Multivitamins Now Linked with Decrease in Breast Cancer Risk
New research presented Sunday at the American Association for Cancer Research annual conference in Washington DC has found that women who take a multivitamin along with calcium supplements may have a reduced risk of developing breast cancer. This study appears to contradict another recent study from the Karolinska Institute that found that multivitamin use was associated with an increased risk of the disease.
The authors of the study, including Dr. Jaime Matta and Dr. Manuel Bayona of the Ponce School of Medicine in Puerto Rico, stated that the interactions of vitamins together, not any single vitamin, may account for the protective effect. “It’s possible that the vitamins work better together than individually,” said Dr. Matta.
The study included 268 women with breast cancer and 457 without the disease, all from Puerto Rico. The authors compared vitamin and calcium intakes, as well as measured the ability of the women’s DNA to repair itself, which is a function critical of preventing cancer cells from forming, particularly breast cancer cells.
Taking a multivitamin reduced the risk of tumors by about 30%, while the addition of a calcium supplement reduced the risk by 40%. Calcium, in particular, was thought to enhance DNA repair capability, while the other vitamins played a more supportive role in cancer prevention. The study appears to corroborate a June 2007 study that found that calcium and vitamin D were protective in reducing cancer risk.
In December 2008, a large trial showed no reduction in cancer risk from vitamin supplements. The study, published in the Journal of the National Cancer Institute found that women who took vitamins C, E and beta-carotene had the same risk of cancer diagnosis and death as those who didn’t.
More recently, a study published in the March issue of the American Journal of Clinical Nutrition found that women who reported multivitamin use were 19% more likely than non-users to develop breast cancer. The women, all between the ages of 49 and 83 were cancer-free at the beginning of the 10-year study conducted at Sweden’s Karolinska Institute. Authors of that study suggest that taking vitamin and mineral supplements significantly increased the density of the breast tissue, which is a strong risk factor for breast cancer. They also indicate that folic acid may accelerate tumor growth.
As with all medical research, both studies come with limitations that should be taken into consideration.
The limitations of the Puerto Rico study include the reliance on questionnaire responses for vitamin intake rather than measuring body levels of the vitamins. The study was also smaller, and focused on a group of women in a very small area of the world. According to Dr. Matta, the women were also likely not to eat the recommended number of fruits and vegetables, and may use vitamin supplements to make up for nutritional deficiencies.
The Swedish study also had drawbacks. Although the study sample size was quite larger, including 35,000 women, the research was also “observational”, which means that the researchers did not compare an interventional group with a control to find a specific mechanism for the association between vitamins and the increased risk for cancer. Dr. David Katz also points out on his Huffington Post report that the women who took multivitamins also used oral contraceptives and hormone replacement therapy more often and exercised less than women not taking the supplements.
The bottom line from the American Cancer Society? "The totality of the evidence to date does not support taking vitamins and calcium for breast cancer prevention," says Marji McCullough, strategic director of nutritional epidemiology for the ACS. "There are other reasons women may wish to take calcium, for example for bone health."