Beta-carotene is a long-chain hydrocarbon, exactly twice the size of a vitamin A (retinol) molecule. When absorbed, it is broken down into vitamin A.
      Beta-carotene is only 1 of about 500 compounds known as carotenoids, and is stored in lung, liver, kidney and fat tissues. The tissues also convert carotene into retinoic acid (an anticarcinogen) as needed.

      Dr. JoAnn Manson, an associate physician at Brigham and Women's Hospital in Boston, in a study of 87,245 nurses, found that women who had a daily intake of 15 to 20 milligrams of beta carotene/day were at a 40 percent lower risk of stroke, and a 22 percent lower risk of heart attack than women who got less than 6 mg./day.
[ A vitamin E intake of 100 mg./day conferred a 36% reduction in risk over those who got less than the RDA of 10 mg.]

      Drs. Charles Hennekens and J. Michael Gaziano (same research institution), in a study of 1271 elderly Massachusettes residents, found that the more beta carotene they consumed, the lower their risk of heart disease, independent of other risk factors for heart disease. Beta carotene reduced the death rate by 40-50 percent.

      A 1992 study from the University of Brussels (Belgium) analyzed the blood of 80 stroke patients for 21 days. Those with above-average vitamin A levels were more likely to survive, recover completely or have less disability.
      Ten patients with very high A levels showed no disabilities within 24 hours after their strokes. Those with high A who did not recover completely had less neurological impairment than those with low levels of vitamin A.

      Dr. Ronald R. Watson, of the U. of Arizona, demonstrated in a 1991 study that 60 older men and women (average age 56) who took 30 to 60 milligrams of beta-carotene daily for two months had more killer cells, T-helper cells and activated lymphocytes than those who did not take the supplement. Extra beta-carotene may booster a faltering, aging immune system.

      At a February meeting in San Diego called Carotenoids in Human Health, a study was presented by doctors from the Oregon Health Sciences Center that indicated 180 milligrams of beta-carotene/day increased CD4 cells (white blood cell type) in some HIV-infected people. Improvement was seen in some patients after four weeks.

      Animal studies have suggested that the carotenoids can prevent radiation-induced skin tumors and chemically-induced mammary and bowel tumors from becoming carcinogenic, as well as impact positively on the prevention of lung, mouth, throat, esophagus, cervix and bladder cancers.

      Dr. John Vena of the U. of Buffalo reported in the 1/93 Nutrition and Cancer journal that a study of 351 men with bladder cancer and 855 cancer-free men showed that carotenoids appear to reduce the risk of developing bladder cancer.

      Dr. Xiang-Dong Wang of the USDA's Human Nutrition Research Center:
"Beta-carotene may be converted to retinoic acid and prevent tumor growth. Retinoic acid has been shown to inhibit the growth of skin and and bladder tumors; it is a very strong preventative agent and treatment for cancer."

[Popular foods with highest levels of beta-carotene (descending order): sweet potatoes, cooked spinach, raw carrots, fresh cantaloupe, acorn squash, Romaine lettuce, uncooked, dried apricots, watermelon, cooked asparagus, summer squash, fresh peaches, corn (cooked on the cob).]

      A study in a 5/93 American Journal of Clinical Nutrition by U. of Michigan scientists, found that beta-carotene is absorbed much more readily when taken in pill or capsule form than when ingested as part of vegetables and fruits.
      Natural food sources' fiber and pectin inhibit the absoprtion of beta- carotene into the blood.
      People who depended on raw fruits and vegetables for their carotene got only half as much as people who took beta-carotene supplements.
[The researchers cautioned that larger studies are needed to confirm their findings, and, of course, people still should consume fruits and vegetables for fiber and numerous other constituents that cannot (or are not yet) found in pill form.]

[Natural Carotene Products Cooperative, Eustis, Fla., produces concentrated beta-carotene crystals derived from carrots, that include   both the cis- and trans- isomers of the molecule, which may be more   effective than the trans- alone.]

      Dr. Thomas E. Edes, an associate professor of general internal medicine at the U. of Missouri School of Medicine, fed lab rats benzopyrene, charcoal-broiled meats and some industrial wastes in an attempt to ascertain whether these carcinogens were preventing vitamin A from getting to the lungs and other tissues (people who smoke have lower- than-normal levels of vitamin A, but the general population is exposed to the same types of carcinogens through different avenues).
      Rats fed benzopyrene had abnormally low levels of vitamin A in their intestines, liver and lungs. Rats fed high doses of beta-carotene (non- toxic - converted to A) maintained normal levels of vitamin A in their tissue, despite exposure to benzopyrene.

      Patients who have suffered strokes and have higher blood levels of vitamin A are less likely to die and more likely to achieve a full recovery.
      In studies on 80 patients admitted to hospital following a stroke, a post-stroke, 21-day evaluation of neurological and functional status revealed that those with high blood vitamin A concentrations recovered fully within 24 hours. 10 of the 80 with high A levels experienced no disability after thier stroke, compared with five patients with low vitamin A concentrations.
      Among the patients who continued to experience neurological problems, those with high vitamin A levels scored better on tests used to measure neurological impairment.

      A study reported at the American Academy of Opthalmology meeting in Dallas in '92 showed that between 30-35% of people with macular degeneration showed some improvement after being given vitamin and mineral supplements.
      Researchers believe that free radicals contribute to the development of macular degeneration, and that vitamins A, C, E and beta-carotene may inhibit the harmful effects.