Multivitamins and breast cancer risk
An observational study of more than 35,000 postmenopausal women which found an association between multivitamin intake and a small increased risk of breast cancer has received wide media coverage. The study can be found here.
The following commentary was written for the Australasian Menopause Society by AMS Board member Professor Martha Hickey MBChB MD FRANZCOG.
Multivitamin supplements are widely used by men and women in the developed world. About 40% of US women reported using multivitamins in 1999–2000 (1). The reasons why people choose to take multivitamins are not well defined, but are likely to relate to perceived benefits for general health and for reduction of specific common conditions such as cardiovascular disease and cancer.
Breast cancer affects up to one in eight Australian women. Any intervention which potentially increases the risk of breast cancer is of significant public health concern since even small increases in risk can translate into large numbers of women affected.
The relationship between multivitamin use and breast cancer is not well understood and previous studies have reported conflicting results. Of concern is a relationship between multivitamin use and increased breast density (2). Increased breast density is important for two main reasons: Firstly, it may be a risk factor for breast cancer; and, secondly, increased density may decrease the ability of mammography to detect a breast abnormality.
A new publication using a prospective cohort of over 35,000 postmenopausal Swedish women without breast cancer attending for mammography (3) reports that multivitamin use was associated with an increased risk of developing breast cancer over a nine-year follow-up period. Twenty-five per cent of women in this study were taking multivitamins. The increased risk was small (relative risk increase of 19%) but was statistically significant (so was not thought to be due to chance). The study was large enough to also account for many other factors known to contribute to breast cancer risk. Taking calcium did not appear to increase breast cancer risk in this study. A Canadian study has recently reported that vitamin D supplements are associated with a reduction in breast cancer risk of 24% (4).
The key message from this study is that multivitamin use may be associated with a small increased risk of breast cancer in postmenopausal women. The increased risk equates to about five extra cases of breast cancer per 1000 women over ten years (5). Since multivitamins have not been shown to benefit women taking a varied and healthy diet, and are a significant expense, the AMS recommends obtaining required vitamins from dietary sources rather than supplements. Advice on health and diet can be obtained from the NHMRC at http://www.nhmrc.gov.au/publications/synopses/dietsyn.htm
1. Radimer K., Bindewald B., Hughes J., Ervin B., Swanson C., Picciano M.F. Dietary supplement use by US adults: data from the National Health and Nutrition Examination Survey, 1999-2000. Am J Epidemiol 2004; 160: 339–49.
2. Berube S., Diorio C., Brisson J. Multivitamin-multimineral supplement use and mammographic breast density. Am J Clin Nutr 2008; 87:1400–04.
3. Susanna C. Larsson, Agneta Åkesson, Leif Bergkvist, and Alicja Wolk. Multivitamin use and breast cancer incidence in a prospective cohort of Swedish women. Am J Clin Nutr 2010 91:1268-1272. First published online March 24; doi:10.3945/ajcn.2009.28837.
4. Anderson L.N., Cotterchio M., Vieth R., Knight J.A. Vitamin D and calcium intakes and breast cancer risk in pre- and postmenopausal women. Am J Clin Nutr. 2010, April 14. doi:10.3945/ajcn.2009.28869 [E-published ahead of print].
5. Jean Hailes Foundation for Women’s Health (2010, April 23). Breast cancer and multivitamins: Jean Hailes experts weigh in. Published online www.jeanhailes.org.au
Content updated 27 April 2010