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New Findings Add to Mounting Evidence: Beta-Carotene Supplements and Related Carotenoids Reduce Risk of Prostate Cancer
May 23, 1997, LaGrange, IL -- Beta-carotene supplements can sharply reduce the risk of prostate cancer in men with low beta-carotene blood levels, according to new findings released by researchers at the Harvard Medical School. Prostate cancer is the second leading cause of death from cancer in men and the American Cancer Society estimates some 334,500 new cases of prostate cancer will be discovered in this year alone.
This research adds momentum to the growing interest in antioxidants called "carotenoids" and their ability to fight cancer. An earlier study by Harvard University researchers showed that men consuming large quantities of tomatoes, rich in a beta-carotene-related nutrient called lycopene, had only about half the risk of prostate cancer as did men who consumed little of the nutrient.1
Meir Stampfer, M.D., and his colleagues have followed the diets, lifestyles, and health of more than 22,000 male doctors in the ongoing Physicians' Health Study. Half of the participants were given beta-carotene (50 mg every other day), and half were given a placebo. The researchers measured the men's blood levels of beta-carotene at the start of the 12-year study. They assumed that these levels reflected dietary intake of beta-carotene that would remain relatively consistent through the following years.
In these latest findings, physicians with low levels of beta-carotene, because they presumably ate few fruits and vegetables, were one-third more likely to develop prostate cancer. However, the men who also took beta-carotene supplements seemed to compensate for their deficient diets. Those who took supplements were 36 percent less likely to develop prostate cancer than those who ate few beta-carotene-rich fruits and vegetables and did not take supplements.
Dr. Stampfer reported his findings May 19 at the annual meeting of the American Society of Clinical Oncology, held in Denver.
Building on the encouraging findings in beta-carotene research, scientists are discovering tremendous health benefits in related carotenoids which have been shown to significantly reduce the risk of cancer. Natural carotenoid supplements contain a mixture of compounds in addition to beta-carotene. These carotenoids are present in amounts and ratios comparable to those in fruits and vegetables. The related carotenoids are called alpha-carotene, lycopene, lutein, zeaxanthin, and cryptoxanthin.
In addition to beta-carotene and lycopene, the carotenoid zeaxanthin has also been shown to be important in increasing communication between normal cells and tumor cells and decreasing the growth rates of tumor cells,2 according to John Bertram, Ph.D., at the University of Hawaii, Cancer Research Center.
Recently, British researchers for the first time described some of the details of how beta-carotene turns on the immune system to seek out, identify, and destroy cancer cells.3
The most recent study on beta-carotene and prostate cancer risk offers new promise for the value of supplementation among people who do not regularly consume fruits and vegetables. Numerous studies have shown that only a relatively small percentage of Americans eat 3-5 servings of fruits and vegetables daily, an amount routinely recommended by health authorities. The National Cancer Institute recommends that people consume 5-9 servings of fruits and vegetables to reduce the overall risk of cancer.
Gladys Block, Ph.D., of the University of California, Berkeley, has reported that only 9 percent of Americans manage to eat 3-5 servings of fruits and vegetables daily, and 45 percent of the population fails to consume any fruits and vegetables on any given day.4
Even the most optimistic appraisal of eating habits shows Americans fall far short of dietary recommendations for fruits and vegetables. Susan M. Krebs-Smith, Ph.D.,
of the National Cancer Institute reported in 1995 that only 32 percent of Americans ate 4 daily servings of fruits and vegetables.5
Furthermore, while adults routinely exaggerate the amount of fruits and vegetables they eat to begin with, food processing decreases beta-carotene levels in the produce they do consume. That means people who do eat their fruits and vegetables may fail to get all of the beta-carotene and other carotenoids they need or believe they get.
According to a study of 2,000 households by the United Fresh Fruit and Vegetable Association, many people believe they should eat more fruits and vegetables. However, the same people over-estimated their consumption of produce by 33 percent.
Another recent study at the Leatherhead Food Research Association, Surrey, England, found that simple handling and processing of vegetables can dramatically lower their levels of beta-carotene. The British researchers found that carotenoid levels decrease rapidly when vegetables are left in open containers, exposed to fluorescent lighting in display cabinets, or cooked.6
The VERIS Research Information Service is a not-for-profit corporation that strives to provide a responsible source of information on the role of nutrition in health, with emphasis on antioxidants, to health professionals, researchers, and health and nutrition educators/communicators worldwide. ###
REFERENCES
1 Giovannucci E, Ascherio A, Rimm EB, et al., "Intake of carotenoids and retinol in relation to risk of prostate cancer," Journal of the National Cancer Institute, 1995;87:1767-1776. 2 Bertram, J.: Personal Communication
3 Hughes DA, Wright AJA, Finglas PM, et al., "The effect of beta-carotene supplementation on the immune function of blood monocytes from health male nonsmokers," Journal of Laboratory and Clinical Medicine, 1997;129:309-317.
4 Patterson BH, Block G, Rosenberger W, et al., "Fruit and vegetables in the American diet: data from the NHANES II survey," American Journal of Public Health, 1990;80:1443-1449. 5 Krebs-Smith SM, "US adults' fruit and vegetable intakes, 1989 to 1991: a revised baseline for the Health People 2000 objective," American Journal of Public Health, 1995;85:1623-1629. 6 Thane C and Redd S, "Processing of fruit and vegetables: effect on carotenoids," Nutrition & Food Science, March/April 1997:58-65.
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