Retinol, retinoic acid, retinoids

Description

Vitamin A is a nutrient that is vital to growth and development. Vitamin A is obtained in two ways:

1. As vitamin A from animal sources such as liver, fish oils, egg yolks, and dairy products As beta carotene from many fruits and vegetables (such as carrots, broccoli, spinach, squash, peaches, and apricots) which the body converts to retinol (a type of vitamin A) in the small intestine.
2. Vitamin A is stored in the liver until needed by the body. Vitamin A and closely related molecules are also known as retinoids.

Overview

Vitamin A supplements have not been proven to prevent cancer in humans. But clinical studies are being done to explore the role of vitamin A and other retinoids in cancer prevention and treatment. High doses of vitamin A are toxic, and long-term use of high-dose supplements may increase the risk of lung cancer among people at high risk, like smokers.

How is it promoted for use?

Vitamin A is essential for normal growth, bone development, reproduction, and vision. It is used to help maintain healthy skin and mucous membranes, like the ones that line the nose and mouth. This helps protect against infections in the respiratory, digestive, and urinary tracts.

Some research suggests that vitamin A and some other retinoids are able to change cancer cells and can also prevent normal cells from becoming cancer. Retinoids are prescribed as a standard medical treatment for some rare types of cancer or pre-cancerous conditions.

Some alternative healers recommend taking carotenoid supplements as part of a regimen to "cleanse" or "detoxify" the body, especially the liver. Others suggest that beta carotene can be used to treat certain types of cancer.

What does it involve?

Vitamin A is absorbed from dietary animal fats, from dietary supplements, and in the form of beta carotene, which is found in some fruits and vegetables and converted to vitamin A by the body. Vitamin A is stored in the liver, so it does not need to be consumed every day.

The best way to get this vitamin is to eat a well-balanced diet. People who eat a balanced diet of fruits, vegetables, dairy products, and animal fats usually get enough vitamin A and beta carotene for good health, but supplements are available. The recommended daily allowance (RDA) of vitamin A is 2,310 IU (0.7 milligrams) per day for adult women (more for women who are pregnant or breastfeeding) and 3,000 IU (0.9 milligrams) per day for adult men.

What is the history behind it?

The discovery of vitamin A dates back to research from the early twentieth century. Over the past twenty years, vitamin A has been extensively studied as a cancer-fighting nutrient in laboratory, animal, and population studies. In addition to studies of vitamin A and cancer prevention, related retinoids have also been evaluated in laboratory studies and in human clinical trials.

Several studies based on dietary surveys of large numbers of people have concluded that eating foods rich in vitamin A is linked to a lower risk of certain types of cancer. But it is not clear whether the protective effect was due to vitamin A or to other helpful substances in these foods.

What is the evidence?

Vitamin A deficiency can cause a lowered resistance to infection, poor night vision or even blindness, poor growth in children, weak bones and teeth, inflamed eyes, diarrhea, and poor appetite. It is rare in developed countries.

Some animal studies have found that vitamin A and other retinoids may enhance the immune system, slow tumor growth, shrink tumors, and make some cancer treatments work better. Some laboratory, animal, and human studies have found that certain retinoids may also inhibit cancer development.

Studies of vitamin A's possible role in cancer prevention have been generally disappointing. Clinical trials have found that vitamin A supplements do not lower the risk for lung cancer in smokers and actually increased their risk for dying of lung cancer and heart disease. Studies of overall health and longevity found no benefit to taking vitamin A supplements, and the US Institute of Medicine does not recommend use of these supplements by the general public. Studies on vitamin A and other types of cancer have been mixed. There have been no consistent findings showing a lower risk of cancers of the stomach, intestines, skin, breast, cervix, bladder, or prostate due to vitamin A in the diet.

The use of vitamin A supplements has also not been proven to reduce cancer risk in humans. It appears that the combination of micronutrients in fruits, vegetables, legumes, and grains is more likely to be helpful than individual vitamins.

A 2007 review of 68 studies of vitamin supplements concluded that people taking beta carotene or vitamin A supplements had a shorter life expectancy than those who did not take these supplements.

Synthetic retinoids that are more potent than natural vitamin A or beta carotene have shown some ability to reverse pre-cancers in the cervix, mouth, throat, and skin. They also may help prevent new tumors in people who have already been treated for these forms of cancer. But more clinical research is needed. Several clinical trials involving retinoids have been completed and others are still going on.

Retinoids are not currently used as a cancer treatment, with one notable exception. A relatively rare type of leukemia, promyelocytic leukemia, often responds to a combination of retinoic acid (a retinoid) and chemotherapy. Patients with this form of leukemia get high doses of a pure form of retinoic acid (derived from Vitamin A) under medical supervision. Treatment of promyelocytic leukemia does not include use of non-prescription vitamin A supplements or dietary changes intended to increase intake of this vitamin.

Studies of other types of cancer such as lung cancer, head and neck cancer, and melanoma found that vitamin A supplements are not helpful as treatments. Some oncologists are concerned that vitamin A and other vitamins that act as antioxidants may even make chemotherapy and radiation therapy less effective when taken during treatment. This is why many oncologists recommend that their patients not take such antioxidant supplements until their treatment is complete.

Are there any possible problems or complications?

This product is sold as a dietary supplement in the United States. Unlike companies that produce drugs (which must provide the FDA with results of detailed testing showing their product is safe and effective before the drug is approved for sale), the companies that make supplements do not have to show evidence of safety or health benefits to the FDA before selling their products. Supplement products without any reliable scientific evidence of health benefits may still be sold as long as the companies selling them do not claim the supplements can prevent, treat, or cure any specific disease. Some such products may not contain the amount of the herb or substance that is written on the label, and some may include other substances (contaminants). The FDA has written new rules to improve the quality of manufacturing processes for dietary supplements and the accurate listing of supplement ingredients. But, the new rules do not address the safety of supplement ingredients or their effects on health when proper manufacturing techniques are used. 

Most such supplements have not been tested to find out if they interact with medicines, foods, or other herbs and supplements. Even though some reports of interactions and harmful effects may be published, full studies of interactions and effects are not often available. Because of these limitations, any information on ill effects and interactions below should be considered incomplete.

High doses of vitamin A supplements can cause nausea, vomiting, diarrhea, loss of appetite, tiredness, headaches, dizziness, blurred vision, poor muscle coordination, itchiness and scaling of the skin, bone pain, hair loss, irregular menstruation in women, osteoporosis, and temporary or permanent liver damage. They can also cause birth defects if taken during pregnancy. Relying on this type of treatment alone and avoiding or delaying conventional medical care for cancer may have serious health consequences.