Dietary supplements of no benefit to patients with cancer or precancerous lesions
Posted: July 18, 2006
NEW YORK (Reuters Health) - Neither dietary modifications nor nutritional supplements such as vitamins, antioxidants, retinol, and garlic alter the disease course of patients with cancer or preinvasive lesions, according to two reports in the Journal of the National Cancer Institute for July 19. However, antibiotic treatment to eradicate Helicobacter pylori retards the progression of precancerous gastric lesions, the authors of the second paper report.
Dr. Steven Thomas and associates at the University of Bristol in the UK conducted a systematic literature review of randomized controlled trials involving the effect of nutritional interventions in patients with cancer or preinvasive lesions up until September 2003. They excluded studies used to treat complications, as well as studies that used synthetic retinoids, vitamin analogues, herbal supplements, and polysaccharide K.
The final analysis included 25 trials regarding nutrition intervention trials for people with cancer, and 34 for people with preinvasive lesions. Trial quality was generally low, with only three using adequate methods to generate and conceal allocation sequence, and masking of all participants.
Dr. Thomas and his team found little evidence to support claims that interventions had any effect, either beneficial or harmful. The only agents with sufficient data to exclude substantial effects on all-cause mortality were antioxidants and retinol.
Based on their findings, Dr. Thomas's group writes, "We should not maintain the notion that nutritional interventions can be promoted because at least they will do no harm."
On the other hand, "encouraging a healthy diet is certainly important because many patients with cancer and preinvasive lesions will live a long time and may die of other diseases related to diet," but physicians "should not state that it is a priority in management of cancer itself."
They also advise that clinicians clarify to patients the lack of evidence regarding the efficacy of dietary supplements.
In the second paper, Dr. Mitchell Gail from the National Cancer Institute in Bethesda, Maryland, and other investigators in the US and in China describe a trial for reducing the high prevalence of advanced precancerous gastric lesions in Shandong Province, China.
In 1994, endoscopies were performed on 3365 subjects aged 35 to 64 years. The investigators report that only 0.18% had normal gastric mucosa.
The 2258 subjects seropositive for H. pylori were randomized to three arms: treatment with omeprazole 20 mg and amoxicillin 1 g twice daily for 2 weeks, or placebo treatment; a twice-daily supplement containing vitamin C 250 mg, vitamin E 100 IU, and selenium 37.5 micrograms for 7.3 years, or placebo; or to a garlic supplement taken twice daily for 7.3 years or placebo.
The 1107 subjects without H. pylori were randomized to either the vitamin or garlic arms, or placebo.
In 1999 and 2003, the subjects underwent repeat endoscopies with biopsies.
Dr. Gail's group reports, "There was no evidence that either vitamin or garlic supplements favorably altered the distribution of precancerous gastric lesions" or the proportion of subjects with dysplasia, gastric cancer, severe chronic atrophic gastritis, intestinal metaplasia or average severity score.
In contrast, the investigators found that "one-time H. pylori treatment ... induced statistically significant reductions in the combined prevalence of severe chronic atrophic gastritis, intestinal metaplasia, dysplasia, or gastric cancer, in histologic severity, and in the progression of precancerous gastric lesions."
However, the antibiotics did not affect the combined prevalence of dysplasia or gastric cancer.
"Together the two articles in this issue of the Journal well illustrate the contemporary status of chemoprevention: hard to summarize, many negative findings, but some hopeful nuggets of progress," Dr. John A. Baron from Dartmouth Medical School in Lebanon, New Hampshire, writes in a related editorial.
Linear Mode
