Beta-Carotene

Overview

Beta-carotene belongs to a group of plant compounds called carotenoids. To date, over 500 carotenoids have been found to occur in nature. Carotenoids are the pigments that provide the yellow, orange, and red coloration in fruits and vegetables. Beta-carotene is the most abundant carotenoid in human foods and is generally thought to be the most important carotenoid for humans.

Beta-carotene, which is also known as pro-vitamin A, consists of two molecules of vitamin A linked together (A-A). Enzymes in the epithelial lining of the intestinal tract split beta-carotene into two molecules of vitamin A whenever the body needs it. (1) Beta-carotene is the most abundant precursor of vitamin A in fruits and vegetables.

Dosage Info

Dosage Range

6-30mg daily, certain medical conditions may warrant significantly higher doses.

Most Common Dosage

6mg (10,000IU) daily.

2mcg beta-carotene (supplement) =
12mcg beta-carotene (dietary) =
1RAE (retinol activity equivalents) = 1mcg retinol

Dosage Forms

Gelatin capsules.

Adult RDI

None Established

Adult ODA

10,000 - 30,000 IU

RDA

  • None established:

Interactions and Depletions

Interactions

Depletions

Active Forms

Beta-carotene.

Absorption

Beta-carotene and vitamin A are both hydrophobic, (fat-soluble) substances that must be broken down by pancreatic digestive enzymes in the intestine in order to be absorbed. This reduces them to micelle size, which allows them to be dispersed in the aqueous environment of the small intestine. After being micellized, both vitamin A and beta-carotene diffuse passively into the intestinal mucosal epithelial cells.

Side Effects

Ingestion of large doses of beta-carotene can result in a harmless side effect called carotenosis (orange coloring in the skin). This coloration is most noticeable on the palms of the hands and the soles of the feet. The discoloration goes away when the dosage is lowered or stopped.

Functions in the Body

Antioxidant:

Beta-carotene functions as a chain-breaking antioxidant. This means it does not prevent the initiation of lipid peroxidation, but rather, it stops the chain reaction by trapping free radicals, which halts the progression of free radical activity., (2) Beta-carotene is capable of quenching singlet oxygen free radicals in humans., (3)

A study involving one hundred fifty three patients with coronary artery disease evaluated the clinical impact of antioxidant supplementation, including vitamin C, vitamin E, beta-carotene, and selenium, on people with low HDL levels in an effort to improve the HDL-C:LDL-C ratio. The participants were followed for 12 months after randomization to one of the three groups. They received either placebo, simvastatin and niacin, or simvastatin, niacin plus antioxidants (vitamin C, vitamin E, Beta-carotene and selenium). The treatment groups compared to the placebo group had significant reductions in plasma cholesterol, triglycerides, and LDL-C. The desired increases in HDL-C were higher in the simvastatin/niacin group than in the simvastatin/niacin/antioxidant group. The investigators noted that the increases in the HDL2-C, Lp(A-I), and HDL particle size noted in the simvastatin/niacin group were apparently blunted by the additional use of the antioxidants. (4)

Chemotherapy stresses the antioxidant defense system and may lead to lower antioxidant levels which could cause an increase in the adverse side effects of the therapy. A study was conducted involving children with acute lymphoblastic leukemia who were undergoing chemotherapy were administered greater intakes of antioxidants. The increased consumption of beta-carotene at 6 months decreased the risk of toxicity. (5)

Clinical Applications

Immune Enhancing

beta-carotene has been shown to enhance both specific and general immune responses in experimental animals.In human trial, a 2 week administration of high dose beta carotene(180mg/day) increased T4 lymphocytes(helper cells) but did not effect T8 lymphocytes(suppressor cells).

Cancer

A summary of beta-carotene/cancer epidemiological studies shows that beta-carotene’s most effective use is against lung cancer. Low levels of beta-carotene are also associated with a greater risk for cancer of the cervix, esophagus, gastrointestinal tract, lung, mouth, throat, neck, and stomach. (6)

Photo-Protection

Beta-carotene protects plants from the free radicals that are produced during photosynthesis. It has been used in the treatment of patients with a genetic light-sensitive skin disorder called erythropoietic protoporphyria (EPP), which is characterized by a burning, swelling, and redness of the skin when exposed to sunlight. Results of a 7-year study showed that 84 percent of individuals increased their tolerance to sunlight without manifesting symptoms. (7) A more recent study found that beta-carotene is taken up into the cell in a dose dependent manner, where it then interacts with UVA radiation in the cell and provides the cell protection from photoaging-associated mtDNA mutation. (8)

Cataracts

One hundred fifty eight patients were followed for three years and daily use of beta-carotene, vitamin C and vitamin E demonstrated a small deceleration in the progression of age-related cataracts. (9)

Symptoms and Causes of Deficiency

Since beta-carotene is the dietary precursor of vitamin A, deficiencies of this nutrient are associated with the symptoms of vitamin A deficiency. Low dietary intake of beta-carotene is associated with a weaker immune system, which is probably due to increased amounts of free radical damage. The incidence of some cancer is also associated with low dietary intake of beta-carotene. Although several drugs are capable of reducing blood levels, the primary cause for a deficiency of beta-carotene is not eating enough fruits and vegetables.

Dietary Sources

Beta-carotene occurs exclusively in plant (fruit and vegetable) foods. Foods containing high amounts of beta-carotene are green leafy vegetables, carrots, sweet potatoes, squash, spinach, apricots, peaches, cantaloupe, and green, yellow, and red peppers.

References

  1. View Abstract: Nagao A, et al. Stoichiometric Conversion of All Trans-beta-carotene to Retinal by Pig Intestinal Extract. Arch Biochem Biophys. Apr1996;328(1):57-63.
  2. View Abstract: Iannone A, et al. Antioxidant activity of carotenoids: an electron-spin resonance study on beta-carotene and lutein interaction with free radicals generated in a chemical system. J Biochem Mol Toxicol. 1998;12(5):299-304.
  3. View Abstract: Mathews-Roth MM. Carotenoid functions in photoprotection and cancer prevention. J Environ Pathol Toxicol Oncol. Jul1990;10(4-5):181-92.
  4. View Abstract: Cheung MC, Zhao XQ, Chait A, Albers JJ, Brown BG. Antioxidant supplements block the response of HDL to simvastatin-niacin therapy in patients with coronary artery disease and low HDL. Arterioscler Thromb Vasc Biol. Aug2001;21(8):1320-6.
  5. View Abstract: Kennedy DD, Tucker KL, Ladas ED, Rheingold SR, Blumberg J, Kelly KM. Low antioxidant vitamin intakes are associated with increases in adverse effects of chemotherapy in children with acute lymphoblastic leukemia. Am J Clin Nutr. Jun2004;79(6):1029-36.
  6. Gaby SK, et al. Vitamin Intake and Health. New York: Marcel Dekker, Inc; 1991:36-39.
  7. View Abstract: Mathews-Roth MM, et al. Beta Carotene Therapy for Erythropoietic Protoporphyria and Other Photosensitivity Diseases. Arch Dermatol. Sept1977;113(9):1229-32.
  8. View Abstract: Eicker J, et al. Betacarotene supplementation protects from photoaging-associated mitochondrial DNA mutation. Photochem Photobiol Sci. Jun2003;2(6):655-9
  9. View Abstract: Chylack LT Jr, Brown NP, Bron A, Hurst M, Kopcke W, Thien U, Schalch W. The Roche European American Cataract Trial (REACT): a randomized clinical trial to investigate the efficacy of an oral antioxidant micronutrient mixture to slow progression of age-related cataract. Ophthalmic Epidemiol. Feb2002;9(1):49-80.