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 Feb. 1 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,” said senior author Cornelia (Neli) Ulrich, Ph.D., 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, Ph.D., formerly a postdoctoral fellow at the Hutchinson Center (now an epidemiologist at Merck Research Laboratory in North Wales, Pa.), found that many of the nation’s 10 million adult cancer survivors use nutritional supplements.

They found 64 percent to 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 researchers also found that many people initiate the use of vitamins and supplements after cancer diagnosis; between 14 percent and 32 percent start taking them after learning they have 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.

“This is disconcerting and suggests that many physicians may not recognize the importance of understanding whether their patients are taking supplements,” Ulrich said.

Knowing about supplement use is crucial, she continues, 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.”

Until research clarifies the effects of vitamin use in cancer survivors, the authors urge health care professionals to communicate openly with their patients about supplement use. “A simple explanation that medical studies show supplement use may not always be beneficial may help cancer survivors make well-informed decisions,” the authors wrote.

The National Cancer Institute funded this research.