There is an area of discovery related to food supplement ingestion and cancer prevention that has been attracting a lot of interest. Namely; does taking food supplement (of mostly indeterminate quality) provide women with a benefit or risk in terms of breast cancer. A recent post reviewed a study of Swedish women, where the indications were of increased risk, compared to other studies that were either indicative of reduced risk, or benign.
This latest study suggests women who take multivitamin tablets along with calcium supplements seem to have a reduced risk of developing breast cancer. Interestingly the Swedish study also indicated that calcium was a mineral of benefit for reducing risk.
At the prestigious American Association for Cancer Research 101st Annual Meeting, April 17-21 a paper was presented by Dr’s Matta and Bayona the results of which expand on the data related to multivitamins and breast cancer. 
We found that taking multivitamins and calcium supplements were strongly protective against breast cancer,” said Dr. Manuel Bayona, a professor in the public health program at the Ponce School of Medicinein Puerto Rico. “Which vitamins exactly? We don’t know because they were multivitamins.”
In the details, this study looked at a relatively small number – 268 women with breast cancer and 457 women without breast cancer, in Puerto Rico. The authors then extracted data on multivitamin and calcium intake. They specifically looked at DNA repair capacity, related to breast cancer and found that those taking multivitamins had a 30% reduction and those taking calcium a 40% reduction in breast cancer risk.
Vitamins and calcium intake are protective for breast cancer and are associated with higher DNA Repair levels (DRC). Vitamins’ intake is an independent protective factor for breast cancer while the protective effect of calcium may be explained by an increased DRC. DRC can be used to monitor the protective effect of calcium in terms of breast cancer risk.
Once again this was a questionnaire based study and the small numbers makes it lose statistical value, but it keeps open the discussion that nutrients may be required in doses higher than one can consume in a normal daily diet (2000kcal) as described by Dr Clayton in his 2009 papers.
 Larsson SC, Akesson A, Bergkvist L, & Wolk A (2010). Multivitamin use and breast cancer incidence in a prospective cohort of Swedish women. The American journal of clinical nutrition PMID: 20335555
 Yeidyly Vergne, Jaime L. Matta, Luisa Morales, Wanda Vargas, Carolina Alvarez-Garriga, Manuel Bayona. Ponce School of Medicine, Ponce, PR . Consumption of vitamins and calcium reduces breast cancer risk by their regulation of the DNA repair capacity. Sunday, Apr 18, 2010, 2:00 PM – 5:00 PM View Summary