By Rebecca Morris-Ostrom for Reflux1A new study indicates that taking antioxidant supplements containing Vitamins A, C, or E may not help prevent gastrointestinal (GI) cancers, and may actually increase the rate of mortality from GI cancer. Selenium supplements may help to prevent liver cancer, although more research is needed.
The report, authored by Dr. Goran Bjelakovic, was published in the October 2, 2004 issue of the Lancet. He and his research team conducted a systematic review of fourteen previously published trials. These trials compared the effects of vitamin supplements to placebos on the development of gastrointestinal cancer. The researchers analyzed studies that compared antioxidant supplements to placebos in the prevention of cancers of the liver, esophagus, stomach, colon, and pancreas. Over 170,000 patients participated in these studies.
Based on the trial results, Bjelakovic concluded that not only do antioxidant pills not reduce the likelihood of cancer, but that they might actually increase the incidence of death from gastrointestinal cancers by as much as 30%. However, selenium taken alone seemed to lower the rate of liver cancer by 10%.
Each of the studies in the review had a different goal, method, and result. Most of the studies involved patients considered at high risk for cancer, while others included healthy participants. Each study used different dosages of the vitamins, including some at a higher dose than most people would take. Some studies used only one vitamin in their comparison to the placebo, while others used a combination of antioxidants.
Several other shortcomings existed in the studies. Many had high participant-dropout rates. In some, the duration of the research trial may not have been long enough to accurately evaluate the effects of the antioxidants. Nine of the studies used participants already at high risk for cancer, so the results may have been skewed.
Because of the limitations of the review, David Forman published a response in the same issue of the Lancet. He argued that these results are preliminary, that they “[do] not offer convincing proof of hazard” and that further research is necessary.
Bjelakovic acknowledged the limitations and advised, “[T]he results should not be translated to the potential effects of vegetables and fruits, which are rich in antioxidants and other substances.” Antioxidants, especially when consumed in fresh vegetables and fruits, are still considered healthy. Studies have shown that they protect against heart disease, cataracts, stroke, dementia, low immune function, and certain types of cancer. In addition, the fiber found in fresh produce is beneficial for the gastrointestinal system.
Spinach, carrots, red bell papers, and tomatoes provide high concentrations of antioxidants. The USDA recommends that adults consume five to nine servings of fruits and vegetables per day. Selenium is found in some seafood, nuts, liver and kidney, grains, and dairy.
