There is little evidence that dietary modification or supplements such as vitamins improve the outcome for cancer patients, say researchers from the University of Bristol, UK.

Food supplements and vitamins are widely used by patients with cancer as an adjunct to conventional treatment. 

Dr Steven Thomas and colleagues at the University of Bristol used electronic database searches to identify 59 trials that had investigated the effects of a diverse range of nutrition interventions in patients with a previous diagnosis of cancer or preinvasive lesions.

Dr Thomas said: “There is little current evidence that specific dietary interventions work, thus on this evidence we cannot recommend their widespread use in cancer management. Clinicians also need to be clear about the limited evidence and give reliable advice, particularly on Internet sites from which many patients with cancer may seek information.

“The large personal expenditure on supplements and dietary modifications by patients with cancer demonstrates an urgent need to understand their effects on cancer outcomes. This vulnerable group of people need to be better informed as diet is one of the few areas of their lives where they may feel they have some control.”

The results, published today in the Journal of the National Cancer Institute, demonstrate that the trials provided little evidence that specific interventions, or groups of interventions, have any effect, either beneficial or harmful on disease-free survival, mortality or recurrence. 

The impact of most nutritional interventions cannot be estimated reliably because of the limited number of trials, many of which are small and/or of low quality.

Some researchers are also worried that some dietary interventions may not be harmless, a concern echoed by a European Union recommendation to tighten sales of supplements.