SEATTLE Use of vitamin and mineral supplements among cancer survivors is widespread, despite inconclusive evidence that such use is beneficial, according to a comprehensive review of scientific literature conducted by researchers at Fred Hutchinson Cancer Research Center and published Friday in the Journal of Clinical Oncology.
"Can vitamin and herbal supplements reduce the adverse effects of cancer treatment, decrease the risk of cancer recurrence or improve a patient's chances of survival? We don't really know. Research into these matters has been minimal," stated senior author Cornelia Ulrich, an associate member of the Hutchinson Center's Public Health Sciences Division. "While supplement use may be beneficial for some patients, such as those who cannot eat a balanced diet, research suggests that certain supplements may actually interfere with treatment or even accelerate cancer growth," she said.
In reviewing 32 studies conducted between 1999 and 2006, Ulrich and co-author Christine Velicer, an epidemiologist at Merck Research Laboratory in North Wales, Pa., found that between 64 percent and 81 percent of cancer survivors overall reported using vitamins or minerals (excluding multivitamins), whereas in the general population only 50 percent of adults reported taking dietary supplements.
Survivors of breast cancer reported the highest use (75 percent to 87 percent), whereas prostate-cancer survivors reported the least (26 percent to 35 percent). Factors associated with the highest level of supplement use overall included a higher level of education and being female, the authors concluded.
The researchers also found that many people initiate the use of vitamins and supplements after a cancer diagnosis; between 14 percent and 32 percent started taking them after learning they had cancer.
"Cancer survivors report that they hope to strengthen their immune system with supplement use or gain a sense of control and empowerment," Ulrich said. However, many cancer survivors who use supplements do not let their doctors know; 31 percent to 68 percent of cancer patients and survivors who use supplements may not disclose this information or their doctors may fail to record it in their charts.
Knowing about supplement use is crucial, she added, because of potential adverse effects. "Evidence clearly suggests the need for caution," Ulrich said. "Some vitamins, such as folic acid, may be involved in cancer progression while others, such as St. John's wort, can interfere with chemotherapy. However, we really need more research to understand whether use of these supplements can be beneficial or do more harm than good."
The National Cancer Institute funded the research at the Fred Hutchinson Cancer Research Center.