Behind the headlines article on news coverage of a study on the use of vitamin supplements and cancer.
A study has claimed that “cancer patients who use vitamin and mineral supplements could risk them interfering with treatment or even making the disease worse”, the Daily Mail reported today. The newspaper says there is a lack of evidence about the usefulness of supplements and that people with cancer are unaware of side effects.
The story is based on a study that reviewed research on supplement use in cancer patients. It reportedly found that between two-thirds and three-quarters of cancer patients take some form of vitamin supplement, compared to about 50% of the general population.
Although the Daily Mail reported that the researchers were concerned about the lack of evidence for the effectiveness of supplements, and the possibility of causing adverse side effects in a vulnerable group, this review only examined how common the use of vitamin and mineral supplements is among cancer patients. There is no report of any harms or benefits of supplement use in the studies included, and the study was not set up to explore a causal link between vitamin use and cancer.
The Daily Mail quoted the lead researcher as saying, “the jury was still out on whether supplements were good or bad for cancer survivors”. This seems to be a statement representative of the current level of evidence and understanding around this issue.
Christine Velicer and Cornelia Ulrich of the Cancer Prevention Program, University of Washington, US, carried out the research. No external sources of funding were reported. The study was published in the peer-reviewed medical journal: Journal of Clinical Oncology.
In this systematic review, the researchers carried out a search of the literature in order to try to quantify the usage of vitamin and mineral supplements in cancer patients and survivors. They also wanted to establish if there are any trends by cancer type, sex, etc, and to identify the areas where further evidence is needed.
According to the researchers, many of the 10 million adults with cancer in the US are choosing to use supplements despite the lack of any clear evidence-based guidance.
The researchers searched electronic databases to find any studies published between January 1999 and December 2006 on the prevalence of vitamin and mineral supplement use among cancer patients and survivors. Selected publications listed in the references of the retrieved articles were also included.
The researchers only included studies in adults in the US, in which supplement use had been measured and that had been published in the seven-year time period. The researchers then looked at the percentage of survivors in each study who reported using supplements and also looked at the details of each individual study, including population size, the way the patients were selected for the study, cancer diagnoses, etc.
The individual studies also looked at characteristics that have been associated with supplement use (e.g. age, educational level). However, these have not been discussed here.
The researchers included 32 studies in their analysis. The studies were carried out in various ways, and the type of supplement, cancer type, and patients that took part also varied. The use of vitamin and mineral supplements differed depending on the site of their cancer.
The authors conclude that “vitamin and mineral supplement use is widespread among cancer patients and longer-term cancer survivors and that, after a diagnosis of cancer, individuals tend to increase use of vitamin and mineral supplements”.
This review has been carefully conducted in a field where reliable evidence is limited and commercial sales messages are common. However, care should be taken when drawing conclusions from this research.
As the authors acknowledge, the review has highlighted the need for further research to better understand the role of supplement use in cancer patients and how it relates to treatment and survival.