Vitamin A - Vitamins

Vitamin A

Vitamin A is a fat-soluble, solid terpene alcohol essential for skeletal growth, testicular and ovarian function, embryonic development, and differentiation of tissues. It is crucial for the normal functioning of the eye. In addition, vitamin A is required for adequate immune system response, builds the body's resistance to respiratory infections, and helps form and maintain healthy skin, hair, and mucous membranes.

Vitamin A is available in several forms. Retinols are a derivative of vitamin A found in foods that come from animals (meat, milk, and eggs), as well as fish liver oils, cheese, and butter. Betacarotene, a pre-vitamin found in leafy green vegetables and yellow fruits, is converted by the body into vitamin A.

Symptoms of vitamin A deficiency include lack of tear secretion, dry or rough skin, weight loss, poor bone growth, weak tooth enamel, night blindness, changes in mucous membranes, susceptibility to respiratory infections, and diarrhea. Many months of a vitamin A deficient diet are required before any adverse symptoms develop, however, and most healthy individuals have a two-year supply of vitamin A stored in the liver.

Vitamin A deficiency can cause several major eye diseases and is a major health problem in many developing countries. One of these diseases, xerophthalmia, characterized by conjunctival dryness with hardening of the tissue, is contracted by approximately 500,000 people each year in India. Half of these reported cases lead to blindness, and only 30% of children with severe xerophthalmia are likely to survive, according to a report by K. Vijayaraghavan in the December 1, 1990, issue of Lancet .

Overdoses of vitamin A can lead to hypervitaminosis A, resulting in fatigue, abdominal upset, brittle nails, and other adverse side effects.

Vitamin A and Cancer.     Vitamin A and its derivatives (betacarotene, retinol) represent one class of anticarcinogenic phytochemicals. Vitamin A has been demonstrated to reduce cancerous tumors in animals and may reduce the risk of lung cancer in humans. In a study published in March 1992 by the New England Journal of Medicine, researchers reported that high doses of a derivative of vitamin A, marketed as the acne drug Accutane, prevent lung, throat, and mouth cancers in people who are at high risk of developing them.

Researchers at the M.D. Anderson Cancer Center of the University of Texas in Houston also successfully treated patients with head and neck cancer using Accutane. Because these patients' tissues already were primed to become cancerous, they were very likely to grow new, separate cancers that were more life-threatening than the first. Accutane prevented new cancers from forming in most patients in the study for nearly three years. However, the drug did not prevent the recurrence of the original tumors, as reported by Frank Murray in Today's Living, October 1992.

Accutane has serious side effects when administered in high doses, but researchers reported that if lower doses also work, the stage will be set for giving Accutane to people who smoke or drink heavily and are therefore at relatively high risk for head or neck cancers. The findings strongly indicated that other cancers might also be preventable.

Vitamin A also appears to lower the risk of breast cancer, according to Alternative Medicine: What Works . In a study of the diets of 89,494 nurses, those who ingested the most vitamin A had 16% less risk of breast cancer. When vitamin A supplements were given to those with the least of it in their diets, their risk also went down. In another analysis of the same data, the nurses with the most vitamin A in their diets had 39% fewer cataracts than those who had the least.

Vitamin A and Cervical Dysplasia.     Fugh-Berman also reports a controlled study of 301 women with cervical dysplasia in which derivatives of vitamin A called retinoids were applied to the cervix, or neck of the uterus. This treatment completely reversed the dysplasia in 43% of women, compared to 27% of those who used placebo cream. However, in severe dysplasia, there was no difference between using placebo and retinoids.

Vitamin A and HIV.     HIV-infected mothers who are deficient in vitamin A while pregnant are much more likely to transmit the virus to their babies. A survey of 338 pregnant, HIV-infected women in Malawi, as reported by Fugh-Berman, found that the HIV transmission rate among mothers with severe vitamin A deficiency was 32% versus 7% among women with healthy levels.

Vitamin A and Pregnancy.     Malnourished pregnant women often suffer from anemia because they lack the nutrient iron that is crucial for carrying oxygen in the blood. A 1993 study suggests that pregnant women have a much better chance of combatting anemia by ingesting vitamin A and iron supplements, instead of iron pills alone. The study, conducted in West Java, Indonesia, included 251 malnourished women who were between 16 and 24 weeks pregnant. One group of women received 2.4 mg of vitamin A and 60 mg of iron; a second group was given vitamin A and a placebo; a third group received iron and a placebo, and a fourth took two dummy pills. Anemia was eliminated in 97% of the women who received both vitamin A and iron pills. By comparison, anemia was eliminated in 68% of those who took only iron, 35% who took vitamin A alone, and 16% who took only the placebos. Dr. D. Suharno, writing in the November 27, 1993, issue of Lancet, warned that extremely high doses of vitamin A can be toxic, however, and cause fetal malformations during the first three months of pregnancy.