I think quite a few people here have posted that they've been advised NOT to take vitamins during treatment, because of the possibility that they could promote the growth of the wrong cells. If your sister is currently being treated for leukemia, it wouldn't surprise me that her doctor told her this.

Cathy

Tongue SCC (T2M0N0), poorly differentiated, diagnosed 3/89, partial glossectomy and neck dissection 4/89, radiation from early June to late August 1989