Beta Carotene Introduction

Beta-carotene is one of several carotenoids that serve as precursors to Vitamin A; other carotenoids include lycopene and zeaxanthin. Beta-carotene is also called Provitamin A because it is converted to retinol (Vitamin A) in the gut. [1]

Beta-carotene has one sixth (1/6) the activity of Vitamin A in the body. And like Vitamin A, beta-carotene is also a fat-soluble nutrient. Due to this characteristic, once the stores of Vitamin A are full, beta-carotene will not be converted in the gut. Excess amounts will then be excreted out of the body via feces or urine.

In the early 20th century beta-carotene was believed to be a vitamin. We now know that this is not the case. However, beta-carotene is still considered conditionally essential in the event of Vitamin A deficiency. Vitamin A deficiencies are very rare in the United States because many dairy products are enriched with this nutrient. In addition, Vitamin A is readily abundant in the majority of meat and animal products consumed by Americans. Vegetarians are also not at risk, as they obtain most of their vitamin A from the beta-carotene found in various fruit and vegetable sources regularly consumed. In other parts of the world, specifically non-Western societies, Vitamin A deficiency does still exist.

Beta-carotene is a potent anti-oxidant. It quenches singlet oxygen and inhibits lipid peroxidation. It is equally effective at reducing oxidative damage caused by free radicals. [2]

Beta-carotene is also considered an immunomodulating nutrient. It increases T helper cells and Natural Killer (Nk) cells, which are vital to our body’s defenses against outside organisms such as bacteria and viruses.

Beta-carotene is also believed to be an effective anti-cancer treatment by being anti-mutagenic. Recently, there have been mixed conclusions from various studies concerning this action. In certain populations, beta-carotene may have a correlation with increased risk of developing certain cancers, namely lung cancer in smokers. Individuals with a history of cancer or an increased risk of cancer (such as smokers) should consult their physician before beginning any supplementation with beta-carotene.

The greatest amounts of beta-carotene is found in colorful fruits and vegetables, being most abundant in orange and yellow hues. The following table lists the amounts of beta-carotene in various foods. The amounts are listed as International Units (IU) and also as a recommended percentage of the established Daily Values. Beta-carotene is not as active biologically as Vitamin A. In fact, only 30% is absorbed in the gut. 30% of that amount is then converted to Vitamin A for physiological use.

Table 1: Selected Food Sources of Beta Carotene [3]

Several of the items listed contain more than 100% of the Daily value as set by the USDA. These foods are considered safe to consume because all of the contained beta-carotene will not be converted solely to Vitamin A. Vitamin A is only considered toxic in high doses. However, beta-carotene can be consumed in doses as high as 180 milligrams (mg) or 300,000 IU with no side effects. This is due to the decreased conversion of beta-carotene to Vitamin A, once Vitamin A stores are full.

There is conflicting research on the benefits of beta-carotene supplementation and cardiovascular disease. For many years, epidemiological studies where showing a correlation between reduced risk of heart disease and carotenoids intake. So when clinical trials were conducted similar results were expected. However, the dietary supplementation of carotenoids showed the exact opposite - an increased risk for heart disease. To date, this conflict in findings exists. It is believed that dietary (food sources) carotenes may be protective, as opposed to high dose supplements, which may prove harmful. [4]

In one study beta-carotene was associated with a decreased risk of developing atherosclerosis, or narrowing of the arteries. [5] Higher dietary intakes of beta-carotene are associated with a decreased risk for coronary artery disease (CAD), and an overall decrease in heart disease in populations that are not at risk. [6] It is suggested that beta-carotene be given as a part of a complete multivitamin and not as a single nutrient. [7]

The conflict studies with heart disease and beta-carotene supplementation is similar to its supplementation and associated benefit on cancer. Epidemiological studies have shown benefit, but certain clinical trials have shown an increased risk for cancer development. [8] This risk is significantly raised in certain “at risk” populations, such as smokers and those with a positive family history. Therefore, researchers suggest that beta-carotene be obtained from natural sources and not synthetic forms, which may be carcinogenic. [9]

Despite these contradictory findings, recent study has found that beta-carotene is associated with a preventative effect in colon cancer in non-smokers. [10]

Beta-carotene is an immune stimulating nutrient. It has been shown to increase the numbers of white blood cells including T cells, monocytes, and natural killer cells. [11] High doses of beta-carotene were able to increase CD4 cells after only two weeks of supplementation in study. [12]

Because of the immune stimulating effects of beta-carotene, numerous trials have been carried out measuring the effects it has on white blood cells in HIV/AIDS. Beta-carotene levels in the blood are decrease in patients with HIV and other autoimmune disorders. [13] The dietary supplementation of beta-carotene caused an increase in CD4 cells by more than 11% and also caused a remission of symptoms such as night sweats, fever, diarrhea, weight loss, and fatigue. [14] Beta-carotene has also been shown to reduce the damage caused by oxidative stress in HIV. Its antioxidant activity have been shown to decrease lipid peroxidation and increase in glutathione levels. [15, 16]

Beta-carotene may also be beneficial for reducing the prevalence of childhood asthma. [17] Research has shown this fat-soluble vitamin to be effective at treating exercise-induced asthma, with a reduction in over 50% of the cases. [18]

Beta-carotene is an effective treatment for erythropoietic porphyria. This disease causes the production of porphyrins, which are cytotoxic molecules that cause increased photosensitivity in some individuals. Beta-carotene protects against this photosensitivity and also the damage to the cell membrane that is caused by the porphyrins. [19]

The usual dosage of beta-carotene is 3 - 15 mg per day or 5,000 - 25,000 IU per day. [20] If one consumes the recommended 5 fruits and vegetables daily, they will consume approximately 3 - 6 mg of beta-carotene. Raw foods can have a lower absorption level than cooked foods, or beta-carotene that is obtained by vitamin supplement.

Because beta-carotene is not an essential nutrient, there are no established reference values for daily intake or upper limit. Beta-carotene is a Provitamin A molecule. Three milligrams (3mg) of beta-carotene is equal to rougly 5000 IU of Vitamin A. Again, beta-carotene is not as readily absorbed as Vitamin A, with approximately 30% of beta-carotene obtained from the diet entering the bloodstream. In addition, beta-carotene is not as active inside the body as Vitamin A. It has 1/6 the activity of Vitamin A.

The following tables list the RDA (Reference daily allowance), AI (Adequate Intake), and Upper Limits for Vitamin A, which is an active metabolite of beta-carotene.

Table 2 : RDA of Vitamin A in RAE (mcg) and International Units (IU) [21]

Table 3: Established Adequate Intake for Vitamin A in Infants [22]

Table 4: Established Upper Limit Intake for Vitamin A [23]

Beta-Carotene Deficiency

Beta-carotene is a conditionally essential nutrient. It only becomes essential when there is a deficiency of Vitamin A. Therefore, there are no deficiency states of beta-carotene. However, there are serious symptoms from a deficiency of Vitamin A.

Persons with a deficiency of Vitamin A can have symptoms such as dry eyes, night blindness, and hardening of the sclera (eye). They can experience changes in their hair and nails such as dryness and brittleness. Vitamin A deficiency also causes a decreased immunity and upsets the function of the gastrointestinal and genitourinary systems. Children with a deficiency of Vitamin A will have poor growth.

Beta-Carotene Toxicity

Beta-carotene has been safely consumed to dosages of 180 mg or 300,00 IU with no adverse side effects. [24] In higher dose, it can cause a benign condition known as carotenemia, where the skin is turned a orange-yellow color due to deposition of pigment. The signs of this condition are most prominent in the palms of the hands and soles of the feet. It is an reversible condition and can be differentiated from jaundice by observing the color of the sclera (whites of eyes). In jaundice the sclera will also be yellow, whereas in carotenemia, they will be white. Jaundice is a more serious sign of liver inflammation and can occur with high doses of Vitamin A.

Women who are pregnant or nursing are advised not to consume more than 6 mg per day, or 10,000 IU, of beta-carotene. [25] This is a precautionary recommendation because of the known teratogenicity of Vitamin A on the developing fetus and infant, and due to the lack of studies examining the safety of beta-carotene supplementation during pregnancy and lactation.

Even though beta-carotene is converted to Vitamin A, it has not been clinically shown to induce hypervitaminosis A. Once the total body stores of Vitamin A are full, beta-carotene is no longer converted to retinol (Vitamin A).

There has been a case report of excessive doses of beta-carotene causing amenorrhea (loss of menstrual cycle), but this has not been shown to be an effect in clinical or epidemiological studies.

The synthetic forms of beta-carotene are associated with an increase risk of cancer and should be avoided.

[1] www.pdrhealth.com Beta-carotene. January 2005.

[2] www.pdrhealth.com Beta-carotene. January 2005.

[3] US Department of Agriculture, Agriculture Research Service 2002. USDA Nutrient Database for Standard Reference, Release 15. Nutrient Data Laboratory Homepage, http://www.nal.usda.gov

[4] www.pdrhealth.com Beta-carotene. January 2005.

[5] D’Odorico A et al. High plasma levels of alpha and beta-carotene are associated with a lowered risk of atherosclerosis: results from the Bruneck Study. Atherosclerosis. 2000 Nov; 153(1): 231-239.

[6] Osgahion SK et al. Dietary carotenoids and risk of coronary artery disease in women. Am J Clin Nutr. 2003 Jun; 77(6): 1390-1399.

[7] Paolini M et al. Beta carotene- a cancer chemopreventative agent or co-carcinogen? Mutat Res. 2003 Jun; 543(3): 195-200

[8] www.pdrhealth.com Beta-carotene. January 2005.

[9] Paolini M et al. Beta carotene- a cancer chemopreventative agent or co-carcinogen? Mutat Res. 2003 Jun; 543(3): 195-200

[10] Nkondjock A, Ghadirian P. Dietary carotenoids and risk of colon cancer: case control study. Int J Cancer. 2004 May 20; 110(1): 110-116.

[11] www.pdrhealth.com Beta-carotene. January 2005.

[12] Alexander M, Newmark H, Miller RG. Oral beta-carotene can increase the number of ODT4+ cells in human blood. Immunol Lett. 1985; 9: 221-224.

[13] Tomaka FL, Cimoch PJ, Reiter MM et al. Prevalence of nutrient deficiencies in patients with HIV-infection. Int Conf AIDS. 1994; 10: 221. (abstract no. PB0898)

[14] Bianchi-Santemaria A, Fedeli S, Santemaria L. Short communication: possible activity of beta-carotene in patients with AIDS-related complex: a pilot study. Yale J Biol Med. 1995; 68: 19-23.

[15] Favier A, Sappey C, Leelere P et al. Antioxidant status and lipid peroxidation in patients infected with HIV. Chem Biol Interact. 1994; 91: 165-180.

[16] Delmas-Beauvieux MC, Pauchant E, Couchouron A et al. The enzymatic antioxidant system in blood and glutathione status in human immunodeficiency virus (HIV) infected patients: effects of supplementation of selenium or beta-carotene. Am J Clin Nutr. 1996; 64: 101-107.

[17] Rubin RN, Navon L, Cassano PA. Relationship of serum antioxidants to asthma prevalence in youth. Am J Resp Crit Care Med. 2004 Feb 1; 169(3): 393-398.

[18] Neuman I, Nahum H, Ben Amotz A. Prevention of exercise induced asthma by a natural isomer mixture of beta-carotene. Ann Allergy Asthma Immunol. 1999 Jun; 82(6): 549-553.

[19] Bohm F, Edge R, Foley S, Lange L, Truscott TG. Antioxidant inhibition of porphyria induced cellular phototoxicity. J Photochem Photobiol B. 2001 Dec 31; 65(2-3): 177-183.

[20] www.pdrhealth.com Beta-carotene. January 2005.

[21] http://ods.od.nih.gov Office of Dietary Supplements

[22] Institute of Medicine, Food and Nutrition Board. Dietary Reference intakes: Vitamin A, Vitamin K, Arsenic, Boron, Chromium, Copper, Iodine, Iron, Manganese, Molybdenum, Nickel, Silicon, Vanadium, and Zinc. National Academy Press, Washington DC; 2001.

[23] Institute of Medicine, Food and Nutrition Board. Dietary Reference intakes: Vitamin A, Vitamin K, Arsenic, Boron, Chromium, Copper, Iodine, Iron, Manganese, Molybdenum, Nickel, Silicon, Vanadium, and Zinc. National Academy Press, Washington DC; 2001.

[24] www.pdrhealth.com Beta-carotene. January 2005.

[25] www.pdrhealth.com Beta-carotene. January 2005.