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2007-8-31 17:39:31 |
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Men taking multi-vitamin supplements often may increase their risk of death from prostate cancer, according to a new study published in the May 16 issue of the Journal of the National Cancer Institute. But experts caution that the study could not establish a causal relation between the risk and use of multivitamins, meaning multivitamin use does not necessarily raise the death risk associated with prostate cancer. The study, a statistical analysis, but not a trial, found that men who used multi-vitamins more than seven times a week were twice as likely to die of prostate cancer as men who never took vitamins. Those men were also at an increased risk of developing advanced or fatal prostate cancer, compared with men who never used multivitamins, reported Karla A. Lawson, Ph.D., of the National Cancer Institute and colleagues. But apparently multivitamin use was not associated with increased risk of developing prostate cancer overall, the study found. The study could not lead to any firm conclusion that taking vitamins definitely increases risk of men dying of prostate cancer. The National Cancer Institute does not change any policy to tell men to stop using multivitamin supplements, according to news media reports. Citing some experts? opinions, the news media uses the opportunity to quickly label taking vitamins as a bad thing, saying that taking multivitamin supplements increases risk of death from prostate cancer. Goran Bjelakovic, M.D., of the University of Nis, Serbia, and Christian Gluud, M.D., of the Copenhagen University Hospital wrote in an accompanying editorial, quoted by Medpage Today, that the findings "underscore the possibility that antioxidant supplements could have unintended consequences for our health." The findings are not new. Some early epidemiological (statistical in nature) studies have already found that multivitamin use was not linked with elevated risk of developing prostate cancer, but it was correlated with advanced prostate cancer. A scientist affiliated with foodconsumer.org who did not want to be named said that the link between increased risk of death from prostate cancer or developing advanced prostate cancer and taking vitamins may suggest that men who heavily took a multivitamin supplement probably had a reason for taking vitamins, meaning that they may have had some underlying conditions which may be the real risk factors for an increased risk of prostate cancer. One possibility is that those who heavily took multivitamins may have been diagnosed with local prostate cancer or precancerous lesions or signs and they were advised by their physicians or influenced by the news media to take vitamins to prevent the localized prostate cancer or their conditions from becoming advanced cancer. But the authors of the study report their findings in their study paper in a tune that sounds like taking vitamins would definitely cause harm to men. The notion prompts the researchers to worry. "Any association between intake of multivitamin supplements and the risk or severity of prostate cancer would have important consequences for public health," the researchers wrote, considering one-third of Americans are taking vitamins, as poll surveys reported early. In the prospective study, researchers followed 295,344 men aged 50 to 71 and free of cancer when they enrolled in the study in 1995 and 1996. Multivitamin use by each participant was surveyed using a self-administered, food-frequency questionnaire. Among the participants, five percent reported using multi-vitamins more than seven times a week and 36 percent took a multivitamin supplement every day. 41 percent reported using a one-a-day type of vitamins, 12 percent using a multivitamins plus iron supplement, and six percent using primarily B vitamins. 50 percent supplements were multivitamins. The health information on prostate cancer was obtained from questionnaires, Social Security Administration death records, and state cancer registries. During the five-year follow-up, 10,241 cases of prostate cancer were recorded including 8,765 localized and 1,476 advanced cancers, cited by Medpage Today. There were 179 cases of fatal prostate cancer over six years of follow-up. The researchers found that multivitamin use was not linked with over risk of prostate cancer, nor with localized prostate cancer. But men taking multivitamins often faced a 32 percent increased risk of advanced prostate cancer and with a 98 percent increased risk of fatal prostate cancer. Taking vitamins was also linked with higher incidences of advanced prostate cancer and fatal prostate cancer. The associations were strongest for men with a family history of prostate cancer, a fact that suggests that the reason they took multivitamins may be because they want to reduce their risk of developing prostate cancer. This possibility reinforces the speculation of the foodconsumer.org scientist. Among the men who had a family history, heavy multivitamin use defined as more than seven times per week was linked to more than doubled risk of advanced prostate cancer and a 15.41 times higher risk of fatal prostate cancer. But the study also found that those who took selenium, ?-carotene, or zinc were among those who faced the highest risk, which is less explainable. "Thus, excessive intake of certain individual micronutrients that are used in combination with multivitamins may be the underlying factor that is related to risk and not the multivitamins themselves," the researchers wrote, cited by Medpage today. Men who heavily used selenium faced a 37 percent increased risk of localized prostate cancer. Those who took selenium plus seven multivitamins a week faced a 5.8 times higher risk of fatal prostate cancer compared to those who did not take selenium supplements, Medpage Today reports. ?-carotene and zinc supplements seemed also to have an impact on the risk of fatal prostate cancer. In the case of zinc, among men who used multivitamins heavily, use of zinc supplements was linked with a 3.36 times higher risk of fatal prostate cancer compared to those who took no more than one vitamin supplement a day. The researchers suggested in their paper that association of zinc use with fatal prostate cancer "could be due to nonessential, potentially harmful trace elements contained in zinc supplements, such as cadmium, a known carcinogen." The key limitation of the study, according to the authors, is that the researchers did not know how long each participant used multi-vitamins. As the duration of multivitamin use is critical, lack of information of this sort could virtually render the results useless. According to the authors, heavy multivitamin users were more likely to have prostate cancer screening using prostate specific antigen. This fact means that the heavy vitamin users were more than likely have some underlying conditions that are linked with higher risk of prostate cancer. For instance, when a high count of antigen was detected, patients may be more likely advised by their physicians to take better care of their health, probably taking vitamins as one of protective measure against their conditions. This is what the foodconsumer.org scientist speculated. Regardless, the authors concluded "the possibility that men taking high levels of multivitamins along with other supplements have increased risk of advanced and fatal prostate cancers is of concern and merits further evaluation." In explaining that use of multivitamins may increase the risk of prostate cancer, Drs. Bjelakovic and Gluud suggested that "antioxidant supplements in pills are synthetic, factory processed, and may not be safe compared with their naturally occurring counterparts." Another explanation by the editorialists is that "reactive oxygen species in moderate concentrations are essential mediators of reactions by which the body gets rid of unwanted cells. Thus, if administration of antioxidant supplements decreases free radicals, it may interfere with essential defensive mechanisms for ridding the organism of damaged cells, including those that are precancerous and cancerous." This explanation sounds more plausible, the foodconsumer.org scientist commented. Still, the study per se could not tell the readers that multivitamin use definitely increases risk of fatal and advanced prostate cancer. |
