Lycopene as cancer preventive gains credence
Growing evidence shows carotenoid’s effectiveness
Folks who love lots of spaghetti with tomato sauce and who slather salsa liberally on their tacos appear to be getting a strong dose of cancer-preventing antioxidants — and maybe something more.
A growing body of evidence links lycopene to a reduced risk of breast, prostate, lung, and stomach cancers, as well as protection against heart disease, age-related macular degeneration, and other age-related problems.
Lycopene, the major carotenoid that gives tomatoes their red color, has been examined in more than 70 studies, which show it neutralizes free radical oxygen molecules before they can cause cell damage. There’s a strong body of evidence that shows that free radicals — natural byproducts of life that can be exacerbated by exposure to smoking, poor dietary habits, emotional stress, and environmental pollutants — contribute to numerous degenerative diseases.
"The consistency of results across studies of varied populations and study designs argues against bias or confounding factors as the explanation for these associations," writes Elizabeth Johnson, PhD, of the Jean Mayer Human Nutrition Research Center on Aging at Tufts University in Boston.
Recent research from Israel has added to the evidence in favor of lycopene and perhaps sheds some light on its mechanism of action.
"We have several ideas about what’s happening here, but probably the most promising is that it interferes with the insulin-like growth factor signaling system and slows or stops reproduction of cancer cells," says Yoav Sharoni, MD, professor of medicine at Ben-Gurion University of the Negev in Beer-Sheva, Israel.1
Sharoni says it is clear that in addition to lycopene’s antioxidant properties, it somehow dramatically reduces the cycle of cell division.
Sharoni’s tissue cultures responded dramatically to exposure to lycopene — reducing the risk of breast and prostate cancers four- to seven-fold.
Not all carotenoids have the same effect, says Sharoni, implying there must be some unique substance in lycopene that produces such potent effects. In fact, the Finnish Alpha Tocopherol Beta Carotene (ATBC) trial and the Beta-Carotene and Retinol Efficacy Trial (CARET) studies showed heavy smokers and asbestos workers developed an increased risk for lung cancer when they received high-dose beta-carotene supplements.2,3
"Our best guess is that lycopene somehow postpones the growth of cancer cells, but we don’t think it prevents the formation of cancer cells," says Sharoni. "But postponing might mean that a cancer that would have otherwise appeared at age 60 or 70 might not appear until age 90 or 100. In my mind, that’s prevention."
Sharoni currently is beginning clinical trials on lycopene and breast cancer.
Among the dozens of other studies showing a wide range of health benefits from lycopene:
• Research that was presented at the 1999 Annual Meeting of the American Association for Cancer Research showed that after taking 15 mg of lycopene twice a day for three weeks, men previously diagnosed with prostrate cancer had smaller tumors and lower levels of PSA, a primary marker for prostate cancer.
• In the 48,000 subject Harvard Physicians’ Study, researchers found that men who ate more than 10 servings of tomato products a week had a 35% lower risk of prostate cancer than men who ate fewer than 1.5 servings.
• A 1997 study published in the American Journal of Epidemiology found that people with more lycopene in their bodies had a significantly lower risk of heart attack than those with lower lycopene levels.
• A Canadian study shows men who ate foods high in lycopene had significantly reduced LDL cholesterol levels after just one week.
• A study published in the Archives of Ophthal-mology in 1995 showed that people with the lowest levels of lycopene were at the greatest risk of developing macular degeneration.
• Data from the ongoing Kentucky Nun Study of 88 elderly Catholic nuns found that those with the highest levels of lycopene had better cognitive function and retained their ability to care for themselves longer than those with lower levels.
• Tufts University researchers found that lycopene shields skin from damaging ultraviolet sunlight, improving skin protection by 46%.
There’s every reason to encourage your patients to increase their consumption of lycopene-rich tomato products as well as other foods high in the nutrient, say the experts.
Lycopene is most bioavailable in cooked tomatoes, says Phyllis Bowen, PhD, associate professor of nutrition at the University of Illinois at Chicago. "For years, we’ve told people to eat as many fresh and raw vegetables as possible. But we’ve found that processing tomato products like spaghetti sauce and tomato juice make the lycopene 2.5 times more easily absorbed." What’s more, the lycopene is not damaged even with hours of cooking, so spaghetti sauce or chili can be simmered for hours, she adds.
"For healthy people, getting at least 30 mg of lycopene in your diet every day is a great strategy for preventing heart disease," says biochemist Sandiv Agarwal, PhD, a research associate at the University of Toronto, author of the Canadian study on cholesterol and lycopene.4
"This is easily achievable in the normal diet without the need for supplements," says Richard B. Van Breeman, PhD, associate professor of medicinal chemistry at the University of Illinois in Chicago. He theorizes that the absorption of lycopene in the human body is very similar to the absorption of cholesterol, so the negative effect of excessive cholesterol can be cancelled out by sufficient lycopene consumption.
Here’s the lycopene content of several common foods:
• Tomato paste, 42.2 mg in two tablespoons;
• Spaghetti sauce, nearly 22 mg in ½ cup;
• Tomato ketchup, more than 15 mg in one tablespoon;
• Tomato juice, 17 mg in an eight-ounce glass;
• Watermelon, 4 mg in a 10-inch by one-inch slice;
• Pink grapefruit, 4 mg in a half-grapefruit.
In addition, lycopene and tomato powder are available as supplements at health and nutrition centers in 5 mg and 10 mg capsules and tablets.
There have been no short-term side effects reported from the use of lycopene at these levels, but researchers say there has not yet been enough research to determine conclusively if long-term side effects can be associated with its use.
References
1. Karas M, Amir H, Sharoni Y et al. Lycopene interferes with cell cycle progression and insulin-like growth factor I signaling in mammary cancer cells. Nutr Cancer 2000; 36:101-111.
2. Tornwall ME, Virtamo J, Haukka JK, et al. The effect of alpha-tocopherol and beta-carotene supplementation on symptoms and progression of intermittent claudication in a controlled trial. Atherosclerosis 1999;147:193-197.
3. Redlich CA, Chung JS, Cullen MR, et al. Effect of long-term beta-carotene and vitamin A on serum cholesterol and triglyceride levels among participants in the Carotene and Retinol Efficacy Trial. Atherosclerosis 1999; 145:425-432.
4. Rao AV, Agarwal S. Role of antioxidant lycopene in cancer and heart disease. J Am Coll Nutr 2000; 19:563-569.
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