In a study of more than 700 women, taking multivitamin tablets in the past five years was associated with 31% lower odds of having breast cancer. The use of calciumsupplements was linked to a 40% reduced risk.
The study involved 268 women with breast cancer and 457 women without breast cancer, all in Puerto Rico. The women filled out detailed questionnaires asking which supplements they took during the past five years, how frequently they took them, and whether they still took them.
The women also gave blood samples so the researchers could measure the ability of their DNA to repair damage, a complex biological process that is critical to preventing cancer.
The findings were presented at the annual meeting of the American Association for Cancer Research.
The study showed that older age, reduced DNA repair capacity, a family history of breastcancer, and not breastfeeding all raised the risk of breast cancer.
When DNA repair capacity was taken into consideration, calcium was no longer protective against breast cancer, suggesting that calcium supplements act to enhance DNA repair, says Jaime Matta, PhD, professor of pharmacology, physiology and toxicology at Ponce School of Medicine in Ponce, Puerto Rico.
Multivitamins remained protective even after taking into account DNA repair, however, suggesting it is associated with other anticancer benefits as well, he says.
Taking supplements of vitamins A, E, or C alone was associated with a slightly lower risk of breast cancer, but the finding could have been due to chance.
All the analyses were adjusted to take into account the effect of other breast cancer risk factors such as age, family history, and having been pregnant.
Matta tells WebMD the finding suggests that vitamins may work better together than individually to lower cancer risk.
Other studies have had conflicting results. Some have suggested that supplement forms of single vitamins such as A and E don't protect against breast cancer. Others have suggested that vitamins are protective.