Vitamin after cancer diagnosis  review 2008 more than 60% supplement and up to 68% of doctors unaware
J Clin Oncol. 2008 Feb 1;26(4):665-73.
Vitamin and mineral supplement use among US adults after cancer diagnosis: a systematic review.
Velicer CM, Ulrich CM.
Fred Hutchinson Cancer Research Center, Department of Epidemiology, University of Washington, Seattle, WA 98109, USA.
Vitamin and mineral supplement use is thought to be common among the 10 million adults in the United States who have been diagnosed with cancer; however, well-conducted studies of this topic are sparse. Moreover, the biologic effects of supplement use among cancer survivors are not well established and not necessarily beneficial. We present a systematic summary of studies published between 1999 and 2006, 32 in total, addressing vitamin and mineral supplement use among US adult cancer patients and survivors. Supplement use is widespread among cancer patients and longer-term survivors. In studies combining different cancer sites, 64% to 81% of survivors reported using any vitamin or mineral supplements and 26% to 77% reported using any multivitamins. 
In contrast, approximately 50% of US adults use dietary supplements and 33% use multivitamin/ multimineral supplements. Between 14% and 32% of survivors initiate supplement use after diagnosis, and use differs by cancer site. Breast cancer survivors reported the highest use, whereas prostate cancer survivors reported the least. Higher level of education and female sex emerged as factors most consistently associated with supplement use. 
Up to 68% of physicians are unaware of supplement use among their cancer patients. These results highlight the need for further studies of the association between dietary supplement use and cancer treatment toxicity, recurrence, survival, and quality of life to support evidence-based clinical guidelines for dietary supplement use among cancer patients and longer-term survivors.

PMID: 18235127 [PubMed - indexed for MEDLINE]