TUESDAY, July 18, 2006 (HealthDay News) -- Nutritional supplements and other dietary changes may do little to help cancer patients alter the course of their illness, according to a major review of research on the subject.
However, because of the limited number and quality of most of the trials studied, the British researchers also said it would be tough to draw definitive conclusions on the effectiveness of such interventions.
"The take-home point is that the field isn't mature enough for us to know if any intervention works," said Dr. John A. Baron, a Dartmouth Medical School professor who authored an accompanying editorial to the findings published in the July 19 issue of the Journal of the National Cancer Institute.
The news about diet isn't all discouraging, added the study's lead author, Dr. Steven Thomas of the University of Bristol.
"There are some promising findings particularly for breast cancer, which suggest a reduction in cancer-specific mortality with healthy diet interventions, although the reviewed studies were small," he said.
Thomas' group of researchers reviewed data from 59 studies in what's known as a "meta-analysis." The research included 25 studies involving patients with cancer and 34 with patients with pre-cancerous lesions. The studies covered dietary interventions including supplements of Vitamins A, C, B6, fiber, calcium, folate and beta-carotene, as well as weight loss, exercise, and calorie-reduction.
Some studies did show some benefit. One study suggested that dietary changes might help reduce the risk for breast cancer recurrence. And two studies that focused on increased calcium intake each pointed to a reduced risk of recurrence of colorectal polyps, which can lead to colon cancer.
Of course, eating well is always important for health, Thomas said. "Encouraging a healthy diet is certainly important for general well-being because many patients with cancer will live for along time with increasingly effective medical treatments."
Baron said the U.K. review included studies that are quite broad, involving people with cancer as well as people with benign lesions. While overall the studies failed to show any value for most supplements in reducing cancer recurrence, Baron agreed that there is some evidence that calcium -- which he has studied -- looks promising as a way of preventing the return of colorectal polyps.
The U.K. report is a "very good paper," said Dr. Dimitrios Trichopoulos, a cancer specialist at Harvard School of Public Health in Boston. But he stressed that trials that focus on disease prevention, such as those reviewed in the analysis, have inherent limitations.
"They can't last long enough [to obtain definitive answers]," he said. It's also difficult to get study participants to comply with specific interventions over an extended period of time, he added.
Still, the common-sense advice to eat right still holds.
"Diet still works," Trichopoulos said, although its effect on cancer recurrence and prevention may not be as great as experts once believed. "My guess is, diet could reduce cancer by 10 to 15 percent," he said. Trichopoulos suggests a diet with little red meat and high amounts of fruits, vegetables and plant based foods.
A second study, published in the same issue of the journal, found that garlic and vitamin supplements did not reduce the prevalence of precancerous stomach lesions or gastric cancer.
In the study, researchers at the Beijing Institute for Cancer Research and the U.S. National Cancer Institute tracked more than 3,000 Chinese adults, ages 35 to 64, who were assigned to one of three treatment groups or a placebo group.
The study did find that one-time use of an antibiotic to kill off the Helicobacter pylori stomach bacteria -- suspected of causing ulcers and stomach cancer-- did reduce the severity and progression of precancerous gastric lesions, however.
More information
For more on healthy eating, head to the American Dietetic Association.
