A study by Swedish researchers published in the American Journal of Clinical Nutrition (AJCN) this week reported that multivitamin use was associated with an increased risk of breast cancer. Understandably, this claim generated a lot of media attention and concern among the general population.

The observational study of over 35,000 Swedish women aged 49-83 years reported a small increase in breast cancer risk amongst women who took multivitamin supplements. Compared to the non-multivitamin users, this increase equates to about five extra cases of breast cancer per 1000 women over 10 years. Interestingly, the study showed a slight decrease in risk for those women who took calcium supplements (about seven less cases of breast cancer per 1000 women over 10 years).

According to Jean Hailes endocrinologist Prof Henry Burger, "It is important to note that those women who used multivitamin supplements also had a higher rate of breast cancer risk factors such as benign breast disease, nulliparity (never had children), use of oral contraceptive pill or hormone replacement therapy and non-smokers. While some previous studies have shown a relationship between nutritional supplements and cancer, other studies have found no effect or in some cases, decreased rates. The same issue of AJCN in which this study is published also includes a study that reports a protective effect of vitamin D supplementation. In addition, a recent study published by the American Association for Cancer Research showed that multivitamins reduce the risk of breast cancer by 30 per cent and calcium reduces this risk by 40 per cent."

Jean Hailes naturopath Ms Sandra Villella advised women to "continue taking their calcium supplements as they were not associated with an increased risk of breast cancer, (possibly due in part to the vitamin D benefit). Vitamins C, E and B6 were also not associated with increased risk. For pregnant women and women preparing for pregnancy, folic acid is important to reduce the risk of neural tube defects and therefore these women should follow government guidelines and continue taking these supplements."

Jean Hailes experts agree that the relationship between breast cancer and multivitamins is inconclusive and deserves further study. Women who take vitamin supplements to treat a deficiency should continue to do so, however women who are taking multivitamins as a preventive measure should be aware that the best source of most vitamins and minerals is through eating wholefoods such as fruit and vegetables. To minimise your risk of breast cancer, women are advised to consume a balanced diet, stay physically active, maintain a healthy weight and keep alcohol intake to a minimum.

Content Updated April 23, 2010