Beta Carotene Health Article

Description

Beta carotene is one of the most important naturally occurring antioxidants. It is a fat-soluble pigment found in plants (notably carrots and many colorful vegetables and fruits) and in the sea alga Dunaleilla salina and D. bardawil. Naturalbeta carotene supplements are derived primarily from D. salina. Beta carotene is one of the major dietary carotenoids and one of the most biologically active of approximately 800 carotenes and more than 1,000 carotenoids present in food. It is responsible for the orange or yellow colors of many fruits and vegetables. In the human body, beta carotene is found in lipids and in fat tissues. Sometimes beta carotene is called provitamin A because it is more easily converted to vitamin A (retinol) in the liver than other carotenoids. Beta carotene is considered to be a conditionally essential nutrient because it becomes essential when vitamin A intake is low.

Beta carotene consists of a chain of 40 carbon atoms, with conjugated double bonds and a ring structure at each end of the chain. Depending on the positions of the molecular groups attached to the carbon chain, naturally occurring beta carotene may be:

• All-trans beta-carotene
• 9-cis beta-carotene
• 13-cis beta-carotene, in smaller amounts

Synthetic beta carotene is primarily all-trans.

In plants and alga, beta carotene and other carotenoids attract light for photosynthesis and provide protection from toxic forms of oxygen. Beta carotene is a powerful antioxidant because it destroys toxic free radicals, including singlet oxygen—an oxygen atom that is missing an electron and is very damaging to human tissue if not taken up quickly and "deactivated."

Vitamin A precursor

Vitamin A is obtained in the diet from animal products or is made in the liver from beta carotene and other carotenoids. Vitamin A is essential for:

• vision and eye health
• normal cell division
• growth
• reproduction and fertility
• immune system function
• skin and mucous membrane health

In sub-Saharan Africa about three million children under the age of five suffer from an eye disorder, caused by vitamin-A deficiency, that can lead to blindness and death. Although red palm oil, a traditional African food, contains high provitamin A, its substitution by imported cooking oils has reduced this dietary source in many homes. Many vegetables and fruits also contain provitamin A, but are not always consumed in adequate amounts. Vitamin A deficiency is the leading cause of blindness worldwide.

In the 1920s vitamin-A deficiency was linked to stomach cancer and to precancerous conditions in the epithelial (lining) cells of the throat and lungs. In 1977 vitamin A supplementation was shown to inhibit certain cancers and to reduce the growth of certain tumors in atrisk animals.

Dietary beta carotene

Daily values (DVs) are determined from the RDA. They are based on a 2,000-calorie diet and usually are expressed as a percentage of an RDA. The IUs and DVs for beta carotene, per serving, in common foods are listed in table 1.

Carrots and sweet potatoes that are more orange contain more beta carotene. New carrot cultivars that contain more beta carotene have been developed and high-beta-carotene sweet potatoes are being introduced into sub-Saharan Africa to treat vitamin-A deficiency.

Other foods that contain beta carotene include:

• avocados
• broccoli
• chard
• coffee
• collard greens
• palm oil and other food colorants
• squash
• string beans
• watermelon
• yams

According to the Institute of Medicine, a daily intake of 3–6 mg of beta carotene will keep the blood level within the range associated with a lower risk for chronic diseases. The recommended daily diet of five or more servings of fruits and vegetables provides 3–6 mg of beta carotene (if carrots, sweet potatoes, papaya, apricots or other very high carotenoid food is used, the RDA can be met in a single serving). In contrast, the average American diet contains 1.3–2.9 mg daily. Vegetarians may have twice as much beta carotene in their blood as compared to non-vegetarians, because they generally consume a lot more greens and fruits.

Beta carotene in food is found within an oil or a matrix of sugars and proteins; and, therefore, the absorption of beta carotene by the body varies greatly. The elderly, and those with bad digestion and liver trouble may be at risk for poor absorption from an adequate beta carotene diet.

Animal sources of vitamin A are more easily absorbed than plant sources of beta carotene, particularly if the vegetables and fruits are eaten raw or whole. Although beta carotene can be converted to vitamin A in the body, it has its own unique physiological functions and beta carotene and vitamin A are not totally identical in the health benefits they deliver. So it is good to eat sources of both. While supplementation is helpful to those who have trouble absorbing adequate beta carotene, getting all or some beta carotene through food sources rather than supplements alone is by far the best. This is substantiated by research showing there are many beneficial carotenoids in foods, and that they may also work together synergistically to optimize health.