Do multivitamin tablets increase breast cancer risk?

Multivitamin supplements are widely used, but a large study involving 35,000 Swedish women aged 49 to 83 found that those who regularly took multivitamins had a higher risk of breast cancer than women who did not.


Based on self-reported questionnaire data, the researchers analysed the women's use of multivitamins as well as details about their health and lifestyle, followed up for 9.5 years until December 2007 to assess the cancer risk. They found that women who took multivitamins were 19% more likely to develop breast cancer than non-users. They also found that women who had taken these supplements for 3 years or more and those who took 7 or more pills a week were at increased risk of breast cancer than non-users, however the increase was very small.

The researchers concluded that "multivitamin use is associated with an increased risk of breast cancer" but they noted that other studies have had conflicting results. The authors said that this study carries an important public health message and recommend women to eat healthy diet instead of using supplements.

Critics say that this study was based on self-reported data that could affect the results. Further research is needed, it is not possible to say which of the supplements may contribute to breast cancer risk.

Source: "Multivitamin use and breast cancer incidence in a prospective cohort of Swedish women". American Journal of Clinical Nutrition, March 24 2010 (full text via Athens)