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[Definitie:] "An ergogenic aid is any substance or phenomenon that enhances performance."
(Wilmore and Costill) 
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Study: Antioxidants don't fight some cancers
AP LONDON - In another blow to the belief that antioxidant supplements improve health, an authoritative analysis has concluded there is no evidence the vitamins ward off common digestive cancers. Some experts say, however, the findings do not mean the cancer-fighting potential of antioxidant pills should be written off. In the report, in this week's The Lancet medical journal, scientists pooled 20 years of research involving more than 170,000 people at high risk of gastrointestinal cancers. Antioxidant supplements investigated included vitamins A, C, E and selenium, in 14 trials.
"The antioxidant pills - except selenium - are useless for prevention of gastrointestinal cancers," said Dr. Goran Bjelakovic, who led the study at Copenhagen University Hospital in Denmark. Bjelakovic said the potential for selenium to combat liver cancer needs a closer look, but that further studies investigating cancer-fighting effects of A, C and E would be a waste of time. The connection between health and antioxidants got attention after some studies suggested they block the heart-damaging effects of oxygen on arteries and the cell damage that might spur some kinds of cancer. Studies examining large populations also have found a link between a diet rich in antioxidant-loaded fruits and vegetables and lower rates of cancer and heart disease. However, when the theory was put to a more rigorous test by giving some people vitamin pills and others fake tablets and following them up for a few years, the supplements generally showed no benefits. Some researchers believe antioxidants might work only when they are in food. The latest study, which looks at cancers of the colon, pancreas, stomach and gullet, comes on the heels of a similar review last year by the U.S. Preventive Services Task Force. That group concluded there was not enough evidence to recommend or reject the use of vitamin supplements to reduce risk of cancer and heart disease. "The conclusions are consistent with other reviews. ... In general, there's not convincing evidence that the use of antioxidant supplements, at least for short periods of time, provides any health benefit with respect to cancer," said Eric Jacobs, senior epidemiologist at the American Cancer Society. Another expert, Jeffrey Blumberg, chief of the antioxidants research lab at Tufts University in Boston, said he worries that doubts raised by the lack of positive findings may dissuade consumers from accepting established benefits of dietary supplements - such as vitamins C, E and lutein for age-related eye degeneration; calcium and vitamin D for osteoporosis and colorectal cancer; omega-3 fatty acids for cardiovascular disease; and folic acid for neural tube birth defects. "I think it is premature to write off antioxidant supplements for cancer prevention," Blumberg said. Vitamins don't block cancers, says study
David Derbyshire Vitamin pills taken by millions of people do not protect against stomach and bowel cancers and might even make them worse, according to a new study published today. A review of 14 trials of vitamins and antioxidant supplements involving more than 170,000 showed they did not reduce the rates of cancer of the stomach, oesophagus, large bowel or pancreas. Dr Goran Bjelakovic, who led the study at the University of Niss in Serbia and Montenegro, said: "Antioxidant supplements do not have any influence on the incidence of gastro-intestinal cancers. On the contrary, they seem to increase overall mortality." However, British cancer experts questioned the findings and stressed that the study did not prove vitamins were dangerous. Millions of people take vitamin pills regularly in Britain. The industry is worth around £300 million a year. Many users believe they mimic the antioxidant effect of vitamins in food which are known to protect against cancer and heart disease. But over the past few years, the benefits of vitamin pills have been questioned by repeated studies. Some nutritionists believe most people get all the vitamins they need in food, and that supplements are a waste of money. Some believe high doses do more harm than good. The latest research, published today in the Lancet, compiled findings from 14 randomised trials. The Serbian researchers found no protective effect of beta carotene, selenium or vitamins A, C and E on a range of cancers compared with a placebo pill. In half the trials, people taking antioxidants were six per cent more likely to die prematurely compared with people taking placebos. Supplements that combined beta-carotene and vitamin A increased the risk by 30 per cent, while combinations of beta-carotene and vitamin E increased the risk by 10 per cent. However Dr Bjelakovic said the quality of the selenium data was poor and more trials were needed. Cancer Research distanced itself from the study yesterday, describing it as "preliminary". Antidoxidants mop up free radicals, the unstable charged molecules that can damage cells and DNA. Vitamins A, E, C and beta-carotene, a pre-cursor to vitamin A, and the trace mineral selenium are antioxidants. Fruits and vegetables are good sources of antioxidants, with high concentrations in spinach, carrots and tomatoes. Patrick Holford, founder of the Institute for Optimum Nutrition, an independent research centre and a supporter of vitamin supplements, said the research had excluded some well designed studies that had shown the benefits of vitamins. "This is one of the most biased and unsubstantiated reports on antioxidants I've ever read," he said. "If you look at the actual results you will see that the only really significant finding is a considerable reduction in gastrointestinal cancer risk with selenium supplementation." Vitamin Supplements May Boost Cancer Risk
David Derbyshire People who take vitamin and antioxidant supplements in the hope they're reducing their risk of gastrointestinal cancer are more likely to die of the disease than those who don't take the supplements, a new study finds. The research, which reviewed the results of 14 major trials with more than 170,000 participants, found a small but statistically significant increase in gastrointestinal cancer deaths associated with supplements containing beta carotene and vitamins A, C and E. [Dit klopt niet helemaal. De studie rept van een stijging in een 'overall mortality'. Waardoor die mensen precies overlijden, dat hebben de onderzoekers niet uitgezocht - redactie.] Four of the trials showed a possible reduction of risk associated with selenium supplements, the report said. In half the trials, there was a 6 percent increased risk of death from cancers of the esophagus, stomach, pancreas, liver, colon and rectum in persons who took supplements, compared to those who took a placebo, the researchers found. But certain combinations of supplements seemed to be more dangerous, the researchers said. A 30 percent higher risk was found for combination supplements containing beta carotene and vitamin A, and a 10 percent risk for supplements combining beta carotene and vitamin E. "The indication that mortality in supplement-taking patients was higher compared to placebo has to be explored extensively in all randomized trials," said study author Dr. Goran Bjelakovic, a professor of internal medicine at the University of Nis in Serbia and Montenegro. "The potential protective effect of selenium should be studied in adequate clinical trials," he added. The study appears in the Oct. 2 issue of The Lancet. It's not clear why antioxidant supplements might have a harmful effect, Bjelakovic said. One possible explanation is that they might interfere with apoptosis, the process in which the body destroys cells that turn abnormal. "Someone who takes supplements can suppress apoptosis and thus can influence the growth of different tumors," Bjelakovic said. "But this is only a hypothesis." Neither the American Cancer Society nor the National Cancer Institute (NCI) recommend vitamin supplements for cancer prevention. A U.S. task force recently reported there is "insufficient evidence" that supplements have any preventive effect. The cancer society recommends getting appropriate amounts of vitamins and minerals by eating a balanced diet. The NCI is conducting a large-scale trial of selenium and vitamin A for prevention of prostate cancer. The trial was started because two earlier studies suggested a possible protective effect. In an accompanying editorial in the journal, Drs. David Forman of Leeds University in England and Douglas Altman of Cancer Research United Kingdom, said, "The prospect that vitamin pills might not only do no good but also kill their consumers is a scary proposition given the vast quantities used in certain communities." If the findings are correct, "9,000 in every million users of such supplements will die prematurely as a result," the editorial said. But it added the review "is a work in progress and does not offer convincing proof of hazard." Eric Jacobs, a senior epidemiologist at the American Cancer Society, said, "There are other things [that] do work in preventing gastrointestinal cancer. One way to prevent colon cancer is to get screened for it. Quitting smoking helps prevent colon cancer as well as lung cancer, and maintaining proper weight can reduce the risk of gastrointestinal cancer."
Vitamins to prevent cancer: supplementary problems
David Forman, Douglas Altman The protocol for Bjelakovic and colleagues’ review stated that the analysis of mortality is only to be considered as exploratory. The reason is that there are many more trials of vitamin supplements available that report mortality as an outcome but have not been included in this review because they did not have endpoints for gastrointestinal cancer. A critical part of the Cochrane approach to reviews is to look at the totality of evidence for the effects of a specific intervention, and Bjelakovic and colleagues’ analysis does not yet meet that criterion since the mortality analysis was exploratory and the unreviewed trials are only now being analysed. For this reason, the results have to be regarded as preliminary. Also, the borderline statistical significance should be considered in relation to some of Bjelakovic and colleagues’ methods. If the more appropriate random-effects meta-analysis had been used the result would not have reached conventional significance (1·06, 0·98–1·15). The heterogeneity of the trials is a key issue. Heterogeneity arose almost wholly from the outlying result from one trial in an anomalous population of smokers, ex-smokers, and occupationally exposed asbestos workers. The other high-quality trials show little heterogeneity, and do not suggest increased mortality (1·02, 0·98–1·06). |
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