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Thomas S. May, M.A.Medical Writer |
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Some Dietary Supplements Can Cause (Not Prevent) Cancer
Thomas S. May, Medical Writer
Introduction Vitamins, minerals, and herbs are big business. US consumers spend billions of dollars each year on dietary supplements in the hope of boosting health and warding off cancer and other diseases. Recent surveys have found that a large percentage of adults in the United States take some kind of dietary supplement regularly. Some of these supplements may be helpful, but there is very little scientific evidence to back up many of the claims made for most of them. In fact, there are growing concerns that some supplements may actually be harmful and may even increase your risk of getting cancer or other serious conditions. One common supplement that has been linked to an increased risk of cancer in some people is beta-carotene--a substance found in carrots and some other vegetables and fruits. Two studies "have shown that at high doses, in a supplement form, beta-carotene may increase the risk for cancer--specifically, for lung cancer in smokers," says Cheryl Rock, PhD, an associate professor at the Department of Family and Preventive Medicine at the University of California, San Diego. In one of the studies, researchers found an 18% increase in lung cancer rates among male smokers who had been taking 20 milligrams of beta-carotene every day for up to 8 years. In another study, a large number of male and female smokers, as well as some asbestos workers, took 30 milligrams of beta-carotene plus 25,000 international units of vitamin A every day for about 4 years. The investigators decided to stop the study when they learned that the rate of lung cancer was 28% higher for those taking beta-carotene and vitamin A than it was for the control subjects, who did not take supplements. Another popular supplement now drawing fire is chromium picolinate, which has been touted as a weight-loss aid and muscle builder. But according to a review article published in the Archives of Family Medicine (Vol. 8-5), these claims aren't supported by solid research. Plus, animal studies have shown that it could even have harmful effects--like damaging chromosomes, making it a potential carcinogen. The authors conclude that people should be cautious of using chromium picolinate over a long period of time.
Harmful Herbs Herbs are generally not part of the regular diet for most people, but hundreds of herbal preparations are sold as dietary supplements in pharmacies, health food stores, and even supermarkets. Calling herbs "dietary supplements" is very dangerous and misleading, according to Stephen Barrett, MD, an outspoken critic of the dietary supplement industry.
"To my mind, a 'supplement' is something that's in the diet--that your body uses," Barrett says. "Herbs are either nothing if there is nothing in them, or if they have an effect they should be considered drugs." Nevertheless, the US Food and Drug Administration (FDA) has classified herbs as dietary supplements, not drugs, and few laws regulate how they are sold.
According to Barrett, a number of herbs clearly cause cancer. These include Aristolochia fangchi, which contains aristolochic acid. An FDA Consumer Advisory issued on April 11, 2001, reports that taking products that contain aristolochic acid has been linked to permanent kidney damage and kidney failure, as well as certain cancers, especially of the urinary tract. Probably many other herbs also contribute to cancer, says David M. Klurfeld, PhD, chair of the Department of Nutrition and Food Science at Wayne State University. And even when we know an herb is harmful, he says, it's very hard to protect the public from it. Sassafras, for example, is banned for human consumption because it causes cancer. "But you can still buy the leaves in some health food stores," he says, "because the package is labeled 'Not for human consumption' or something similar. Of course, the package will tell you how to make tea from the leaves."
FDA Can't Protect You Barrett also claims that the US government cannot now protect the public from potentially harmful herbs. One of the reasons for this, he says, is that the dietary supplement industry has managed to weaken the laws regulating their product--resulting, for instance, in herbs earning the "supplement" label. The US Congress defined the term "dietary supplement" in the Dietary Supplement Health and Education Act (DSHEA) of 1994. According to the DSHEA, a dietary supplement is a product taken by mouth that contains a "dietary ingredient" intended to supplement the diet. The "dietary ingredients" in these products may include one or any combination of the following:
Because they have been classified as supplements, herbs can't be controlled and regulated in the same way that drugs are--even though most herbal supplements are taken for their supposed beneficial effects on health. Therefore, Barrett suggests that the FDA should "stop pretending" that they have an effective monitoring and enforcement program. "I think they should shut down their enforcement program and tell the public that if you want to be on your own, you're on your own," he says. "If you want to have protection, you tell Congress to give us a law that we can use to protect you. Right now, the setup is such that we can't protect you."
Thomas S. May is a medical
journalist based in Toronto, Ontario, Canada. He has a master's degree in
psychology from Simon Fraser University in Burnaby, British Columbia. Source: Medscape Health
Reprinted from Medscape Health for Consumers.
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