Ten carotenes, colored molecules synthesized only in plants, show vitamin A activity. In other words, they function like vitamin A. However, only the alpha- and beta-carotenes and cryptoxanthin are important to man, and beta-carotene is the most active. Beta-carotene and other carotenoids that can be converted by the body into retinol are referred to as provitamin A carotenoids. Hundreds of different carotenoids are synthesized by plants, but only about 10 % of them are provitamin A carotenoids.

Beta-Carotene also helps prevent night blindness and other eye problems, skin disorders, enhance immunity, protects against toxins and cancer formations, colds, flu, and infections. It is an antioxidant and protector of the cells while slowing the aging process.

Recent reports show natural Beta-Carotene aids in cancer prevention. It is important in the formation of bones and teeth. No vitamin overdose can occur with natural Beta-Carotene. About two decades ago, it was reported that beta carotene offered a notable measure of photoprotection to individuals with porphyria. (Beta-Carotene helps to protect the eye and vision).

Increased consumption of fruits (apricots have more beta carotene than carrots) and vegetables is associated with a lower risk of cancer. Supplementation with Beta-Carotene may have a similar benefit.

It might just be other compounds in the vegetables such as lutein and lycopene3 that offered the protection. Beta carotene is remarkably safe and free of side effects. Beta carotene is closely related to vitamin A, but there is a big difference. Large doses of vitamin A definitely can cause health problems. If one chooses to take supplemental beta carotene, it is hard to achieve the blood levels that have proven helpful in porphyria by diet alone. Beta carotene comes in a 30mg pill. Some must take ten or more per day to see benefit. This would be like eating about 2 lbs. of carrots every day.4

The decision to take supplemental beta carotene can be difficult to make. You might want to consider it in summer, if your skin is quite fair, if sun exposure is unavoidable, and/or if your disease is severe. Although available without a prescription, it would be important to discuss the matter with your doctor, who likely would monitor blood levels periodically. Interest in systemic photoprotection continues to develop. Last year, a substance called PL was found to triple tolerance to UV light in healthy volunteers.5

Beta-carotene is an antioxidant and boosts the immune system. As with many supplements, beta-carotene is not the same in its natural and synthetic states. Natural beta-carotene consists of two molecule types; synthetic beta-carotene contains only one of these. While many of the benefits of beta-carotene can be found in both forms, some have argued some properties, such as its antioxidant effect is only found in its natural form but there I not scientific proof of the claim. Beta carotene deficiencies often occur in people who do not eat leafy green vegetables. When supplements are used, vitamin E supplements are also necessary, as beta-carotene appears to reduce blood levels of vitamin E.

Beta-Carotene is often low during the more advanced stages of HIV. Supplementation of 300,000 IU daily may help increase the number of CD4+ cells found, CD4+ cells are a type of white blood cells that are low in AIDS patients.
Low Beta-Carotene levels are often associated with the development of lupus. Taking this supplement may help ease some of the arthritic problems associated with this condition. Eating foods with beta carotene also lowers the risk of macular degeneration.

Vitamin A is a major source of beta carotene and has also been shown to reduce the risk of cataracts. The most common beta-carotene supplement intake is probably 25,000 IU (15 mg) per day, though some people take as much as 100,000 IU (60 mg) per day. Beta-Carotene appears to have potential in the prevention and treatment of cancers, including lung cancer, and oral cancer. Other members of the antioxidant carotene family include cryptoxanthin, alpha-carotene, zeaxanthin, lutein, and lycopene, but most of them do not convert to significant amounts of vitamin A.

Scientific Explanation:
Fat-soluble vitamins pass with the chylomicrons into our lymphatic system. Vitamin A, first presenting as a precursor, beta-carotene, is cleaved to form retinol, which is then recombined with fatty acids before entering the chylomicron.
Beta-carotene, the principal yellow pigment of the carrot is of health importance because the animal organism apparently is able to cleave the molecule at the point of symmetry with the production of vitamin A. The vitamin, which functions directly in vision, is a component of a pigment, called visual purple, present in the retina of the eye.

References
1. Mathews-Roth MM. Systemic Photoprotection.
Dermatol Clinics. 1986;4:335-39

2 Omaye ST, et al. Beta carotene: friend or foe.
Fundam Appl Toxicol. Dr Joseph Malak 1997;40:163-74

3 Nishino H. Cancer prevention by natural carotenoids.
J Cell Biochem Suppl. 1997;27:86-91

4 Mangles AR, et al. Carotenoid content of fruits and vegetables: an evaluation of analytic data. JADA. 1993;93:284-296

5 Gonzalez S, et al. Topical or oral administration with an extract of Polypodium leucotomos prevents acute sunburn. Photodermatol Photoimmunol Photomed. 1997;13:50-60