Milk Products and Breast Cancer
According to the 2010 report by the World Cancer Research Fund International, the authority on diet and cancer, no conclusions can be drawn between milk products and breast cancer due to limited evidence. However, some newer evidence suggests an inverse association between dairy intake and breast cancer risk.
Basic Facts on Breast Cancer
There is no single cause of breast cancer; however, there are several risk factors:1
- Personal history of breast cancer;
- Family history of breast and other cancers;
- BRCA gene mutations;
- Hormone replacement therapy;
- Oral contraceptives;
Breast cancer is the most common cancer among Canadian women. About 1 in 9 Canadian women is expected to develop breast cancer during her lifetime.1
According to the 2010 Continuous Update Project report from the World Cancer Research Fund International, the authority on diet and cancer, there is limited and non-conclusive evidence on the association between milk and milk products and the risk of both pre- and post-menopausal breast cancer.2
A 2015 meta-analysis of 22 prospective cohort studies (n = 1,566,940) evaluated the association between dairy intake and breast cancer risk.3
- Higher dairy consumption (>600 g/d) was associated with a 10% lower risk of breast cancer, as compared to lower dairy consumption (<200 g/d);
- Additionally, a dose-response relationship was found, indicating an inverse and linear association between dairy intake and the risk of breast cancer:
- Per additional 250 g/d dairy intake, risk was reduced by 3%;
- Per additional 500 g/d dairy intake, risk was reduced by 6%;
- Per additional 750 g/d dairy intake, risk was reduced by 9%;
- Higher yogurt and low-fat dairy intakes were associated with a risk reduction of 9% and 15%, respectively;
- No association was observed between whole milk, low-fat/skim milk, cheese/butter or high-fat dairy and breast cancer risk.
The mechanisms by which the consumption of milk and milk products may influence the risk of breast cancer are not clear. Nevertheless, there are key components in milk, namely calcium, vitamin D and lactoferrin, which appear to play important mechanistic anticarcinogenic roles.
A 2016 meta-analysis has shown that there is an inverse dose-response relationship between calcium intake and breast cancer risk among both pre-menopausal and post-menopausal women.4 Calcium participates in the regulation of apoptosis, cell proliferation and differentiation.
Animal studies have shown that a high calcium intake inhibits hyperproliferation of mammary glands and can inhibit mammary carcinogenesis. The anti-proliferation and pro-differentiation properties of calcium may also decrease benign proliferative epithelial disorders.5
Vitamin D plays potential mechanistic roles through its anti-cancer and anti-inflammatory properties.
Calcitriol, the hormonally active form of vitamin D, exerts anti-proliferative, pro-apoptotic and pro-differentiating effects in many malignant cells.6-8 Vitamin D also opposes estrogen-driven proliferation in mammary glands by reducing progesterone and estradiol levels.7,9
A meta-analysis found an inverse association between circulating 25(OH)D and breast cancer risk among post-menopausal women.10
Bovine milk lactoferrin has also been found to be protective against breast cancer. It appears that lactoferrin has the ability to interact with certain receptors and modulate the genetic expression of molecules involved in the cell cycle and apoptosis machinery.11
Conjugated linoleic acid
Some experimental and in vitro studies have shown that conjugated linoleic acid, which is a naturally occurring fatty acid found in milk products, may protect against mammary carcinogenesis. However, the results are conflicting.12,13
Evidence suggests that the consumption of milk products is not associated with an increased risk of breast cancer and may, in fact, be associated with a reduced risk of breast cancer.
More research is needed on the roles of specific milk products such as yogurt and cheese.
Associations may also be different for pre- as compared to post-menopausal women. Additional studies are needed for definitive answers.
Calcium, vitamin D and lactoferrin may be important anti-cancer milk components. More studies are needed to elucidate their precise mechanisms in the reduction of breast cancer risk.
- Canadian Cancer Society. 2016. What is breast cancer? www.cancer.ca. Accessed August 3, 2016.
- World Cancer Research Fund/American Institute for Cancer Research. 2010. Continuous Update Project report: Food, nutrition, physical activity, and the prevention of breast cancer. www.wcrf.org. Accessed August 2, 2016.
- Zang J et al. The association between dairy intake and breast cancer in Western and Asian populations: a systematic review and meta-analysis. J Breast Cancer 2015;18:313-322.
- Hidayat K et al. Calcium intake and breast cancer risk: meta-analysis of prospective cohort studies. Br J Nutr 2016;116:158-166.
- Chen P et al. Meta-analysis of vitamin D, calcium and the prevention of breast cancer. Breast Cancer Res Treat 2010;121:469-477.
- Gandini S et al. Meta-analysis of observational studies of serum 25-hydroxyvitamin D levels and colorectal, breast and prostate cancer and colorectal adenoma. Int J Cancer 2011;128:1414-1424.
- Krishnan AV and Feldman D. Mechanisms of the anti-cancer and anti-inflammatory actions of vitamin D. Annu Rev Pharmacol Toxicol 2011;51:311-336.
- Rohan TE et al. A randomized controlled trial of calcium plus vitamin D supplementation and risk of benign proliferative breast disease. Breast Cancer Res Treat 2009;116:339-350.
- Knight JA et al. Vitamin D association with estradiol and progesterone in young women. Cancer Causes Control 2010;21:479-483.
- Bauer SR et al. Plasma vitamin D levels, menopause, and risk of breast cancer: dose-response meta-analysis of prospective studies. Medicine (Baltimore) 2013;92:123-131.
- Duarte DC et al. The effect of bovine milk lactoferrin on human breast cancer cell lines. J Dairy Sci 2011;94:66-76.
- McGowan MM et al. A proof of principle clinical trial to determine whether conjugated linoleic acid modulates the lipogenic pathway in human breast cancer tissue. Breast Cancer Res Treat 2013;138:175-183.
- Arab A et al. The effects of conjugated linoleic acids on breast cancer: a systematic review. Adv Biomed Res 2016;5:115.