Multivitamins and Risk of Breast Cancer

In May this year, the American Journal of Clinical Nutrition (AJCN) published a study which reported an increased risk of breast cancer in women who took multivitamins (1). This resulted in a lot of concern amongst women and significant media attention. Interestingly, the same issue of this journal published a study showing the vitamin D to be protective against breast cancer.

There have been many other large studies that show no relationship between multivitamin supplementation and increased risk of breast cancer. These include: a study published in the American Journal of Epidemiology that looked at the breast cancer risk in nearly 38,000 women in the US and showed no increased risk except for those women having more than 10g alcohol per day (2); and another study of nearly 162,000 women that showed no particular benefit and no increased risk of breast cancer with multivitamin use (3).

The study published in May followed over 35,000 Swedish women aged 49-83 years. The researchers asked the women at the beginning of the study whether they took vitamin supplements and then checked the cancer registry 10 years later to see who had developed breast cancer. The researchers donít know if any of the women continued to take vitamins through the ten year period. The results showed an increase of about 5 cases per 1,000 women over 10 years and showed a decrease of 7 women per 1000 for those who took calcium supplements (1).

The women who took multivitamins were also more likely to have had benign breast disease, not had children and used the oral contraceptive pill or hormone replacement therapy, which all increase the risk of breast cancer. Whilst these factors were accounted for, itís still only an estimate.

Itís important to recognize that these kinds of studies do not show causal links - they give researchers some idea of where to look next or they show an association. While studying ďEpidemiology 101Ē, one of the examples thatís often given to illustrate this point is the strong link between having blue hair and breast cancer. Of course, having blue hair doesnít cause breast cancer Ė the link is that older women tend to dye their blue and breast cancer is strongly linked to increasing age. Blue hair is a confounding factor. Often the media jump to conclusions and make these associations appear to be a causal link.

The importance of vitamins and minerals in pregnancy and pre-conception cannot be underestimated (4), especially folate and B vitamins, iron, zinc, calcium, copper, iodine and vitamin D and new research about the importance of vitamin A (5). The article published in January 2010 in Human Reproduction Update is particularly thorough and explains in detail what evidence is currently available (4).

There is also a large body of evidence about the importance of vitamins and minerals in male fertility (6, 7). It is preferable to obtain all the required micronutrients from the food we eat, but in this day and age, unless you put an enormous effort into your diet then you canít always be sure of what you are consuming. I therefore always recommend that women trying to conceive (and women who are pregnant) have a good quality adult multivitamin.

References:

1. Larsson SC, Akesson A, Bergkvist L, Wolk A. Multivitamin use and breast cancer incidence in a prospective cohort of Swedish women. American Journal of Clinical Nutrition. 2010 May 1, 2010;91(5):1268-72.

2. Ishitani K, Lin J, Manson JE, Buring JE, Zhang SM. A Prospective Study of Multivitamin Supplement Use and Risk of Breast Cancer. Am J Epidemiol. 2008 May 15, 2008;167(10):1197-206.

3. Neuhouser ML, Wassertheil-Smoller S, Thomson C, Aragaki A, Anderson GL, Manson JE, et al. Multivitamin Use and Risk of Cancer and Cardiovascular Disease in the Women's Health Initiative Cohorts. Arch Intern Med. 2009 February 9, 2009;169(3):294-304.

4. Cetin I, Berti C, Calabrese S. Role of micronutrients in the periconceptional period. Human Reproduction Update. 2010 Jan-Feb;16(1):80-95.

5. Sidell N, Feng Y, Hao L, Wu J, Yu J, Kane MA, et al. Retinoic Acid Is a Cofactor for Translational Regulation of Vascular Endothelial Growth Factor in Human Endometrial Stromal Cells. Molecular Endocrinology. 2010 January 1, 2010;24(1):148-60.

6. Kao SH, Chao HT, Chen HW, Hwang TI, Liao TL, Wei YH. Increase of oxidative stress in human sperm with lower motility. Fertil Steril. 2008 May;89(5):1183-90.

7. Al-Azemi MK, Omu AE, Fatinikun T, Mannazhath N, Abraham S. Factors contributing to gender differences in serum retinol and alpha-tocopherol in infertile couples. Reprod Biomed Online. 2009 Oct;19(4):583-90.

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