Antioxidant Vitamins and B-Carotene in Disease Prevention
By James A. Jackson, Ph.D.
Many studies have shown the relationship between free radical generation (mainly oxidants) and some pathologies associated with aging. The evidence that antioxidant vitamins and B-carotene may play an important role in promoting health and reducing the risk of chronic diseases has been accumulating for over 20 years. The evidence has become so great that The American Journal of Clinical Nutrition devoted the complete December 1995 issue to proceedings from a symposium held in Berlin, Germany, on October 1-12, 1994, titled “Antioxidant Vitamins and B-Carotene in Disease Prevention.” Although it is impossible to present all the articles here, it is gratifying to note that many of the authors restate or recommend ideas and theories that The Center has been promoting for years.
Vitamin E also was effective in preventing cataracts.
Dr. Richard Doll, in discussing chronic and degenerative diseases, stated that cancer, heart attacks, and strokes cause 3/4 of all deaths at 35-69 years of age, and 2/3 at older ages. The risk of dying before age 70 is 25 % (16% in women and 30% in men). Since chronic and degenerative diseases are the result of a series of changes built up over a time and may be produced by many different agents, the author says that it is possible to prevent, or delay many diseases.
Dr. Mark Levine and others reported that the RDA for vitamin C, 60 mg/d, while preventing scurvy, may not represent optimal vitamin C amounts. The amount needed for optimal human health is unknown. They also reported that vitamin C has little toxicity and is usually represented by abdominal bloating and diarrhea. This may occur after doses of greater than 2 g are taken at once.
Drs. M.J. Stampfer and E.B. Rimm reported that people from two large studies who used supplemental vitamin E for longer than 2 years had 40% lower rates of cardiovascular disease. Vitamin E from dietary sources only and doses less than 100 IU/d had no similar effect. Drs. G van Poppel and R.A. Goldbohm reported that dietary B-carotene caused a significant reduction in cancer from the following sites: lung (10 studies of 3067 people); stomach (7 studies of 3386 people); esophagus (4 studies of 1796 people); cervix (2 studies of 630 people); pancreas (2 studies of 376 people); colon, rectum (5 studies of 2316 people); and prostate (3 studies of 571 people).
Dr. A. Taylor and others reviewed aging, antioxidant status, and cataracts. Cataracts are the leading cause of blindness throughout the world. In the U.S., cataracts increase from an incidence of 5% at age 65 to over 40% at age 75 or older. Age related cataracts in the U.S. cost $5 billion/year. A delay in cataract formation by 10 years would reduce the prevalence of cataracts by 45%. Cataracts form because the lens is 98% protein and is not replaced as a person ages. Therefore, as proteins are damaged by free radicals from exposure to ultraviolet light, smoking, oxygen, or metabolic diseases, they accumulate and precipitate in the lens causing cataracts. Many studies have shown that supplementation with vitamin C causes a reduction in cataract formation. One study showed that people who consumed more than 300 mg/d had 1/3 less cataracts than those not supplementing. Another study showed that those consuming about 490 mg/d of vitamin C had 25% less cataracts than those consuming less than 125 mg/d. Vitamin E also was effective in preventing cataracts. Persons who consumed vitamin E supplements of more than 400 IU/d had 56% less cataracts than those not supplementing with vitamin E.
One of the most interesting articles was by Dr. A. T. Diplock who reported on the safety of antioxidant vitamins and B-carotene. The author restated the possibility that major diseases which afflict humans worldwide may be preventable by improving the dietary intake of antioxidant nutrients, and that optimal intakes of antioxidants may not be achievable by diet alone; supplements may need to be taken. He stated the toxicity of vitamin E was ‘very low, even at high doses. The possible exception is in persons with a vitamin K-associated blood coagulation disorder. Toxicity of B– carotene has not been reported, even with doses as high as 50 mg/d. In some people with high doses, yellowing (or hypercarotenemia) of the skin may occur. Massive evidence exists that vitamin C at doses of greater than 1 g/d is safe and that adverse effects do not occur in healthy subjects ingesting large amounts of vitamin C.
This edition of The American Journal of Clinical Nutrition is available in The Center’s library. Although technical in some instances, it would , still be worthwhile to stop by the library and review the journal if you have an interest in this subject.